Re: Bleeder (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Sat, 20 Oct 2007 14:26:54 -0700
From: Barton B. Anderson <bartb@xxxxxxxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: Bleeder (fwd)

MMC, 1/2W, 10M ohms (if ESR is similar to common CD capacitors). Mount 
directly across each cap if you have enough caps in series to minimize 
the voltage across each cap. If only a few MMC's in series (less than 
10), it may prudent to use a couple 5M resistors in series (to increase 
arc voltage across the resistors).

As far as "bleeder", maybe not the correct term in this case. Equalizing 
resistors would be a better term although bleeding also occurs (but the 
time duration is long, so don't think of it in terms of a "bleeder"). 
The transformer does the real bleeding. Disconnect the transformer from 
the charged cap at the right time and the bleed will be very slow. You 
can get zapped in that situation. A bleeder is designed to bleed down a 
charge in some amount of time, but bleeders can fail open. NEVER rely on 
bleeding as a safety device. Been there, done that, got ZAPPED!

Why 10M ohms? Due to common CD caps ESR. This value provides a low loss 
resistive approach to equalizing the voltage across the string without 
waisting a lot of power across the resistor. But, if you use a cap with 
a vastly different ESR value, you will need to adjust the equalizing 
resistor for the same efficiency.

BTW, the cap will work without the resistors. Are you more likely to 
kill a cap? Of course you are. Will it actually kill the cap? Depends on 
the caps ESR and the number of caps in series. The equalizing resistors 
are simply a low cost safety device for the caps themselves. Their not a 
human safety device.

Imagine 10 resistors in series and 10,000V across the series string. 
Obviously your going measure 1000V or very near across each resistor. 
That is the basic idea of equalizing the voltage across each cap. To 
keep the voltage drop across each one as "similar" to the next as 
possible. Although any value resistor will do this, it is important to 
get the value high enough so that power is not waisted in the resistor 
itself. The ESR of each cap plays a role in that voltage drop because it 
is in parallel with each resistor. We arrive at 10 Meg resistors to 
achieve this situation with Cornells common MMC capacitors. If a 
different capacitor is used, there might be a better resistor value to 
optimize the string.

Take care,
Bart





Tesla list wrote:
> ---------- Forwarded message ----------
> Date: Sat, 20 Oct 2007 12:04:22 -0700
> From: Anthony R. Mollner <penny831@xxxxxxxxxxxxx>
> To: Tesla list <tesla@xxxxxxxxxx>
> Subject: Bleeder
>
> I'd like to ask a question and find out what the common consensus is
> regarding bleeder resistors. What does the group recommend for bleeder
> resistors on an MMC bank? 1/2 watt, 5 watt, 1 meg, 10 meg etc.??
> Tony
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