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'[EE]: Solar 240 Inverters'
2002\07\08@102238 by ards, Justin P

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240v inverters are expensive (I know batts and panels are also expensive),
so I was considering if it was possible (apart from being *extremely
dangerous*)to have 2 banks of 18 x 12v batts so I have a DC supply of
240-0-240.  Could cheaply test design using 9v batt to begin with.

Then perhaps a AB amplifier driven with a 50hz sine wave to power a 250vac 5
amp load. (If you think I have NOT thought about it in-depth then you might
be right)

Not too familiar with amplifier design but think it would also make an
excellent power supply for a massive power audio amp.

I was considered that transistors don't handle such high voltage rails but
then they must use some sort of transistor on the output of inverters.

Is this line of thought way off.

Justin

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2002\07\08@105830 by Herbert Graf

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{Quote hidden}

       Pretty much. Doing it this sort of way results in your driver transistors
being in the linear region most of the time, this is bad since ALOT of power
is dissipated. That is why almost all invertors out there are switchers,
their transistors are never in the linear region (or the equivalent in MOS)
for very long.
       Note that AC voltage is expressed in RMS terms, NOT peak, so to do what you
are proposing (skipping the need to have a step up converter) you need your
rails to be 240 * sqrt(2) ~= 346V, plus losses in the transistors.
       I suggest you look into switchers, the type of wave you must supply is
dependant on what your load is, resistive loads don't care about wave shape
so you c feed them whatever is easiest for you (in which case your 240V
rails would be fine), if you have a reactive load things get much more messy
(PWM, sinusoidal modulation if need be). TTYL

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2002\07\08@122822 by Lawrence Lile

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Yep, Herbert is pretty much right on the money.  When I contemplated this
idea a while back, I was intending to use a 48V battery bank and a step-up
transformer to change my 48V chopped PWM waveform into something resembling
120VAC.  240VAC would be the same kind of problem just with a different
transformer.  A class AB amplifier delivering 5000 watts will consume about
5000 to 10000W in the process!  Holy Heat Sink, Batman!

The only reason I chose 48V is I happened to have a 120:48V transformer with
enough uummph to handle the load.  I would have rather looked into 24VDC.
However, with lower voltrages you must handle higher curretns for the same
power, and the currents in an interter of just a few KW get very large very
fast.

I would probably avoid high voltage DC busses, since I am the poor schmoe
that will eventually put his thumb across the terminals.

Keep it simple:  Construct a straightforward unit that just makes 50 HZ
square waves first.  It won't be so efficient, nor sinusoidal, but you'll
bet the big power components working right first.  Then convert it to PWM
(prolly only a software conversion).  Amazingly enough, a lot of things run
fine on square waves including computers.

--Lawrence


> > Is this line of thought way off.
>
>         Pretty much. Doing it this sort of way results in your driver
transistors
> being in the linear region most of the time, this is bad since ALOT of
power
> is dissipated. That is why almost all invertors out there are switchers,
> their transistors are never in the linear region (or the equivalent in
MOS)
> for very long.
>         Note that AC voltage is expressed in RMS terms, NOT peak, so to do
what you
> are proposing (skipping the need to have a step up converter) you need
your
> rails to be 240 * sqrt(2) ~= 346V, plus losses in the transistors.
>         I suggest you look into switchers, the type of wave you must
supply is
> dependant on what your load is, resistive loads don't care about wave
shape
> so you c feed them whatever is easiest for you (in which case your 240V
> rails would be fine), if you have a reactive load things get much more
messy
> (PWM, sinusoidal modulation if need be). TTYL
>
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>
>

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2002\07\08@124540 by Olin Lathrop

face picon face
> 240v inverters are expensive (I know batts and panels are also expensive),
> so I was considering if it was possible (apart from being *extremely
> dangerous*)to have 2 banks of 18 x 12v batts so I have a DC supply of
> 240-0-240.  Could cheaply test design using 9v batt to begin with.

