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 Ed.

On 26 Feb 2002, at 12:50, Tesla list wrote:

> Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<evp-at-pacbell-dot-net>
> 
> Tesla list wrote:
> > 
> > Original poster: "Shaun Epp by way of Terry Fritz <twftesla-at-qwest-dot-net>"
> <scepp-at-mts-dot-net>
> > 
> > > ---SNIP---
> > > 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.
> > 
> > Are you saying Radio Shack has good resistors??
> > 
> > Shaun Epp
> > 
> > > Regards,
> > > Malcolm
> > >
> 
> 	2.5 kV rating???
> 
> ED

Here is the data, straight from the horse's mouth:

Philips VR37 series. High Ohmic/High Voltage.
     The VR series of resistors comprise of (sic) a metal glazed film 
deposited on a high grade ceramic former with end caps and welded 
tinned electrolytic copper termination wires. The body is protected 
with a light blue insulating lacquer.
     These resistors are for applications in which high resistance, 
high stability and reliability are required at high voltages. The 
resistors meet the safety requirements of IEC65. Value and tolerance 
markings is (sic) by four or five band colour code in accordance with 
IEC62. Rated at 70C mounted horizontally in free air.
Climatic category 55/155/56.

Rated dissipation at 70C     0.5W
Resistance tolerance         +-5%
Temperature coefficient      200ppm/C
Limiting element voltage     3500VDC or 2500VAC
Insulation resistance        10^4 MOhm
Operating temperature range  -55C to 155C

They cost NZ$0.65/unit, and for quantities above 300, NZ$0.59/unit.

     I have used these in a range of HV applications including 
bleeders in MMCs. I can attest to the quality and reliability.
    In the same breath, I would like to add that in my extensive 
equipment repair experience (which is ongoing), I have encountered 
failures in both carbon film and carbon comp. resistors with rather 
modest (by comparison) voltages impressed across them, the failures 
being a combination of poor long-term tolerance and a tendency for 
high ohmic values to go skyward on the part of carbon comp resistors, 
and the latter in particular for carbon film. In particular, there 
appears to be an ongoing philosophy by some SMPS manufacturers that 
saving a couple of cents on unsuitably rated resistors in their eqpt. 
is good for the customer. I wish to advise them that this is far from 
true and is a false economy at best.

Regards,
Malcolm