Searching \ for '[EE] Questions on Electric Vehicle high power elec' in subject line. ()
Make payments with PayPal - it's fast, free and secure! Help us get a faster server
FAQ page: www.piclist.com/techref/power.htm?key=power
Search entire site for: 'Questions on Electric Vehicle high power elec'.

Exact match. Not showing close matches.
PICList Thread
'[EE] Questions on Electric Vehicle high power elec'
2008\05\25@103209 by Byron Jeff

flavicon
face
Hi folks,

I'm kind of surprised that with the surge in fuel costs that a thread on
electric vehicles (EV) had not got jump started here.

I have questions at the bottom if you are not interested in the background.

I have the goal of quickly putting together a lead sled, a pickup full of
lead acid golf cart batteries, for daily driving in order to bring some
cost control to my transportation costs.

I'm well aware that there are a ton of other options, including lithium
based batteries. I'm also aware of the limitations. However, I'm determined
to get off gas for the regular commute in a cost effective manner.

If you're interested in seeing a video blog of an EV being put together go
to youtube and search for n2confusion. He has about 37 videos of the actual
destruction/reconstruction process of a lightweight EV.

Also there's a very active forum community at diyelectriccar.com. I'm
posting over there as ga2500ev.

An EV really isn't too terribly complicated, with only 4 major components:

1) Donor vehicle with manual transmission
2) Battery bank.
3) Electric Motor
4) Control, charging, and monitoring electronics

The first three are fairly stock entities with (so far) static costs. Find
a vechicle with a busted Internal Combustion Engine (ICE), pull the engine,
mate the electric motor to the transmission and hook up the battery bank to
the motor. My plan is to start this project with cheap available
components:

1) Still looking for a donor truck. Probably will end up with on off
craigslist. With a blown engine, it won't be more than $500.

2) Going to start with a battery bank consisting of Eveready GC2 Golf Cart
batteries from Sams. 6V, 225 Ah, $75 each. A 144V system of 24 batteries
will run $1650 + tax, no shipping and weigh about 1650 lbs.

3) Still searching for good availably and price. WarP 9's have 6 week or
more lead times and run in the $1700 to $1800 ballpark.

That leaves the electronics. From both a cost and integration standpoint
there's a lot to be left desired with control electronics. The major
subsystems:

1) PWM motor controller. Not a fundamentally complicated piece of
equipment. Accepts a limited number of control inputs (5k throttle pot,
brake switch) and controls via PWM a high powered switch between the
battery bank and the motor. An example is the Curtis 1231C controller:

http://www.electricvehiclesusa.com/product_p/co-1231c-8601.htm

I'm almost ready to choke on the $1400 price tag.

2) Battery charger. Again not too complicated for lead acid battery packs.
A lot of DIYers use individual chargers to each battery. But a decent charger
runs upwards of $800.

3) DC-DC converter. Takes the battery pack and replaces the alternator with
a converter.

4) Voltage and current monitoring. A lot of systems have separate current
monitoring for display and for the controller to prevent overstressing the
motor. The battery charger also requires voltage monitoring.

The prices for these components seem outrageous when you consider that the
core of most of these modules are high powered switches. IGBT modules such
as:

http://tinyurl.com/3t86km

Are available surplus for less than $50. These modules are more than stout
enough to handle both the controller and charging loads.

It seems to me that a DIY electronics builder could put together an
integrated controller/charger for a fraction of the cost of the commercial
equipment. I think my problem is the difference in understanding the theory
and the actual engineering.

Questions:

For the controller does the power electronics consists of more than the
IGBT, freewheeling diode, and smoothing cap bank?

Any suggestions for a freewheeling diode for a 144V x 600A controller?

Battery charging is a voltage/current limited charge dump. Presuming that
you have a 240VAC source, would the best control be to rectify to DC then
use a buck converter to get the correct voltage/current? If that's the case
then any suggestions on how to get an appropriate inductor? Same for the
DC/DC converter.

It seems to me that a significant cost in EV development could be greatly
reduced with the judicious application of DIY electronics. With PICs,
IGBTs, and a bit of knowledge, a complete electronics system for an EV
could be realized for a couple of hundred bucks instead of a couple of
thousand.

Thanks for reading. Look forward to any suggestions you may offer.

BAJ

2008\05\25@141104 by Djula Djarmati

flavicon
face
> 3) Still searching for good availably and price. WarP 9's have 6 week or
> more lead times and run in the $1700 to $1800 ballpark.
>
> That leaves the electronics. From both a cost and integration standpoint
> there's a lot to be left desired with control electronics. The major
> subsystems:
>
> 1) PWM motor controller. Not a fundamentally complicated piece of
> equipment. Accepts a limited number of control inputs (5k throttle pot,
> brake switch) and controls via PWM a high powered switch between the
> battery bank and the motor. An example is the Curtis 1231C controller:
>
> www.electricvehiclesusa.com/product_p/co-1231c-8601.htm
>
> I'm almost ready to choke on the $1400 price tag.

Before doing the electronics all by yourself, I would try FANUC CNC
spindle motors and controllers like these:

cgi.ebay.com/Fanuc-spindle-motor-a06b-0759-b970_W0QQitemZ180243520740
(30kW at 40%ED, 22kW continuous)
cgi.ebay.com/FANUC-DC-SPINDLE-SERVO-DRIVE-MODEL-SP12_W0QQitemZ220237949247
(I don't know if this one fits the motor, it's just an example)

These motors and controllers are very rugged, protected from overload,
short circuit, etc. and you also get regenerative braking since they
brake by dumping energy to DC rail. The controller keeps the set rpm
automatically and goes in reverse.

The only drawback is they expect 200V 3-phase which is around 300V on DC
rail. The price for these starts at $1000 for each item.

If you make it work, you can experiment in making your own by looking
the way FANUC did it. If you go this way, let me know and I can find
some datasheets.

Djula

2008\05\25@143313 by Peter

picon face
> 2) Going to start with a battery bank consisting of Eveready GC2 Golf Cart
> batteries from Sams. 6V, 225 Ah, $75 each. A 144V system of 24 batteries
> will run $1650 + tax, no shipping and weigh about 1650 lbs.

The goal of the electric car is to be light, in view of the low power density of
the batteries. The law of diminishing returns kicks in fast if you end up with a
ton of batteries lugged around for no good reason. The best way is to use a
battery as small as possible and change it often (with another freshly charged
one). In the 70s and 80s there were trials with such changeable packs for public
transportation (electric bus). At the time they did not catch on.

Imho, try to work the problem backwards: how much do you travel between pit
stops, what class of EV can do that now (wikipedia helps), how much it
weighs/costs, then see how you could build a vehicle of that class or refurbish
a used one.

Available data suggests 20-100 km range for curb weight << 1 ton.

Electronics for electric traction are not so trivial. There is inrush limiting,
kickback handling, dynamic braking (motor tries to generate - you can't just cut
the drive, the voltage will raise high enough to blow the insulation on the
motor if you do that) etc etc. 'Simple' PWM requires a bridge circuit from >500W
or so and so on.

Plus the torque/rpm characteristics of usual electric motors are not suitable
for road traction use without some suitable controllers. The easiest hack is to
rely on the gearbox and implement a step relay that will shunt in more or fewer
cells (tapped series stack). This provides both drive and regenerative braking
in a brutal way, and is the 'old' (and tried) way of doing it. Fork lift trucks
and the like built according to these principles tended to last 30-40 years.

Imho obtain a book on electric traction control (road and rail) and read it. It
will likely open your eyes. I never did anything larger than 50-100A traction
(12-24V) and I think that just keeping cpu-deadly spikes and kickback under
control will keep you busy for weeks.

Most older (pre thyristor) battery chargers are of the variac type, manual or
automatic, newer ones are thyristor based. Charge equalization in a series
battery is a problem. Nothing is as simple as it seems. The price tags on the
items you quoted probably reflect the low production numbers and the man-hours
put into fixing the problems that had to be fixed.

good luck,
Peter


2008\05\25@144849 by Byron Jeff

flavicon
face
On Sun, May 25, 2008 at 02:15:40PM -0400, Djula Djarmati wrote:
{Quote hidden}

Which makes it a non starter. Used EV controllers can be had for about 1/2
that price.