You don't need the same DC voltage as the AC voltage because you can run it
thru a transformer.  240VDC wouldn't be enough to create 240VAC anyway,
because the peaks of the 240VAC sine wave are at 240 * sqrt(2) = 340V.

> Then perhaps a AB amplifier driven with a 50hz sine wave to power a 250vac
5
> amp load. (If you think I have NOT thought about it in-depth then you
might
> be right)

An AB amplifier would be rather ineficient.  How close to a sine wave does
the load need?  Creating a decent and regulated power sine voltage is a
tricky.  It is usually done with PWM driving a transformer, more like a
class D amp.  If the load can tolerate substantial harmonics (like a light
bulb, for example), then it becomes easier.  Simple inverters use a center
tapped primary.  The center is connected to +DC, and opposite ends are
banged alternately to ground.  The result is lots of harmonics, but that is
OK in some applications.

> Not too familiar with amplifier design ...

I wouldn't tackle a 1.2KW inverter with sine wave output as a "first"
amplifier project!  There is a reason these things are expensive, and that
there are people who specialize in such circuits.  Don't try this at home.
Mistakes at these voltages and powers can be seriously dangerous.  Things go
BANG and you can end up dead and your house a pile of smoldering cinders.

> I was considered that transistors don't handle such high voltage rails

Not true.

> but then they must use some sort of transistor on the output
> of inverters.

Typically not.  The output of an inverter is usually the secondary of a
transformer.  The transistors are on the primary side, which is usually at a
lower voltage.


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2002\07\08@135238 by Rick C.

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Sure they are expensive, but what you propose will probably cost more in design,
assembly, testing, replacing tested parts at least twice, troubleshooting,
safety circuits, mechanical layout including air flow. I run my whole house from
a 48 volt battery system with a 4kw solar array and I use the Xantrex SW4048
(4kw 48volt) sine wave inverter/grid tie. Believe me, you cannot make one any
cheaper than this one.
http://www.gridtie.com/products/hybrid/sw.html
The voltages you would be working with are too lethal to risk. Even 48 volts
will send you into orbit if you're not careful.
http://www.vvalley.com/solar to see a picture of my system.
Rick


"Richards, Justin P" wrote:

{Quote hidden}

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2002\07\08@172923 by Mike Singer

picon face
Olin Lathrop wrote:
.
.
.
> I wouldn't tackle a 1.2KW inverter with sine wave output as a "first"
> amplifier project!  There is a reason these things are expensive,
> and that there are people who specialize in such circuits.  Don't try
> this at home. Mistakes at these voltages and powers can be
> seriously dangerous.  Things go BANG and you can end up
> dead and your house a pile of smoldering cinders.
. .
.
  Agree.    Much more safe way is to get UPS (uninterruptable power supply) to the project. The one with cool start ability (may be started on accumulator batteries without 220v). The best way is, as for me, to emulate an accumulator battery by system consisting of sun battery, accumulator battery and PIC-based controller.
Will work under clouds, will stand overload.

  Mike.

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2002\07\09@140018 by Peter L. Peres

picon face
On Mon, 8 Jul 2002, Mike Singer wrote:

>Olin Lathrop wrote:
>.
>.
>.
>> I wouldn't tackle a 1.2KW inverter with sine wave output as a "first"
>> amplifier project!  There is a reason these things are expensive,
>> and that there are people who specialize in such circuits.  Don't try
>> this at home. Mistakes at these voltages and powers can be
>> seriously dangerous.  Things go BANG and you can end up
>> dead and your house a pile of smoldering cinders.
>.
>   Agree.
>   Much more safe way is to get UPS (uninterruptable power supply)
>to the project. The one with cool start ability (may be started on
>accumulator batteries without 220v). The best way is, as for me,
>to emulate an accumulator battery by system consisting of sun
>battery, accumulator battery and PIC-based controller.
>Will work under clouds, will stand overload.

