Fwd: [TCML] Check the Discharge Time of my Bleed Res

["garry neeley" <bamacoiler@xxxxxxxxx>]

Dr. Resonance wrote:
I've never ever used any bleeder resistors in
any TC I've ever built and have never received or detected any stored
charge.

I have also never used bleeder resistors.  I have had the crap shocked out
of me by the tank circuit of a dc resonant charged tesla coil.  In this
configurtion both the mmc and the doubler caps held a charge until you
shorted them out.  I recommend bleeders because one day I was tuning this
coil and I barely touched the spark gap when I was bent over by the coil.
All the energy in the caps discharged across the gap and a single streamer
struck me right in the forehead from the topload.  Could have been very
bad.  It wiouldn't have ever happened with the addition of some simple cheap
resistors.
Happy sparking,
Bamacoiler

---------- Forwarded message ----------
From: piranha <piranha@xxxxxxxxxx>
Date: Wed, Oct 8, 2008 at 9:34 PM
Subject: Re: [TCML] Check the Discharge Time of my Bleed Res
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>


Hi,

This seems simple, but it is not :)

For the MMC safety case. Just charge the whole cap to say 10V or any battery
voltage laying nearby. Then disconnect the battery, count to ten, and go
probing around with the good ol' meter for any caps that have a significant
fraction of voltage on them. They should all be just about a total dead
zero. If you find a cap with say 1V on it, the bleeder is not working.

It is difficult to measure the cap's value in this way since the voltage
dies off very fast with the bleeder resistors. But don't worry about it. The
caps are tested at the factory very well. Far better than you can ;) Their
machines cost more than most people's homes!!

The equation for a voltage on a cap with a resistor is:

Vo(t) = Vi x EXP (-t / (R x C))

Vo(t) is the voltage at a moment in time.
Vi is the starting voltage at the time instant when the power source is
removed.
EXP is that funny key on the scientific calculator :D Also e^x.
R is the resistance across the cap in ohms.
C is the capacitance in 'Farads'.
t is time is seconds.

If we have a 0.150 uF cap with 10Meg of resistance across it and we charge
it to 10V and take away the battery, we have:

Vo(t) = 10 x EXP (-t / (10e6 x 0.15e-6) or Vo(t) = 10 x EXP(-t / 1.5)

So after say 2 seconds we have:

Vo(t) = 10 x EXP(-2 / 1.5) == 2.636 volts.

If one has that cap charged to 10,000 volts and then you throw you body
across after 10 seconds, we have:

Vo(10) = 10000 x EXP (-10 / 1.5) == 12.7 Volts. You will be allowed to live
:D

Best Regards,

Terry



bunnykiller wrote:

> Hey P Tuck...
>
> what is the starting voltage?
>
> Scot D
>
>
> P Tuck wrote:
>
> Hello.
>> I am about to bench test my new MMC Cap of 0.02143 uF (CD's using 2
>> strings
>> of 14 each) using a makeshift inductance.
>> Each individual cap' has a 10 Meg bleed res' across it and I work this out
>> as a discharge time of 10 sec's, to discharge to 1% of the supply voltage.
>> This in my case will be 100v when connected to a 10K supply.
>>
>> Am I right on my timing?
>> Philip
>>
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>>
>>
>>
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