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Variac help please!

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John Haine20/11/2018 22:34:37
2454 forum posts
132 photos

I've got an old 100-RM Variac, made by Zenith, rated 8 A at up to 270 V. I inherited it with my father's workshop and it has spent several years neglected under various benches gathering grot and swarf. Needing to run up the supply volts on a VFD that's been in storage for 3 years I thought that I'd better give it a bit of TLC and have spent most of the afternoon on it. I've got to the stage where there is good continuity between wiper and coil for most of the track but there's still a bit that's intermittent.

I have dismantled the brush assembly, cleaned it up and lightly re-oiled it and adjusted the springs, I'm wondering if the brushes are too worn. So...

Does anyone know what length the brushes should project from their little carriers? At the moment there's 2.5 mm, the same on each, is that OK or should I try to find or make some new ones?

Thanks in advance for any help!

Emgee21/11/2018 00:01:46
1085 forum posts
199 photos

Hi John

2.5mm sounds OK to me, about the same as on variacs I have. The intermittent contact point is most likely around the place where the variac has been mostly used. Best wipe the coil track with alcohol to ensure no oil present.


John Haine21/11/2018 13:10:44
2454 forum posts
132 photos

Thanks MG. I've now tested the thing under power rather than just testing continuity and actually it seems to work OK, so I'll see how it goes with the existing brushes. It only gets used once in a blue moon, not worth the price that RS charge for replacements!

Phil Whitley21/11/2018 19:49:52
814 forum posts
105 photos

Check out eastern transformers Ebay shop! He stocks a range of Indian made Variacs which are very well made too! Bought one for a speed control on an old mig welder, to replace the original unit which was also a Zenith. Got a 6amp rated variac with a built in spare brush for £52, as opposed to just under £100 for a lower rated British (?) made one. Works perfectly,and built like ours were in the sixties!! No connection other than a very satisfied customer.


John Haine21/11/2018 21:20:57
2454 forum posts
132 photos

Thanks for the tip Phil. The one I have seems to be working OK now, but if it packs up I'll know where to go.

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