MOT Power Supply

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

Original poster: "Christoph Bohr by way of Terry Fritz <teslalist-at-qwest-dot-net>" <cb-at-luebke-lands.de>

Hello everybody!

Two weeks ago I came up with some questions concerning MOT Power-supplys.
I finaly got a 4-pack of Mots running under transfomer grade mineral oil 
and just wanted to share my experiences as MOTs seem to become quite 
popular over the last months.
The whole pack is stored in a plastic container that contains the oil and 
it works without any arcing or corona and stays very cool even after quite 
long runs on a jacobs ladder. The duty-cycle by now is limited by the 
shorted MOT I use as ballast to limit the pirmary current, after some 
minutes it got so hot, smoke started coming from the primary winding so I 
will have to put this one unter oil, too.
During my tests with the jacobs-ladder I took some measurements that were a 
little confusing to me ( correct wiring is assured by low voltage 
mesurements I took ):

 > even without secondary load, I can't connect the suppy without ballast 
to a 230V / 16 amps wall socket because the breaker trips instantly, should 
the current really be that high at this point? will I have to install 
myself a 30amp service?

 > With the ballasting MOT it draws around 3,5 amps without load and around 
20 Amps when an ark is forming on a connected jacobs ladder, but though the 
breaker is only rated at 16amps it wont trip, even after long runs. ( btw: 
I'm bothering this breaker since I was five or six, as this is at my 
parents garage where I do must of my experimenting. so it might be a little 
worn, though I don't know if this can be a cause - sorry in advance, but 
those were the "wild years" of experimenting :-)

 > the measured voltage across the input is around 140 Volts ( 230V line 
voltage at the input of the whole thing ). On the archives I read that 
inductive ballasts would drop the current but wouldn't affect the voltage 
that much so the 140V seem quite low to me?!

 > if my conclusions about the voltage are right I can only have about 
4800V, pretty low for a spark-gap TC, but it runs anyway.

As sayd, I allready tried this supply today in TC-use. I had to short 1 gap 
of my 7-segment static gap. The arcs were quite the same lenght ( no 
meausrements taken jet )
as with my 6-OBIT supply I used until it broke some weeks ago. But the 
sound is not like that "resonant carging" sound but very noisy an 
high-frequent. To me it seems that the supply must deliver a lot more 
current, just as desired, but the performance of the coil is pretty much 
the same. I wonder if this might be because of the low output-coltage...

I saw some people using secondary ballasting with the caps that come from 
the microwave ovens. I have these too, but I haven't tried this jet, as my 
supply trips the braker even without load anyway. Im not that convinced 
that the caps will stand the high stresses they would be exposed to, too.
I have 4 caps, all rated 0.9µF 2100V~ / 1800V=, can I use these caps 
riskless or do I need anything else?
Maybe some of you who have made experience with this kind of supply ran 
across the same problems, so how did you solve them.
After all, I think MOTs are a great way to go, especially in Germany where 
Pole-Pigs are not common and thatfor almost unavailable.

So everybody get yourself a MOT-supply ;-) ...no just joking, but any 
suggestions are welcome.

Best wishes and happy coiling!

Christop Bohr