Re: which type for bleeder resistors?

["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 Antonio,

On 29 Jul 2002, at 21:04, Tesla list wrote:

> Original poster: "Antonio Carlos M. de Queiroz by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <acmq-at-compuland-dot-com.br>
> 
> Tesla list wrote:
> > 
> > Original poster: "Laurence Davis by way of Terry Fritz
> <twftesla-at-qwest-dot-net>" <meknar-at-hotmail-dot-com>
> 
> > are these overkill, or just what I need?
> > I've never had to price megohm resitors, but the price seemed high to me.
> > (the caps are cheaper than the resitors!?)
> 
> You can use regular inexpensive 10 MOhm resistors. Their size is
> important, but if you keep, say, 1000 V per capacitor/resistor,
> anything with more than 1 mm of length will work. I made an MMC
> using small 10 M resistors (1/8 W?), with two in series across
> each capacitor for better safety. They work well, at 1000 V per
> capacitor, not even getting warm (they dissipate at most 12.5 mW).
> 
> Antonio Carlos M. de Queiroz

If they are 1/8W, it is not a good idea. Their resistances *will* 
tend to go high and eventually open-circuit over time. The problem 
with that is that an excessive voltage burden will be thrown onto one 
of the caps.

       I fix SMPS all the time where the manufacturers thought they 
could get away with using under-rated resistors in a high voltage 
situation.

Regards,
malcolm