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'[EE]: high-power generator/motor'
2001\11\15@172822 by Andy Meng

picon face
Hello,

I am making a generator for a large radio-controlled vehicle. The purpose
will be to keep the main 12V batteries (about 30Ah worth) charged. The
engine I am using is a 4-cycle R/C aircraft engine, about 1HP (.61 in^3
displacement). The engine will be coupled to the generator, which will then
be controlled by a PIC.

The generator also needs to be able to start the engine by acting like a
motor. The engine speed will be controlled by the PIC by means of a servo,
with the PIC adjusting the speed for a certain voltage output from the
generator. However, I don't know which type of motor/generator would be best
suited for this purpose. Since everything is DC, I assume it would be easier
to use a DC (permantent magnet) motor/gen. Efficiency isn't really
important, since the project is mainly for fun. I think 20 amps from a
generator (only about 250W, with about a 750W input) would be about right,
but it has to be about 14V output (to charge up the sealed lead-acid battery
bank), and turn with a good amount of torque (current is mostly
insignificant on engine start-up) to start the engine (with 12-13V input).
If anyone has ideas on what type of motor/gen to use, I would really
appreciate it.

Thanks,

Andy Meng
N8MX
http://www.qsl.net/n8mx


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2001\11\15@182531 by mike

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face
On Thu, 15 Nov 2001 17:18:37 -0500, you wrote:

{Quote hidden}

Something out of a cordless drill might be in the power & voltage
ballpark.
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2001\11\16@011307 by Lawrence Glaister

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face
Sounds like fun... it seems from my experience that you will have some
difficulty finding a generator for 20amps that is relatively small. I am
thinking that you may be able to use a small car alternator to generate
the DC you require. Since you have a PIC involved, perhaps you could
drive the alternator phases (A/C) and use the alternator like a 3 phase
motor for starting your gas engine.Once the engine is running, you can
switch the alternator into generation mode.  The rpm ranges for the
motor and alternator are close, I would start with a 2-1 reduction
between the motor and the alternator. You will probably have to do some
bench work to see if the aternator has enough low end torque to start
the r/c engine. Keep us informed of your project... I would love a
similar unit to keep my ham shack battery charged during power outages.
cheers

On Thu, 2001-11-15 at 14:18, Andy Meng wrote:
> Hello,
>
> I am making a generator for a large radio-controlled vehicle. The
purpose
> will be to keep the main 12V batteries (about 30Ah worth) charged. The
> engine I am using is a 4-cycle R/C aircraft engine, about 1HP (.61
in^3
> displacement). The engine will be coupled to the generator, which will
then
> be controlled by a PIC.
>
> The generator also needs to be able to start the engine by acting like
a
> motor. The engine speed will be controlled by the PIC by means of a
servo,
> with the PIC adjusting the speed for a certain voltage output from the
> generator. However, I don't know which type of motor/generator would
be best
> suited for this purpose. Since everything is DC, I assume it would be
easier
> to use a DC (permantent magnet) motor/gen. Efficiency isn't really
> important, since the project is mainly for fun. I think 20 amps from a
> generator (only about 250W, with about a 750W input) would be about
right,
> but it has to be about 14V output (to charge up the sealed lead-acid
battery
> bank), and turn with a good amount of torque (current is mostly
> insignificant on engine start-up) to start the engine (with 12-13V
input).
> If anyone has ideas on what type of motor/gen to use, I would really
> appreciate it.
>
> Thanks,
>
> Andy Meng
> N8MX
> http://www.qsl.net/n8mx
>

=====================================================================
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1462 Madrona Drive                   http://jfm.bc.ca/
Nanoose Bay, B.C.                    http://members.home.com/cncstuff
Canada          V9P 9C9              http://gspy.sourceforge.net
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2001\11\16@015350 by Gennette, Bruce

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No help here with a specific type, but you should be able to do it easily
with a DC motor *IF* you modify the petrol engine for decompressed starting.

