RE: Check Your MMC Bleeder Resistors?

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

Original poster: "Basura, Brian by way of Terry Fritz <twftesla-at-qwest-dot-net>" <brian.basura-at-unistudios-dot-com>

Terry,

I have numerous hours on the Mini-Twin (some runs as long as 15-min) with no
problems. My 6" coil has many many hours on it throwing 6-7' arcs and there
is no indication of a problem with the resistors or the caps....

Regards,
Brian B.

 -----Original Message-----
From: 	Tesla list [mailto:tesla-at-pupman-dot-com] 
Sent:	Saturday, July 07, 2001 7:42 PM
To:	tesla-at-pupman-dot-com
Subject:	Check Your MMC Bleeder Resistors?

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Ed,

At 11:36 AM 7/7/2001 -0700, you wrote:
>
>Terry
>
>	I still worry about deterioration of those resistors due to
operating
>at much beyond their rated voltage.  Has anyone ever measured any after
>a few hours of operation?  In my experience they usually fail open, an
>unsafe thing if you're expecting them to discharge the bank.
>
>Ed
>

I just checked the resistance values on my coil's MMCs.  The big coil has
not gotten much use in recent years but my small coil with it's EMMC
certainly has.  The resistance values are all within 2% of their markings
and they are 5% to begin with.  So, I cannot detect any deterioration.

However, maybe it is a good idea to ask ALL users of MMCs to check their
resistors just to be sure and see if there are any problems out there.  

One can simply ohm across each resistor with a meter that reads resistance
high enough for the resistance being measured.  The values you read will
look lower than spec since they are in circuit with the rest of the
resistors in the array.  I think the formula is:

Rm = 1 / (1 / (Rr x STRING / (ROWS - 1) + Rr * (STRING - 1)) + 1 / Rr)

where:

Rm = Measured resistance of a single resistor
Rr = Rated resistance of a single resistor
ROWS = Number of rows in the MMC
STRING = Number of strings in the MMC

Of course, the resistance tolerance rating gets into that too...

That failing, the resistance will look "around" 5 to 10% low...  If any
resistors measure "above" their rating given the tolerance, they are
definitely bad.

I would ask all users of MMC with bleeder caps to please check them to see
if the resistors are holding up ok.  If your's are good or bad, please let
me know either way at the e-mail address below so we can all get some idea
of the number of people that did this and their results.  I will report the
numbers back to the list in a few days.  Also include a brief description
of your MMC and how much use it has had.  Hopefully, we can get a real good
idea of how they are doing and if we need to be concerned or not.

terry-at-hot-streamer-dot-com

Cheers,

	Terry