Brushless Exciter Diode

[bill1055]

We have a 100 KVA three phase brushless alternator in our shop for repair. One of the diodes on the rotating ring needs to be replaced. The diodes have no identification markings on them-either worn off or never existed. The excitation voltage is 46 volts, and 2 amps current. Would a 50 volt, 15 amp diode be a suitable replacement, or do I need to upsize? The diode is stud mounted to the heatsink with a M6 thread.

 

[itsmoked]

Probably. Not as much voltage head-room as I'd like to see. I'd go for more than twice the expected voltage in this kind of application with inductances involved.

I'd use this one instead:
VS-70HF120M

Not because you need 1200V ability but because it's the only one Digikey carries with M6 threads included.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[LionelHutz]

Generally speaking, you can usually get the same case size and current rated device in various voltages up to 1200V or 1600V, so it makes no sense to use a lower voltage rated device than that level. So, the 15A rating should be fine but there is no reason not to go way higher in voltage.

 

[waross]

At 240 Volts that set will put out about 240 Amps.
That is controlled by the AVR output of 2 Amps.
The rotating diodes will see more than 2 Amps but less than 240 Amps.
15 Amps may be a little light.
However the part recommended by Itsmoked is rated at 70 amps.
70 Amps is probably enough.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[bill1055]

Thank you all for your assistance, I will go with the recommended device. Thank you Bill for an explanation on sizing rationale.
Bill