My point is that the component costs are only about 15 percent of the
retail price of these controllers. Paying $1400, or even $1000, doesn't
make a lot of sense when the parts can be assembled for $150.

> If you make it work, you can experiment in making your own by looking
> the way FANUC did it. If you go this way, let me know and I can find
> some datasheets.

As I stated in my original post, nothing about any of the technology is too
particularly complex. The controller is little more than a PIC driving a
IGBT driver which drives the IGBT with a PWM signal. The input comes from a
standard 5k throttle pot going right into the ADC input of the PIC.

The battery charger, for lead acid, again is little more than taking full
wave rectified DC and buck regulating to thre required voltage. Same for
the DC to DC converter.

I'm really just wanting to make sure I don't miss a crucial design
component. And looking for suggestions on some of these high power
components, such as inductors and ultra fast recovery diodes.

BAJ

2008\05\25@153611 by Harold Hallikainen

face
flavicon
face
When I attempt to do high power electronics, I tend to generate a lot of
smoke and dead parts. Good luck on the controller!

On the charger, I did a very simple one for an EV. The high voltage
battery circuitry is isolated from the chassis. The neutral of the AC line
is connected to the negative side of the battery string. Each phase (two
sides of a 240VAC line or thee phases of a 3 phase wye) goes through an
SCR, then are commoned, then go through an incandescent lamp to the
positive end of the battery string. The SCRs allow you to turn the charger
on and off. The incandescent lamp provides a current limit. By choosing
battery voltage and lamp, you can charge the battery string pretty simply.
The brightness of the lamp starts bright, then dims as the batteries
charge.

To power 12V equipment, I used a universal input switching supply (one
that takes 90VAC to 250VAC with no line voltage switch). It can be driven
directly by the battery string.

To monitor battery condition, I did a simple PIC based monitor on each
battery. It measures battery voltage, temperature, and current. Current is
measured by measuring the voltage drop on the cable going to the battery
"below" this one in the string. The monitor also has a big resistor and an
FET driven by the PIC. When the battery voltage gets too high, charge
current is shunted around the battery (power dumped into the resistor) by
PWMing the FET. If the battery voltage is higher than the set point, the
duty cycle is stepped up. If the battery voltage is below the set point,
the duty cycle is stepped down. Finally, the battery condition is reported
over an opto isolated "Aloha" network. Each unit randomly sends a packet
of data out its uart. The uart drives an opto where the LED is off in the
mark condition and on in the space conditions. The phototransistor on the
opto drives an open collector bus that is isolated from the PIC. The bus
drives another PIC that drives a display and control system that shows
battery condition and controls the charger (drives those SCRs).

This was done for a friend's EV. I ride the bus to work...

Harold




--
FCC Rules Updated Daily at http://www.hallikainen.com - Advertising
opportunities available!

2008\05\25@160227 by Byron Jeff

flavicon
face
On Sun, May 25, 2008 at 02:32:33PM -0400, Peter wrote:
> > 2) Going to start with a battery bank consisting of Eveready GC2 Golf Cart
> > batteries from Sams. 6V, 225 Ah, $75 each. A 144V system of 24 batteries
> > will run $1650 + tax, no shipping and weigh about 1650 lbs.
>
> The goal of the electric car is to be light, in view of the low power density of
> the batteries.

My goal is to build something that I can afford. I battle with the guys on
the DIYEV list all day long about investing tens of thousands of dollars
into lithium batteries. But it's an investment that doesn't make sense to me.

When lithium batteries are reliable, easily available, and about double the
price of lead acid, then I'll consider switching. Until then, it's lead
acid because from a cost standpoint, there's simply no comparison at this
point.

> The law of diminishing returns kicks in fast if you end up with a
> ton of batteries lugged around for no good reason. The best way is to use a
> battery as small as possible and change it often (with another freshly charged
> one). In the 70s and 80s there were trials with such changeable packs for public
> transportation (electric bus). At the time they did not catch on.

Can't store a battery bank at work, which is the only logical place to
swap. The bottom line is that I'm stuck carrying the bank around.

> Imho, try to work the problem backwards: how much do you travel between pit
> stops, what class of EV can do that now (wikipedia helps), how much it
> weighs/costs, then see how you could build a vehicle of that class or refurbish
> a used one.

All that analysis is already done. That really wasn't the purpose of this
thread, though I'm happy to talk about it if you like.

The bottom line is that if you carry enough lead around, you can get
reasonable ranges for a daily drive. That's my goal.

> Available data suggests 20-100 km range for curb weight << 1 ton.

I'm well aware. The challenge is that to carry enough lead to get a useful
range, you exceed the GVWR of the vehicle.

Trucks are designed to carry that kind of weight.

A better tack is to improve the aerodynamics of the vehicle. Trucks are
pretty much a rolling brick with awful coefficients of drag. If you improve
the CD with sloped bed caps, mirror deletion, wheel covers, and the like,
you can greatly improve the range of the vehicle without changing the
weight. See a sample here:

http://ecomodder.com/forum/583-commercially-produced-aerodynamic-pickup-bed-cap.html

> Electronics for electric traction are not so trivial. There is inrush limiting,
> kickback handling, dynamic braking (motor tries to generate - you can't just cut
> the drive, the voltage will raise high enough to blow the insulation on the
> motor if you do that) etc etc. 'Simple' PWM requires a bridge circuit from >500W
> or so and so on.

OK. That's a start. Why kind of hardware is necessary to handle these
issues? I thought the dynamic braking and back EMF was handled by the
freewheeling diode?

> Plus the torque/rpm characteristics of usual electric motors are not suitable
> for road traction use without some suitable controllers. The easiest hack is to
> rely on the gearbox and implement a step relay that will shunt in more or fewer
> cells (tapped series stack).

No. Bad idea. The one thing that I've learned in my research is that you'll
destroy the pack using that technique.

The whole point of PWM is that the full pack voltage is applied all the
time. That means that you'll get maximum torque as limited by the
controller and the switch and max RPM generated by the PWM ratio.

All of this is known engineering. No modern PWM controller ever does
anything but apply the full pack voltage to the motor. Soft start and rmp
are controlled by the PWM ratio, and nothing else, from my research.

> This provides both drive and regenerative braking
> in a brutal way, and is the 'old' (and tried) way of doing it.

Series wound motors. Not going to do regen braking. That energy is just
going to be lost.

> Fork lift trucks
> and the like built according to these principles tended to last 30-40 years.
>
> Imho obtain a book on electric traction control (road and rail) and read it. It
> will likely open your eyes. I never did anything larger than 50-100A traction
> (12-24V) and I think that just keeping cpu-deadly spikes and kickback under
> control will keep you busy for weeks.

They are called Isolated Gates for a reason. What makes you think those
kickbacks are going to cross back into the gate?

> Most older (pre thyristor) battery chargers are of the variac type, manual or
> automatic, newer ones are thyristor based. Charge equalization in a series
> battery is a problem. Nothing is as simple as it seems. The price tags on the
> items you quoted probably reflect the low production numbers and the man-hours
> put into fixing the problems that had to be fixed.

Thanks for the encouragement! ;-)

But I'm going to press on. Because at the end of the day my time is
currently worth less than my dollars. So if I can spend time solving these
problems instead of spending money, then I'll come out ahead in the end.

BAJ

2008\05\25@171835 by Byron Jeff

flavicon
face
On Sun, May 25, 2008 at 03:35:44PM -0400, Harold Hallikainen wrote:
> When I attempt to do high power electronics, I tend to generate a lot of
> smoke and dead parts. Good luck on the controller!

Thanks. What do you find is the typical cause of the release of the "magic
smoke"?

> On the charger, I did a very simple one for an EV. The high voltage
> battery circuitry is isolated from the chassis.

That's my game plan. Did you have a DC/DC converter and 12V backup battery?
If so then I presume that negative is connected to the chassis?

> The neutral of the AC line
> is connected to the negative side of the battery string. Each phase (two
> sides of a 240VAC line or thee phases of a 3 phase wye) goes through an
> SCR, then are commoned, then go through an incandescent lamp to the
> positive end of the battery string. The SCRs allow you to turn the charger
> on and off. The incandescent lamp provides a current limit. By choosing
> battery voltage and lamp, you can charge the battery string pretty simply.
> The brightness of the lamp starts bright, then dims as the batteries
> charge.

