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Re: [TCML] Mot power supply question

Hi Andrew,
     I can't answer your question but I can provide some experience...  I
use 2 MOTs, because they are extremely hardy in this configuration (they
only fail when I use poor RF grounding).  If you are looking for mini pig
power levels that won't suffice (maybe, see below).  I can say when I used
to try 4 MOT setups they were much more durable when I ran a sync spark
gap, they instantly fried when I ran async.  I can also say they instantly
fried when I ran with no ballast, so maybe your current draw is too high?
 I would suggest backing off to two MOTs and trying to coax more power, use
a much bigger tank cap (ungodly huge) and parallel MOTs to lower input
impedance.  Your tank impedance is what determines current draw, you can
use higher V to overcome R (multiple MOT chains) or you can use a larger C
to give a bigger I.  I don't know if that trick will work up to PIG power
levels, but it is worth looking into.  Another thing that might help is
running MOTs NOT in saturation, for example do a 4 MOT stack with only 60V
per leg, then parallel a second chain, so you have 4 times the steel of a
standard 2 MOT stack, which could handle ungodly current, and ballast
accordingly (your C should limit current so a ballast will likely be
redundant).  For the record, were it me, I would abandon this idea, I've
fried literally dozens of MOTs trying to extend them, oil or
no, floating core or no, it never worked well for me.  Evidence
suggests people do do this, even out to 8 MOTs, but I believe that is in
240V land, maybe their MOTs are better out there?  I have no evidence to
support that, but it is what it is.  With 2 MOTs I get ~60 inch sparks,
maybe that is kid stuff for you, but it works every time I turn it on, and
like I said, virtually bullet proof (unless you forget your RF ground).  I
hope I haven't burst your bubble, and best of luck with your project!

Scott Bogard.

On Thu, May 16, 2013 at 11:37 AM, Andrew Webster <andrew600rr@xxxxxxxxx>wrote:

> Hello List,
> I have a quick question on Mot stacks. I have my coil up and running
> great with my 4 pack, but my goal, at least until I can find a pig, is
> a 6 pack. I started out this way but have had problems burning up my
> mots. Not always the last ones on the legs either. So far I have
> killed 6 of them and have now acquired 2 more and want to give this a
> go again.
> A bit of history here for you.
> All of the mots before were unmodified except for disconnecting the
> core and secondary on the back 4.
> The middle 2 are center grounded.
> Input is 120 at a max of 30 amps ballasted with 2 mots in series and
> the secondary side shorted.
> All mots are under oil.
> Now to further improve things I will be pulling the shunts out and
> removing the filament windings which had not been done before.
> The new stack will not be matching but I have my weakest ones in the
> back (Matched) the middle ones are also matched and the last ones in
> the stack are not matched but are very beefy.
> I do not want to burn any more up and was wondering if there is any
> advise out there in regards to this to make this more successful then
> my last few attempts. I have dug and dug in the list and through
> google but it seems most of the data linked to this is no longer
> there.
> Thanks in advance!
> -Andrew
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