Re: MMD (not another acronym!) --> HV Diodes and Failures

• To: tesla-at-pupman-dot-com
• Subject: Re: MMD (not another acronym!) --> HV Diodes and Failures
• From: "Mike Nolley" <mnolley-at-mail.slc.edu> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)
• Date: Thu, 09 Mar 2000 07:48:48 -0700
• Approved: twftesla-at-uswest-dot-net
• Delivered-To: fixup-tesla-at-pupman-dot-com-at-fixme

> Original Poster: "Kevin Ottalini" <ottalini-at-mindspring-dot-com>

    comments below.

> I highly recommend never potting or encapsulating these high-power
> diodes as an array unless you are using a string of say low voltage
> 1KV diodes. Then, only encapsulate one set (20KV worth for 10KV-15KV
> operation) and use four of those to build the bridge.

    I am using a string of 1 kv diodes--I will probably encase them in wax.


>  Other than that,
> I was a little confused by the statement:
>
> > Multi-string MMD's seem to be impractical for size reasons, and
> > silly to boot as the 1kv, 6A diodes would seem to be sufficient
> > for any system under 84 kva ; )
>
> This implies that you believe the tank capacitor to be optional ...
> which it is not.

    You may have misunderstood the acronym-- I meant multi-mini-diode.  I will
probably not be using an MMC for the tank capacitor, but rather one of the fair
radio 100kv jobs.

> One thing you didn't mention though was the limiter resistor
> between the caps and the bridge.  You *MUST* put some sort of
> limiter into the circuit or the current surges are certain to
> blow the diodes out.  This will also help prevent cascade failure
> problems if the caps or the diodes fail.

    If you mean a resistor between the rectifiers and the tank--then yes, I'm
using 2 5 kohm, 200W resistors on each leg.  I'm not sure if this is enough to
"critically" damp, but I will be adding bypass caps before I fire the coil up.
    My doubler configuration is quite different than the one you show on your
site--
    instead of one transformer input, I am using four, each one being fed into
a one stage "doubler" for full-wave DC.
    I was intrigued by your site and very impressed by your coil, especially
the beautiful ribbon primary.  Also, your thoughts on voltages above 15kv got
me to thinking about my own coil--since it is CW--does it really need 15kv?
I'm wondering whether the extremely high frequency might require a lower
voltage, higher current power supply.  If so, then no worries.  I won't have to
worry about doubler capacitors anymore ; )
            --Mike

• Prev: Re: Interesting Skin Depth Data
• Next: Re: Saturatable reactor Questions
• Index(es):
  • Main
  • Thread