Decompressed starting? - A PIC powers a solenoid that holds the exhaust
value (of the engine) open.  You then run the combination electric
motor/petrol engine up to a moderate speed (monitored by the PIC),
disconnect the 'run' connections to the motor and release the solenoid.
After a few seconds (for the engine to start and warm a little) the PIC
switches in the charger connections.

Bye.


On Thu, 2001-11-15 at 14:18, Andy Meng wrote:
> Hello,
>
> I am making a generator for a large radio-controlled vehicle. The
purpose
> will be to keep the main 12V batteries (about 30Ah worth) charged. The
> engine I am using is a 4-cycle R/C aircraft engine, about 1HP (.61
in^3
> displacement). The engine will be coupled to the generator, which will
then
> be controlled by a PIC.
>
> The generator also needs to be able to start the engine by acting like
a
> motor. The engine speed will be controlled by the PIC by means of a
servo,
> with the PIC adjusting the speed for a certain voltage output from the
> generator. However, I don't know which type of motor/generator would
be best
> suited for this purpose. Since everything is DC, I assume it would be
easier
> to use a DC (permantent magnet) motor/gen. Efficiency isn't really
> important, since the project is mainly for fun. I think 20 amps from a
> generator (only about 250W, with about a 750W input) would be about
right,
> but it has to be about 14V output (to charge up the sealed lead-acid
battery
> bank), and turn with a good amount of torque (current is mostly
> insignificant on engine start-up) to start the engine (with 12-13V
input).
> If anyone has ideas on what type of motor/gen to use, I would really
> appreciate it.
>
> Thanks,
>
> Andy Meng
> N8MX
> http://www.qsl.net/n8mx
>

=====================================================================
Lawrence Glaister VE7IT              ve7itspamKILLspamshaw.ca
1462 Madrona Drive                   http://jfm.bc.ca/
Nanoose Bay, B.C.                    http://members.home.com/cncstuff
Canada          V9P 9C9              http://gspy.sourceforge.net
=====================================================================

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2001\11\16@021752 by Alexandre Domingos F. Souza

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face
>Decompressed starting? - A PIC powers a solenoid that holds the exhaust
>value (of the engine) open.  You then run the combination electric
>motor/petrol engine up to a moderate speed (monitored by the PIC),
>disconnect the 'run' connections to the motor and release the solenoid.
>After a few seconds (for the engine to start and warm a little) the PIC
>switches in the charger connections.

       Common thing on model helicopters. Easy and nice to do. But hardly with a solenoid...


---8<---Corte aqui---8<----

Alexandre Souza
EraseMEtaitospam_OUTspamTakeThisOuTterra.com.br
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2001\11\16@092615 by t F. Touchton

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Lawn tractors use a motor/generator combination that may work for you.
Look for a model that has nice big headlights.

My father used to have a Workbird.  The generator on that thing was used to
start the engine, then charge the battery and run all kinds of accessories.
I was told that this type of generator was the precursor of alternators.
Seems they may have been common on old, old, old cars... 40's and 50's.
You might find something at a restoration shop.

Scott F. Touchton
1550 Engineering Manager
JDS Uniphase



                   Andy Meng
                   <@spam@n8mxKILLspamspamYAHOO.CO       To:     KILLspamPICLISTKILLspamspamMITVMA.MIT.EDU
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Hello,

I am making a generator for a large radio-controlled vehicle. The purpose
will be to keep the main 12V batteries (about 30Ah worth) charged. The
engine I am using is a 4-cycle R/C aircraft engine, about 1HP (.61 in^3
displacement). The engine will be coupled to the generator, which will then
be controlled by a PIC.

The generator also needs to be able to start the engine by acting like a
motor. The engine speed will be controlled by the PIC by means of a servo,
with the PIC adjusting the speed for a certain voltage output from the
generator. However, I don't know which type of motor/generator would be
best
suited for this purpose. Since everything is DC, I assume it would be
easier
to use a DC (permantent magnet) motor/gen. Efficiency isn't really
important, since the project is mainly for fun. I think 20 amps from a
generator (only about 250W, with about a 750W input) would be about right,
but it has to be about 14V output (to charge up the sealed lead-acid
battery
bank), and turn with a good amount of torque (current is mostly
insignificant on engine start-up) to start the engine (with 12-13V input).
If anyone has ideas on what type of motor/gen to use, I would really
appreciate it.

