Induction Generator.pdf

Induction Generator

An Easy to Build and Operate

Induction Generator

B elieve it or not, nearly everyone you know has at least

one induction generator and probably more . That's right!

You say that is impossible... well, read on!

Within every home in America there are motors that can be operated as generators. They

may not be labeled as generators, but they will function just the same. These motors are

often called "squirrel cage motors" and are in washing machines, dryers, water pumps and

other devices too numerous to mention.

...............................

Typical electric squirrel cage motors

Besides being numerous and cheap, they will generate AC voltage of the purest sinewave.

They use no brushes and do not produce any RFI.(Radio Frequency Interference) A motor

converted to an induction generator will power flouresent and incandesant lights,

televisions, vcr's, stereo sets, electric drills, small power saws and other items.

OK, what is so great about it? There is nothing complicated about the conversion,

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Induction Generator

no weird rewiring, no complicated math...nothing! There are no brushes to wear out.

They can not be overloaded; if too much of a load is applied to the generator, it simply

quits generating. Removing the load will usually cause the generator to start again.

Speeding up the motor will help if it doesn't start right away.

Yes, but... are there problems? Well, there is no active voltage regulation, but

keeping it within a tested load rating can keep it within any voltage parameters that you

set. I feel that a voltage range between 105 and 126 volts is perfectly reasonable.

A motor converted to an induction generator will not start another squirrel cage motor

unless that motor is about 1/10 of the horsepower of the induction generator. In other

words, a 1 horsepower motor used as an induction generator will start a 1/10 horsepower

or less, squirrel cage motor. It is best to NOT use an induction generator to drive

motors. The added inductance of the motor will cancel out the capacitive reactance of

the capacitors and cause the generator to quit producing electricity.

The generator will not start under a load. Not a problem! You shouldn't attach any load to

a generator until it is at running speed. This is actually kind of a fail-safe feature.

So far, that is about all of the problems that I've found and I consider those minor.

How do you convert one?

By adding capacitors in parallel with the motor power leads, and driving it a little above

the nameplate RPM, (1725 RPM ones need to turn at approximately 1875 RPM, and 3450

RPM ones at 3700 RPM) the motor will generate AC voltage! The capacitance helps to

induce currents into the rotor conductors and causes it to produce AC current. The power

is taken off of the motor power leads, or the capacitor leads, since they are all in parallel.

This system depends upon residual magnetism in the rotor to start generating. Almost all

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the motors I've tried begin generating just fine on their own, with the appropriate capacitor

connected of course! If it doesn't start generating, try speeding the motor up. That will

usually get it going. However, it is extremely rare to find one that doesn't start.

If a motor doesn't start generating on the very first try , then apply 120 vac or even 12 or

more volts DC to the motor for a few seconds. That will usually work to magnetize the

rotor and your generator will start by itself from then on.

It is important to not shut the generator down with a load connected to it. This tends

to demagnetize the rotor and can cause it to not self-energize. That is, the motor will turn,

but it will not produce voltage. It is not a serious problem since the rotor can be

remagnetized by following the instructions in the paragraph above.

I've only found one motor that would not consistantly generate (out of a dozen or so that

I've tried over the years) and it was one with a bunch of wiring coming out of it; it may

have been a multi-speed AC motor. I had a 120 volt AC relay in the circuit that

temporarily added a 200 uf starting capacitor across the permanent 160 uf running

capacitor (Using the Normally Closed contacts) to get it generating. When 120 volts was

produced, the relay contacts opened up and removed the 200 uf from the circuit. That

worked, but it was not dependable. I just gave up on that one.

The capacitors used must be the type designated as "running" capacitors and NOT

"starting" capacitors. Starting capacitors are used for a very short time, usually less than a

second or two, and would be destroyed by being connected across the AC line

continously. Running capacitors are designed to be connected while the motor is powered.

NOTE : Make sure the caps say, "NO PCB's". PCB's aren't used anymore for capacitor

construction because it was a dangerous chemical composition. If the caps are old, and

you are not sure, don't use them. Be safe!

It is necessary to experiment to find the best value of capacitance to get one working. Start

with about 150 to 200 uf for motors 1 horsepower and under. More capacitance equals

more voltage output. The final value should be able to produce about 125 VAC when it is

putting out 60 hertz with no load. Then plug in100 watt light bulbs until the voltage drops

to what ever lower limit you set. Mine will do about 1050 watts before dropping to 105

VAC.

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Typical Running Capacitors...GOOD! .......................Starting cap...Bad!

In the following example, I used a 1 horsepower motor from a Sears water pump that I

bought at a junk yard for $10.00. This motor was capable of operating off of 115 or 230

volts at 13 or 7 amperes respectively.

Typical waterpump motor

Motor: A. O. Smith 1 Horsepower : 115 / 230 VAC : 13 / 7 AMPS : 3450 RPM

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Capacitor: 200uf 330vac. This was made by paralleling 4 capacitors that were 65uf,

35uf, 50uf and 50uf. All of these were rated at 330vac or better. All test results are from

this capacitor set. ( NOTE : The final version of this generator has 225uf of capacitance.)

Output Capability: This Induction generator has an no load voltage of 125.9 VAC at

60 hz. The generator successfully powered 1050 watts of lightbulbs with a voltage drop of

10.9 VAC to a full load voltage of 105 vac. During the power test, the generator was

driven by a 1.5 horsepower electric motor and there was a loss of RPM when the load was

increased. I attribute some of the voltage drop to this lack of driving power.

The ex-motor, now an induction generator is driven by a well used 3.75 HP B&S

lawnmower engine. A total of 950 watts of lights were ran for about 15 minutes with the

generator only getting warm. The voltage went from 126 volts open to 110 volts AC under

this load.

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