Re: PFC on MOT Pair

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

Original poster: "S & J Young by way of Terry Fritz <twftesla-at-qwest-dot-net>" <youngs-at-konnections-dot-net>

Matthew,

Since your MOTs will reflect the reactance of the load they are supplying,
we can't answer your query without knowing the nature of your load.  For
example, if the MOTs will be used in a filtered DC supply, the filter caps
may very well provide all the PFC you need.

Best to get a bunch of motor run caps and just start paralleling them across
your primary windings and monitor current.  When you get the minimum
current, with the MOTs supplying the intended load, you will have the right
amount of PFC capacitance.
--Steve
----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Saturday, February 02, 2002 7:55 PM
Subject: PFC on MOT Pair


> Original poster: "Matthew Smith by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <matt-at-kbc-dot-net.au>
>
> Hi All
>
> College was a long time ago and I can't remember how to work this out -
> anyone help?
>
> Two MOTs - primaries in parallel, secondaries in series; they are rated
> for 240V input and both have approximate turns ratio of 1:7.95, each
> giving approximately 1.9kV.
>
> Mains frequency is 50Hz.
>
> I have determined the primary restistances to be 2.7 and 3.0 Ohms and
> the secondary resistances 85 and 109 Ohms respectively.  These figures
> were measured using a Wavetek 27XT and confirmed using decade resistance
> + Wheatstone Bridge of a "traditional" Megger tester.  (The inductance
> didn't half make the needle vibrate at low cranking speeds - like trying
> to measure AC with a DC voltmeter.)  I attempted to measure inductance
> using the Wavetek, but it was either two low or too high to register.  I
> have yet to check primary current since I currently lack a CT and don't
> like using DMMs directly for current measurement! (I've had one fry
before.)
>
> I guess that is not enough data to calculate the value of a PFC
> capacitor but I would like to know
>
> a) is there a rule of thumb value for capacitor sizes for an array like
> this?
> b) what is the actual formula that I should be using, if I had the
> inductance figures (which is what I guess that I'm missing)?
>
> Cheers
>
> Matthew Smith
>
>
>