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Re: Capacity Value Transformation

Tesla List wrote:
> 
> Original Poster: "J. B. Weazle McCreath" <weazle@hurontel.on.ca>
> 
> Hello Coilers:
> 
> While reading a text on A.C. motors I came across an interesting circuit
> that might have application in Tesla coil power supplies.  The value of
> a capacitor can be increased by the use of a transformer, as in this
> example.  A transformer with a primary/secondary voltage ratio of 1:2
> has a 20 uF. capacitor connected across its secondary.  This causes an
> apparent capacity equal to the ratio squared times the capacitor value,
> in this case 80 uF., to be across the primary.
> 
> I'm wondering if by using a relatively low KVA rated 1:2 ratio transformer
> one could achieve power factor correction with relatively small values of
> PFC capacitors.  This would be particularly useful for larger coils that
> require capacitors in the hundreds of micro-farads for PFC.  The primary
> of the "capacitor transformer" would simply be paralleled with the MOT or
> pole pig primary.  One cap of 40 uF., a readily obtainable value in oil
> filled motor run caps, would yield an apparent capacity of 160 uF. in the
> power transformer primary circuit.
> 
> At present I do not have the facilities to check this idea out in actual
> practice, so I'd be interested in hearing from anyone who does try it.
> Thoughts, criticism, and other comments are of course welcome.
> 
> 73, Weazle, VE3EAR/VE3WZL
> 
> Listening: 147.030+ and 442.075+
> E-mail:    weazle@hurontel.on.ca
>            or ve3ear@rac.ca
> Web site:  www.hurontel.on.ca/~weazle

Weazle,

This technique should work exactly as you suggest! In fact, this
approach is used inside high power factor NST's and ferro-resonant
constant voltage transformers. In a high power factor NST, a third (or
tertiary) winding is combined with a smaller value capacitor so that it
"appears" to be a much larger valued capacitor connected across the
mains input to provide power factor correction. It should work in
conjunction with an external transformer as well.. - got for it!

-- Bert --
-- 
Bert Hickman
Stoneridge Engineering
http://www.teslamania.com