Re: Ammeter readings with MOT power supply

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Justin <rocketfuel@xxxxxxxxxxxxx>

Hi Chris,

I believe you're on the right track about the power factor.

I'm in a similar position of just getting started with using MOTs as
current limiters and I found this site to be very helpful:

http://www.vias.org/feee/acpower_04.html

Also I found this company in the archives as a good supplier of PFC
caps:

http://www.usamfg.net/files/MARCH21-25.pdf 



I'd be happy to compare notes off-list if you are amenable!

Cheers,

Justin






On Tue, Mar 27, 2007 at 06:40:57PM -0600, Tesla list wrote:
> Original poster: "Breneman, Chris" <brenemanc@xxxxxxxxxxxxxx>
>
> Hello,
>
> I've almost finished the MOT power supply for my first Tesla coil,
> but have a few questions about its operation.  The supply consists of
> two MOTs with the primaries in parallel and secondaries in series and
> a third MOT in series with the parallel arrangement of the first two
> acting as a ballast.  The ballast has its high voltage winding
> shorted.  All of them run on 120V.  In addition to the transformers,
> I also have a 15A circuit breaker in series with the circuit, and the
> house has its own 15A breaker on this circuit.
> I recently received a 15A analog panel ammeter which I wanted to use
> in the circuit to monitor current drawn.  It is placed in series
> between the breaker and the ballast.  When I run the power supply
> with the hv end shorted, no breakers trip, but the ammeter reads off
> the scale.  When I replaced the analog meter with a digital
> multimeter capable of reading up to 20A, it read "Overload".  What I
> don't know if if more than 15A is really flowing, and if it is, why
> it isn't tripping the breakers, and if it isn't, why do the meters
> show that it is?
> The only possible cause I can think of for this discrepancy is that
> the power factor is probably greatly offset by the highly inductive
> load, but why wouldn't the breakers trip in this case?  I also tried
> the circuit with a 10uF PFC capacitor, and saw no difference in
> behavior.  If the problem is the power factor, do you think a 180uF
> PFC capacitor would be reasonable for such a supply?  The open
> circuit voltage is slightly over 5kV and the short circuit current is
> slightly over 500mA (that is, assuming these readings from the
> digital multimeter are correct; I determined these values indirectly
> by measuring current through different resistances on the hv side).
>
> Thanks a lot,
> Chris
>
>