Current Limiting and MOTs

Hi Bart and all,
 Bart wrote:
" MOT's generally have magnetic shunts and are therefore self current

While this is generally true, these magnetic shunts are designed to run a
magnetron and that is the catch. The magnetron does not seem to act as a
complete short.

I have measured various MOTs (hoping to be able to use them). 8 out of 10
different manufacturers I measured, will burn up in a complete short.
Depending on the type, either the primary gets so hot, that it starts to smoke
or the secondary will get very hot in a few seconds (no smoke, tho).

The Gardner variety seems to be massively overbuilt and capable of surviving a
complete short. These MOTS are about twice as big (core size) as a "normal"
Their insulation is also nicely overrated. I was able to connect 4 of them in
series (with no center-tap grounding) and they did not arc over. I added a
fifth MOT and it started to arc from the core to primary. However, the fifth
one was NOT a Gardner. So my idea was using 2 x 4 Gardner MOTS under oil for a
nice compact 13.8kV 700mA PSU. I would have grounded the "center tap" between
MOT#4 and MOT #5, so that the MOTS would have never seen more than 4x their
output voltage (which they survived) Unfortunately (for me) the Gardner
variety is impossible to come by, so I gave up on this idea. 

Another problem with seriesed MOTīs is the fact that EACH MOT MUST have a
seperate safety gap (even the Gardner type) across it (for Tesla usage). A
single safety gap across all MOTs doesnīt seem to work. (Similar to the H&R

For more info on my experiments and comments about MOTs have a look at the

Will Payne has a nice MOT psu supply idea. The only problem with his setup
(was discussed on the List, too) is that you will need 12 MOTS to build it.
Finding 12 MOTS of the exact same type and company (same batch would be best)
is next to impossible. I do NOT recommend mixing MOTS of different types (even
if V & A are the same). Each manufacturer builds his MOTs a little different.

MOTless greets from germany,