Re: Diode Strings

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

Original poster: "Richard W." <potluckutk-at-comcast-dot-net> 


----- Original Message -----
From: Tesla list <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Wednesday, August 18, 2004 9:14 PM
Subject: Re: Diode Strings


 > Original poster: "Jim Lux" <jimlux-at-earthlink-dot-net>
 >
 >
 > More of an issue in the past when devices weren't as consistent.  There is
 > good reason NOT to put capacitors in (see later (say, last 10-15 years) of
 > ARRL handbook for an explanation).
 >
 > Resistors equalize the reverse voltage drops if reverse leakage currents
are
 > different from piece to piece.  This is an issue if you're using mystery
 > surplus parts that are 20 years old in a big bin, but not really an issue
if
 > you're using all new parts from the same lot.
 >
 > Back when diodes were expensive, it was a good trade to use fewer diodes
and
 > add resistors (when diodes were $0.50 and resistors $0.03...).  Now, you
can
 > just add a bunch more diodes to give yourself some margin and be done with
 > it.  If you follow conservative practice (i.e. expected reverse voltage <
 > 0.5 PIV rating on diode), then you don't much care if some turn off faster
 > or slower than others, or if the reverse voltages don't distribute
perfectly
 > evenly.
 >
 >
 > On the other hand, if your diodes are from random lots OR are arranged in
a
 > way that might lead to inconsistent temperatures/voltages, then equalizing
 > resistors might be useful.
 >

Got them from Futurlec-dot-com $.17 in lots of 100. So I'm pretty sure they may
be from the some batch lot.

http://www.futurlec-dot-com/Diodes/6A10pr.shtml

 >
 >From:
 >Robert H
 >
 >... but a bridge has 2 strings in the circuit at any given time ...
 >

Good point. Hadn't thought of that. So 30/leg should be fine. I could just
as easily add more anyway.

 >
 >From:
 >KEN
 >
 >As for recovery time, what I found (the destructive way of course) is that
 >when you rectify the input for a tesla coil, you aren't dealing with a
 >simple 60hZ setup. You will get RF back into the rectifer assembly ...
 >

Now there's the red flag I'm looking for.

So here's more details in light of this particular matter:
I'll be using a charging reactor and another string of diodes in series with
the DC supply output which will be filtered by 12 - 23uF 4100V Aerovox
discharge capacitors 4.5"x3.5"x7" oil filled (no pcbs) in series and each
with two paralleled 10 meg high voltage 5W resistors as bleeders.
I'll be using Steve Young's setup of using a charging reactor (200mH) and
diode (another string) in series with the output of the DC supply.

Steve has had no problems so I'm ASSuming the choke may be filtering out the
unwanted RF.

Rick W.
Salt Lake City