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Re: DC, MOTs & PFCs



Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

You are precisely right.   In fact, the same is true of a non-DC coil,
because the tank/primary cap, to a certain extent, corrects for the
inductance of the transformer.  The load characteristics (in a power factor
sense) of a tesla coil primary circuit (spark gap and all) are not
particularly well characterized (at least, compared to a fairly simple thing
like a lightly loaded induction motor), so your best bet for PFC is to try
various values and see. (or base your compensation on what others with
similar circuits have found).

I note that if you are running a triggered or rotary gap, the phasing of the
breaks (relative to power line phase) will change the power factor.


----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Tuesday, November 27, 2001 8:09 PM
Subject: DC, MOTs & PFCs


> Original poster: "S & J Young by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<youngs-at-konnections-dot-net>
>
> List,
>
> My MOT filtered DC supply with no load benefits from about 135 mFd of PFC
> capacitance to drop the AC line current.  But I was surprised to discover
> that at load, the PFC correction actually increased the current!  Why?
>
> I think the answer is that with no load, the DC supply filter caps are
> essentially disconnected from the secondary, via the diode, almost all of
> the 60 Hz cycle.  But at load, they are effectively in parallel with the
MOT
> secondary for most of the load cycle.  This capacitance (about a
microFarad)
> gets reflected back to the primary as a rather large cap and acts as a PFC
> cap.  So adding more on the primary doesn't help.
>
> Engineers - am I interpreting the situation correctly?
>
> --Steve
>
>
>
>