Hi all,
There are so many knowledgeable people on this reflector, I'm sure
someone will have the information I need.
I am repairing an old generator (alternator) set. I spliced the broken
wire in one of the field coils, and replaced the diode bridge. I still
need to replace the capacitor used in the DC supply from the diode
bridge to the field coil. I don't know what value of capacitance to use.
It is about an 8 kW 120/240 VAC alternator powered by an 1800 RPM single
cylinder Diesel engine. The field coils (four coils in series) have a
total series DC resistance of about 47 ohms. I was thinking that the RC
time constant of the capacitor and the field coil resistance ought to be
on the order of magnitude of about 1/60 of a second (to keep the field
current flowing between cycles of the alternator output which feeds the
diode bridge). However, if I calculate the capacitance needed to
accomplish that, it comes out to hundreds of microfarads. With a voltage
rating of 200 VDC this would be a sizeable capacitor, even with a modern
capacitor. This is a 60 year old machine. The original old capacitor is
about 1/2 inch diameter and an inch long. So my reasoning is clearly wrong.
Anyone with experience with generator sets that would know an
appropriate capacitance value?
Thanks,
Ken N6KB
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