Generator Problem

[sailorphil9]

Hi



I'm looking for some advice on a generator problem.



Generator: 120/240 V 8KW single phase, brushless alternator type (ref Nigel Calder). It is a marinised trailer generator, originally Italian ‘Genset’ brand, now part of Mase. No documentation available from Mase. Engine (Kubota) good, back end failed due to salt water cooling leak after 17 years use.


I had the back end re-wound, new diodes on the rotor. New 500 V capacitor on excitation windings. Refitted.
The connections are:
2 wires exciter circuit to capacitor
2 coil outputs + 1 N wire (rewind engineer said didn’t know what this neutral was for, but there was a connection point on the control panel terminal block for it when I dissembled the unit).


Before connecting to the control panel I carefully ran the unit to check the outputs. All outputs isolated, open circuit. ‘N’ wire isolated.
Exciter output 369 V. OK I was told.
Windings 1: about 110V
Windings 2: about 120v
Pretty much what I expected, as I hadn’t tuned the engine to precisely 3,000 rpm.
After about 10 mins running the stator got warm and the outputs fell to zero.
I assume that the coils have burned out.
I can see no evidence of an energy dump in the control panel (wiring loom too complex for me to trace), no heat sinks or resistors. The terminal block on the control panel has some cooling fins. The outputs were not connected to the terminal block when I tested them.
So, my questions are:
Did the coils burn out because they were in open circuit when I tested them?
Are the coils normally shorted in the 240/0/120 switch unit for no-load running?
I’m now wondering whether the terminal block has some hidden tech.
All opinions welcome.
Thanks
Phil

[RaymondR]

Introduce a nostril to close proximity to the alternator, sniff vigorously and see if said nostril detects a burnt insulation smell. Lack thereof may indicate no burnt out wiring and the problem elsewhere.

My AC theory is minimal but that excitation voltage appears a little high. My hazy recollection of the specs on the last one I replaced on my 240V AC genset was 24uf 400V but I could be mistaken (they blow up if you use your genset and an inverter welder to crank a 50hp Kubuto)

[smac999]

gens run open circuit when not transferred on ac switch. should be able to run open circuit for ever. not the cause

[RaymondR]

Are you sure that the field and excitation coils are not swapped in the wiring?

[sailorphil9]

@RaymondR Thx. Good question. There was no smell.


The capacitor was a direct replacement.

[sailorphil9]

Originally Posted by smac999

gens run open circuit when not transferred on ac switch. should be able to run open circuit for ever. not the cause

That seemed obvious to me, until someone asked me what happens to all the energy in the coils (not sure if there is any). Hence my question.

[sailorphil9]

Originally Posted by RaymondR

Are you sure that the field and excitation coils are not swapped in the wiring?

The voltages seem ok 110+120=230 when the outputs are connected. The man who did the rewind copied what was there. 369 V would be too high for the output I think.