[TCML] Re: MOT Shunts

[John Smith <zzerotime@xxxxxxxxx>]

In response to Jon who asked:

What voltage were you running your MOTs at initially, when they were
>> burning out? Do you think that perhaps running them with an external
>> ballast had more of an effect than removing the shunts (ie, what was the
>> voltage/current at each MOT before and after ballasting)?
>>
>> It would be nice to nail down the issue of MOT shunts once and for all
>> and determine the best choice when using them in a TC supply. I've got a
>> MOT I'll run some experiments with and publish the data when I am done.

I started experimenting with MOTs in a 4 MOT stack on a 6 inch coil last
year.  In my setup I wasn't powering them through a variac, just straight 
mains voltage (right at 120v according to my meter).  All MOTs had shunts
and I used a choke type ballast. The MOTs were placed in a plastic toolbox
and submerged in mineral oil. The first pair was center grounded.  
The coil ran well except the oil would get very hot, so hot that if it were
a little cool outside, steam would pour out.  It smelled like burning
plastic and I could see black particles in the oil which came from the 
secondary windings on some of the MOTs.
  So I did some research (probably here on the list archives) and found
that I could reduce the heat by taking the shunts out.
  I purchased some more MOTs (all the same brand and model as before) and
built a 6 MOT stack, this time removing the shunts.  I placed them in a
larger plastic toolbox and submerged them with oil.  The first pair is 
center tap grounded and I made a safety gap on the HV terminals of the 
toolbox.  No filters and no vacuum to the box.  On the 6 inch coil, It 
would just eat up my strike ring (which is boring) so I removed it.  I 
had repeated strikes to the primary and it still worked fine.  Last run
on the 6 inch coil was July 4th of last year.  
  I was a little concerned about the primary strikes so I did what anyone
on the list would do....I built a 12 inch coil.  I figured a bigger and 
taller coil would make primary strikes less likely.  I'm Still using the 
same 6 MOTs and I am very happy.  I'm getting 6-8ft sparks with the occasional primary strike. It seems bulletproof compared to any NST setup.  Ive fried a few of those and that was enough.  NSTs are expensive! I bought all of my MOTs for 8 bucks each plus shipping. (shipping was more expensive!)

I don't claim to know any better than anyone here, in fact I know I don't.
I can just tell you what my experience is.  In my opinion, I wouldn't build
another MOT coil without removing the shunts. 

This link is to my coil running with its old toroid (8x33).  Notice the 
primary strikes and my safety gap firing in the background

http://www.youtube.com/watch?v=M9p4h1Md8kc


John S.
Griffith, In


      
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