Re: MOTs in series

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>

At 07:25 PM 1/2/2007, you wrote:
> Hello,
>
> This is probably a stupid question, but I was wondering what exactly 
> the problem with having several MOTs in series is.  The web sites 
> that I have found that discuss this topic all say that the problem 
> is that the insulation on the secondary isn't sufficient to prevent 
> arcing to the core, but what if the core is at high voltage as well?

The voltage rating from core to primary isn't all that wonderful 
(probably something like 2kV for a HiPot test to get UL)


>  Like, if the secondaries were strung together, with the hv output 
> of one secondary attached to the core of the next MOT?

Yes.  On MOTs, the "cold" end of the HV secondary winding is 
connected to the core.  Physically, that's the inner layers, so the 
insulation requirement is reduced.  MOTs are a VERY cost sensitive 
application, so they don't spend a penny more on kraft paper or 
varnish than they absolutely need to.

>   I think that each MOT would not have a potential difference from 
> the secondary to the core of more than the original rating for a 
> single MOT, and since the primaries are electrically isolated from 
> the high voltage across the secondaries, arcing to them shouldn't 
> be a problem, unless maybe something on the secondary was 
> grounded.  Is this correct?

Primaries are electrically isolated, but not with enough breakdown 
strength to run a series string of MOTs.  It "might" work with two in 
series, for a while.

> Also, I was wondering if you could parallel the primaries instead of 
> connecting them in series, so that different MOTs could be connected 
> to different outlets/circuits/breakers (assuming they were all in-phase).

Sure..


> Thanks a lot,
> Chris