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Re: Powerstat Type 10B Repair Help

Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>

Hi,
Variac brushes are "special". You really need just the "right one". There is all kind of "magic" to brushes and how much winding to winding voltage, current, power, etc. they take. Some people have made them from other types of brushes, but I am not sure they run them at the full variac rating and such to really stress them. If they burn, they tend to destroy the windings so it is sort of a risk.
We used some very old variacs (20 years old and we got them used...) that were in constant production use every day. Running at about 75% of their current rating 16 hours a day (high-line, nominal, low-line thing)... We never replaced brushes in them! I am just wondering why some brushes wear out. Maybe there is a rough spot on the surface or something. Ours had there fair share of "events", but maybe the hydraulic breakers tended to prevent damage to them. Perhaps if they are used hard in lighting applications they simply do just wear down more...
If the brush is still operable, I would just leave the old warn one in... Sometimes you can reposition the rotor so the brush holder is closer giving you more wear distance. 

Cheers,

        Terry


At 05:12 PM 4/24/2006, you wrote:

Tesla list wrote:


Original poster: Mark Fergerson <mfergerson1@xxxxxxx>
I recently acquired a type 10B Powerstat for US$1.00 which is a steal, but when I got it home I noticed that the wiper button is missing. Can I just whittle a new one from say a D-cell center carbon, or would that be too resistive? Any better suggestions before I go ahead and burn the house down? 

  TIA


  Mark L. Fergerson
Better to go to a motor shop and find a carbon brush as close as you can to the size you need, then file it down. The "carbon" from a flashlight cell tends to be very contaminated. The brush is intended to have enough resistance so that the power lost do to the current created when it shorts adjacent turns of the variac is acceptably low. 

Ed