Sounds like a plan.

> To power 12V equipment, I used a universal input switching supply (one
> that takes 90VAC to 250VAC with no line voltage switch). It can be driven
> directly by the battery string.

Again did you ground it to the chassis?

> To monitor battery condition, I did a simple PIC based monitor on each
> battery. It measures battery voltage, temperature, and current. Current is
> measured by measuring the voltage drop on the cable going to the battery
> "below" this one in the string.

Interesting. Did you do empirical measurements to figure out the current
draw on the cable?

Also how exactly did the individual PIC monitors affect the overall state
of charging? You only dumped charge current at the top of the string,
right? So if some batteries were above the set point and others were below,
then what did the overal charging system do?

How much difference would it be if there were only an overall voltage and
current of the string?

{Quote hidden}

Cool.

> This was done for a friend's EV. I ride the bus to work...

Wish I could. It would literally take 3 hours each was for me to ride the bus
between work and home. And I haven't even dealt with the pickup and
delivery of kids to school yet. Just isn't an option.

>
> Harold
>
>
>
>
> --
> FCC Rules Updated Daily at http://www.hallikainen.com - Advertising
> opportunities available!
> -

2008\05\25@181535 by olin piclist

face picon face
Byron Jeff wrote:
> Paying $1400, or even $1000,
> doesn't
> make a lot of sense when the parts can be assembled for $150.

Try the real world for a change.  You've clearly never designed a commercial
product and dealt with it all the way into production.

Parts                                      150
Knowing which parts to put where           100
Assembly, test, fallout, and repair         50
Paying back cost of setting up produciton  200
To pay for support when you call after
 having done something stupid             300
To cover liability costs when you do
 something stupid but blame us anyway     100
Cost of capital to get into this business   50
To pay back regulatory compliance and
 testing costs                            100
To make a living                           300
----------------------------------------------
Total                                   $1,350


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.

2008\05\25@181802 by Gerhard Fiedler

picon face
Byron Jeff wrote:

>> Imho obtain a book on electric traction control (road and rail) and read
>> it. It will likely open your eyes. I never did anything larger than
>> 50-100A traction (12-24V) and I think that just keeping cpu-deadly
>> spikes and kickback under control will keep you busy for weeks.
>
> They are called Isolated Gates for a reason. What makes you think those
> kickbacks are going to cross back into the gate?

At least through gate capacity, possibly also ground effects.

Gerhard

2008\05\25@202848 by Sean Breheny

face picon face
I have to agree that there is a LOT more involved in this than you
seem to be taking into account, Byron. High power motor drive
electronics is NOT easy to design. Consider this for a moment: if you
want to keep your heatsinking requirements to a minimum, you will need
to turn the IGBTs on and off very fast. This means that the current in
some parts of the circuit will have rise/fall times of something like
100 ns. Now look at the di/dt which you have in 600 amps switching in
100 ns. That's 6 gigamps per second. If you have a 1 nanohenry stray
inductance (which is nothing), you will see a 6V drop across it during
this turn on/turn off transient. 6V is easily enough to cause any one
of a number of bad things to happen: destruction of digital I/O,
spurious triggering of IGBT gates, IC latchup, etc.

What tends to happen in this arena is that you pile a whole bunch of
FETs or IGBTs together and expect it to work and a whole string of
tough problems spring up due to stray inductance, gate capacitance,
etc. Since a sudden glitch can cause a short circuit (if both high and
low side IGBTs are turned on at the same time), you can destroy your
IGBTs in a fraction of a second.

I once had a motor driver prototype running on a bench when suddenly
there was a tiny "tink" noise. Before I knew what was happening, the
fuse inline with the battery pack burst into two 4-inch long blue jets
of flame. After I disconnected the battery, I found that a whole bunch
of the FETs were toast. Something had turned on high and low side FETs
together, they instantly failed shorted, which caused something like
1000 amps to flow, which exceeded the interrupting rating of my fuse,
caused it to arc over, carbonizing and then igniting.

If you want a learning experience, then build it yourself. If you want
to save money, buy the stuff new or used. You will go through several
sets of parts in your development and it will end up being 2x the cost
of the whole thing new.

Sean


On Sun, May 25, 2008 at 6:17 PM, Olin Lathrop <spam_OUTolin_piclistTakeThisOuTspamembedinc.com> wrote:
{Quote hidden}

> -

2008\05\25@205431 by Byron Jeff

flavicon
face
On Sun, May 25, 2008 at 06:17:40PM -0400, Olin Lathrop wrote:
> Byron Jeff wrote:
> > Paying $1400, or even $1000,
> > doesn't
> > make a lot of sense when the parts can be assembled for $150.
>
> Try the real world for a change.  You've clearly never designed a commercial
> product and dealt with it all the way into production.

Hobbyist. Not trying to sell it.

{Quote hidden}

I understand each and every one of those costs. But as someone who has the
wherewithal to assemble and program it myself, everything after the first
three or possibly four items have no meaning to me.

I didn't say that charging $1400 wasn't reasonable. I said that my paying
that price wasn't. Two completely different things.

I have no problems paying for houses, cars, appliances, flooring, and the
like for exactly the reasons you outline above.

But when it's an item as a hobbyist I can actually put together myself?
That's a whole nother argument.

BAJ

2008\05\25@211056 by Apptech

face
flavicon
face
> ... which caused something like
> 1000 amps to flow, which exceeded the interrupting rating
> of my fuse,
> caused it to arc over, carbonizing and then igniting.

A good but expensive lesson to learn. This is where the
reason that "HRC"* fuses exist and are specified, or
required under certain standards.

One discussion. Much more available on HRC.

       http://www.panickker.net/article5.htm

       Russell


* High Rupture Capacity.


2008\05\25@235251 by Spehro Pefhany

picon face
At 12:04 PM 5/25/2008, you wrote:


>They are called Isolated Gates for a reason. What makes you think those
>kickbacks are going to cross back into the gate?

*Insulated* gates, not isolated gates.

{Quote hidden}

In knowledge, anyhow. Assuming you have the time, background knowledge,
test equipment and dollars to get all the way to a reliable system.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
.....speffKILLspamspam@spam@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com



2008\05\26@113534 by Peter

picon face
Byron Jeff <byronjeff <at> clayton.edu> writes:
> My goal is to build something that I can afford. I battle with the guys on
> the DIYEV list all day long about investing tens of thousands of dollars
> into lithium batteries. But it's an investment that doesn't make sense to me.

So don't buy lithium. But why buy an immense golf cart battery stack? It will
work for sure, in fact there is an ancient (circa 1900) electric truck (pickup)
in the local technical museum. The bed is paved with lead acid batteries and
there is a cover above it so it can take some cargo too. The entire body and
cabin was made of wood, as expected, and the batteries were not 100Ahish from
the size. It has been a long time since I saw it, I was a kid at the time.

> Can't store a battery bank at work, which is the only logical place to
> swap. The bottom line is that I'm stuck carrying the bank around.

Why is it the only logical place to swap? And why swap if you only have one
set? Swapping is an idea to keep in mind. Today you swap lead acid, tomorrow
lithium or who knows what. You have to start somewhere, why not start small and
see where it is going.

> > Available data suggests 20-100 km range for curb weight << 1 ton.
>
> I'm well aware. The challenge is that to carry enough lead to get a useful
> range, you exceed the GVWR of the vehicle.
>
> Trucks are designed to carry that kind of weight.

True, they are also designed not to drive very fast and fuel efficiency was not
quite so high on the priority list for US pickups afaik. Most electric cars
aren't speed cars either.

> OK. That's a start. Why kind of hardware is necessary to handle these issues?
> I thought the dynamic braking and back EMF was handled by the freewheeling
> diode?

What freewheeling diode? Surely you know that most design topologies will not
scale for a power level 1000 times greater than that of the original design?
Please locate the relevant course curriculum at your university (you are on an
edu domain) and see the reading list there for recommended articles and books.

Try Google with:

 electric traction power electronics site:.edu filetype:pdf

for >10k links.

> > Plus the torque/rpm characteristics of usual electric motors are not
> > suitable
> for road traction use without some suitable controllers. The easiest hack is
> to
> > rely on the gearbox and implement a step relay that will shunt in more or
> > fewer cells (tapped series stack).
>
> No. Bad idea. The one thing that I've learned in my research is that you'll
> destroy the pack using that technique.

