Re: suitable bleeder resistors for MMC

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

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Shaun,

On 22 Feb 2002, at 8:13, Tesla list wrote:

> Original poster: "Shaun Epp by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<scepp-at-mts-dot-net>
> 
> I was wondering what the groups stance is on the 10 MegaOhm resistors that
> are used on the Geek Group MMC.  If we assume 2000 Volts max and 10 megaohms
> across each cap--  the power is only 0.4 watts, but a 1/2 watt resistor, the
> next size up,  is only rated a few hundred volts.  I've seen some resistors
> made by  IRC that will handle ~ 3kv at 1/2 watt, I'd have to check the exact
> specs but they'd work, the only thing was they were very expensive, $3 to $4
> Canadian each .  What resistors are people using since my MMC capacitors
> didn't come with resistors?  I want to get some that will be reliable, easy
> to get ahold of and cheap!

I'm using 10 MegOhm 1/2W metal film resistors manufactured by 
Philips. These are rated for 2.5kV if I remember rightly. I'm 
impressing 1.5kV max across them. They are available from RS 
Components.

     I've recently come to regret my choice of 10M since my small 
test cap charger (a flyback supply) is running out of steam above 
13kV or so. I should have used 33MOhms or higher. The resistors in no 
way share voltage across the individual caps in a string at TC 
frequencies. The best they can do is ensure the caps start out equal. 
Accurate cap matching is the best solution to voltage sharing. You 
can happily parallel strings whose final values are different.

Regards,
Malcolm