Design the bleeders on a per-capacitor basis. Each capacitor should
have its own bleeder.
If you are arranging your MMC as 3 parallel sets of 8 series
capacitors, each capacitor will see 1kV RMS (if you're not sizing for
mains resonance). Then a 10 Mohm resistor will dissipate 0.1 watt
(P=V^2/R), and will discharge the capacitor to a safe voltage in 3
seconds (1kV discharges to 50V in 3 time constants, t=3*R*C)
You could also use 2M resistors (0.5 watts, 0.6 seconds), or 20M
resistors (0.05 watts, 6 seconds), or ...
Be sure that the resistor will withstand the voltage, as well as being
able to dissipate the heat. You should either
1. Find resistors that are rated for 1kV
2. Put two smaller resistors in series for each capacitor
or
3. Use them beyond their voltage rating and hope they don't arc over.
Henry
2010/2/22 John Byström <zrc@xxxxxxx>:
I know this question has been brought up before, but they
were a bit old posts and I don't know if there is anything new
in the "Tesla world" and opinions and rules maybe have
changed.
For my 8kV 50mA NST I'm gonna have a 37,5nF MMC bank,
with 0.1uF capacitors. If I've made the calculations right from
the formulas I found, I need a resistor with the value 20Mohm
and handle 3,2W. How important is this?
Because I probably gonna order both the capacitors and
resistors from Elfa, and they don't have any over 1/2W. Does
that mean I need around 6-7 resistors over each capacitor?
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Henry Hallam
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