Film-Tech Forum ARCHIVE: Recommendations for carbon arc rectifier repair

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Posted by David Buckley (Member # 2600) on 01-02-2007, 06:04 AM:

Our carbon arc rectifier has developed a fault, which I believe (as in I hope it is, but haven't actually got the test prods out yet) will be a couple of popped diodes, pictures:

The carbons run at around 60A, does anyone still repair these things and have suggestions of appropriate diodes? Does anyone recognize this rectifier? It was locally made in NZ under licence from Westinghouse. heres the makers nameplate, the manufacturer no loger exists as a company.

If theres no knowledge of this old beast, then perhaps some general advice? Should I build a like for like with half a dozen diodes, or use a three phase module? How much do I need to over-rate the diodes for, current wise?

Posted by Monte L Fullmer (Member # 2797) on 01-04-2007, 03:42 AM:

course, you know that you'll have to take out all of the diodes to test - get them isolated from the circuit.

Then, make sure that you don't cross negative and positive diodes around when putting them back in...

Posted by Kenneth Wuepper (Member # 1174) on 01-04-2007, 07:36 AM:

David,

I assume that your problem is the supply protection operates and blows a fuse or trips a circuit breaker. If this is true, you might try this method of locating the problem:

Eliminate the components in the circuit one at a time. First loosen the clamps to the diode pins that are seen in your second photo. Wrap a paper (copier type is ok) between the post and the clamp of all diodes. This will isolate the diodes from the transformer and other components. If the protection still operates, there is a problem in the power wiring or the transformer.

Since the diodes are now electrically isolated (and still on their heat sinks) you can test them with a meter to determine shorted or open diodes.

Be sure to clean all of the connections with fine abrasive cloth before reassembling the unit. (Crocus Cloth)

Hope this was a help.

KEN