treadmill permanent magnet DC motor as generator

[almac]

live on the main rd will fix a good muffler after getting everything else right, it will be a vertical mounted setup something like this.. so far i have tested both the victa engine and the treadmill motor both work, have removed both and will clean them up , mount them later. DSCN0953.JPG
2fe43feaecd6b56ff7ce403343b8e882.jpg

[Bala]

Your neighbours in the suburbs will love a victa engine running for hours at 3600rpm!!!!

[almac]

thanks bala for giving me the reliable RPM for both engine types, i had no idea and could not find it on the net. so the 2 stroke i have will do. a pulley ratio of 6:1 will give me the 500RPM i need with good HP. will also make throttle adjustments for RPM 6x more accurate. should work well. this is intended for successive cloudy winter days so might only use it a couple of times a year. sensij a properly designed generator is about $500 then i will need a 24v DC power supply as well, another $300. this lawnmower and treadmill motor so far has cost $0

[Bala]

As was basically mentioned earlier. I doubt the unit is designed for anything more than occasional use. Life expectancy would be short if run hard for long periods

[sensij]

Most domestic 4st mowers will be about 3.5hp @ 3600rpm. They will have almost no hp at 500rpm.

The lawn mower motor will run much faster than 500 RPM. The intention is for the treadmill motor, which is used to convert the lawn mower motor's output to electricity, to be geared down as needed to hit the target charge voltage.

I think the exercise is an interesting engineering project, but as a practical way to maintain an off-grid system... not so much. It is not hard to imagine that the inefficiency incurred by repurposing equipment in this way, used in unintended ways, without the normal protective circuits, will end up costing more than just buying a properly designed generator.

[Bala]

Most domestic 4st mowers will be about 3.5hp @ 3600rpm. They will have almost no hp at 500rpm.

[Logan005]

As I recall a treadmill motor is as much a brake as it is a generator. I doubt they are designed for continuous duty, much less continuous duty as a generator. I have seen many used in wind generator designs, but I wonder how they are doing a year or 2 later. If you get your idle governed, I think it could work, but you are going to want a Hydro/wind Charge controller, so as not to damage your batteries. If you get a year out of it would be amazing.

[almac]

I have owned a victa 2 stroke mowers for over 30 years, and spent 4 years as a mechanic at a Victa dealership. My current one is over 15years old. They are a simple robust engine. There has only really been one major change to them which was in the early 80s? They change the engine and carb design. The later carb is a bit of a pain.

Basically:

This engine will run up to 5000 rpm if you want, standard operating would be around the 3600rpm as with most stationary engines.

They are air governed and the way the carb throttle system operates makes small/acurate RPM adjustments hard.

The governor will be slow to react to engine load compared to mechanical governing that is in most engines.

They are noisy and use a lot of fuel compared to a 4 stroke.

If you do use it you will need to leave the cutter disc on, it acts as a flywheel.

hi bala, thanks for the info, RPM at 3600 is too high for the treadmill motor, i would be aiming for about 500 RPM to get around 32Vdc. will see more lawnmowers on the kerb around here so should find a 4 stroke , even if i dont the local markets have 4 stroke mowers for around $50

[Bala]

I have owned a victa 2 stroke mowers for over 30 years, and spent 4 years as a mechanic at a Victa dealership. My current one is over 15years old. They are a simple robust engine. There has only really been one major change to them which was in the early 80s? They change the engine and carb design. The later carb is a bit of a pain.

Basically:

This engine will run up to 5000 rpm if you want, standard operating would be around the 3600rpm as with most stationary engines.

They are air governed and the way the carb throttle system operates makes small/acurate RPM adjustments hard.

The governor will be slow to react to engine load compared to mechanical governing that is in most engines.

They are noisy and use a lot of fuel compared to a 4 stroke.

If you do use it you will need to leave the cutter disc on, it acts as a flywheel.

[jflorey2]

im thinking the PWM charge controller would be a starter. the current doesnt just disconnect with PWM it gradually reduces.

You're mixing two different terms and coming to the wrong conclusion IMO.

PWM controllers "just disconnect." That's how they work. The term "pulse width modulation" means that an internal switch turns on and off, and the width of the on-pulse is changed (hence the name) to control how much power, ON AVERAGE, the battery gets. But at any given time it's off or on; it is only over the course of several minutes that it averages to a lower current.

Also, as batteries reach full charge they gradually take less current. So even if you have a PWM controller, and the switch inside is closed, the battery will take less current. That's not a function of the controller, it's a function of the battery.

an over speeding 2 stroke lawnmower i can live with ,its not as though i wont hear it over speeding.

Well, if you can afford the consequences of that, go for it and see what happens. You'll certainly learn a lot doing it.

(BTW Sensi's idea is a good one; a dump load controller makes a lot more sense than a series PWM controller, and will not result in overspeed as the battery reaches full charge. Make sure to size the dump load larger than the maximum output of the generator.)

[almac]

thanks, now i have to work out how many watts the DC motor can put out. the spec plate says 220Vdc 6.5A 2HP , could it put out 1400W ? something like this?

http://www.ebay.com.au/itm/NO-BASE-Gen-4-charge-controller-10-000-watt-440-AMP-24-volt-solar-wind-turbine-/181989263113?hash=item2a5f67c709:g:1-AAAOSwJkJWlKbq

[sensij]

One more time. Use a dump load controller. If you set it up to cut over to the dump load if the lawn mower stops or if the battery voltage hits the bulk charge target, then you don't need a diode, and you don't need to stand there to turn everything off in the right sequence.

[almac]

im thinking the PWM charge controller would be a starter. the current doesnt just disconnect with PWM it gradually reduces. an over speeding 2 stroke lawnmower i can live with ,its not as though i wont hear it over speeding. at least the batteries wont cop an over voltage. i can set the RPM range of the 2 stroke engine to stay within the PWM controllers input voltage

[jflorey2]

of course i dont want to ruin the batteries so i will need a charge controller after all.

That may not do what you want. Imagine a case with a PWM controller. When the battery is low you'll open the throttle wide to get a decent amount of power to the battery. Then the battery will charge. At some point the switch will open. The motor will then become completely unloaded and will overspeed.

With an MPPT controller you have another problem. Most MPPT controllers are expecting a solar panel - and their V/I curves are dependent only on insolation, and the open circuit voltage doesn't change much with time. With a generator, as soon as you reduce its load, the RPM will increase over the course of several seconds, and the MPPT controller will have to react to that. MPPT controllers may not be able to anticipate a rapidly rising RPM, and you'll see the same problem.

(You'll see the same problem eventually no matter what you do; the controller will effectively "open" and the motor will overspeed.)

explain why the motor wont need a diode to stop the batteries feeding back jflorey2

Because as long as the motor is running and providing power it will transfer power to the generator. So your system would work like this:

1) Motor is off. Generator switch is off. Nothing is moving.
2) You open the throttle on the motor. Still nothing happens; motor hasn't started yet.
3) You close the switch. If it is really a commutated motor, then it starts running at its base speed. The motor spins as well and starts producing power.
4) You run the motor as long as you like.
5) When you are done you close the throttle (actually a fuel cutoff or ignition kill works better here.)
6) You open the switch. Both motor and generator stop. No power flows anywhere.

If you add a diode, you've just added .5 volts of loss and removed the option of using the generator to start the motor.

[inetdog]

If the motor is brushed you don't even need the diode. If the motor is brushless you will need six diodes.

If the motor is brushed and the OP does not use a CC in the system he will need a single series diode to prevent back current into the motor when the engine is stopped or idling.