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Registered Member #96
Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061
Just found this. Its interesting to note that nearly any induction motor (such as one from a defunct washing machine) can be used, as typically these have multiple windings which can be configured as needed.
Interestingly, I wasn't aware of the DC pulse requirement to make them "initialise", makes sense once you consider the way they work.
Obviously any medium to large sized capacitor will work here, even an MMC made of many small salvaged low voltage capacitors would probably work although it would take time to construct.
Registered Member #103
Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845
There's a way to do it without capacitors too, by using a sine wave inverter to generate the required phase shift. An inverter will allow power flow both ways, to the motor will generate back onto the DC link, boosting its voltage!
Registered Member #3108
Joined: Thu Aug 12 2010, 05:37PM
Location: Worthing, England
Posts: 72
Ah, so that is how they are used as generators. I one time tried to use an induction motor (with no capacitor!) as an generator to see how much voltage I can get and I got pathetic results. So I chucked out my motor..
Registered Member #2463
Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546
Using washing machine motors or dryer motors works well as "induction generators"
This was a part of a "motor class" a while ago;
Some points-The motor has to be spun above the speed needed to operate the centrifugal starting switch.. The capacity is critical, typically +/- 1 ufd to find the "sweet point". You dont need the DC flash to get it started. Residual magnetism in the rotor will do, but, the output load is switched in after the voltage builds, and the if the load is too high, you will collapse it and have to start again.
The output frequency will depend on the saft speed, but forget trying to 400 Hz or 25 Hz from a 60 or 50 Hz motor.
A good rule of thumb for capacity to start with is full load amps in capacitive reactance. (ballpark 20 ufd = 1 amp).
Standalone induction generators, like this get their excitation from the capacitors, ie their reactive volt-amps needed to magnetize the rotor.
Without the capacitors, an induction motor can reverse the power flow back to the utility if driven above their syncronous speed 1800 for a 1725 RPM motor @ 60 Hz. -and- This makes your electric meter go backwards nothing is added , just the motor. We have a nifty demo of this with a kilowatthour meter and a motor with a variable speed.drive--we arranged it so the variable speed driver was a DC generator, connected to a DC power source, and by by adjusting the DC, the system either drew power from the mains, and generated DC current, or consumed DC current and spun the power meter backwards. The demo also showed the reversal of the torque in the drive train.
Induction generators are routinely used to simply collect excess power in industry especially with pumps.
Here's a photo of the table setup of the "Electric Motor" classroom setup used between 1990 and 2003. There are two motor generator setups, ihe induction generator (driving a tape recorder) to show how speed slipped under load., and the "power flow " reversal gear with the kwh meter.
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Recycle surplus AC induction motor as generator
