Re: transformer quandary

Tesla List wrote:
> Original Poster: ROBERT CRESSLER <59CREROB-at-menasha-dot-com>
> 2) dual pri. input...... is this actually just a 230 volt feed or
>    two transformers effectively in parallel with the total
>    kva equal to the above?

Probably two separate windings, which you can run in parallel for 115V
line or series for 240V line. An ohmmeter will tell you if the windings
have any internal connection.

> 3) will a voltage amplifier help me out say a doubler or
>    maybe a tripler ---(is unfiltered dc ok for tc use?)
unfiltered DC is ok, remember the bleeders on the caps, though

Also, check the insulation rating on the transformer. Some plate
transformers with a center tapped secondary are really only insulated
assuming that the center tap is grounded. I have a 5800V plate
transformer that is only insulated to 6kVRMS, because they assumed it
would run into a fullwave rectifier, where the max voltage on an output
to ground would only be about 4kV. Hopefully, yours is insulated to 9 or
10 kV, then you can run it with one leg grounded, and then use a "full
wave" doubler (2 diodes, 2 caps) to get 15 kV DC out...

> 4) can I just increase the primary input voltage? or use
>    combo of input tap like from 115/141 as input with
>    current limiting.......? 240 into one leg of the pri?

Probably not, because the volts per turn will be too high and you'll
either saturate the core or breakdown the secondary insulation. They
don't put all that much extra insulation on the winding, certainly not a
factor of 2. And, the core will probably start to saturate at around a
30% overvoltage. You can just measure the noload current as you run the
input voltage up. You'll hit a point where the current will start to
increase much faster.

> 5) will I need to have a PFC cap?  or two?

Depends on your load. Plate transformers don't have inductive current
limiting like a Neon transformer, so they don't inherently need PFC.  If
you build a DC supply with moderate sized filter capacitors (a few uF),
you probably do want some sort of inrush current limiting when you first
turn it on. A 40W light bulb in series works nice.

Jim Lux                               Jet Propulsion Laboratory
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