Re: C/W Multiplier PSU - Reasons Why Not

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

Welll... A CW multiplier works just fine if the filter capacitors in the
multiplier are MUCH bigger than the load capacitance, otherwise, you tend to
discharge the whole stack.  Also the more stages, the longer it takes for
the stack to come to equilibrium, because the charge has to work its way up
the ladder, a little bit at a time, and you get caught in a situation where
the charge moving around goes as  1/n on each step with n always getting
bigger.. Works great at 1 step (1/1), not so hot at 3 steps (1/3), really
poor at 20 steps (1/20).  If the load current is small, then the discharge
current (which discharges all caps simultaneously, to the same degree) isn't
as big a deal.

However, if you have a supply for lots of caps cheap, and the mass tolerance
(it will be heavy), then a CW multiplier is one way to do it.  Practically
speaking, by the way, you're better off using a higher voltage transformer
and fewer stages than a low voltage transformer and lots of stages.  I went
through this a number of times, trying to get ever higher voltages, but
constrained to MOTs, NSTs, and the like (because 50 kV transformers just
aren't that common...while the others are available easily).  As long as
parts are free, it's great, but as soon as you start paying for diodes and
capacitors and the structure to hold them, the money is better invested in a
higher voltage transformer.  There is also the not inconsiderable amount of
time required to assemble a complex structure like this (ask anyone who has
soldered an MMC how long it takes, just in "touch labor" to gather the
parts, drill the holes, trim the leads, twist wires, do the solder joints,
etc.  It always seems to take much longer than you expect...




----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Saturday, March 09, 2002 10:07 AM
Subject: C/W Multiplier PSU - Reasons Why Not


> Original poster: "Matthew Smith by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <matt-at-kbc-dot-net.au>
>
> Hi All
>
> A question has started bugging me to the point of getting me out of bed
> in the middle of the night to ask it of you...
>
> Various power supplies using multiple MOTs (microwave oven transformers)
> have been mooted, some with straight forward rectification, some with
> voltage doublers.
>
> I know that if it were feasible, we'd be doing it but could someone give
> me a technical explanation as to why we don't just use a single MOT and
> a Cockroft-Walton multiplier made from a collection of MOT diodes and
> MOT caps?  Are the capacitors too high in value or the diodes too low in
> current rating, not enough "juice" to charge the tank cap or...  No,
> I'll stop guessing and await an informed answer.
>
> TIA
>
> Cheers
>
> Matthew Smith
>
> Insomniac,
> South Australia
>
>
>