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

[mddeming@xxxxxxx]

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 more 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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