Does it not make a lot of sense to use a high voltage DC storage battery
and a sine former (using magic sine etc) and to charge it with a dc/dc
upconverter from the solar panels and/or a wind generator and/or mains
grid and/or generator for such power levels ? Because I think that it
*significantly* reduces switching and I^2R losses at high load time. With
~8-10 24V batteries in series and charge equalization control this could
supply significantly more than 5kW for a short time. The lower current per
battery would mean that inexpensive smaller batteries could be bought in
bulk. At 5kW the current would be somewhere near 60A (120V system,
including something for efficiency). This is permissible even for small
tractor starting batteries. The upconverting solar charger could be of the
optimal energy transfer type (easy with this config). A failed battery can
be removed from the system and its place shorted over with very little
change in output parameters (though not without a short power break).

Peter

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2002\07\09@171409 by Lawrence Lile

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Quite a logical approach, Peter.  You've always got the problem of getting
12V (or other solar cell voltage) to be 120V (or 240 take your pick).
Either you have to solve this with a transformer, or an upconverter as you
suggest.  An upconverter might be a really efficient way to do the job, with
less weight and cost than a bulky high amperage transformer.

Now, switching 240V*1.414 puts you in the realm of IGFETs, and out of the
realm of super-efficeint mosfets, which wimp out pretty much above 100V.
OTOH, you are switching much smaller currents, so the efficiency may wash
out.

You also have less isolation from input to output with this scheme vs a
transformer.  You probably want to tie your grounds together anyway.  Uh-oh
I just thought of something.  Your upconverter is going to make 340VDC.
Your output H-Bridge is going to flip this from one side to the other.  One
pole of your output is neutral, which is connected to earth.  So your solar
cells CANNOT be referenced to ground, in fact they will have 340V AC riding
on top of them.  ouch, this does not sound good.  What is a good way to
handle the grounds in this system?


Would a shorted output transistor expose your solar cells to a 240VAC main
voltage?  Maybe some good fusing*, crowbars, and transorbs are a good idea
on the low voltage side.

--Lawrence

*Fuse (definition) - a device usually protected by semiconductors.  Often
found intact in melted-down electronics.



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2002\07\09@225008 by ards, Justin P

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What I had in mind was to use a separate solar panel and small inexpensive
regulator  for each battery.  This eliminates the dc/dc upconverter.  This
sounds expensive using 20 regulators, 20 solar panels and 20 batteries (at
12v),  but the regulators are all low power and second hand 33 watt panels
are cheap.  Smaller batteries are easier to handle and if one fails it is
not a huge loss.

I have spoken to people transporting big 2v cells and the problems they
have.

Peter what is a "sine former (using magic sine etc)".  That is the last
piece of the system.

Justin
<snip>

Quite a logical approach, Peter.  You've always got the problem of getting
12V (or other solar cell voltage) to be 120V (or 240 take your pick).
<
>
> Does it not make a lot of sense to use a high voltage DC storage battery
> and a sine former (using magic sine etc) and to charge it with a dc/dc
> upconverter from the solar panels and/or a wind generator and/or mains
> grid and/or generator for such power levels ? Because I think that it
> *significantly* reduces switching and I^2R losses at high load time. With
> ~8-10 24V batteries in series and charge equalization control this could
> supply significantly more than 5kW for a short time. The lower current per
> battery would mean that inexpensive smaller batteries could be bought in
<snip>
> Peter
>

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2002\07\09@230107 by ards, Justin P

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Rethink, all the panels could be put in series with one high voltage
regulator.  Simply use a relay and switch it in and out the panel array
depending on the batt bank voltage.

What I had in mind was to use a separate solar panel and small inexpensive
regulator  for each battery.  This eliminates the dc/dc upconverter.  This
sounds expensive using 20 regulators, 20 solar panels and 20 batteries (at
12v),  but the regulators are all low power and second hand 33 watt panels
are cheap.  Smaller batteries are easier to handle and if one fails it is
not a huge loss.

I have spoken to people transporting big 2v cells and the problems they
have.

Peter what is a "sine former (using magic sine etc)".  That is the last
piece of the system.

