Re: [TCML] MOV destruction

[sparktron01@xxxxxxxxxxx]

Dennis

Another possibility...

How did you wire the MOV's into the circuit?  If you soldered them into
a perfboard, did you HEATSINK them while soldering them?

If the MOV's are overheated during the soldering process while
assembling your Terry Filter, the MOV's operating voltage will be
degraded (read... REDUCED) to point a catastrophic failure can
happen at nominal applied voltages.  I have seen this failure
phenomena in industrial equipment; so be sure to heatsink
your MOV's if soldering onto PCB's; or better yet, use mechanical
lugs for wiring these components into a power circuit.

Regards
Dave Sharpe, TCBOR/HEAS
Chesterfield, VA. USA

 -------------- Original message ----------------------
From: otmaskin5@xxxxxxx
> Hi, I'm trying to figure out what happened in my most recent coil melt down and 
> was hoping someone out there could help me out.? I had just replaced my old 
> capacitor bank with a 0.02uF MMC on my 15/60 coil.? I thought I had the coil 
> reasonably well tuned & was running it for about 3 or so minutes.? The coil & it 
> seemed to be behaving fairly well, producing strikes that somethime reached over 
> 50 inches...when it just stopped running.? I detected an oil type odor & first 
> thought I had blown a cap somewhere.? Eventually I found the MOVs on my Terry 
> filter were destroyed.? There was remnants of molten metal on and around the 
> MOVs, several of them had cracks or splits in them & an oily substance had been 
> ejected from the MOVs.? 
> 
> I tested the NST & both legs seem to be healthy, so the MOVs apparently died in 
> the line of duty protecting the NST (thankfully).
> 
> I have not heard of MOVs coming apart in this manner.? From everything I've 
> heard, they just quietly do their job when there is a voltage surge.? Before I 
> replace the MOVs and start running the coil again, I'm trying to get an idea of 
> what caused this to happen & what I need to correct in the system going 
> forward.? 
> 
> I had 8 MOVs?(1800V ZNR) in series to ground on each leg of the transformer.? 
> This essentially duplicated MOV arrays?that I have seen?others' using on their 
> 15/60 coils.? My variac maxes out at 130v - also,?I didn't see any strikes to 
> the primary or lower deck?at the time this occured.
> 
> I am wondering whether I should have had more MOVs in series to handle greater 
> voltage.? If so, what is the right number? 
> 
> Or were the MOVs adequate, but was there some other problem that caused this 
> which I need to correct?
> 
> I would appreciate any ideas.? Thanks, Dennis Hopkinton MA???
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