Power resistor calculation

Hi,
I need calculate resistor 2.4 ohm let's say from Vishay:
I am taking 100W power resistor with overload rating is x10 for 5s.
Ambient temperature is 100deg. According graph derating it will be 80%. So effective power dissipation will be 80W.
Now I need dissipate 3000W. The pulse duration the resistor withstand is 3000W/(80W*10(factor)*5s~1.33s
The maximum working voltage will be V=sqrt(3000W*2.4ohm)= 84v.
Please review it and comment
Thank you

stanislavb said:

Hi,
I need calculate resistor 2.4 ohm let's say from Vishay:
I am taking 100W power resistor with overload rating is x10 for 5s.
Ambient temperature is 100deg. According graph derating it will be 80%. So effective power dissipation will be 80W.
Now I need dissipate 3000W. The pulse duration the resistor withstand is 3000W/(80W*10(factor)*5s~1.33s
The maximum working voltage will be V=sqrt(3000W*2.4ohm)= 84v.
Please review it and comment
Thank you

Click to expand...

Dissipation means hat a device (resistor) would heat up in a given environment. To prevent its overheating, a suitable environment must be modified to sink the heat. Hence the name "heat sink".
For resistors, a suitable heat sink can be a mount on an aluminum plate or a ridged structure that would radiate and conduct the heat elsewhere. For high power, also a water bath may be good.
Always consider an increased power flow, therefore a larger and more efficient heat sink to use. Select a resistor rated for a higher power dissipation, to make a safe device with a longer life.
Commercial heat sinks like ridged Al blocks come with the heat flow specification. Using a fan offers an improved heat flow. I my designs, I always ran tests with measuring the temperature increase over time, and made modifications to ensure the temperature will stabilize at an acceptable level. Car headlight lamps are a good heat sources, their power can be adjusted by DC voltage to a desired level, and are cheap if they break during a test.

I've found very interesting this application from Vishay:

**broken link removed**

I think it could help you in your calculation

albbg said:

I've found very interesting this application from Vishay:

**broken link removed**

I think it could help you in your calculation

Click to expand...

Thank you for this reference! I only warn the readers from the simple extrapolation suggested in the intro. MOst such resistors fail when overloaded as indicated, by short duty cycle. I succeeded always by described experiments.