DIY Electric Car Forums banner

Car alternator used in motor mode.

17550 Views 5 Replies 5 Participants Last post by  Coulomb
You know that alternators can run as motors. It needs a big and complicated electronic unit.
The rated power in generative mode is about 1400 Watts for a 14 Volts 100 Amperes altenator, 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 approche good it.
36 Volts is get by three lead-acid gel batteries.

For the regenerative mode (alternator) it needs to connect the three batteries in parallel and the inside alternator regulator allow batteries charging. You can connect an extra resistor for extra braking then batteries are charged.

For one little quadricycle with one alternomotor by wheel assumes approximatively 4 kiloWatts usable power. I take care about converter and alternomotors efficiency. The motor are not in the wheels for the confort of the vehicule but need gearbox (ratio 10) and cardan joints. For vehicule with or without suspensions.

Four synchronus motor need a curent sensing control. This is verry complicated beacause synchronuse alternator in motor mod are controled by sensing the angle of rotor and control unit work on phase between stator and rotor.

Big work for an electronician like me but not impossible.
1 - 6 of 6 Posts
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?
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.

I have a alternator and want to convert it to motor.
can u give me the details of how it can be done??:confused:
There are discussions about using alternators as motors on several different forums.

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
... 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!
See less See more
1 - 6 of 6 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.