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Re: Transformer build up
Tesla List wrote:
>
> Original Poster: Mike Nolley <mnolley-at-mail.slc.edu>
>
> MOT's, at least where I live are fairly easy to come by, esp at
microwave
> repair yards and junkyards.
> The transformers are usually the sturdiest components-- hence the broken
> microwaves usually have intact transformers.
> I would think that a MOT power supply for a TC, given proper
ballasting,
> etc. would provide a low-cost (free!) alternative to pole-pigs...
> although the jury is still out on their long-term effectiveness and
> resistance to breakdown. The center tap idea is a provocative one, I'll
> have to pursue that when I get back to Oregon... Thanks!
> _-_-MIke
The real problem with a cascaded MOT scheme is the insulation for the
second transformer in the cascade. (I assume here that you are hooking
the primaries in parallel and the secondaries in series?) The core will
be sitting at several kV, and the insulation from the primary to the
core may not be designed to take that much load. You might check what
the HiPot test voltage on a typical MOT is. It is probably in the few kV
range, if they even HiPot test them (i'll bet they do, to meet UL or
CSA). Then, for short impulses anyway, the insulation will hold up.
I've built a similar contraption using 4 of the 4500V 450mA illumination
transformers with the 600V tertiary winding (avail from H&R and also
C&H). I used the 600V windings back to back to get power to the
transformers which have their core sitting at HV. I also centertap
grounded the output, to reduce the stress. The only problem is that the
magnetic shunts of the low side transformer limit the total current to
the cascade, limiting the output to 8 kVA per side.
That system works great as sort of a "mondo" NST (18 kV+ at 450 mA makes
for a very nice jacob's ladder). It is very heavy though. Each of those
transformers weighs in at 20-30 lbs. I built mine on an aluminum plate
bolted to one of those hand trucks you carry trash cans out on. Wheels,
handles, etc.