Re: DC, MOTs & PFCs

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

Original poster: "Rick Williams by way of Terry Fritz <twftesla-at-qwest-dot-net>" <richardwwilliams-at-earthlink-dot-net>

Steve,

I'm no engineer but without load you're closer to resonance than with a load
which raises inductive reactance. Under load, in your case,  there may not
be enough PFC capacitance.

I've noticed the same thing while determing PFC simply by trial and error,
adding/removing caps.
One Franceformer NST, 15/30, pulls 700 ma with a load and 100uF PFC. Without
a load current goes up to 2 amps due to more capacitive reactance. However,
without PFC current under load is 4.25 amps.

With say 50uF the no load current would be less than with a load.

Rick W.
SLC






----- Original Message -----
From: Tesla list <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Tuesday, November 27, 2001 9:09 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
>
>
>
>