Calculations for Motor-Driven Generators

You can get the 230/460 volts single phase out of it but thats about it and anything else will need a transformer.

The capacitor type exciter method has no voltage regulation and the frequency is based on the motor RPM with a slight variation due to magnetic slip. They are a very poor power source by all standards.

If you need accurate and reliable back up power that can be driven off of a belt drive your better off picking up a generic AC generator head from eBay for a few hundred dollars.

OK, thank you for that information! So, just curious, I could still use this motor for my needed application? What type of transformer out there would I most likely use to change that to single phase 110 volt? My goal was to use components that I could easily pick up at a low cost, say used components at appliance shops.

With a 25 Hp motor as your power source, you are looking at a maximum off about 18 KW output, which would be enough for your application. You would need a 2:1 stepdown transformer rated at at least 18 kW to get to 120 V, assuming you wire the motor for 230 V. Now, what you will have is a poorly regulated power supply that is going to bog down each time your refrigerator compressor kicks in, which is going to quickly kill the compressor. It would ultimately be a whole lot cheaper to buy the appropriate generator than to try and cluge together a system that is going to destroy everything else you own...and not save you all that much over the cost of the appropriate equipment anyway.

Hi Coreyralls, despite all previous post, I have to say that a 3 phase motor with squirrel cage rotor, can not be used as a generator.

Not for any safety or other fact.

Such kind of motor is not reversible.

Or maybe I'm wrong, if so I would like to know why.

devita; your wrong! big wind generators are induction motors, a 3 phase is reversible unless a mechanical device keeps it from turning. perry

Hi Perry , as I state

I have to say that a 3 phase motor with squirrel cage rotor.

What do you mention is the same ALTERNATOR used at CARS , they have it's rotor "excited" by a DC current.

Ok, I obviously have not tried this yet, thus the reason I am here trying to gain a better understanding of how all this works first. I have read many reports of people using induction motors as a generator with usable results, less than perfect I am sure, but still usable. Is this a misconception??

It sort of works most of the time but not well.

It works by using one or two of the three phases to produce a sort of LC tank circuit that keeps the motor excited while its turning so in a sense yes it does work like a generator of sorts. But it has several major limitations and or problems that a real generator does not have that make all the difference as to why it is not a good choice for power.

Problem one. No voltage regulation as the load varys. The output voltage will usually have to be set too high at no load and then will drop too low at moderate loads.

Problem two. The output frequency is never stable. The nessisary slip in the magnetic fields as the rotor turns tends to also create a noticeable frequency drift above that of the engine as the load changes.

Problem three. There is no overload surge capacity. Once your load goes above a certain amp draw point the exciter LC tank circuits collapse and you have no output until everything is unhooked and it regenerates its exciter circuit power again.

Problem four. You still require a transformer to step down the 240 volt output to 120/240 volts in the power levels you need which could cost close to as much as just buying a real belt driven generator would any way.

So yes it generates electricity. But it generates electricity in a way that is highly unstable in all factors that are important for not damaging appliances and all most everything you would want to power in an emergency. So factor in how much replacing most of your electrical stuff will cost and then see which is cheaper in the end because it will eventually happen.

Go ahead and build it. But when half of your stuff is burned out from over or under voltage and frequency swings just be pleased that the other half still works!

Hi TCMECH, I learn a new one today.

Where can I see such a diagram of this application.?

Dear sir,

Thanks for your response to my question.

I asked the question in reference to the

Magniwork experiment that is highlighted

on their website. Please give me your

vew on the same.