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Driving Alternator wired as BLDC motor with VESC6

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Driving Alternator wired as BLDC motor with VESC6

Hi all,

I'm about to start a project using a car alternator rewired as BLDC motor, I think in VESC terms this will be considered a large inrunner. Alternator doesn't have permanent magnets so I plan to engergise the field coil with 12V supply, although I may experiment with varying this, I've understood higher V on field coil will mean higher amps which will mean stronger field = more torque, lower speed, or vice versa - hence this is interesting variable but I presume there is an optimum value where I'll get most overall power out of the system and after that resorting to mechanical gearing will be optimum.

I'll also be experimenting with the alternator phase coils wired in Delta Vs wired in Y (star) configuration.


Assuming initial bench tests go ok I'll continue to try to determine through experiment the effective KV of the motor (for a given field coil voltage), determine torque for a given Voltage / current, and stall torque etc.

If the alternator can provide enough power as a motor then I want to use it to power a pedal go kart, if I can determine some parameters for the motor I can then think about gear ratios...


I'm interested in any Advice on how how to design experiments to measure the values of the motor and any advice or thoughts anyone has for a newcomer to VESC configuration and especially considering my slightly different use case - primarily advice on how not to blow up my nice shiny VESC6 device.. (I understood lowering default erpm value is a good start, and of course watch temperatures like a hawk).

Many thanks,


Last seen: 2 weeks 6 days ago
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Joined: 2016-12-27 20:19
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Benjamin built that setup already. He used a 75/300 VESC. 

It works. 

Last seen: 3 years 7 months ago
Joined: 2020-01-15 19:36
Posts: 3

Frank - was this project (Benjamin with alternator and 75/300 VESC) written up anywhere? I haven't seen it, and like many others I was about to go down the same path. Would be good to understand what has been done before. 


Last seen: 8 months 1 week ago
Joined: 2017-09-21 08:55
Posts: 17

I have done this. A 70a car alternator wired as wye and a ~3a rotor current (5v) gives me about 130kv. I was using a 13s 48v lipo battery.

I actually recommend running the rotor at a lower voltage using a buck converter as (at least with my alternator), 12v would have dissipated over 100w in the rotor.

I used this buck converter:

My setup is good for about 2-3kw, though the alternator gets extremely hot. because it doesn't have permanent magnets to demagnetize and is designed to live in an engine bay this isn't a problem.

It does lower efficiency slightly though. efficiency is not an alternators strong suit anyways and I would pin it at around 85-90% where a regular bldc motor is 92+%

my max I could get to work reliably was ~75 phase amps at 48v.

The vesc 4.2 and 6 (fsesc6.6) drives it  in foc and bldc mode pretty happily.

I suggest adding the ams magnetic encoder as that improved my low speed performance significantly.

I also experimented with on the fly field weakening. changing the rotor current based on duty cycle and speed.

This worked ok, though I had to turn up the sensored switchover speed because the foc algorithm is not happy when you vary the kv (proportional to lambda) at lower speeds.

If you do this, calibrate the vesc foc at your minimum rotor current.


For a go cart in the 2-4kw power level, a 120-200a alternator is probably your best bet. semi truck alternators are beasts.

There are also the "alternators" for mild hybrids that are actually reasonably powerful drive motors as well.

They tend to be a bit higher voltage and may be induction motor based vs magnets or field windings though, so watch out. someday the vesc will be able to drive induction motors. not today though.

flyingbrike's picture
Last seen: 6 months 4 weeks ago
Joined: 2020-05-14 15:39
Posts: 9

Hello there.

I tried this setup and it works but ...

I use a Scam 100/200 amp Vesc compatible controller.
The motor is car alternator converted. No sensors yet.
Startup from 0rpm is difficult and bogs.
The power is good until i drive up-hill. After 30sec or so, the power drops to 10% or so. When i stop en restart, it runs normal again. Notting gets hot or even warm. Battery's are strong 13s 35ah 54v
I have tryed +100 setting-tweaks , but no sollution.
Any idee's?
I want to install hall sensors, where do i possition  them?

Silent Revolution is NOW !

Avin Raikwar
Last seen: 2 years 8 months ago
Joined: 2020-10-26 15:45
Posts: 3   , here is link to install hall sensor on alternator, hope this helps.

flyingbrike's picture
Last seen: 6 months 4 weeks ago
Joined: 2020-05-14 15:39
Posts: 9

hi there. I installed a new controller HI200   75200. and went to 16s.

The alternator is 12v 180amps.

So i run it now at 180fase amps and 120amps battery current. 

Lots of torque and no more power limits uphill. 

But still 1 issue : high rpm.  I can run max at 38000erpm. That should double to 80000. How do i do that?

I tsted 13s 54v qnd 16s 67v . very little improvement.  HELP 

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