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[AMPS] resistors

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Subject: [AMPS] resistors
From: (measures)
Date: Sun, 16 Jul 2000 17:07:45 -0700
We all know of wattage ratings for resistors - I'm interested in specs on 
>voltage ratings of large resistors.  

?  depends on the unit.   Globar makes some energy absorbing resistors 
with much capability.  

>2 watt carbon resistors and 1 watt 
>carbon film resistors are rated at 500 volts.  I presume that is to limit 
>the voltage gradient 

?  True

>or stress across the resistor so that it doesnt act as a 
>fuse or firecracker.  What about large resistors often used as bleeders on 
>hv power supplies?  

The most reliable bleeder/equalizer resistor I have run into is a MOF 
type made by Matsushita.  We have sold over 6000 100k-ohm 3w units with 
no failures reported.  The max. rating is 500v (2.5w max.).  If one is 
not sure of the capabilities of a resistor,  measure the current vs. 
voltage very carefully with a DMM.  .  As long as current does not 
increase faster than voltage, no internal breakdown is taking place.  

>I use 200 watt resistors in series and have never had any 
>problems.  I assume they can stand hv due to their long length, 

?  good point.  However, high bleeder current is definitely not justified 

>about 10" 
>long, to spread out the voltage gradient.  Does anyone have any specs on 
>their actual voltage rating? 73 Bob W7LR
depends on the resistance.  200w c. 100k-ohm ww resistors do not have a 
reputation for high reliability.  My guess is that the wire is pretty 
flimsy.  This is probably why they are typically not rated for 200w of 
actual dissipation.  

cheers, Bob

-  Rich..., 805.386.3734,  

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