Thanks,

Andy Meng
N8MX
http://www.qsl.net/n8mx


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2001\11\16@093816 by Eoin Ross

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Can't speak for all lawn tractors - I have one with a Briggs & Stratton 8hp vert shaft motor - the starter motor is just that, a motor only, under the flywheel is a bunch of coils & diodes and a heap of magnets in the flywheel - this is the charger for that lawnmower.


>>> spamBeGoneScott.TouchtonspamBeGonespamUS.JDSUNIPHASE.COM 11/16/01 09:25AM >>>
Lawn tractors use a motor/generator combination that may work for you.
Look for a model that has nice big headlights.

My father used to have a Workbird.  The generator on that thing was used to
start the engine, then charge the battery and run all kinds of accessories.
I was told that this type of generator was the precursor of alternators.
Seems they may have been common on old, old, old cars... 40's and 50's.
You might find something at a restoration shop.

Scott F. Touchton
1550 Engineering Manager
JDS Uniphase



                   Andy Meng
 
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2001\11\16@112633 by Brandon Fosdick

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face
{Quote hidden}

20 Amps sounds like a lot for charging. The vehicle I set up for my thesis uses
a single 7Ah 12V battery and that only charges at about 3.8 Amps at the max
charge rate. So yes, 5 such batteries would charge at about 20 Amps, but only if
you're trying to fast charge dead batteries.

For the generator we're working on we're only spec'ing it to produce a little
more current than the electrical system needs. If the generator is supplying at
least enough power to run the electronics then you only need to recharge the
bats enough to make up for the energy used at startup cause nothing else is
draining them. That doesn't require a whole lot of current.

If the generator produces significantly too much power you're going to have
problems once the batts are fully charged. For one, you'll notice a significant
change in engine performance. And, since the engine will be heavily loaded with
fast charging the batts right after start up, it will produce a lot less power
during takeoff, which is when you really need it.

Can I ask what you're doing that needs 30Ah worth of batteries? Our plane (with
vid cam(s), autopilot, and several transmitters) is designed to fly for 2 hours
with only a 7Ah batt. You must have a really big plane to carry all that weight
(about 10kg/22lb?). Got any nice pictures for us? :)

I'm also concerned that you're only using a 0.61 in3 engine for all that weight.
We're using a 1.8in3 (Saito FA-180) and it could be a little bigger. Our plane
tops out at 15Kg(33lb) when wet and only 17% of that is batteries. Assuming the
same mass fraction puts your vehicle at about 58kg(130lb). You're going to need
an AMA waiver for something that big (I see from your webpage that you're in the
US). Its definately more than a 60 size engine can push. We have another plane
here that pushes the 55lb limit. It uses a Zenoah G-62 (3.8 in3) and barely gets
off the ground.

Good luck. If you want to see what we've done have a look at http://uav.umd.edu.

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2001\11\16@161208 by Peter L. Peres

picon face
The condition for the generator to act as a starter is to supply enough
torque to turn over the engine when cold. This may require serious
overvolting (temporary) or a DC permanent magnet brush motor.

The first thing you need to do is find out the turnover torque of the
motor. This is not in the motor data sheet and here is how you can measure
it:

Get a cable pulley and mount it on the motor shaft, put 10-20 turns of
solid fishing line (10kg or more breaking strength) on the wheel and fix
the end to the pulley rim (you can use sticky tape - the turns will hold
the pull force without loading the end. Put a plastic bag on the free end
of the line and add packages or canned food, bags of rice, sugar, etc (or
weights if you have that) to it, until the motor turns over and the bag
falls down (the motor is held in a vise on a table, the bag hangs down)
(NOTE: DISBALE THE IGNITION. ON A MAGNETO MOTOR REMOVE THE HV CABLE FROM
THE SPARK PLUG(S) OR SHORT EACH PLUG TO THE BODY AND TEST EACH SHORTING
WIRE). This will give you the required torque (torque (kgm) =
weight_used(kg) * radius_of_pulley(m)), which you should double for good
measure. Once you have the torque and the starting speed (usually 1/2 of
the slowest given running speed), you can try to find a suitable motor or
generator.

