resistors of a lower power rating

9am53 · 15th May 2005, 03:50 AM

if the resistors in my amp are originally rated at 1/2 watt, and I replace them with 1/4 watt ones, what can happen? they work fine...now, I am just thinking that tey may fry...

rpapps · 15th May 2005, 03:57 AM

They can overheat, change in resistance value or simply go open circuit.
Measure the voltage accross them and use the e^2/r formula to work out the power being dissipated.
It's good practise for reliability to use resistors rated at least twice the power they are actually dissipating.

Cheers
Rob

kmtang · 15th May 2005, 04:06 AM

Simply measure the voltage across the resistor. Then calculate the power dissipation of it with P=V*V/R.

Most of the time people put a higher power rating. With this calculation, you should know exactly what it should be.

For reliable operation, you should allow at least 50% margin on the resistor wattage rating.

Johnny

15th May 2005, 03:50 AM	#1
9am53 diyAudio Member Join Date: Feb 2005 Location: Ontario	resistors of a lower power rating if the resistors in my amp are originally rated at 1/2 watt, and I replace them with 1/4 watt ones, what can happen? they work fine...now, I am just thinking that tey may fry... __________________ Guitar is Good

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15th May 2005, 03:57 AM	#2
rpapps diyAudio Member Join Date: Jul 2004 Location: nowhere of interest	They can overheat, change in resistance value or simply go open circuit. Measure the voltage accross them and use the e^2/r formula to work out the power being dissipated. It's good practise for reliability to use resistors rated at least twice the power they are actually dissipating. Cheers Rob

15th May 2005, 04:06 AM	#3
kmtang diyAudio Member Join Date: Nov 2004 Location: Vancouver	Simply measure the voltage across the resistor. Then calculate the power dissipation of it with P=V*V/R. Most of the time people put a higher power rating. With this calculation, you should know exactly what it should be. For reliable operation, you should allow at least 50% margin on the resistor wattage rating. Johnny