Re: suitable bleeder resistors for MMC

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

Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-qwest-dot-net>" <evp-at-pacbell-dot-net>

> 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

	VERY impressive numbers, and well worth noting by anyone considering HV
applications.  Dirt cheap at that price.  How long are they?

Ed