The doubling is to supply extra power required when the motor sucks rich
mixture at start with choke on and carb clapet closed - the test is done
dry, without fuel. A diesel engine may start anyway and tick over a few
times. Be prepared for this. Do not tie the end of the fishing line
solidly to the pulley (this is why).

The theoretical starting power required is Pstart = PI*Start_Rpm*Torque/30
(Rpm is rot/min not rot/sec, torque in kg*m!) if I am not wrong. This
needs to be supplied for a couple of seconds at least. Note that the
expression above can be 'rule of thumbed' to Pstart = 10*Start_Rpm*Torque,
taking into account the doubling above).

Most reasonable sized small motors will result in obscene starting powers
required (>30W even for a 0.049 Cox Black Widow). Good luck finding a
generator that can be overloaded like this to act as a starter. Also look
at inertial starters. These are pretty common where low weight is required
but the mechanics involved can be tricky to duplicate @home.

Multi-cylindered engines have less starting torque requirements than
single pistons and boxers.

The simple measurement trick also works with other mechanisms that need to
be 'instrumented' for servo or motorized drive (e.g: how much power is
needed to raise the blinds in your bedroom etc).

Peter

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2001\11\16@171621 by Mark Skeels

picon face
I have a diesel generator at home.

I don't know exactly how this works, but there is a lever which somehow
momentarily reduces the compression. Push in the lever; then when you pull
the rope or crank the starter, after a short time interval the lever pops
back out to it's starting position, engaging full compression. Makes the
generator possible to start with a pull rope.

Mark

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2001\11\16@205125 by Gerhard Fiedler

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At 21:57 11/16/2001 +0200, Peter L. Peres wrote:
>This will give you the required torque (torque (kgm) =
>weight_used(kg) * radius_of_pulley(m))

Actually, to be physically correct, torque is in Nm (force [N] * length,
not mass [kg] * length); in this case: torque [Nm] = g * weight [kg] *
radius [m]; (g is approx 9.8 m/s^2).

>The theoretical starting power required is Pstart = PI*Start_Rpm*Torque/30
>(Rpm is rot/min not rot/sec, torque in kg*m!) if I am not wrong.

Here it becomes obvious why Nm is an easier to use unit than kgm; the power
calculation gets immediately clear. Pstart = 2 * PI * start_rps * torque;
(where start_rps is now rot/sec, torque in Nm and Pstart consequently in
Nm/s=W.)


There are lots of good arguments for using the SI (International System of
Units) -- for some interesting reading see the NIST web site (a US
government agency). One of these good arguments is that it eliminates all
the conversion factors between the different units that exist for the same
quantity in different disciplines.

ge

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2001\11\17@043636 by gtyler

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I have done this. (run a automitive alternator as a motor) It produced
incredible torque while it lasted, but had problems running at high rpm
where it blew the fets due to the slow opto sensor used for feedback of
position. I know it would have worked if I had put more time into it.

{Original Message removed}

2001\11\18@095559 by Alex Holden

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On Fri, 16 Nov 2001, Mark Skeels wrote:
> I don't know exactly how this works, but there is a lever which somehow
> momentarily reduces the compression. Push in the lever; then when you pull
> the rope or crank the starter, after a short time interval the lever pops
> back out to it's starting position, engaging full compression. Makes the
> generator possible to start with a pull rope.

Some old cars had a control which opened up vents in the cylinder heads
to allow an underpowered starter motor to spin the engine. When the motor
had got the engine spinning fairly fast, you would knock the vents closed
and let the inertia stored in the flywheel overcome the compression and
start the engine.

