On 5/17/11 10:15 PM, Kipton Moravec wrote:
> While the power rating (W) says you can use a 1/4 W resistor, the
> voltage does not.
>
> Carbon Film Resistors have maximum working voltages for their size.
> (From Xicon Datasheet)
>
> 1/8 W 200V
> 1/4 W 250V
> 1/2 W 350V
> 1 W 500V
>
> So I would use a 1 W resistor.
>
Or a string of 1/4W units.
However that doesn't address the desire, expressed earlier, of fitting
it inside an existing housing.
The maximum voltage rating on a resistor comes from many factors:
breakdown over the surface (depends mostly on physical size.. assume
10kV/cm of length as a good working rule of thumb)
breakdown between conductive traces in the metal film -> very difficult
to know what the real number is without a test. All the mfr guarantees
is that it's bigger than the rating voltage
Thermal dissipation - 200V on a 100 ohm resistor is asking for
destruction. For this, there's some amount of time averaging (not a lot
for those tiny 1/8 watt), but it's something to think about.
The other aspect is that the leads provide a thermal path to the outside
world (for a lot of diodes and transistors, the leads are the primary path)
Really, the only way to know is to try it out (and then report back
here!). Spend the nickle on a resistor and try it at full power and see
what happens.
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