Re: rectifier stack experts?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Crow Leader by way of Terry Fritz <twftesla-at-qwest-dot-net>" <tesla-at-lists.symmetric-dot-net>

> Original poster: "BunnyKiller by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<bigfoo39-at-telocity-dot-com>

[cut]

> rectifying  15KV is easy in the low amp rating  ( < 1A)  but handling
> several amps at 15KV is a whole new story ( 105KVA ...  wish I had that
> much power to the shop)
>
> you will need 100 diodes (1000V 1A )...   25 per side ( 4 sides) for
> full wave...  this is how they rectify some X-Ray machines...

Unfortunately this does not work as nicely as it sounds. Xray machines use
matched diodes, not imported trash lowest cost/quality 1N4007s. You are
limited to less than 1 amp even with a small string of 1N400x diodes. You
don't run them at maximum rated current, and capacitors don't draw even
current when powered a rectifier. My 1990's General Instrument rectifier
book suggest derating current 20% for capacitive loads. We're at 800mA max
so far for a simple power supply, and that's testing the limits there
without special cooling.

> series 25 per side and configure as a full wave ...     this will handle
> the load and voltage up to .95 A -at- 15KV...  but hey   thats still 14KVA

Not quite, or so I'm told. I was told by a few folks you want a 100% safety
factor at such voltages. Assuming 15kV input with +10% line variation you
can get upto 23.1kV. If say two diodes blew out of your 25 long string, the
rest will end up failing for whatever reasons made the first short out. My
previous rectifier was rated 50kV per leg at 2A continous forward. I was
supplying it off two 15kV 30mA transformers and it failed in maybe an hour
of use.

Microwave ovens run at several kV, but their high voltage diodes are usually
rated around 12kV and up. This makes me believe the 100% safety factor one
rep was talking about makes some sense.

I wish and was hoping this was an "easy" component to make, but it turns out
it's not. This is part of the fun though, but blowing diodes is getting
costly and old now.

KEN