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Re: UK Neon Sign Transformers



Original Poster: "Steve Young" <youngs-at-konnections-dot-com> 

Hi Steve, All

My comments about MOTs are based on extensive testing. I thought 6 of these in
series would make a nice pig substitute (13.8kV-at-700mA) as I canīt get a
decient size pig in germany. 

However, my tests have shown you canīt series more than 2 or 3. Otherwise you
will get lots of problems with arcovers, etc. To protect multiple MOTS (in
series) you also need to connect a safety gap across each MOT. This means if
you run them under oil (you have to) you would need two feed thrus for each
MOT, making your xformer box look like it has mumps or something (read:
unpracticle). Using 2 and running a DC coil (or a toob TC) would of course
work, but I like "real" (AC) TCīs more.

A two MOT setup can be wired, so that no MOT sees "overvoltage". All you have
to do is connent the wire between MOT #1 and MOT #2 to ground. This way each
MOT insulation only sees its own voltage with respect to ground. However, if
you start connecting more (pairs) the only way to do this (to keep from
overstressing the MOT insulation) is to use isolation transformers. This makes
the whole setup more complicated and lots more expensive. (You need a 3.2kVA
isolation xformer for each pair of 1.6kVA MOTs unless you run the primaries in
series (240v), too, but then you would need a 1.6kVA 240V isolation
xformer.....)

Also donīt forget a voltage doubler only doubles the voltage to a certain
loading. This depends on the caps used. A smaller cap will drop your voltage
more than a doubler setup using big caps (giving equal loads).

So my comment that MOTS arenīt  worth a darn for our AC coils still holds
true.
 
Coiler greets from germany,
Reinhard

 Reinhard and all,
 
 Don't give up on MOTs!
   
 <SNIP> 
 > 
 > My testing has also shown me that MOTīs are not suitable for TC work. In
 order
 > to protect seriesīd MOTs (if you can find ones that will stand up to
 > seriesing) you need a safety gap across EACH MOT and run them under oil.
 A
 > single safety gap across all MOTs will NOT (NO!) protect them. I speak
 from
 > experince. A MOT (or two) would be intersting for a toob TC,tho. But for
 our
 > DWC coils they arenīt worth a darn.
 > 
 > Coiler greets from germany,
 > Reinhard
 > 
  I agree MOTs in series are asking for trouble due to voltage stresses. 
 However, MOTs can still be a good power source for TCs IF you use DC. 
 Consider two MOTs with their grounded cores tied together.  Each MOT drives
 a half wave voltage doubler of opposite polarity.  You end up with 9 to 11
 KV DC at a couple KW between the outputs of the two doublers.  You have to
 use care with the rest of the primary circuit as both outputs are plus and
 minus about 5 KV with respect to ground.  Doublers can be microwave oven
 diodes and caps--you will need to dismantle a bunch of salvaged ovens to
 get enough parts.  (Talk to a thrift store about getting bad ovens--usually
 the HV parts are still OK.)  The composite output caps will have to be 4 in
 series/parallel to withstand the about 5 kv across them.  My supply uses 4
 diodes and 10 caps total.
 
 Convert to D. C.,
 
 Steve Young