[NJARC] how to calculate the wattage for a candohm resistor

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P = I X E     EQ#1

I = E / R       EQ#2

Substituting I in EQ#1 with E / R of EQ#2 you get:
P = ( E X E ) / R or E squared divided by R

So (122 V X 122 V) / 25000 ohms = 0.6 watts

You can also go to: http://www.sengpielaudio.com/calculator-ohm.htm and use this calculator either to verify or calculate.

I would use a two watt or higher wattage resistor as a substitute.  I would not use a carbon composition resistor because they do not hold their value well over time.

You will have to do the above calculation for each section of the candohm resistor.
Jim


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Sent: Monday, March 24, 2014 5:43 PM
Subject: [NJARC] how to calculate the wattage for a candohm resistor
 

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I need to replace a candohm resistor with four resistances and because candohm resistors never show the wattage I am trying to calculate this for the first time.
So my understanding is that you measure the voltage across a good section of the candohm....say in this case 25K then calculate Voltage squared divided by 25K = Watts dissipated. Then use a wattage that is double the calculated number.
So if this is correct I measured......122 volts DC across the 25K resistor....so 122 SQRT (square root) I was never that good at math) is 11.045 divided by 25000 and I come up with 4.418 and doubled is about 10 watts......did I screw this up......10 watts does seem like a nice number.

thanks much 
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