Author Topic: What is the best way to regulate these scooter motors for power generation?  (Read 2718 times)

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whatusernamesareleft

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I have a couple 24VDC motors from a power scooter.  I was thinking about making a DC generator with them, however I would need a speed reducer on these as well.


Mary B

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Strip the gearbox off for starters so you just have the motor. Not sure why you would need a speed reducer...

What battery voltage are you looking to charge? Generally these are going to require pretty high RPM to even reach 12 volts.

And where did you find them? I need a pair to build a target carrier robot for my gun range so us disabled users don't have to walk down the 300 yard lane to swap targets! I need the power because it will have to be armor plated with AR500 steel!

whatusernamesareleft

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I was mentioning a speed reducer because I can hand spin it by the wheel and get about 12 volts,  almost 14 volts if I really try.  It makes sense to try to get the gear box off. 
I was thinking about putting it to use for a quieter 12 volt generator to charge batteries and run my power inverters that I have to power things when the utility goes out.  I would hope a 6 hp could do this job.
We ended up with this power scooter after someone passed away.
I think these could put out maybe 20 amps each at least, maybe less than 15amps since they are 24v

george65

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I think you are really off track here!  ;0)

You would want the gearbox on as those things turn about 2700 RPM and a higher speed would give more power with less stress on the engine.
Remember, you are reversing the power flow so the gearing speeds the motor up not slows it down.  That's a good thing in this case.

I have played with these and you are not going to get consumption amperage out of them as a generator.  It all depends what their rating is to start with. Could be 150W, could be 350. As a generator their are losses because you are not doing what they were designed to.

If you are looking at a 6 HP engine to drive these, you are looking at the wrong sort of unit.  Use a regular car alternator.  A 6 HP engine will laugh at that which means you can gear the thing up with a 6-8 pulley on the motor which means you can run the motor nice and slow and quiet.  Even at fast idle you will produce a heap more amps with an alternator than you ever will with one of these motors.  You will have problems coupling them to a 6HP in either belting which will put side thrust where it was not intended or in getting a coupling to do what is probably an 8mm on the motor and a 19-25 on the engine.

The other thing with the motors being brushed is they will wear out infinitely quicker than an alternator. Where I am, those motors are also worth much more so you'd be better off selling the motor and buying an alt by far. It will have a pulley and of course is designed to be belt driven. Put a pulley on the engine, make a bracket or base to mount the motor and alt which you can put your battery on and switches, lights or wheels and you are there.
 Also a single wire alternator has the charging regulation built in. You'd need a solar controller or something for the motor.

If you were to overload the motor, which is highly likely with an inverter, you'll fry it real easy.  With a modern twin fan enclosed alternator, you are going to have to try REALLY hard to accomplish that and I'd still say you'll more than likley fail.
You could easy get 70A out of an alternator, not going to get that with a motor.  If you want more 120+ alts are common now.  If you were after all out power you could  put a 4" pulley on the engine and  drive 2 alts off a 6HP motor. My lister 6/1, My China diesel and the 5 HP petrol Kawasaki I have will all drive 2x80A alts to their limit.  You'd cruise at 120A which will give you a max of 1200W+ on the inverter and get your batteries charged up fast as possible. 

You should look at your inverters and their rating to work out what they need. There are a lot of variables such as the inverters efficiency, the actual voltage you put into them ( they will usualy go 11 to 16V) and other things but a good safe rule of thumb on a 12V system is conveniently a factor of 10.
That means if you divide your inverters output in watts by 10, you'll get the amps you need to feed into it to run it to full output.

If you have a 1000W inverter, you'll need 100A to maintain battery level. If the inverter is 600W, you'll need 60A and so it goes. Most likely you'll be able to get a little more but you'll never run your battery down or come up short if you calculate on this.
Even if you got 20A out of the DC motor, that's only going to support a 200W load which isn't a lot.

And before any of the electrical purists start nitpicking, no, the 10X factor is not absolute BUT, it is an easy to work factor and rule of thumb that has a measure of built in tolerance to all the usual variances in the equation. 

My suggestion is to look at this another way and use a regular car alternator rather than your motor.  It's basicly the wrong tool for the job.
 It will work but with severe limitations in output, longevity, control, setup and real cost.

whatusernamesareleft

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That makes a lot of sense.  I just have a couple modified sine wave inverters, one is 800 watts and the other is 400 watts.  Thanks for pointing me in the right direction.

george65

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You are more than welcome.
It would be good to see how your project goes.  I have built a few of these things myself.  They are simple, fun and work well with inverters.
The other thing you can use as I am with the solar setup I am playing with is a Computer UPS. These are Pure sine wave and you can use them on things like say your fridge. If you get frequent power outages and have them hooked up to batteries, You can keep the food cold longer.

You need one that is called online rather than line interactive or one that " Cold Starts"  The line interactive and non cold start units need 110/240 to fire up before they will work from the battery. I have a few mod sine wave alts and I can boot them up from that although neither the inverter or the UPS seem to like it so I disconnect as soon as I get them UPS lit.  I have an APC 1500 and 3000W units now and like most of the larger UPS will cold start.

They also only run off 24V which is convenient.  I removed the batteries and made my own external leads so I can put them on car batteries.  The big units run car battery leads so I have no worries about them getting enough juice. I was given some real nice new Eaton units a while back but they run 90V in series connected battery's so are impractical for the way I want to use them.

I saw a vid on YT not long ago that showed a guys setup similar to what you want. It was all on a nice frame and had the motor, alternators, batteries, inverter, a light  and 12V sockets.  The frame was on large wheels and the thing was capable of 2Kw so could run essential house hold appliances.
He also had an additional muffler on the engine to keep it quiet. Not sure how well they work, in my experience most of the noise from an industrial engine is either intake or just mechanical racket.

For the inverters you have, You'd want 120A @ 12V to run them to capacity.  If you want to run something like a UPS you'll need to get a 24V alt.
For 12V You could get a single alt or double up on some smaller ones. Positives and negatives to both approaches so whatever suits. I have access to all the 80A alts I want so go with them. Smaller alts are also a lot cheaper than the larger ones. If you really want to go whole hog, get yourself a Leece Neville. You can get external controllers for them to run 12, 24, 36 or 48V and with the efficiency that rivals any other alt you can get. 

You can have a lot of fun with this stuff and learn a lot too.
Nothing better when the lights go out and you can save the day with your home made power station.

DamonHD

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Nothing better when the lights go out and you can save the day with your home made power station.

Indeed!

Damon
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