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Re: UK MMC bulk order
Deano,
Just a note on your resistors. 1/2 watt resistors typically have a voltage
rating of only 350 volts. You are really pushing it with 1600 volts across
it! It would be better to use 4 or 5 in series to prevent breakdown which
could result in overvoltaging the other caps in your string.
--Steve
----------
> From: Tesla List <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Re: UK MMC bulk order
> Date: Tuesday, July 06, 1999 12:24 PM
>
> Original Poster: "David Dean" <deano-at-corridor-dot-net>
>
> >Does anyone have any definite findings either way for the need for
> >equalising resistors in an MMC? I seem to remember seeing a comment
> >that they were unlikely to help.
> >
> >
> YES.
> I made a small EMMC with 11 of the .056uf 1600v Panasonic caps. I just
> soldered the leads together and took it over to the bench and hooked it
> across a NST and a spark gap to see what would happen.
> blasted it for about half a second. got interrupted.
> Came back two days later to get something else off the bench. Brushed
> against the middle of the string with the back of my hand (not on
purpose)
> and got a nasty surprise. Even though the end to end voltage was 0, some
of
> the caps seemed to have a full charge on them. I then broke out the meter
> and found that 4 caps had over a 1000 volts left. others had varying
> amounts. An interesting thing was that the polarity was random. That
> convinced me. I got some 10M 1/2W carbon film resistors and put a
resistor
> across each cap. Then I charged the thing to 20kv and checked it again.
> Nothing. The bleeder resistors cost $0.06 ea. 22 x .06 = $1.32, a very
small
> price to pay for safety.
> It may not make any difference to performance, but for such a small cost
and
> piddling amount of trouble, it just does not make any sense to leave them
> out. Also the random polarity of the residual charge left on the
individual
> caps of a "discharged string" might well cause trouble after time.
> BTW my mmc consists of two strings of 11 for a total of 10nf. I put the
> strings side by side inside a 1 1/2" O.D. polypropylene tube 12" long.
> perfect fit. Potted with epoxy resin. A 1/4" X 1 1/2" brass bolt serves
as a
> stud on each end. Much smaller than the equivalent rolled poly in oil
> version.
> just My $.02
> deano
>
>