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

[piranha <piranha@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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