Leroy Somer alternator Could this be right?

[OperaHouse]

I'm working on a Leroy Somer MA1326 6KV four pole single phase brushless alternator. I searched the web for technical information and didn't find much. I was told this this would work for about 10 minutes and the lights would then fade. I couldn't get it to produce more than 10 volts.

I traced out the wiring and found much of what I expected. Rotating rectifier from the exciter to the alternator and AC power output is rectified to subtract magnetic field of the exciter to regulate output voltage. What bothers me is the alternator output depends totally on residual magnetism. The exciter's stator field is built up only when current is drawn from the alternator. I would have expected some electrical path from the alternator section to the exciter. OR...at least a capacitor on the output to build up some field.

Multiple attempts cleaning connections never got the output over 10V. Shorting out the 45 ohm feedback resistor would drop the voltage to 5V. This at least indicated the rotor electrical path was somewhat working. I put 8VAC @3A on the rotor coil to check the diode bridge. Wouldn't call that a real flash, but after putting everything back the alternator worked. Attached is the schematic for the exciter stator field. I can't get over that it relies on
residual magnetism with no way to build up the field until current is drawn.

 

[waross]

Are you sure about the number?

Look at this link and scroll down to page 4.

http://www.leroy-somer.com/documentation_pdf/alternateurs_pdw/notices_pdf/3945a_en.pdf

Bill
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"Why not the best?"
Jimmy Carter

 

[OperaHouse]

This is a much older (10 years or more) model. It had a big logo ED38 on the label. This has distinct alternator and exciter sections. I thought the diodes shorting out the coils was novel. If it stops working again I will try plugging in a capacitor to the outlet. Removing the covers is a pain