Auto Alternator
11-22-2007, 12:37 PM
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Auto Alternator
This may be a bit off of the subject but I would like an answer.
I modified an automotive alternator by removing the diodes and voltage regulator. The result is a synchronous 3 phase motor. Next I connected it to a Mystery FM80A ESC and 18 volts. It runs O.K. at some settings and appears to have a very low KV number as it runs at a low RPM. It will run at 12 volts but not very well.
Note that the rotor, instead of having permanent magnets has an electro magnet which can be varied from 0 to 12 volts to change the KV rating. To run at 12 volts the rotor was down around 1 volt. At 18 volts I could go up to 3 to 4 volts. From that I assume I need a battery of 50 to 100 volts to get it to run with full rotor voltage. More battery voltage would allow it to run at higher RPM.
The open circuit voltage when used as a generator is about 150 volts RMS at 15,000 RPM and full rotor excitation. Note that as RPM goes up the maximum rotor excitation drops, and at very high RPM the maximum appears to be 6 volts on this alternator.
The maximum rotor excitation is the point where more excitation does not linearly increase the output voltage.
Auto alternators are Lundell designs and have a rotor with claw foot shaped poles. The main windings overlap, phase A windings are 2/3 overlapped with the B windings, etc. There are 12 windings for each phase and 12 poles on the rotor, 6 North and 6 South poles.
My question is why are the rotor poles claw shaped, does it help or hurt the performance as a motor?
I modified an automotive alternator by removing the diodes and voltage regulator. The result is a synchronous 3 phase motor. Next I connected it to a Mystery FM80A ESC and 18 volts. It runs O.K. at some settings and appears to have a very low KV number as it runs at a low RPM. It will run at 12 volts but not very well.
Note that the rotor, instead of having permanent magnets has an electro magnet which can be varied from 0 to 12 volts to change the KV rating. To run at 12 volts the rotor was down around 1 volt. At 18 volts I could go up to 3 to 4 volts. From that I assume I need a battery of 50 to 100 volts to get it to run with full rotor voltage. More battery voltage would allow it to run at higher RPM.
The open circuit voltage when used as a generator is about 150 volts RMS at 15,000 RPM and full rotor excitation. Note that as RPM goes up the maximum rotor excitation drops, and at very high RPM the maximum appears to be 6 volts on this alternator.
The maximum rotor excitation is the point where more excitation does not linearly increase the output voltage.
Auto alternators are Lundell designs and have a rotor with claw foot shaped poles. The main windings overlap, phase A windings are 2/3 overlapped with the B windings, etc. There are 12 windings for each phase and 12 poles on the rotor, 6 North and 6 South poles.
My question is why are the rotor poles claw shaped, does it help or hurt the performance as a motor?
