Re: MMC resister problem

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

Original poster: "Justin Hays by way of Terry Fritz <twftesla-at-qwest-dot-net>" <pyrotrons2000-at-yahoo-dot-com>

Hi Steve,

Your friend could fix the problem by not using resistors.

Through my experience, there is only a single good reason to use
resistors on an MMC. And that is, for safety. If the resistors are
rated properly, they will discharge every capacitor in your MMC bank
in less than 30 seconds or so, so you don't have to worry about an
annoying zap every time you touch your capacitor. By annoying, I mean
a non-lethal "ow dangit that hurt" sort of shock. But remember the
severity of the shock depends on the size of the capacitors, and the
voltage they are charged to when they're touched.

If you are using big capacitors for your MMC, I suggest doing two
things:

1. Using a single HV resistor across the entire MMC, as a bleeder to
get rid of the unwanted charge after the coil turns off. REMEMBER, in
a properly working tesla coil, the secondary winding of the power
transformer will short out the capacitor. But if this winding fails
and burns open, this will not protect you so I suggest the single
bleeder resistor to make sure.

2. Shielding the open connections of the MMC with plastic or some
other suitable insulator.

If your cap's are small there is no real safety concern, so I would
omit the resistors entirely.

Aside from safety issues, resistors are useless on an MMC capacitor
in my opinion. Even properly rated resistors dissipate power, are not
cheap, and can cause other problems if not properly designed into the
MMC. If wire-wound resistors are used, this means you are placing an
inductor in parallel with every capacitor in the bank ---> meaning
that this LC tank will ring whenever the spark gap fires.

I'm unsure of the exact voltage rating of the common 1/4W resistors,
but I'm sure it's not more than 7 or 800V. The resistors will flash
over if their voltage rating is exceeded.

Take care,

Justin Hays
KC5PNP
Email: justin-at-hvguy-dot-com
Website: www.hvguy-dot-com


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