Not if the voltage equalization devices work as deisgned (i.e. in *both*
directions).

> Series wound motors. Not going to do regen braking. That energy is just
> going to be lost.

Too bad. Literature seems to indicate compound or parallel motors with separate
excitation are best for traction if using simple pwm controllers as you intend
to use.

> They are called Isolated Gates for a reason. What makes you think those
> kickbacks are going to cross back into the gate?

There is no need for the kickbacks to cross into the gate. You will have
something like 200 Amps at 150 Volts switched (at pwm frequency if you do it
your way) into  a loop of wire at least a meter long with a coil of several
Henrys at the other end (the motor) inside a reflective metal box, with
harmonics into VHF and UHF. That will put enough volts into circuit board
tracks nearby to glitch almost anything even without pwm.

> Thanks for the encouragement!

I just said what I know. I doubt whether the 'expensive' controler makers break
even when the market is slow (like it seems to be all the time for some
reason).

> But I'm going to press on. Because at the end of the day my time is
> currently worth less than my dollars. So if I can spend time solving these
> problems instead of spending money, then I'll come out ahead in the end.

That's a good excuse to buy, borrow most of the relevant books you can lay
hands on. There is no point in rediscovering hot water or repeating other
people's mistakes. You could make your own ^^ . Besides $100 in (used) books
should get you further than $1600 in batteries at this time imho.

$0.001
Peter


2008\05\26@130530 by Harold Hallikainen

face
flavicon
face

> On Sun, May 25, 2008 at 03:35:44PM -0400, Harold Hallikainen wrote:
>> When I attempt to do high power electronics, I tend to generate a lot of
>> smoke and dead parts. Good luck on the controller!
>
> Thanks. What do you find is the typical cause of the release of the "magic
> smoke"?
>

I think the chief cause is inexperience in design of high power circuitry.
I used to work in broadcast and could keep 20kW stations running, bud did
not have to design the transmitters.


>> To power 12V equipment, I used a universal input switching supply (one
>> that takes 90VAC to 250VAC with no line voltage switch). It can be
>> driven
>> directly by the battery string.
>
> Again did you ground it to the chassis?

The high voltage string was isolated from the chassis. The negative side
of the 12V was connected to the chassis.

>
>> To monitor battery condition, I did a simple PIC based monitor on each
>> battery. It measures battery voltage, temperature, and current. Current
>> is
>> measured by measuring the voltage drop on the cable going to the battery
>> "below" this one in the string.
>
> Interesting. Did you do empirical measurements to figure out the current
> draw on the cable?

Yes... A clamp on DC ammeter was used to come up with a scaling factor.


>
> Also how exactly did the individual PIC monitors affect the overall state
> of charging? You only dumped charge current at the top of the string,
> right? So if some batteries were above the set point and others were
> below,
> then what did the overal charging system do?

There was one of these monitor and charge balancing boards on each
battery, so power was dumped on each battery that had excessive voltage.
Something I did not mention before is that the circuit boards are mounted
on the negative side of each battery. I used a TO-220 resistor for the
power dump. The thermal path heat sunk the resistor to the battery
negative terminal, since it has a lot of mass.

Harold

--
FCC Rules Updated Daily at http://www.hallikainen.com - Advertising
opportunities available!

2008\05\26@151031 by Peter

picon face
Jeff, please take a look at this document. It contains several interesting
items, including a drive scheme and DOT road testing schedules:

http://scholar.lib.vt.edu/theses/available/etd-102497-12366/unrestricted/final.pdf

good luck and keep us posted,
Peter

2008\05\26@151139 by Byron Jeff

flavicon
face
On Mon, May 26, 2008 at 11:35:03AM -0400, Peter wrote:
> Byron Jeff <byronjeff <at> clayton.edu> writes:
> > My goal is to build something that I can afford. I battle with the guys on
> > the DIYEV list all day long about investing tens of thousands of dollars
> > into lithium batteries. But it's an investment that doesn't make sense to me.
>

> So don't buy lithium. But why buy an immense golf cart battery stack? It
> will work for sure,...

I presume you mean why not buy the golf cart battery stack?

That's exactly my game plan.

> > Can't store a battery bank at work, which is the only logical place to
> > swap. The bottom line is that I'm stuck carrying the bank around.
>

> Why is it the only logical place to swap? And why swap if you only have
> one set? Swapping is an idea to keep in mind. Today you swap lead acid,
> tomorrow lithium or who knows what. You have to start somewhere, why not
> start small and see where it is going.

You probably needed to keep the context of the poster that asked the
question. Let me see if I can add it back in...

Here it is...

---------------------------------------
> The law of diminishing returns kicks in fast if you end up with a ton of
> batteries lugged around for no good reason. The best way is to use a
> battery as small as possible and change it often (with another freshly
> charged one). In the 70s and 80s there were trials with such changeable
> packs for public transportation (electric bus). At the time they did not
> catch on.
---------------------------------------

As I stated, not an option.

{Quote hidden}

They can be if you make them light enough. But not my priority.


I'll tackle the rest of the post later.

BAJ

2008\05\26@195036 by Cristóvão Dalla Costa

picon face
On Sun, May 25, 2008 at 1:04 PM, Byron Jeff <byronjeffspamKILLspamclayton.edu> wrote:

> > This provides both drive and regenerative braking
> > in a brutal way, and is the 'old' (and tried) way of doing it.
>
> Series wound motors. Not going to do regen braking. That energy is just
> going to be lost.
>


Then why bother at all? A significant part of the energy used to move cars
and trucks ends up as waste heat in the brakes. IIRC something in the order
of 60% -- specially with a heavy vehicle in city driving where speeds < 80
km/h and aerodynamic drag is not the dominant factor.

Now factor the increased weight of the lead batteries you want to carry over
the empty truck/car and you just waste that much more energy. Consider how
heavy the batteries will be and the waste accelerating and stopping that
mass that will just end up as heat on the brakes.

I'm sorry, but if you're going to all that effort to make an economical
vehicle, either go all the way and do the regenerative braking, or don't. A
half-assed solution is probably going to be a headache in the long run.

I have a pdf of a paper of the Catholic University of Chile where they
converted a truck to electric power using batteries and a ultracapacitor
bank for regenerative braking. I don't know if I can post it, but just
google "regenerative braking university chile" and a downloadable pdf will
be among the first links.

HTH

2008\05\26@215803 by Mike Reid

picon face


In the April 28 issue of Design News, the cover article is on battery
technology.

They show that gasoline packs 80 times more energy than lithium-ion
batteries and 250 more times than lead-acid batteries.

http://www.designnews.com/article/CA6551948.html

Above is a link to a number of articles on their website about designing
electric cars.

The April 28 article is titled, "It's Not a Slam Dunk."

They asked five experts to estimate the specific energy and cost of EV
batteries as they stand today.  Here are the approximate averages of their
responses:

Battery                        Specific Energy (W-hr/kg)                cost
($/kW-hr)

Lithium-ion                                140
$770

Nickel-metal hydride                110
$850

Lead-acid                                50
$100

$= US dollars (check the web hourly for how much it's falling:)


I didn't search for the above mentioned article but it's worth finding and
reading.



2008\05\26@230342 by Byron Jeff

flavicon
face
On Mon, May 26, 2008 at 07:50:14PM -0400, Crist?v?o Dalla Costa wrote:
> On Sun, May 25, 2008 at 1:04 PM, Byron Jeff <.....byronjeffKILLspamspam.....clayton.edu> wrote:
>
> > > This provides both drive and regenerative braking
> > > in a brutal way, and is the 'old' (and tried) way of doing it.
> >
> > Series wound motors. Not going to do regen braking. That energy is just
> > going to be lost.
> >
>
>
> Then why bother at all?

Because the design is a balance of cost, efficacy, complexity, and range.
It takes quite a bit of infrastructure, and therefore cost and complexity,
to implement regen braking. You have to have a certain type of motor (AC or
shunt wound), you have to have a controller than can handle it. You have to
have improved battery management systems.

> A significant part of the energy used to move cars
> and trucks ends up as waste heat in the brakes. IIRC something in the order
> of 60% -- specially with a heavy vehicle in city driving where speeds < 80
> km/h and aerodynamic drag is not the dominant factor.

