Re: C/W Multiplier PSU - Reasons Why Not

["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,

Sorry you are losing sleep over your question!  Yes, one could do as you
say, and it would work fine for low power (less than one KVA).  Most people
use more than one MOT because they want more power.  2 MOTs is good for 2
KVA, and 4 in series is starting to have the power of a small distribution
transformer (4-5 KVA).  Others use more than one MOT because they want to
stay with AC or level shifted AC, whereas your C-W multiplier will be DC.

In a C-W multiplier, the current halves each time you double the voltage.
To accomodate differing currents in the stages, a properly designed C-W
quadrupuler  would have 4C in the 1st stage, Then 3C, 2C and C in the last
stage.  All but the 1st stage require caps with twice the MO cap voltage,
meaning you need to use groups of caps in series.  You end up needing a lot
of MO caps, many in series-parallel, to get the job done, and they will take
up more space than using a second MOT.  And the MO diodes in the first stage
or two may not handle the current (may exceed the 350 ma they are rated
for.)  An advantage of the C-W multiplier or any filtered DC supply is that
the filter caps act like PFC caps and you typically will not need to do
further power factor correction to keep primary current minimized.

--Steve


----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Saturday, March 09, 2002 11:07 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
>
>
>