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Re: Bleed resistors for MMC caps

Original poster: Chris Cudahy <ccudahy-at-yahoo-dot-com> 

  The safety issue that the bleed resistors avoid is
having the total capacitor charged to zero volts with
individual cells in the series string charged to non
zero volts. When shorting out something like this:
  0v     2kv     0v

You get something that looks like:

0v --|     | 2kv

  This is possible because the caps can become reverse
charged. So it's possible to short out a string of
caps and still have high voltages on somee of the caps
in a string. Which would give someone a nasty
surprise! To fully discharge a string by shorting it
you would need to short each terminal of each cap at
the same time.
  The bleed resistors across each cap automatically
discharge the caps within a few seconds, at the cost
of a small amount of power.


P.S. Thanks for the responses to my question. Someone
local offered to sell me some left over 3.5kv
resistors, so I'm happy :)  It is interesting to know
that regular 1/2W resistors are underrated enough to
work for this, it sounds similar to how underrated the
MMC caps are!

--- Tesla list <tesla-at-pupman-dot-com> wrote:
 > Original poster: Tom Wideman <twidem01-at-baker.edu>
 > What if the relay were powered by an independant DC
 > power
 > source?
 > ---- Original message ----
 >  >Date: Tue, 08 Jun 2004 08:36:13 -0600
 >  >From: "Tesla list" <tesla-at-pupman-dot-com>
 >  >Subject: Re: Bleed resistors for MMC caps
 >  >To: tesla-at-pupman-dot-com
 >  >
 >  >Original poster: "Mark Broker"
 > <mbroker-at-thegeekgroup-dot-org>
 >  >
 >  >Each capacitor needs its own bleeder resistor.
 > Placing one
 > large resistor
 >  >across the MMC could lead to a condition in which
 > capacitors in a string
 >  >could be individually charged but yet maintains a
 > net
 > charge of zero.  I'm
 >  >not certain what conditions these are, but I still
 > think
 > it's a very good
 >  >idea to use individual bleeder resistors.
 >  >
 >  >The transformer will actually short the entire
 > capacitor
 > when the power is
 >  >removed anyway, so your relay wouldn't have much
 > effect.
 >  >
 >  >Mark Broke
 >  >Chief Engineer, The Geek Group
 >  >
 >  >
 >  >On Mon, 07 Jun 2004 18:27:59 -0600, Tesla list
 > <tesla-at-pupman-dot-com> wrote:
 >  >
 >  >>Original poster: Tom Wideman <twidem01-at-baker.edu>
 >  >>
 >  >>Instead of using some sort of bleed
 > resistor....could you
 >  >>use a normaly closed contact off a solid relay?
 > So that
 >  >>when the circuit is off the relay redirects all
 > gathered
 >  >>electrons to ground? Just a thought....tell me
 > what you
 >  >>think.
 >  >>
 >  >>-Nano2e
 >  >
 >  >
 >  >

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