All true.

> Now factor the increased weight of the lead batteries you want to carry over
> the empty truck/car and you just waste that much more energy. Consider how
> heavy the batteries will be and the waste accelerating and stopping that
> mass that will just end up as heat on the brakes.

I'm well aware.

> I'm sorry, but if you're going to all that effort to make an economical
> vehicle, either go all the way and do the regenerative braking, or don't.

Don't do regen braking, or don't do the vehicle?

> A
> half-assed solution is probably going to be a headache in the long run.

What headache? As you stated the wasted energy will be burnt on the brakes.
What you lose in efficiency, you gain in spades in simplicity and lower
costs.

> I have a pdf of a paper of the Catholic University of Chile where they
> converted a truck to electric power using batteries and a ultracapacitor
> bank for regenerative braking. I don't know if I can post it, but just
> google "regenerative braking university chile" and a downloadable pdf will
> be among the first links.

I'll certainly take a look for it.

BAJ

2008\05\26@231750 by Byron Jeff

flavicon
face
On Tue, May 27, 2008 at 12:56:27AM -0400, Mike Reid wrote:
>
>
> In the April 28 issue of Design News, the cover article is on battery
> technology.
>
> They show that gasoline packs 80 times more energy than lithium-ion
> batteries and 250 more times than lead-acid batteries.

That's well known. One number that I saw in an article (can't quote it off
the top of my head) pointed to a gallon of gas having the equivalent of 15
kWh worth of usable energy at its typical 25% efficiency. That's the same
capacity of a lead-acid pack weighing over 1500 lbs.

{Quote hidden}

I believe that I had seen it. I liken driving an EV to a vehicle that has a
1 gallon gas tank and can only be refilled at home.

It has its challenges. However, my daily commute takes less than a gallon
of gas to pull off. So there is hope.

BAJ

2008\05\26@232504 by Byron Jeff

flavicon
face
Peter,

I think I accidentally deleted your post about the AC inverter paper.

However in my searching I found a really useful motor control handbook by
Richard Valentine:

http://tinyurl.com/6yujn9

And the whole book is previewable under Google Books.

So I have some decent reading material now.

Thanks for the suggestion,

BAJ

2008\05\27@032253 by Peter

picon face
Peter <plpeter2006 <at> yahoo.com> writes:
> Jeff, please take a look at this document. It contains several interesting
> items, including a drive scheme and DOT road testing schedules:
>
>
http://scholar.lib.vt.edu/theses/available/etd-102497-12366/unrestricted/final.pdf

You can find older posts in archives, like here:

http://article.gmane.org/gmane.comp.hardware.microcontrollers.pic/142456

Peter


2008\05\27@060818 by Michael Rigby-Jones

picon face


> -----Original Message-----
> From: EraseMEpiclist-bouncesspam_OUTspamTakeThisOuTmit.edu [piclist-bouncesspamspam_OUTmit.edu] On
Behalf
> Of Byron Jeff
> Sent: 25 May 2008 11:33
> To: @spam@piclistKILLspamspammit.edu
> Subject: [EE] Questions on Electric Vehicle high power electronics
>
>
> 1) Still looking for a donor truck. Probably will end up with on off
> craigslist. With a blown engine, it won't be more than $500.

Starting with a very heavy American truck and then making it much
heavier with lead acid batteries doesn't strike me as a sensible
starting point for an electric vehicle.  Why not start with something
lightweight to start with and then you don't need as many batteries or
such a powerful motor?  The electronics then become cheaper/simpler.

Mike

=======================================================================
This e-mail is intended for the person it is addressed to only. The
information contained in it may be confidential and/or protected by
law. If you are not the intended recipient of this message, you must
not make any use of this information, or copy or show it to any
person. Please contact us immediately to tell us that you have
received this e-mail, and return the original to us. Any use,
forwarding, printing or copying of this message is strictly prohibited.
No part of this message can be considered a request for goods or
services.
=======================================================================

2008\05\27@070209 by Peter

picon face

1979: http://www.econogics.com/ev/lep.htm

Full schematics and driving instructions. Wetware controller.

Peter


2008\05\27@082425 by Byron Jeff

flavicon
face
On Tue, May 27, 2008 at 06:07:54AM -0400, Michael Rigby-Jones wrote:
>
>
> > -----Original Message-----
> > From: KILLspampiclist-bouncesKILLspamspammit.edu [RemoveMEpiclist-bouncesTakeThisOuTspammit.edu] On
> Behalf
> > Of Byron Jeff
> > Sent: 25 May 2008 11:33
> > To: spamBeGonepiclistspamBeGonespammit.edu
> > Subject: [EE] Questions on Electric Vehicle high power electronics
> >
> >
> > 1) Still looking for a donor truck. Probably will end up with on off
> > craigslist. With a blown engine, it won't be more than $500.
>
> Starting with a very heavy American truck and then making it much
> heavier with lead acid batteries doesn't strike me as a sensible
> starting point for an electric vehicle.  Why not start with something
> lightweight to start with and then you don't need as many batteries or
> such a powerful motor?  The electronics then become cheaper/simpler.

A couple of points.

First is that I'm only looking at compact trucks. Vehicles in the range of
the Chevy S10, Ford Ranger, Mazda B2200, Nissan Frontier, and the like.
They have curb weights in the mid to high 2000 lbs, which isn't too
terribly bad for a vehicle. You then get to strip out all the associated
ICE components, which will give you about 400 lbs back, putting you in the
low 2000s. The curb weight of the converted truck should still come in
under 4000 lbs.

The tradeoff with very light vehicles and lead acid is both maximum weight
and drivability. Trucks are actually designed to carry heavy loads, whereas
lightwight cars are not.

The second problem is that every less battery you carry has a double effect
on range. The first is that you lose the energy capacity of the battery.
The second is that the remaining batteries have to work harder to power the
car, which ups their amp draw. Due to an effect called the Peukert effect,
the faster you draw power from a battery, the less total energy you can
extract. So point in fact you really want to up the voltage.

Now you can combat that by using 12V batteries instead of 6V golf cart
batteries. But when you double the voltage, you half the energy capacity,
presuming that the 12V and 6V batteries are about the same size and weight,
which they often are. Reducing your energy capacity by half cuts your range
by half.

The only positive side is what you outlined. Carrying less weight will get
you further. However, the gains in weight you gain are heavily offset by the
losses in energy capacity and efficiency you lose. In short a lightweight
truck carrying a heavier battery pack will get you further than a
lightweight car carrying a lighter battery pack.

As for simplicity, trucks are much easier to convert than cars. They have
both a bed, and space under the bed, to carry batteries. You don't have to
worry about having batteries in the passenger compartment. And as outlined
before they are designed to carry the weight. Stock compact trucks have a
rated payload in the ballpark of 1500 lbs, and that's before any suspension
upgrades.

LionEV, which specializes in Lithium battery conversions, shows an example
of converting a Ford Ranger here:

http://www.lionev.com/DIY_Ranger.html

BAJ

2008\05\27@085702 by Byron Jeff

flavicon
face
On Tue, May 27, 2008 at 07:01:29AM -0400, Peter wrote:
>
> 1979: http://www.econogics.com/ev/lep.htm
>
> Full schematics and driving instructions. Wetware controller.

The controller is too simple. In today's age of cheap power electronics,
there's no reason to go with a two stage contactor driven motor.

So I'd like to get back to original point. Valentine's book, of which I
need to order a copy, gave an excellent set of rules of thumb:

1. Due to inductance effects, mount the power electronics on the motor.

2. A freewheeling diode is necessary to combat kickback and back EMF.

3. Use opto drivers between the control electronics and power circuitry.

4. You have to find balance between audio noise, power losses due to
switching, and switching rise/fall times.

All excellent advice.

I guess I'll wait for the book to be delivered, then start back with some
more pointed questions.

BAJ

2008\05\27@091845 by Sean Breheny

face picon face
Hi Byron,

While I still think you are underestimating the motor drive
electronics, it is clear that you have done some good homework.
However, I think you should try to restate what you say below
mathematically. Then I think you will find that the equations for
range vs. battery mass and performance vs. battery mass will both have
optimal points. In other words, I don't think that adding more and
more batteries will continue to get you much more range. I think it
will at least level off if not begin to drop again at some point.

