Convert AC motor to AC alternator 1

[dvx]

I have a brushless AC motor:

3/4 HP, 3450 RPM, 110/220v

Is it possible for me to use this motor as an alternator?

If we achieve 3450 RPM on this alternator what do you think we will get for output interns of voltage, (HP) watts?

Thanks guys, I wait for your comments.

 

[waross]

You may be better if you add the slip RPM instead of subtracting it.
3600RPM - 150 RPM = 3450 RPM
3600RPM + 150 RPM = 3750 RPM
Try a small motor starting capacitor for excitation. Once you get a voltage output you may calculate the correct value of capacitor for the voltage you need. The ratio between voltage and capacitance is fairly linear.
You may have to "Flash" the motor windings with a 12 Volt automotive battery before starting to turn the motor to establish some residual magnetism.
Google "induction generator".

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[jraef]

Using residual magnetism alone is not guaranteed to work, there are a lot of variances in motor manufacturing that make it somewhat hit or miss.

What Bill was suggesting though highlights the "second half" of the equation for turning an AC motor into an alternator. Those two halfs are:
1) Super synchropnous speed as Bill pointed out above, meaning using an external force to turn the motor FASTER than it's synchronous speed by the same amount as it's slip percentage; and
2) Magnetic fields by way of excitation of the stator windings.

Remember, an AC motor is NOT a permanent magnet, it is an ELECTRO-magnet. So in order for it to establish a magnetic field by which it can generate power, it needs electricity. Therefore it's essentially a Catch-22; as a general rule an AC induction motor will not "self" excite so it will not generate it's own magnetic field, which is what it needs in order to generate at all! But it will, if connected to the "grid", use the grid power to excite it's windings and then the first half of the equation is all you need, the super synchronous speed. So that is why wou will see induction generators used in things like wind mills, because they are connected to the grid for excitation and generation. But you rarely see induction motors used as "island mode" alternators, which means stand-alone not connected to anything else.

In some cases, as Bill alluded to and I mentioned above, there will be some "residual magnetism" in the iron core of the motor, and when combined with the right amount of capacitance to store it from one cycle to another, that can build up enough excitation voltage to turn the motor into the electromagnetic machine it wants to be. There are tricks to making that work more reliably, but it takes some effort, talent and a little bit of luck in finding a motor that used iron in it's construction with the right amount of magnetic permeability to retain enough magnetism when not powered. Another trick is what Bill said, to "flash" the motor with an external voltage source and let the capacitors do the rest.

How much capacitance and knowing how to connect it is part of the "talent" mentioned above. So yes, it can be done, but it's not quite as simple as just hooking it up and spinning it fast.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[wayne440]

Here is one example.

http://www.qsl.net/ns8o/Induction_Generator.html

 

[LionelHutz]

You need to confirm if this a permanent magnet motor? If so, then the motor output (Volts/Hz) would be linear with the speed and it should reach nameplate rated values at about 3450rpm. You should also be able to get around 3/4Hp of output from the thing.

 

[dvx]

Thank you all for your input,

This is not my first time on this forum. Every time I had a question you guys seem to be on top of the issue.

I tried to attach some photos of the motor I am talking about but i am working of the iPad and I couldn't upload the attachments. How do I make sure or find out if the motor I have is in fact a permanent magnet motor? It's not new in fact I think it could be 15 or so years old.

This is the info of the motor:

GENERAL ELECTRIC

MOD 3J88FB5 / FR 39 / TYPE KC / HP 3/4 / PH1 / v 110/220 / RPM 3450 / A 9.2/4.6 / CY 60 / WY

I will try to attach the pictures once I am at my desktop

Once again thank you all for your input

 

[jraef]

That's an AC single phase induction motor, not PM.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[dvx]

Thank you gentlemen,

Your advice is appreciated.

Kind regards,

Dennis