I'm working on a Leroy Somer MA1326 6KV single phase brushless alternator. I searched the web for technical information and repair tips and found nothing. So I thought others might be interested in hoe these work. This was a construction light tower so it has seen a lot of the environment. I was told this this would work for about 10 minutes and the lights would then fade. I can't get it to produce more than 10 volts.
After removing the covers and blowing out the mud bee nests and digging into it I find there are two sections alternator and exciter. These comprise three circuits. The first is the regulator.
The diodes and mov are on this board and the resistor is this
This takes the actual output power, rectifies it to reduce the magnetic field of the exciter section. Shorting the 45 ohm resistor reduced the AC output from 10 to 5V. That verified that section was working. Resistance tests showed the wiper on the resistor was loose so the generator likely experienced some over voltage at times.
The next circuit takes voltage from the alternator stator, rectifies it and powers the exciter. I know I drew the opposite,it was late and this is the only way it makes sense.
There is a diode on each side. These tested good. One heatsink will have to be removed to get to the bridge on the shaft.
Third circuit is rotor with rotating rectifier.
This has a 25A potted metal bridge rectifier mounted to the shaft. Since this is the only thing left not tested it is likely the problem. I will remove one wire from the AC terminal of the bridge and apply battery current to it testing both directions in the next couple of days. Visually looks fine except for the varnish I have to remove.