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Re: [TCML] mmc cap protection by spark-gaps-any ideas?



Oops,
I dropped a term, Sorry. P=E^2/R=12,000x12,000/200,000,000=144/200=720mw/string, or 1.44W out of 2.88KW, or 0.05%. Sorry for the carelessness, but it still makes the claim of waste seem pretty farcical.

Matt D.

-----Original Message-----
From: mddeming@xxxxxxx
To: tesla@xxxxxxxxxx
Sent: Mon, 18 Aug 2008 4:42 pm
Subject: Re: [TCML] mmc cap protection by spark-gaps-any ideas?


Hi Connor, 
 
Congratulations on not zapping yourself, YET. 
With resistors running about 1-2 cents each in bulk, I can't see that it is a major expense for added safety.  Many older coilers (30-yr experience+) believe they got to be that way by using both a J-stick AND discharge resistors. 
Using 20 10-meg resistors would "waste" three MILLIWATTS per string. 
I find it hard to believe that you could really notice a loss of 0.006 watts out of 2880 watts total.  That's about 0.0002%! Seems like a very small price to pay for the added safety. 
 
Matt D. 
 
-----Original Message----- 
From: CONOR WHYTE <cjwhyte@xxxxxxx> 
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx> 
Sent: Sun, 17 Aug 2008 11:37 pm 
Subject: Re: [TCML] mmc cap protection by spark-gaps-any ideas? 
 
 
I don't use resistors on my MMC. I find these waste energy and cut down on my  spark length. I  use CDE 942C series 1.6Kvdc 680nF capacitors, I use 20 per  string 34nF @ 32Kvdc x2 . I run 12Kvac @ 240mA. I have been running my MMC now 
for 2 years and have had 0 problems.  
Quite often many people are scared about residual charge in the cap bank this is  why people add the resistors. It bleeds charge away after the unit is turned 
off. You can do this with a discharge wand MUCH cheaper. 
Like I said I have never used them. It is a waste of energy.  
If you feel like you want to protect your cap bank, I'd might make an 
extra gap 
that one could adjust. 
maybe say to be safe a 3.5cm gap 35Kv.  I would also make sure the MMC total DC  rating is around 3x that of the input voltage.  12Kvac -- 32-36Kvdc.  Another  factor I would also check is the tolerance rating of the capacitors most are  5%... which is ok... CDEs on the other hand are 10% and can handle much more 
voltage spikes. 
  
 
----- Original Message ----- 
From: vatercox@xxxxxxx 
Date: Monday, August 18, 2008 10:47 am 
Subject: [TCML] mmc cap protection by spark-gaps-any ideas? 
To: tesla@xxxxxxxxxx 
 
Dear List 
I have 30 x 47nF polypropylene metal foil caps, each rated at 2 
kVDC 
which I intend to wire as three strings of 10 capacitors for 
approximately 14nF at 20kV DC. While normally each capacitor in 
an MMC 
would be protected by a 10- or m
ore megohm high voltage resistor 
these 
have proved difficult to obtain (due to lack of demand?). In liu 
of 
this would it be possible to protect each cap with a miniature 
spark-gap -perhaps a pair of closely-positioned stiff wires 
connected 
to the capacitor leads notwithstanding the fact that 2 kV is 
usually 
regarded as a bit on the low side for satisfactory spark-gap
operation 
 
Jolyon Francis Vater-Cox 

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