Re: Diode Strings

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

Original poster: "David Rieben" <drieben-at-midsouth.rr-dot-com> 

Rick,

You may wish to consider the diode "sticks" removed from an
x-ray HVDC generator (x-ray transformer). These diode "sticks"
are amazingly small for their mammoth voltage ratings.
(app. 1" wide x 6" long x 1/16" thick G-10 PCB with usually
15 to 25 individual diodes soldered in a series configuration).
There are NO balancing resistors invovled here
either. They are generally rated at 150 kV pk -at- appr. 1 amp.
Of course they are designed to operate at or near their max
ratings submerged in oil and usually at a low duty cycle.
However they can easily withstand the relatively "low" voltage
from a 14.4 kV pig without the need for oil-submersion and the
current rating may be the only issue for a really high powered
coil.

David Rieben


----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Wednesday, August 18, 2004 8:34 AM
Subject: Diode Strings


 > Original poster: "Richard W." <potluckutk-at-comcast-dot-net>
 >
 >
 > Hi all,
 >
 > I have 200 1000V 6A diodes (6A10). Recovery time is ~2.5uS
 >
 >
<http://pdf.searchdatasheets-dot-com/pdf/266/266448.pdf>http://pdf.searchdatashe
ets-dot-com/pdf/266/266448.pdf
 >
 >
 > I hope to use 30 in each leg of a bridge to rectify 14.4Kv from a pig.
 >
 > 6A10s are general purpose diodes so I doubt they're manufactured with
 > comparatively tight tolerances. Seaching the mailing list I've read
 > something that the first diode to turn off can take the full applied
 > voltage and could cause failure if the diodes used aren't at least close
to
 > being matched.  This seems plausible if the diode turned off at the peak
of
 > the AC voltage swing but that doesn't seem likely. If the diodes begin to
 > turn off relatively close to zero crossing then I don't see that it would
 > matter so much. Say I have 30 1000PIV diodes in a string with 15Kv
applied.
 > Close to zero crossing the the collective voltage drops shouldn't even be
 > close to individual diode PIV. I know there are many that have had success
 > using 1N4007s but I'm just curious and maybe a bit cautious.
 >
 > So, am I missing something or is my logic in error?
 > I've also read about pros and cons using voltage balancing resistors so
 > that's on my mind too.
 > And how does recovery time figure into a diode string operating at 60Hz or
 > is 60Hz too slow to even worry about?
 >
 > I prefer to ask first than use the "powerup/duck" method.
 >
 >
 > Thanks!
 >
 > Rick W.
 > Salt Lake City
 >
 >