Induction motor - generator conversion

[BioHazard]

I'm looking for a low cost <500 watt generator head. I've read plenty about using induction motors as generators, though I've never actually tried before.

First of all I have read you get about 500 watts per rated motor hp when used as a generator head, is this true as a rule of thumb?

Secondly, would this particular motor make a good generator?
https://www.surpluscenter.com/item.asp?item=10-2531&catname=electric

I would like to try and use the motor to start a small engine from grid power, then unplug and generate it's own power. I understand I need to spin the motor at slightly faster than it's rated speed, in this case 1710 RPM. Is there an exact speed it needs to spin to produce the right voltage and frequency, like a standard gen head, or is there some tolerance in there? What happens if I spin it up to 2000 RPM?

[mike90045]

What happens if I spin it up to 2000 RPM?

You can't, if you are backfeeding the grid.  It just turns into power fed into the grid, and you have to overpower the local grid, to get past 60 hz.

RPM = Frequency out.   if you spin at spec freq, you get 60 hz.  faster, and you get 66hz or 73 hz, and maybe a bit more voltage.
Much faster than label RPM and you get a snarly mass of wire and iron like a fishing reel backlash (rotor explodes from centrifugal force)

[Ronmar]

For standalone generation with an induction motor, you will need some capacitance to provide the excitation.  This unfortunatly determines the output voltage, so there is no regulation.  Ok for powering the string of lightbulbs in the jungle village(fixed load), but not so great for powering a house with varying loads...  What are you planning on powering?  Induction motors as generators don't do as well with inductive loads as they do with resistive loads...  They work great backfeeding the grid as the grid provides all the excitation/ regulation.

[BioHazard]

Hmmmm...I'm just trying to come up with a small load that I can measure in watts, compared to fuel efficiency with the engine it's attached to. Kind of hard to explain exactly what I'm doing. I don't really have any particular load in mind, I could just use some light bulbs or heating elements...I just want to be able to measure the output with a standard kilowatt meter.

[Tom Reed]

Would an 3 phase induction motor work ok rectified and fed into a mx60 charge controller?

[Ronmar]

Would an 3 phase induction motor work ok rectified and fed into a mx60 charge controller?

I have wondered that very thing myself...  How would a 3 phase work with fixed capacitors, making 3 phase rectified DC like an auto alternator does.  Would it be clean enough to be accepted by the charge controller or an inverter/charger? 

[Lloyd]

Me,(but I'm no EE) thinks it would if tied to the bats, as they would be like a big spring, and absorb any ripple just like in the auto alternator.

Big Q, is how do you the keep it excited properly...so that it doesn't bounce all over?

Lloyd

[BioHazard]

How about this:

I plug a 1hp induction motor into the grid, unmodified.

I use that motor to start a 6hp engine. Now I overspeed the induction motor, while still plugged into the grid.

Will that feed back into the grid without modifying the motor with capacitors? I could have an equal sized or larger load running somewhere else attached to the grid so that my meter never reverses.

No, I'm not going to kill any lineman. This will be completely baby-sat...

[mike90045]

How about this:

I plug a 1hp induction motor into the grid, unmodified.

I use that motor to start a 6hp engine. Now I overspeed the induction motor, while still plugged into the grid.

Will that feed back into the grid without modifying the motor with capacitors? I could have an equal sized or larger load running somewhere else attached to the grid so that my meter never reverses.

No, I'm not going to kill any lineman. This will be completely baby-sat...

Should work, I guess you will have to try it.

[Ronmar]

Me,(but I'm no EE) thinks it would if tied to the bats, as they would be like a big spring, and absorb any ripple just like in the auto alternator.

Big Q, is how do you the keep it excited properly...so that it doesn't bounce all over?

Lloyd

Well it would neeed to be excited with fixed capacitors across the legs, before it gets rectified.  But that is the problem, fixed capacitors, means fixed output, so it would vary with the load applied.  But since that is what happens with a solar panel or wind plant, this should be maneagable with a proper charge controller/inverter.  To the charge controller it dosn't matter what the input is, as long as it is within a specified range.  But how much filtration will be neded to get the ripple within limits acceptable by a charge controller/inverter?  They do it with wind plants, so I am sure it is doable...

Biohazard, what you describe should work, and any excess you generate beyond what you use will just pass back into the grid...  Think of it like plumbing.  If you feed into the system downstream of your meter(house/load side), the pressure(voltage) there will be a litle greater than that upstream of the meter.  Your downstream loads creat a slight drop in pressure when energized which normally draws power in from the grid thru your meter.  So your downstream loads will consume that excess energy first...

[BioHazard]

Biohazard, what you describe should work, and any excess you generate beyond what you use will just pass back into the grid... 

Yeah...my major issue is keeping that from happening, because I'm not sure how my fancy digital smartmeter will deal with it. Next thing I know a black SUV will show up and a bunch of guys with guns will come break down my door.....

I never thought I would miss the old spinny meter!

[bschwartz]

I still have a spinny meter.   
Made my grid tie easy.

[BioHazard]

I still have a spinny meter.  
Made my grid tie easy.

What, do you live under a rock?!  

I looked at some property that had a 100 year old farmhouse on it that needed to be torn down. Didn't look like it would take much more than a big gust of wind to knock it over. It had been abandoned for decades and boarded up.

I couldn't help but notice, the power company still came and switched out the power meter on that house with the new digital one.  

[Carlb]

We have both solar and wind grid tied to our home.  The electric company had to replace our original digital meter with a newer one because the original digital one would not go backwards it actually would just keep counting up no matter which direction the electricity was flowing. Some digital meters will read both directions some will not.

carl

[deeiche]

rm /