RE: More MOT supply questions

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

Original poster: "Dave Hartwick by way of Terry Fritz <twftesla-at-qwest-dot-net>" <ddhartwick-at-earthlink-dot-net>

Mike,
Based on empirical observations of MOT supply behavior and MOT insulation
issues in general, I would clearly opt for maximum winding core clearance
over any inductance mismatch issues, especially for the outer MOTs carrying
the most voltage, even on a 4 pack in oil. If your MOT primaries are
connected properly, individual MOT inductance characteristics should not an
issue.
Clean your MOTs thoroughly as per Ted L's recommendation. I use a modified
version of Tim J's circuits. http://users.rcn-dot-com/tcobaugh/motpsu.htm

I'm open to correction on this one and I clearly yield to Tim J, Greg
Hunter, and Ted L from NZ and others on these questions, for they have more
actual experience with MOT supply driven coil operation than I do. Let me
say, however, that I have safety gaps on each MOT in my 6 pack and I've not
regretted that inclusion. Set at about 3/8-1/2", I've seen them fire when
operating at what might be considered running at the ragged edge--meaning,
large main gap distance settings, and >5 kVA power levels.


You will be quite amazed at the power levels available from an MOT supply,
especially if you remove the shunts. Shunt removal does require external
ballast. My shunts are not removed and ballasting has not been
necessary--overall behavior in this config has been quite manageable. Also,
I'm only currently using 25 nf tank C which by most accounts, is way to
small for max MOT power extraction.

My thinking at this point is that a straight 6 pack--no voltage doubling or
tripling--is the sweet spot. A 4 pack offers <10 kV, and an 8 pack produces
nearly 20 kV. Assuming you can make an 8 pack work--Tim J has MOTs with
unusually large winding/core spacing--Tank C and insulating issues become
more difficult at those higher voltages. Greg had some trouble with silicon
inclusion in his fine voltage doubled supplies, but may have recently solved
this problem.
http://hot-streamer-dot-com/greg/main.htm

I truly think that MOT supplies are a major coiling development, on par with
MMC caps. I'm not sure a Pole transformer is necessary now if you've
constructed a good MOT supply, though I'll still probably procure another
PDT from Dr. Resonance to replace the one I killed. (A PDT is necessary for
every coilers lab if for no other reason than to caress it.) I'm thinking
that a 6 pack made with 12 MOTs would be killer:  6 units of 2 paralleled
MOTs connected in series for even MORE current capability.

Dave H



Original poster: "Michael Strube by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<mjstrube-at-earthlink-dot-net>

Thanks to all who weighed in on the crimp-solder-quick connect issue.
Very helpful advice--amazing how such a seemingly simple question can
have so many facets to it.

I have another question. I am now selecting the MOTs that will be part
of the 4-pack that I am building. I have 30 or so MOTs around my shop to
choose from and not a pair that are duplicates (not a rare situation I
understand). All are of the 2200 volt variety. I know that the outer
MOTs will need to hold off the higher-than-usual voltage and I've seen
the recommendation to choose MOTs (usually older ones) that have the
greatest winding-to-core spacing. I have a small number that would fit
that bill just fine. But, they have different primary and secondary
inductances. For example, one has a primary inductance of 46mH and a
secondary inductance of 13H. Another has a primary inductance of 24mH
and a secondary inductance of 7H. On the other hand, among the numerous
small-spacing MOTs that I have, I can match up several pairs so that
they have very similar inductances.

So, the question: Is it better to have the outer MOT pair matched on
inductances and not worry about the winding-to-core spacing, or, to make
sure the winding-to-core spacing is large but the inductances
mismatched? Can't have both at the moment and given the number of MOTs I
have now and their wide variation, I'm not hopeful that further
scrounging would allow matching inductances AND having large spacing.
Let me add that the MOTs will be under oil (I'll occasionally use a
level shifter design for this supply), so perhaps the spacing is less of
an issue in my case.

Thanks in advance for any help.

Mike