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Re: DC Supply
Tesla List wrote:
>
> Original Poster: Mark Finnis <mefinnis-at-medicine.adelaide.edu.au>
>
> At 06:29 21/09/98 -0600, Greg Leyh wrote:
>
>
> Anyone got a round dozen HT rectifiers lying around ??
> (I am assuming I will need one bridge per phase)
In a classic three phase full wave bridge, you only need 6 diodes
because the transformers would be connected in delta. I'd have to think
about the implications of the grounded secondary centertap on this,
since it sort of makes your system connected in Wye.
As for type of rectifiers: Tubes are nice because they are really tough.
If you can find surplus tubes, they aren't very expensive (Say $5-10
each). The problem will be the flock of filament transformers you will
need.
Therefore, I'd go with the semiconductor rectifiers. Your NST's are
probably a nominal voltage of something like 15 kV (peak voltage of 1.4
times that (21 kV), however, because of the grounded centertap, you
really are going only need half that. You can get replacement microwave
oven rectifiers are around 14 PIV at 200 mA, but they are a bit pricey
($14 each).
You should also talk to K2AW's Silicon Alley (Westbury NY), who sells HV
semiconductor rectifiers fairly inexpensively. I got some 14 kV, 1Amp
units from him that have been quite tough.
You can also string a bunch of the 6kV HV diodes available from a number
of mail order sources (like All-Electronics (www.allcorp-dot-com)), but
you'll need to pot it in silicone or oil. I wouldn't bother with the
parallel resistors and capacitors commonly seen in a string of these.
Just put enough diodes to get double the voltage you want. If the
diodes all come from the same manufacturing lot, their switching
characteristics will be well matched enough to avoid problems.
> The other question not answered thus far was would the rectifiers help
> protect NSTs from return spikes ?
Nope... In fact, the rectifiers will likely protect the NST by blowing
first.