# AC Motor as generator



## MrCrabs (Mar 7, 2008)

Whats going to turn the motor to make it generate electricity when you want to use it as a charger?


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## Madmac (Mar 14, 2008)

During driving the motor will generate power during regenerative breaking. When charging the motor is disconnected and the mains is connected in its place....with a few other bits of electronics.

The electronics that controls and conditions the regenerative breaking does the same when connected to the mains. The diodes in the H-Bridge rectify the mains the same as they do for the motor when breaking.

Charger is obtained for about 100 euro's of bits and can be controlled to take whatever power is available up to 100Amps for a 100AHr battery pack. To make a commercial product power factor correction would be needed to be added, but for home use it gives a very low cost solution.

Madmac


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## MrCrabs (Mar 7, 2008)

Ok... I misunderstood what you meant in your first post.


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## Dennis (Feb 25, 2008)

Madmac,

An AC induction will not develop any net voltage when just simply turned on its shaft. You must have power applied such that the frequency becomes less resulting in the rotating magnetic field becoming less in speed. The rotor will have to be spinning faster than the revolving magnetic field to get generated voltage on the output. Simply letting off the accelerator will do the trick because the momentum of the vehicle prevents the rotor from dropping in speed suddenly while the revolving field will be getting less since the accelerator pedal is not in use. Now you will need to do some PID control of how fast the speed switching frequency ramps down when the user lets off the accelerator pedal. Thats up to you to optimize and you to allow a user to adjust how fast the regen breaking works when the user lets off the accel pedal. Have fun.


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## Madmac (Mar 14, 2008)

Hi Dennis

I appreciate that the motor has to be driven to do this, it would make for an interesting world if power was generated with no magnetic fields.

What I need to know is the variation in the voltage generated as the motor rotation is faster than the drive frequency and how this varies with load. To complete the design of a power converter (also used as mains charger) for conditioning the regen voltage to a level to charge the battery pack, I need some figures to design around. Is it a direct relationship that can easily be modeled or is it very specific to each motor design?

Motor manufacturers seem to supply very little information on this mode of use. Other that dealing with the need to stop and causing the DC rail to pump (protection by heavily loading the rail). Obviously the total energy available can be worked out.

Madmac


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