Also, you say that going to a higher voltage reduces your total
energy. That's not true. If you have a 6V 100AH battery, it is about
the same size as a 12V 50AH battery. If you design your system
properly for each power source, you should be drawing half the current
from the 12V setup compared to the 6V setup and get comparable usage
time (i.e. range).

Sean


On Tue, May 27, 2008 at 4:25 AM, Byron Jeff <TakeThisOuTbyronjeffEraseMEspamspam_OUTclayton.edu> wrote:

{Quote hidden}

> -

2008\05\27@094320 by Michael Rigby-Jones

picon face


> -----Original Message-----
> From: RemoveMEpiclist-bouncesspamTakeThisOuTmit.edu [piclist-bouncesEraseMEspam.....mit.edu] On
Behalf
> Of Byron Jeff
> Sent: 27 May 2008 09:26
> To: Microcontroller discussion list - Public.
> Subject: Re: [EE] Questions on Electric Vehicle high power electronics
>
>
> The second problem is that every less battery you carry has a double
> effect
> on range. The first is that you lose the energy capacity of the
battery.
> The second is that the remaining batteries have to work harder to
power
> the
> car, which ups their amp draw

Surely with a lighter car they wouldn't have to work so hard?

Mike

=======================================================================
This e-mail is intended for the person it is addressed to only. The
information contained in it may be confidential and/or protected by
law. If you are not the intended recipient of this message, you must
not make any use of this information, or copy or show it to any
person. Please contact us immediately to tell us that you have
received this e-mail, and return the original to us. Any use,
forwarding, printing or copying of this message is strictly prohibited.
No part of this message can be considered a request for goods or
services.
=======================================================================

2008\05\27@110840 by Byron Jeff

flavicon
face
On Tue, May 27, 2008 at 09:39:11AM -0400, Michael Rigby-Jones wrote:
{Quote hidden}

It's a multivariable knapsack problem. It's not easy to solve at all.

BAJ

2008\05\27@112959 by Byron Jeff

flavicon
face
On Tue, May 27, 2008 at 09:18:18AM -0400, Sean Breheny wrote:
> Hi Byron,
>
> While I still think you are underestimating the motor drive
> electronics, it is clear that you have done some good homework.

Thanks.

> However, I think you should try to restate what you say below
> mathematically. Then I think you will find that the equations for
> range vs. battery mass and performance vs. battery mass will both have
> optimal points. In other words, I don't think that adding more and
> more batteries will continue to get you much more range. I think it
> will at least level off if not begin to drop again at some point.

True. But that marginal point is well above the 144-156V bank that I'm
planning on implementing.

My emprical example is the "Red Beastie" found here:

http://www.evalbum.com/037

It's a compact truck that's carrying 40 lead acid batteries in a 120V by
450Ah pack. The 16 extra batteries it carried represented a 1000 lbs
additional load. But the expected range is close to double of what I expect
to get.

> Also, you say that going to a higher voltage reduces your total
> energy. That's not true. If you have a 6V 100AH battery, it is about
> the same size as a 12V 50AH battery.

That's correct.

> If you design your system
> properly for each power source, you should be drawing half the current
> from the 12V setup compared to the 6V setup and get comparable usage
> time (i.e. range).

That presumes that you're going to double the voltage of the 12V pack over
the 6V one. But because of the motor and the control electronics, it's
generally no possible to do either. So you end up with packs of
approximately the same voltage. That means you have 1/2 the number of
batteries in the 12V pack as the 6V one. So the total energy is reduced.

The bottom line is that you'll exceed the gross vehicle weight rating and the
voltage rating of the motor well before you reach the marginal dropoff of
carrying more lead. And you can carry more lead without exceeding the
voltage rating of the motor by carrying 6V batteries.

BAJ

2008\05\27@122134 by Alan B. Pearce

face picon face
>Starting with a very heavy American truck and then making it much
>heavier with lead acid batteries doesn't strike me as a sensible
>starting point for an electric vehicle.  Why not start with something
>lightweight to start with and then you don't need as many batteries or
>such a powerful motor?  The electronics then become cheaper/simpler.

Yeah, I was thinking along the lines of a Ford Ka with 4 wheel electric
motors for a commute vehicle.

2008\05\27@122714 by Peter

picon face
Peter <plpeter2006 <at> yahoo.com> writes:
1979 'brute force' Renault 12 conversion: http://www.econogics.com/ev/lep.htm

I am posting this again as the bit dog ate my posting.

Peter


2008\05\27@170023 by Gerhard Fiedler

picon face
Byron Jeff wrote:

>> If you design your system properly for each power source, you should be
>> drawing half the current from the 12V setup compared to the 6V setup
>> and get comparable usage time (i.e. range).

> That presumes that you're going to double the voltage of the 12V pack over
> the 6V one.

Why? You can parallel them also.

> But because of the motor and the control electronics, it's
> generally no possible to do either. So you end up with packs of
> approximately the same voltage. That means you have 1/2 the number of
> batteries in the 12V pack as the 6V one. So the total energy is reduced.

Or instead of 24 6V batteries in series, you use 2 x 12 12V batteries (12
in series, 2 parallel strings, or 12 sets of 2 parallel batteries in
series). Should get the same energy density, or a higher one. A 12V battery
is nothing more than 2 6V batteries in one case. With less casing, the
overall energy density of the pack should be (a little) higher with 12V
batteries.

Gerhard

2008\05\27@183557 by Byron Jeff

flavicon
face
On Tue, May 27, 2008 at 04:58:48PM -0400, Gerhard Fiedler wrote:
> Byron Jeff wrote:
>
> >> If you design your system properly for each power source, you should be
> >> drawing half the current from the 12V setup compared to the 6V setup
> >> and get comparable usage time (i.e. range).
>
> > That presumes that you're going to double the voltage of the 12V pack over
> > the 6V one.
>
> Why? You can parallel them also.

That requires a committment to parallel strings from the beginning and you
have to add batteries in pairs.

So then exactly what does it buy you? By the time you've added enough
batteries to match your 6V, you have the same number of batteries anyway.

So it ends up being a wash. Except for the fact that 6V batteries have
thicker plates and so they are more robust.

{Quote hidden}

See above.

The only reason to go with 12V batteries is if you plan to lessen the
number of batteries you plan to carry. If you're not, then 6V are the
superior choice.

How did we get here? I was hoping to focus this discussion on design issues
on high power motor electronics, not vehicle choice (it's going to be a
pickup truck), battery type (it's going to be lead acid), battery voltage
(it's going to be 6V batteries), regenerative braking (the motor is going
to be a DC series wound motor, so no regen), or costs (it's a hobby build
so I'm not interested in why there's a nearly 10x markup of a commercial
product over the cost of components).

There are seriously thought out reasons for each of these choices. I'll
keep discussing them, but the original intent of the thread is virtually
dead. Again it seems to me a an integrated EV controller solution that
incorporates charging, PWM motor control, monitoring, and user interface
would have some utility due to system integration. Motor control and user
interface both need to know the current, charging and user interface both
need to know the voltage. A lot of EVs actually have two or three shunts in
the power loop to give info to the controller, user display, and charger
for example.

Let's start with a simple question. The PowerEx IGBT module 1200V @ 600A is
commonly available. According to the data sheet:

http://theelectrostore.com/datasheets/cm600ha24h.pdf

It integrates a reverse connected freewheeling fast recovery diode. My
question is that a motor controller must integrate such a diode to keep
spikes down when the IGBT turns off. Controllers such as the ones outlined
in Valentine's book show that diode across the motor. Is it sufficient to
have that diode across the IBGT? The presumes that the IGBT is going to be
mounted on the motor to keep the leads as short as possible.

BAJ

2008\05\28@004702 by Sean Breheny

face picon face
Hi Byron,

Can you point me to the actual diagram showing the diode directly
across the motor? The main point of that diode is to protect the IGBT
(and possibly also to preserve the brushes in the motor and keep
efficiency up). It is best, usually, to put it closest to the IGBT as
possible. This minimizes the inductance which is unclamped when the
IGBT turns off (the current will continue to flow through the motor
and its supply wires).

I suspect that the reason why the book shows the diode across the
motor is that the diode integrated into the IGBT is in the wrong
direction if you are only using a single IGBT (instead of an H
bridge). In this case, it probably assumes that there is also a diode
inside the IGBT module.