Justin
<snip>

Quite a logical approach, Peter.  You've always got the problem of getting
12V (or other solar cell voltage) to be 120V (or 240 take your pick).
<
>
> Does it not make a lot of sense to use a high voltage DC storage battery
> and a sine former (using magic sine etc) and to charge it with a dc/dc
> upconverter from the solar panels and/or a wind generator and/or mains
> grid and/or generator for such power levels ? Because I think that it
> *significantly* reduces switching and I^2R losses at high load time. With
> ~8-10 24V batteries in series and charge equalization control this could
> supply significantly more than 5kW for a short time. The lower current per
> battery would mean that inexpensive smaller batteries could be bought in
<snip>
> Peter
>

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2002\07\10@154242 by Peter L. Peres

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On Tue, 9 Jul 2002, Lawrence Lile wrote:

>Quite a logical approach, Peter.  You've always got the problem of getting
>12V (or other solar cell voltage) to be 120V (or 240 take your pick).
>Either you have to solve this with a transformer, or an upconverter as you
>suggest.  An upconverter might be a really efficient way to do the job, with
>less weight and cost than a bulky high amperage transformer.
>
>Now, switching 240V*1.414 puts you in the realm of IGFETs, and out of the
>realm of super-efficeint mosfets, which wimp out pretty much above 100V.
>OTOH, you are switching much smaller currents, so the efficiency may wash
>out.

60A is not so small.

>You also have less isolation from input to output with this scheme vs a
>transformer.  You probably want to tie your grounds together anyway.  Uh-oh
>I just thought of something.  Your upconverter is going to make 340VDC.
>Your output H-Bridge is going to flip this from one side to the other.  One
>pole of your output is neutral, which is connected to earth.  So your solar
>cells CANNOT be referenced to ground, in fact they will have 340V AC riding
>on top of them.  ouch, this does not sound good.  What is a good way to
>handle the grounds in this system?

The charger dc/dc converter can be an isolating one. Also the batteries
will flip around at 60Hz (both the - and the + rails) so you cannot ground
the batteries. This is a small price to pay for getting rid of a large
transformer. I also think that major major major losses will occur in the
transformer proper, besides in the switching elements, if using low
voltage battery storage. I guess I'd put the batteries in a large ABS
cabinet (shed) built to IP2 or more and provide interlocks and an outer
shield.

You could also use a 1:1 isolation transfomer on the output. This could be
a part of the sine filter. A 1:1 transformer will not have that much loss
and it is probably easier to come by as a standard part even at 5kW+
rating.

>Would a shorted output transistor expose your solar cells to a 240VAC main
>voltage?  Maybe some good fusing*, crowbars, and transorbs are a good idea
>on the low voltage side.

I guess using a isolated dc/dc converter for the charger is a very good
idea. It would only need to handle peak charging current/power for short
times. The average power would be low.

Peter

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2002\07\10@160352 by Lawrence Lile

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An isolating DC-DC converter at these amperages is no trivial task either.
I understand how regular DC-DC converters work, by kicking an inductor with
various schemes, but how does an isolating DC-DC converter work?  Flying
capacitor?

--Lawrence

{Original Message removed}

2002\07\10@171314 by Peter L. Peres

picon face
On Wed, 10 Jul 2002, Richards, Justin P wrote:

>What I had in mind was to use a separate solar panel and small inexpensive
>regulator  for each battery.  This eliminates the dc/dc upconverter.  This
>sounds expensive using 20 regulators, 20 solar panels and 20 batteries (at
>12v),  but the regulators are all low power and second hand 33 watt panels
>are cheap.  Smaller batteries are easier to handle and if one fails it is
>not a huge loss.