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2001\11\20@164353 by Andy Meng

picon face
20 amps might be a lot, but it will also be used to run about 10A worth of
drive motors (when they are running), and I would like if the batteries
could be charging at the same time as the motors are running. Also, the
engine can't run all of the time that the vehicle is in motion, since one of
the requirements is indoor operation. It would be nice to not have to run
the engine very often (it could get expensive at $10/gal for fuel!). The
plan is to use four 7Ah 12V batteries, so hopefully they will be able to
handle the higher charge currents. If the voltage to the batteries is held
at a constant level (say, 14V), the current should control itself, right? (I
dont have much experience with battery charging circuits) All I should have
to worry about is increasing engine speed to keep the voltage constant
(since the drive motors will be turning on and off).

Don't worry, this isn't an aircraft. :-) There is no way I would expect such
a (relatively) small engine to handle so much load. The engine is only going
to be used for driving the gen. We might not need so much capacity, but the
two drive motors each draw about 5A, and the electronics, cams, and
transmitter will probably be around another amp, and we would like to get a
lot of range. However, since we will have the engine to recharge the
batteries, we probably won't need so much capacity to run for a long time.
But, if we go with less batteries, the engine would be too big. Many
balances to set up... Also, do you know if it OK to run such an engine
(4-cycle .61) with only a little power being drawn off of it? (basically
idle) I know that some engines last longer if run under load. BTW, your
project looks really interesting. The flight data graphs are neat.

Thanks for the help,
Andy

> 20 Amps sounds like a lot for charging. The vehicle I set up for my thesis
uses
> a single 7Ah 12V battery and that only charges at about 3.8 Amps at the
max
> charge rate. So yes, 5 such batteries would charge at about 20 Amps, but
only if
> you're trying to fast charge dead batteries.
>
> For the generator we're working on we're only spec'ing it to produce a
little
> more current than the electrical system needs. If the generator is
supplying at
> least enough power to run the electronics then you only need to recharge
the
> bats enough to make up for the energy used at startup cause nothing else
is
> draining them. That doesn't require a whole lot of current.
>
> If the generator produces significantly too much power you're going to
have
> problems once the batts are fully charged. For one, you'll notice a
significant
> change in engine performance. And, since the engine will be heavily loaded
with
> fast charging the batts right after start up, it will produce a lot less
power
> during takeoff, which is when you really need it.
>
> Can I ask what you're doing that needs 30Ah worth of batteries? Our plane
(with
> vid cam(s), autopilot, and several transmitters) is designed to fly for 2
hours
> with only a 7Ah batt. You must have a really big plane to carry all that
weight
> (about 10kg/22lb?). Got any nice pictures for us? :)
>
> I'm also concerned that you're only using a 0.61 in3 engine for all that
weight.
> We're using a 1.8in3 (Saito FA-180) and it could be a little bigger. Our
plane
> tops out at 15Kg(33lb) when wet and only 17% of that is batteries.
Assuming the
> same mass fraction puts your vehicle at about 58kg(130lb). You're going to
need
> an AMA waiver for something that big (I see from your webpage that you're
in the
> US). Its definately more than a 60 size engine can push. We have another
plane
> here that pushes the 55lb limit. It uses a Zenoah G-62 (3.8 in3) and
barely gets
> off the ground.
>
> Good luck. If you want to see what we've done have a look at
http://uav.umd.edu.
>
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2001\11\20@164401 by Andy Meng

picon face
I don't know if I want to try to modify the engine to have a compression
release! It would take a lot of work... it would probably be easier just to
have a higher torque motor for starting.
Thanks,
Andy

{Original Message removed}

2001\11\20@164956 by Andy Meng

picon face
I have been considering using a motorcycle alternator, which seems to be
about the correct size. Most use a seperate motor and stator mounted under
the ignition cover (I think), but I have seen some for street bikes on the
internet that appear to be a complete unit, like a smaller version of a car
alternator. I might be able to use the PIC to drive it, but it might also be
easier to just use a seperate DC motor just to start it. Another advantage
of this would be that I could spin the alternator slower (such as 1/2 the
speed of the engine) and not need twice the torque (since the power would be
going through the reduction the opposite direction) to start the engine. I
will let you know how this works out. Part of the current drain from the
batteries that the generator will charge is an ATV transmitter, cameras, and
a 2m ham transceiver used to receive control data.

Thanks for the help,
Andy N8MX

{Original Message removed}

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