There are a number of ways to do PWM. For example, you can have an H
bridge or just a single IGBT (depending on whether you need to reverse
direction). You can rely on the freewheeling diodes to conduct, or you
can actively short across them on the legs of the H bridge which
conduct during that part of the cycle. You can turn one pair of IGBTs
on during the "on" part of the cycle, and then turn the other pair on
for the "off time" (this way, 50% PWM=0 torque). You can also short
across the motor during the "off" part of the cycle. Each of these has
their advantages and disadvantages in each application.

I like to view a typical motor drive as a type of switching power
supply (buck converter). The PWM and the motor inductance transform a
high voltage/ low current (at the battery) into a low voltage/ high
current (in the motor windings). Incidentally, in motors which DO
regen, this also works in reverse and automatically forms a boost
converter to charge the batteries.

You should consider having a capacitor bank to lessen the ripple
current seen by the batteries. This reduces the (negative) effects of
the battery resistance, wire resistance, and wire inductance (wire
here being the leads from the batteries to your controller).

To a certain extent motor inductance is your friend as it allows you
to reduce the PWM frequency and still maintain a low current ripple in
the motor (reduces I2R losses). Lower PWM freq allows lower IGBT or
FET switching losses (since the switching element usually has a
constant transition time and this gets repeated more times per second
at a higher PWM freq). On the other hand, lower PWM frequencies may be
annoyingly audible and high motor inductance can in some cases
actually reduce motor performance (because the winding inductance acts
to limit current and cause phase shifts which make the pre-defined
commutation points less optimal).

Beware of the specs of modules such as this. They are usually very
unrealistic. For example, most of the specs are given for a Tj=25C,
which could only possibly happen (during continuous operation) if you
had a LN2 cooled heatsink! I would bet that if you work out the
details for this module, with a realistic heatsink and ambient
temperature, it can only do something like 400A continuous.

Beware also that an IGBT is essentially a FET driving a BJT.
Therefore, they share some of the pathologies of each. They are
sensitive to voltage spikes on the gate (which can punch through it).
They also have a (fairly constant) collector emitter saturation
voltage when fully on instead of an on resistance like a FET. They are
susceptible to second breakdown (unequal current sharing in different
parts of the BJT junctions) which limits the safe operating area to
something smaller than a rectangle. They are also slower than FETs.

The main reason for choosing an IGBT over a FET is the higher Vce max
voltage for IGBTs. If you can get away with using FETs, I'd recommend
those instead.

Bear in mind, for example, that at 400A continuous, this module is
going to be dissipating more than 400W. This is not including
switching losses.

Sean


On Tue, May 27, 2008 at 2:37 PM, Byron Jeff <RemoveMEbyronjeffspam_OUTspamKILLspamclayton.edu> wrote:
{Quote hidden}

> -

2008\05\28@100258 by Byron Jeff

flavicon
face
On Wed, May 28, 2008 at 12:46:57AM -0400, Sean Breheny wrote:
> Hi Byron,
>
> Can you point me to the actual diagram showing the diode directly
> across the motor?

There are samples in the images on this page:

http://www.simreal.com/content/CustomMotorDriver

{Quote hidden}

I thought the diode needed to be reverse connected. The PowerEx module
calls it a reverse connected ultra fast recovery diode. It's connected with
the cathode facing the collector, just like the diode in the image on the
web page.

> There are a number of ways to do PWM. For example, you can have an H
> bridge or just a single IGBT (depending on whether you need to reverse
> direction).

Single direction. I'm planning on keeping the transmission and the clutch
so the transmission can reverse the car.

> You can rely on the freewheeling diodes to conduct, or you
> can actively short across them on the legs of the H bridge which
> conduct during that part of the cycle.

> You can turn one pair of IGBTs
> on during the "on" part of the cycle, and then turn the other pair on
> for the "off time" (this way, 50% PWM=0 torque).

No H-bridge. It's a single IGBT module.

{Quote hidden}

Interesting.

> You should consider having a capacitor bank to lessen the ripple
> current seen by the batteries. This reduces the (negative) effects of
> the battery resistance, wire resistance, and wire inductance (wire
> here being the leads from the batteries to your controller).

The suggestions that I've seen is using motor run capacitors such as the
ones that you often see in air conditioning units.

{Quote hidden}

I got that from what I've read in Valentine's book preview. I need to
locate a copy of the book locally if possible.

> Beware of the specs of modules such as this. They are usually very
> unrealistic. For example, most of the specs are given for a Tj=25C,
> which could only possibly happen (during continuous operation) if you
> had a LN2 cooled heatsink! I would bet that if you work out the
> details for this module, with a realistic heatsink and ambient
> temperature, it can only do something like 400A continuous.

That's fine because there's no way I'm going to be driving the motor with
400A continuous. If the continuous draw is more than 100A, then I'll be out
of juice so fast, that I'll be sitting on the side of the road.

It's overengineered for the application both the peak voltage and peak
current.

{Quote hidden}

Thanks for the design info. The primary reasons for looking at IGBTs are
cost, availability, packaging, and the fact the similar controller
solutions use them. Plus they are overengineered for the application so
it's less likely I'll actually smoke them.

Every application I've seen that have used FETs ended up paralleling a set
of them to get the requisite current capacity.

I'm really looking for simple, cheap, reliable, and available. I know I can
pick up 3 or 4 of the IGBTs off Ebay for around $100 and be reasonably
assured that they will work in the application.

If anyone can suggest a FET module that has similar characteristics, then
I'd be happy to take a look at them.

> Bear in mind, for example, that at 400A continuous, this module is
> going to be dissipating more than 400W. This is not including
> switching losses.

Again the continuous amps are going to be less than a quarter of that. Heat
sinking is going to be a design issue I still have to deal with.

Thanks for the overview. It really helps.

BAJ

2008\05\28@102324 by Apptech

face
flavicon
face
> No H-bridge. It's a single IGBT module.

Byron,

Do you have the IGBT module already?
And what is the part number.
If you haven't got it yet I may be able to supply something.
What specs (current and voltage etc) or part number?


       Russell

2008\05\28@113759 by Byron Jeff

flavicon
face
On Wed, May 28, 2008 at 10:22:35AM -0400, Apptech wrote:
> > No H-bridge. It's a single IGBT module.
>
> Byron,
>
> Do you have the IGBT module already?

Nope.

> And what is the part number.

PowerEx CM600HA-24H

> If you haven't got it yet I may be able to supply something.
> What specs (current and voltage etc) or part number?

You can find a sample here:

http://tinyurl.com/648p67

These are 600A 1200V modules. They are way overengineered for the
application which is going to be 144V with a max amperage of 350-400A in
short pulses.

Ebay folks seem to have a ton of them available for a reasonable price.
Enough to purchase a couple of hot spares if necessary.

BAJ

2008\05\28@200759 by Apptech

face
flavicon
face
>> Do you have the IGBT module already?
> PowerEx CM600HA-24H
> http://tinyurl.com/648p67
>
> These are 600A 1200V modules. They are way overengineered
> for the
> application which is going to be 144V with a max amperage
> of 350-400A in
> short pulses.

Ah. Better than mine.
I just checked what I have and they are "Trilingtons" - 3
transistors in a Darlington cascade. 1000V, 400A.
IGBT will be much nicer to drive and the cost is low enough
to not matter wrt the rest of the project.

The 400A is close to their 400A max rating (for very very
small values of close). Most things get grumpy near the
edges. Using two may be a very good idea [tm] if you can
current share OK. Also, as they are BJT output second
breakdown SOA becomes an issue. I'd check data sheets VERY
carefully. Best guide is what others have reliably achieved
with them already.



       Russell


2008\05\28@213704 by Byron Jeff

flavicon
face
On Wed, May 28, 2008 at 08:07:10PM -0400, Apptech wrote:
{Quote hidden}

Actually in my searches today I found a couple of extremely useful
resources. The first is that the Electric Vehicle Discussion List has a
wiki with everything from Donor car selection to DC motor controller design
tips. You can find it here:

http://wiki.saymoo.org/EvdlGems/CategoryEvdlGems

One of the pages echoed a post in this thread that stated that IGBTs are a
poor choice because of the awful voltage drop. So poking around Digikey I
happened upon some 200V 120A MOSFETS from Ixys that are running about $42
each. You can find the datasheet here:

http://ixdev.ixys.com/DataSheet/96538.pdf

I figure that parallelling 4 of them should get me in the right ballpark.
I plan to current limit in software anyway.

