# Car alternator used in motor mode.



## rbgrn (Jul 24, 2007)

Ok I was thinking about this the other day. Of course you can get an alternator to run like a motor but what's the longevity of doing that? Would it wear out right away?


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## amidesign (Jul 26, 2007)

The longevity is good beacause rotor have bearings. And for exitation the brushs are dimentioned for long and hard work. In extra benefit the alternator have a fan for cooling.

My last car, a Mitsubishi run 345'000 km (555'224 miles).
In generative or motor mode the same energy is used, Same working conditions mean same life time.


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## anand.ssukhi (Jul 23, 2009)

I have a alternator and want to convert it to motor.
can u give me the details of how it can be done??


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## Salty9 (Jul 13, 2009)

There are discussions about using alternators as motors on several different forums.

http://endless-sphere.com/forums/viewtopic.php?f=30&t=16328

http://www.rcgroups.com/forums/showthread.php?t=905411

http://www.rcgroups.com/forums/showthread.php?t=1123956&highlight=reem

In my opinion, the last one has the best concentrated info. The biggest problem I see in using an alternator as a motor is in finding a good reliable reasonably priced controller. Good luck


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## Coulomb (Apr 22, 2009)

amidesign said:


> ... for running in motor mode it needs 36 Volts power supply.
> 14 x sqrt(2) x 2 = 39.6 Volts, 36 Volts is not equal but it approaches good enough.


You would normally drive a 14 V RMS motor with DC of about 14 * 1.414 = 20 VDC; you get the factor of 2 by using a push-pull circuit. You could probably use a 24 V battery for this, and maybe overvoltage the alternator a little (if it overheats, just don't use the full voltage available). By using a 6 transistor circuit (you need three drivers, one for each phase), you can regen into the battery without changing the battery configuration (leave it as 24 V).

But remember that the alternator is designed for a voltage such that 14 V is a diode drop over about 87% (from poor memory) of the peak of the waveform. So it would be running at just over 10 V RMS. Three 12 V batteries would be about 2.5x what it is designed for, and being not very efficient, it could well overheat very quickly.

At such low voltages, three single ended drivers might be more efficient, but then you have the hassle of switching the batteries for regen.

I assume that the point of running the alternator as a motor is in a mild hybrid setup. Alas, even 4 kW is so mild that I doubt you'd be able to measure the effect, i.e. it could well be way too mild!


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