I am playing with a few modified automobile alternators to assess their utility for high torque and high speed drive applications with adjustable KV.
These alternators are quite cheap on ebay (e.g. https://www.ebay.com/itm/Alternator-180-Amp-Fits-10-17-DODGE-3500-PICKUP-543296/123471140236). And they are beefy. They range from 150A to 250A, which is about 2kw-4kw at 15V DC output. Torque wise they can do 10Nm to 20Nm depending on the size. The best part is that they have adjustable field strength through the slip ring supplied rotor field winding. That widens their effective speed range significantly. Most of them are rated to 18000rpm mechanically and electrically.
To use them as BLDC servos I have made the following modifications:
stator: To support high output current most alternators are winded as 3 phase generators with 2 independent sets of delta in parallel and rectified. I remove the rectifiers and reconnect the 2 deltas in series and in wye, this generally lowers the kv by a factor of 3~4.
rotor: Remove voltage regulator and supply DC (1-10V) directly.
encoder: Mount magnet at the slip ring end (back end) of the shaft and AS5048 encoder on back cover.
I have tested driving these alter-motors with ODrive 3.6 with rotor field excited with fixed 5V DC and that worked quite well after some tuning. I would like to drive the rotor field with the second axis and test real time current control. Can I use the “brushed motor” support in https://github.com/madcowswe/ODrive/pull/362 for this?
For now my use case is limited to 2 preset field current levels: high torque and high speed. Would I need 2 sets of tuned gain parameters then?