I'm going to finish reading through the build your own controller page
here:

http://wiki.saymoo.org/EvdlGems/CategoryMotorControllers?highlight=%28EvdlGems%5C/CategoryEvdlGems%29

Lots of useful tips.

BAJ

2008\05\28@220421 by Apptech

face
flavicon
face
> One of the pages echoed a post in this thread that stated
> that IGBTs are a
> poor choice because of the awful voltage drop. So poking
> around Digikey I
> happened upon some 200V 120A MOSFETS from Ixys that are
> running about $42
> each. You can find the datasheet here:
>
> http://ixdev.ixys.com/DataSheet/96538.pdf
>
> I figure that parallelling 4 of them should get me in the
> right ballpark.
> I plan to current limit in software anyway.

My Trilingtons have a Vcesat max of 3V at 400A with 8A base
drive :-)
Hmmm - that would be 1.2 kW dissipation in the device.

Abs max power dissipation is 3.12 kW.
Rjc = 0.04 C/W
So junction-case rise is 50C.
To limit case rise to say another 50C above ambient would
need a 0.04 C/W heatsink.
That explains the heatsinks they are on :-).
Not enough though - maybe ?0.1 C/W? with fan cooling?
Heat pipe open water boiling would do it. BUT that puts the
junction at 150C+ in extreme cases - a "bit naughty" [tm].
BUT sealed heat pipe at < 100C action would do well enough.

   "Why is the car body warm?"
   'I'm using full throttle.'


       Russell McMahon


2008\05\28@221157 by Tobias Gogolin

picon face
Looks like you gain only about a volt of reduced loss,
However you get mighty close to the voltage rating!
Maybe rather consider to further increase the system voltage rating instead;
to 360 V for example like some of the commercial hybrids with AC drive....

On Wed, May 28, 2008 at 2:38 PM, Byron Jeff <RemoveMEbyronjeffTakeThisOuTspamspamclayton.edu> wrote:

{Quote hidden}

> -

2008\05\29@022204 by Sean Breheny

face picon face
Hi Byron,

I think you are going to have to do some testing and/or simulation to
get a very good handle on the current involved (if you haven't already
done so)

In order of preference for "gotchas" and ease of use I'd say:
1) Single FET
2) Single IGBT
3) Parallel FETs

Parallel FETs have their own weird issues. For example, they might not
both turn on at exactly the same time so you have some fraction of the
time when (at worst) only one is carrying full current. Also, even
though they have a positive temp coeff on Rds_on (so that they
automatically share current well when fully on), that ONLY applies to
the fully on state. At least some FETs have a positive temp coeff on
CURRENT in the partially-on state. This means that the hottest one
will snap on first and take all the current (AND experience ALL of the
turn-on transient power dissipation). These are not insurmountable but
not at all trivial.

I would only advocate a single FET (or even parallel ones) if you
could be well within (say at least 20% below) their max Vds spec.

Also, bear in mind that motor current will not in general equal
battery current. This is because your motor inductance is keeping the
motor current fairly steady while the battery only sees that current
during the "on" portion of the duty cycle. This is the buck converter
action going on. So, as a rough example, if you are running at 50%
duty and the motor winding current is 200A, your battery will only see
about 100A.

As for the diode across the motor - I looked at that page and it looks
to me as if it is the same as what I said - the diode is in a
different direction (as seen by the motor inductance) than the
freewheeling diode inside the IGBT. Think of the inductor current
during the PWM "on" time. Now think of the path it has to take to stay
flowing in the same direction when the IGBT switches off. You will see
that the internal diode in the IGBT (or FET) tries to block the
current, but one right across the coil does not block the current. The
diodes are in the same direction as far as the supply rails are
concerned, but from the point of view of the motor winding current,
one is a stop sign and the other is a GO.

You will ultimately need quite a bit of protection circuitry in order
to prevent something like a stalled motor or shorted wires from frying
your expensive controller.

I would HIGHLY recommend that you trying lashing up a quick drive for
say a 100W motor or even a 1000W motor as a learning exercise. You
could do it with a PIC or a function generator, gate drive IC, and
either a FET or an IGBT (or try both). You would be able to see the
kinds of things we are talking about.

Sean


On Wed, May 28, 2008 at 5:38 PM, Byron Jeff <EraseMEbyronjeffspamspamspamBeGoneclayton.edu> wrote:
{Quote hidden}

> -

2008\05\29@091743 by Alan B. Pearce

face picon face
>    "Why is the car body warm?"
>    'I'm using full throttle.'

Self heating in winter, though ...

2008\05\29@201405 by Byron Jeff

flavicon
face
On Thu, May 29, 2008 at 02:21:35AM -0400, Sean Breheny wrote:
> Hi Byron,
>
> I think you are going to have to do some testing and/or simulation to
> get a very good handle on the current involved (if you haven't already
> done so)

I haven't. I'm still in the design phase.

> In order of preference for "gotchas" and ease of use I'd say:
> 1) Single FET
> 2) Single IGBT
> 3) Parallel FETs

OK. Will at least at first glance single FETs are out. So it looks like
back to IGBTs.

{Quote hidden}

Understood. It was one of the reasons I was looking to these single IGBT
modules. I understand they come with a basketfull of issues too.

> I would only advocate a single FET (or even parallel ones) if you
> could be well within (say at least 20% below) their max Vds spec.

That's the game plan. I was looking at 200V parts. I don't plan to run them
over 144V.

> Also, bear in mind that motor current will not in general equal
> battery current. This is because your motor inductance is keeping the
> motor current fairly steady while the battery only sees that current
> during the "on" portion of the duty cycle. This is the buck converter
> action going on. So, as a rough example, if you are running at 50%
> duty and the motor winding current is 200A, your battery will only see
> about 100A.

Got it.

{Quote hidden}

Hmm. So that means that a separate diode is required.

> You will ultimately need quite a bit of protection circuitry in order
> to prevent something like a stalled motor or shorted wires from frying
> your expensive controller.

I plan to throw the entire array of safety circuitry at it. I'm still
trying to wrap my head around the essential components necessary to get
even a basic controller going.

> I would HIGHLY recommend that you trying lashing up a quick drive for
> say a 100W motor or even a 1000W motor as a learning exercise. You
> could do it with a PIC or a function generator, gate drive IC, and
> either a FET or an IGBT (or try both). You would be able to see the
> kinds of things we are talking about.

That was my plan. Does the voltage significantly impact the issue? By this
would testing at 12V give a good sense of the issues that are going on?

Thanks for the advice.

BAJ


'[EE] Questions on Electric Vehicle high power elec'
2008\06\01@000418 by Sean Breheny
face picon face
Hi Byron,

Voltage does impact things (not the absolute voltage but how close you
are to the rating of the devices), but in order to keep the problem as
simple as possible, I would start out with a voltage which is several
times lower than the max of the part (i.e., like 12V on 36V or 50V
parts).

Sean


On Thu, May 29, 2008 at 4:15 PM, Byron Jeff <RemoveMEbyronjeffKILLspamspamclayton.edu> wrote:
{Quote hidden}

> -

2008\06\17@040522 by Alan B. Pearce

face picon face
The OP on this thread may like to dig out this 'magazine' from Freescale, as
it appears to have a fair bit of (general) stuff on motor driving, although
it does appear to be mains powered stuff. I have put in the URL as it comes
off the Freescale email (but without my identifier in it). I don't know how
well this will work, and it expects you to log in to download.

If you want to try searching other ways it is Beyondbits3 that you are
looking for. May or may not be useful for your project.

http://www.freescale.com/webapp/site_cons.newsletter_metrics.framework?newsletter_id=NL242008&type=CLICKTHROUGH&url=https%3A%2F%2Fhttp://www.freescale.com%2Fwebapp%2FDownload%3FcolCode%3DBEYONDBITS3%26amp%3BnodeId%3D0127260061788213CF333D%26amp%3Blocation%3Dnull

More... (looser matching)
- Last day of these posts
- In 2008 , 2009 only
- Today
- New search...