I'm putting a 3 phase generator to work for the workshop. It's 13.5KVA so not too big. It's from the 1960's but looks in good condition. The previous user says it worked his shop machines. I know him and accept that. Well I ran it on load here today for the first time. A simple 4 core cable feeding 3, 2KW heaters, one on each phase to neutral. (I know they weren=92t earthed). At first it all worked beautifully. The 3 ammeters and voltmeter all read just what I wanted. I increased one heater to 3kW which is the max I could achieve. I know it=92s an unbalanced load but it should have been OK. I left it running for about 20 mins to warm her up and blow a few cobwebs away. When I checked again, both volts and amps had dropped by about 50%. I turned all the elecs off and checked for hot joints etc but everything seemed OK. There=92s now no output voltage, even with the load disconnected.
By now it was dark so I gave up. Tomorrow I shall have another look. The alternator has 3 wires out, one for each phase. I assume the other is a neutral and have earthed it to a ground spike. As the output fell slowly and equally over all 3 phases, I don=92t think it=92s a winding problem.
Anyone any idea where I should start? Can alternators lose their excitation?
John