It isn't just that, you can buy bulk surplus stuff and save serious $$$.
Also if something breaks you can quickly swap a module and fix it. You
can't do that with a large turnkey installation. Just do some real good
thinking on connections and layout. You will have a large number of
interconnects and failsafe systems and such, and you need to think a bit
about how to do this right. I'd think about honking big screw-clamp rows
mounted on a custom-built rack to hold the whole installation, with short
wires connecting the identical modules up front. The batteries and dc/dc
converters would be on the shelves of the rack. 20 batteries will weigh
towards a ton so spend some time on mechanical construction and such.
Breakers and such I would put on rails screwed to same rack. The rack
should be solid but non-combustible and insulating. Fire retardant treated
wood might work. Charge equalization is a must. If the dc/dc converters
are not insulating then the solar panels will float at high voltage. You
can't have that, thus use insulated dc/dc converters. They are not so hard
to get, esp. at 30W.

Peter

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2002\07\10@171322 by Peter L. Peres

picon face
On Wed, 10 Jul 2002, Richards, Justin P wrote:

>What I had in mind was to use a separate solar panel and small inexpensive
>regulator  for each battery.  This eliminates the dc/dc upconverter.  This
>sounds expensive using 20 regulators, 20 solar panels and 20 batteries (at
>12v),  but the regulators are all low power and second hand 33 watt panels
>are cheap.  Smaller batteries are easier to handle and if one fails it is
>not a huge loss.
>
>I have spoken to people transporting big 2v cells and the problems they
>have.
>
>Peter what is a "sine former (using magic sine etc)".  That is the last
>piece of the system.

A chopper that produces something resembling a sine wave after a filter.
Usually it is implemented as a H bridge with thyristors or bipolars or
FETs or IGBTs and controlled by a small CPU, like a PIC.

With your system you also have the option to implement a power buck
regulator followed by a H bridge to change output phase every half period.
That would make a nice clean output. A 5kW buck regulator at 300V is not
so hard to make. Don't expect this to be a picninc though, whichever
solution you pick, you are looking at months of work, assuming you have a
life. There is also the solution of running 120V DC in the house and have
120V AC (at low power) only for appliances that need it.  For example you
can run all your lights on DC without trouble. HOWEVER your local
electrical code has the last word on this.

Peter

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2002\07\10@180014 by Peter L. Peres

picon face
On Wed, 10 Jul 2002, Lawrence Lile wrote:

>An isolating DC-DC converter at these amperages is no trivial task either.
>I understand how regular DC-DC converters work, by kicking an inductor with
>various schemes, but how does an isolating DC-DC converter work?  Flying
>capacitor?

It's a bog plain transformer on ferrite, usually driven with push-pull or
a H bridge, and optically insulated feedback from the secondary. Look at
your PC's power supply and any other mains SMPSU for clues. Up to about
500W you can use off the shelf parts excepting the trasformer.  Beyond
that it's EE territory. Also, good luck making one of those pass FCC or EC
if done in DIY. Flying capacitor schemes are not used in isolating dc/dc
converters afaik.

Peter

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2002\07\11@082101 by Alan B. Pearce

face picon face
>You could also use a 1:1 isolation transfomer on the
>output. This could be a part of the sine filter. A
>1:1 transformer will not have that much loss and it is
>probably easier to come by as a standard part even
>at 5kW+ rating.

Use the sort of isolation transformer that is used when using power tools
outside. Trouble is these seem to have been put aside in favour of earth
current trip units.

Back to the original issue, the project I am currently on has to drive a
compressor which consists of a piston with voice coil type arrangement to
drive it. We are using an H-bridge circuit driven by an Intersil HIP4080
using 75kHz PWM, with suitable filtering to drive it at frequencies in the
range 20-60Hz. One of the requirements for this is that there is a need to
control the harmonic content, as there is a closed loop DSP system around a
pair of these compressors to minimise vibration. Once the project is over I
want to pick up a set of components to use in an Invertors for a UPS. A
suitable transformer on the output will give me the 240V AC output I require
from this, and the power output comes down to a suitable selection of the
output FETs and transformer.

With this sort of arrangement trying to do anything with a high voltage
battery stack just does not make sense at all. The dangers of having
problems with a low voltage stack are bad enough, but with a large stack
then the problems multiply, and the housekeeping to stay away from problems
with it.

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