MOT experiences

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Peter Lawrence by way of Terry Fritz <twftesla-at-uswest-dot-net>" <Peter.Lawrence-at-Eng.Sun-dot-com>


First some good news. A Microwave Oven with a rotating plate has a great 
little motor for making a rotissary for coating a secondary coil with resin.
6-rpm is perrrrrfect!

The very small ovens I got use small (6-lb) MOTs with 1900vac rated caps.

I put two of these MOTs in series, and after tuning my TC (small, 3.5"x12")
with an NST, switched over to the MOTs.

Evidently MOTs put out hellish current. My static gap put out more noise
that my my TC output. The output spark was semi-continuous (the high current
of the MOTs let the tank charge up 1000s of times per second) and extremely
bright, even with the lights on. The pointed breakout wire above my torriod 
started glowing orange hot at the tip.

The MOTs burned out my Tungsten-Carbide spark gap like NSTs burn out brass,
previously using NSTs my T-C spark gap never needed cleaning.



Next, having read that a voltage doubler also acts as a current limiter, I
tried putting the original MO caps and diodes (carefully swapping the
orientation of one of the diodes) back into the circuit.

I was worried, so I put Terry Fritz's NST-Filter circuit in also.

I fired it up and,...  nothing.

Turns out that the 3-K-Ohm filter resistors I got at a local parts recycler 
were actually mis-placed 3-Ohm resistors, so much for filtering...

The diodes are fried.  So now the question is (after getting the right
resistors for the filter) where to get HV diodes, and just how HV do they
need to be...


I am also wondering how to calulate the LTR Tank Cap value for a MOT, I'm
not sure Terry's method of putting a 1K resistor across it and measuring
voltage will apply, as these will probably cook the resistor, and maybe
the MOT too. Probably the whole Res/LTR concept is a moot point for a MOT,
does anyone want to comment on that?


For large TCs with SRSGs MOTs must be great, for my "small" TCs with static
gaps there are some bugs to work out. I'm not giving up on MOTs since they
are so easy to get and (nearly) impossible to destroy.

-Pete Lawrence.