Car Alternator as Traction motor?

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Car Alternator as Traction motor?

This topic has 9 replies, 5 voices, and was last updated 18 November 2011 at 18:40 by Sub Mandrel.

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18 November 2011 at 15:25 #78059
Peter Bell
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@peterbell11509
Had an enjoyable browse through the Model Engineer in the library this morning and was interested to read that a talk will be given by Bob Walker on brushless motors at the ME exhibition.

But what really made my ears prick up is that one of the topics he will be covering will be using a car alternator (16ARC) as a three phase traction motor with a continous rating of 950watts.

Cannot attend the exhibition so wont be able to hear the talk direct and just wondered if anyone has hear of this technique before?

Thanks Peter
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18 November 2011 at 15:25 #4188
Peter Bell
Participant
@peterbell11509
18 November 2011 at 16:01 #78063
Anonymous
It’s fairly common in cars that have a ‘stop-start’ system to use a single electrical machine as both starter motor and alternator. In simple terms a three phase electrical machine can act equally well as a motor or generator. I would have thought that 950W isn’t a problem. One of the reasons for the push to 48V SLI (starting, lighting, ignition) car systems was that the loads were pushing beyond a kilowatt; which is loadsa amps at 12V.

Regards,

Andrew
18 November 2011 at 16:17 #78065
DMB
Participant
@dmb
I was told sometime ago that Rolls-Royces have a combined alternator/starter motor system. This means that the device is permanently engaged with the engine, resulting in silent starting, eliminating the terrible screech when the Bendix mechanism operates for starting most other cars. Also, there is a `slave` battery in the boot.

Perhaps one of the wealthier forum members with such a machine, can confirm the above.
18 November 2011 at 16:27 #78066
Peter Bell
Participant
@peterbell11509
I recently read that the stop start technology now extends to motor cycles. I suppose it’s the same reason why most commercial vehicles are 24 volt, under the bonnet on the stop/start car I looked at it certainly seems tight with 48volts.

What I was interested in really is about using some readily available technology to drive the alternator and it did cross my mind the that perhaps the person who is giving the talk has written a book on it or is know to this forum or even appears on it?

Regards Peter
18 November 2011 at 16:37 #78068
Billy Mills
Participant
@billymills
The motor demo has been at MEX. It is a great idea, the car alternator has three delta wired windings so you can drive it from a variable frequency drive as a variable speed motor. The VFD was made from a couple of IC’s and 6 Mosfets. The designer had a very nice demo rig on show.

As the rotor is designed for a 12V system the voltages for motor use are conveniently low. The idea of 2 or 3 phase drive of very small motors is widespread in electric flight. Some of the early pioneers rewound floppy drive motors. The power to weight ratio of these motors ( with rare earth magnets) is very high at about a HP per pound weight.

Billy.
18 November 2011 at 16:49 #78070
Billy Mills
Participant
@billymills
Rollers do have two accumulators. When your driver is waiting for you he can run the electrics without the engine running. The other battery will always be able to start the engine.

The combined motor/generator idea is described in a book called “Modern Starting,Lighting and ignition systems” it was published in 1917.

Billy.
18 November 2011 at 17:35 #78077
Peter Bell
Participant
@peterbell11509
Billy,

It is the VFD bit that interests me really. Do you have any info about it or what the electric flight motors use. Or is there another forum which covers it?

Just been playing about with a pulse width mod circuit for a solenoid and I think its the first time I have successfully used power mosfets!

Peter
18 November 2011 at 18:30 #78083
Billy Mills
Participant
@billymills
You can buy the VFD’s for electric flight for not very much, they run around 20-50A for flight times of 10 min or so. The VFD is very simple. An oscillator drives a counter which then outputs the phase drive signals to the mosfets via a standard IC. You do need to know about fast switching, a 100MHz scope or faster is needed to check operation properly if you were rolling your own.

Scrap PC motherboards are one source of free mosfets, motherboards don’t last long these days, but heavy current mosfets are dirt cheap anyway. Have a google for electric flight Peter.

Billy.
18 November 2011 at 18:40 #78084
Sub Mandrel
Participant
@submandrel
If anyone want details of driving BLDC (brushless DC motors) there are a couple of useful datasheets on the Atmel

Control with sensor

Control without sensor

These are a bit of heavy going, but for thiose who want to know they describe the theory of how they work OK and you DON’T need to understand the microcontroller side.

Neil
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