[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

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