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How to Make a Generator from a Universal Motor

04/25/2012 12:42 PM

Hi -

I have a universal motor from a corded electric weedwacker that I would like to turn into a generator. Normally the motor runs on 110V, 4A, but being a universal motor (AC motor with brushes) it can also run on DC.

I dont think this is a normal AC induction motor. Just spinning the motor at 1300 rpm gives me a measly .7 vDC output. I read somewhere if I energize a coil? stator or rotor? by applying a temporary DC voltage I could generate more electricity. Then I think I can disconnect the DC voltage after a short time as the spinning motor becomes self sustaining as a generator. Do you know how to do this? There are only 2 wires coming out of the motor, a pos and neg.

Greg

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#1

Re: How to Make a Generator from a Universal Motor

04/25/2012 12:48 PM

the spinning motor becomes self sustaining as a generator
You might want to do a little more study on this one. Your statement smells like you are dabbling in "alternative energy" which is usually spelled "scam science".

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#2

Re: How to Make a Generator from a Universal Motor

04/25/2012 1:10 PM

It's been a long time since I've studied this stuff, but as I recall the field and armature windings are series wound. This means you'll have to disconnect the two and apply an external voltage to the armature to produce enough magnetism to generate anything in the field windings.

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#6
In reply to #2

Re: How to Make a Generator from a Universal Motor

04/25/2012 2:39 PM

YES, GA CI, makes me think, is there such thing as a series generators?

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#8
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Re: How to Make a Generator from a Universal Motor

04/25/2012 3:08 PM

I'm not an EE, but based on what I know, it wouldn't make much sense to series wind a generator.

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#3

Re: How to Make a Generator from a Universal Motor

04/25/2012 1:26 PM

You can't have it both ways. That would be perpetual motion, only a dream so far.

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#4

Re: How to Make a Generator from a Universal Motor

04/25/2012 2:01 PM

I don't believe the OP is asking about perpetual motion, I think you are reading into the words Self Sustaining too much here.

I think the OP is referring to the stator coils being energized by the power of the system being generated as Self Sustaining, instead of having to power the coil from an external source. I don't think they are looking to get energy from nothing, just to turn a motor into a generator.

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#5
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Re: How to Make a Generator from a Universal Motor

04/25/2012 2:19 PM

What turns the motor/generator? The motor can't power itself and generate power, too.

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#7
In reply to #5

Re: How to Make a Generator from a Universal Motor

04/25/2012 3:07 PM

Yes THANK YOU anonymous poster!

I am NOT expecting to get free energy!! Maybe the wording in my question was unclear for the rest of you who think I'm trying to make a perpetual motion machine.

I am currently spinning this motor with a hand drill or eventually a windmill. So I am putting energy into it, just trying to turn it into a generator.

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#9
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Re: How to Make a Generator from a Universal Motor

04/25/2012 4:44 PM

Well Greg, the problem is that you don't have sufficient magnetic field to get it started. Even if you did, that brushed rotor is going to be full of losses and it will end up taking a significant amount of your generated energy to sustain the magnetic field. The principle of generating electrical energy requires cutting magnetic flux lines with a coil. That being said, there are several types you can use, but a universal motor makes a lousy generator. If you insist, however, you will need to separate the rotor from the stator windings and apply DC power to one of the coil sets. The other will produce some kind of output, but if it is full wave rectified, "DC" then you may run into another problem like saturation of the core.

So, take another look in the garage. Perhaps take a look at what is used on one of those gas powered generators you get at Lowes. Just don't expect to get any more out of the motor (uh... I mean generator) that its ratings or you will let all of the smoke out.

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#10
In reply to #7

Re: How to Make a Generator from a Universal Motor

04/25/2012 5:20 PM

Why not just get a generator on Ebay for $50 that is ready to go?

http://www.ebay.com/sch/i.html?_nkw=wind+generator+motor

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#11

Re: How to Make a Generator from a Universal Motor

04/25/2012 8:12 PM

Generally motors are designed to convert electricity into mechanical motion. Reversing the process will work, it just won't be efficient.

The older automotive generators had a field coil that was energized by the battery. The field coil sets up the magnetic field through which the armature turns. A series wound motor won't quite do the same thing. You may get better results if you separate the field coil from the armature winding. Note again, this motor wasn't designed to do that so it's hard to say what you'll get. Your 0.7 volts may be due to residual magnetic field in the steel laminations.

Check out www.fieldlines.com for info about wind turbines and generators. It's a treasure trove of useful tidbits and the crowd that hangs out there have some serious experience with generators, windmills, solar, etc. Be sure to search their site. I'm sure someone has asked this question there before. It's probably been answered several times in as many different ways.

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#12

Re: How to Make a Generator from a Universal Motor

04/26/2012 7:29 AM

I think what you have is a series wound motor, that is, the field and armature are connected in series. If you spin it without any load and just a voltmeter connected, there is no current in the field windings and all the generating you're getting is from the residual magnetism in the core. Try connecting a load, like a light bulb, and see what happens.

If you wanted to rewire it, you could connect the field in parallel with the armature. It should then generate voltage without any load.

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#13

Re: How to Make a Generator from a Universal Motor

04/26/2012 10:35 AM

Thanks for your comments guys. I may actually try to separate the stator and rotor coils and see if I can get any appreciable electricity out of this. I have several of these types of motors lying around, and enjoy the learning opportunity

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#14

Re: How to Make a Generator from a Universal Motor

04/26/2012 10:58 AM

Connect it up mechanically in a lathe or by a power drill and connect a load, a lamp or something. I think you'll find it gets started on it's own from the tiny amount of residual magnetism in the field & armature. The output depending on the revs and load. In theory a universal motor should work in reverse, i.e. at the nominal revs say 1500 rpm, a 4 amp load, say 25 ohms, it will give 110vdc as an output.

Unless you disconnect the field windings and power it separately with a DC PSU you'll have no control over the volts produced.

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#15

Re: How to Make a Generator from a Universal Motor

04/27/2012 1:32 AM

I think you'll find that with the armature and field in parallel the field resistance will be so low you will loose what you gain creating the field.

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#16

Re: How to Make a Generator from a Universal Motor

04/27/2012 11:44 AM

Don't use a motor, they are simply not efficient enough, though many do.....

Don't use anything with brushes/armature. Too much maintenance and wear and tear.....

You did not say what voltage you want, but 12 volt car alternators are cheap and designed to do the job, they are also set up to charge 12 volt batteries. They work when it rains and are very robuistly built. You may need to get them spinning at quite a speed fopr proper output, 1000 RPM or close to, a test with a power drill will help you to decide.....

Or use a a truck alternator and get 24 volts.

For generating voltage at a lower RPM, take out the rotor coil and replace with a strong circular magnet. You lose the voltage control though.......as the output is then related to RPM only, both voltage and current.

Need more power, use more of them!!!

If you want AC, take out the diodes. Some are single phase, some are 3 phase.....count the numbers of diodes to tell you what you have, 4 = single phase, 12 = 3 phase if I remember correctly.....

Do remember that to get the required aC frequency may be an even larger problem.....

There are plenty of YouTube videos showing how its done. Search on YT with "car alternator wind turbine", watch all the videos.....

Best of luck.

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