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



How much energy is lost in the MMC resistors? Surely it is a small percentage?

It seem to me that most people highly recommend them for safety reasons.

Dave Nelson
----- Original Message ----- From: "CONOR WHYTE" <cjwhyte@xxxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Monday, August 18, 2008 2:01 PM
Subject: Re: RE: [TCML] mmc cap protection by spark-gaps-any ideas?


That was what I was trying to say. Some MMC designs I have seen use an over volt gap over the entire MMC to protect it. -- are you saying this is a bad idea? mike hammer used this design and it proved reliable for him. personally I have never used it. The caps i use allow me lots of breathing room. CDEs are simply awsome!! The resistors are safety for the operator. Like I said it is a waste of energy and $$.
You can simply discharge a gap with a discharge wand after the power is off.


----- Original Message -----
From: S&JY <youngs@xxxxxxxxx>
Date: Monday, August 18, 2008 12:26 pm
Subject: RE: [TCML] mmc cap protection by spark-gaps-any ideas?
To: 'Tesla Coil Mailing List' <tesla@xxxxxxxxxx>

No, no, no! Don't do that! If one or more of the
gaps fires, the other
caps in series will overvolt which could cause them to
fail.

The resistors are not to protect the caps. They are to
protect you from an
accidental dangerous shock by bleeding down the voltage stored
in each cap
in a few seconds after you turn off power.

You can make good high voltage resistors by series connecting 5
2 meg 1/4
watt resistors. Connect one of these resistor strings
across each cap.
Yes, lots of soldering, but the resistors are only 1 US cent
apiece (get
them in lots of 100 from Jameco).

--Steve Y.

-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx]
On Behalf
Of vatercox@xxxxxxx
Sent: Sunday, August 17, 2008 3:23 PM
To: tesla@xxxxxxxxxx
Subject: [TCML] mmc cap protection by spark-gaps-any ideas?

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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