Author Topic: Reistor Rating  (Read 620 times)

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Offline Rolf98Topic starter

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Reistor Rating
« on: January 17, 2020, 09:05:12 pm »
I think i have caugh a case of beeing dumb. I am currently looking into what formula is the right one for calculating a Power Resistor
I usally calculated them via V * A = W
But i also read about I^2*R = W
In my current circuit (An electronic load) which one would be correct as a load resistor.
I am thinking it would be V*A because its the load. (Attached a pic. I circled it in blue. Yes i stole that picture of off google  :horse:)

 

Offline bob91343

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Re: Reistor Rating
« Reply #1 on: January 17, 2020, 10:06:27 pm »
Both formulas are correct and yield the same result.  See Ohm's Law.

Having said that, in many cases one should take into account parasitic parameters such as stray capacitance, lead inductance, resistor inductance and distributed capacitance, etc.  This is because a resistor isn't just a resistor any more if the frequency is high.

But for dc or slowly variying stimuli, any of the formulas will suffice.

If the resistor is nonlinear, a graphical method can work, or a wattmeter.
 

Offline Vovk_Z

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Re: Reistor Rating
« Reply #2 on: January 17, 2020, 10:07:44 pm »
P = I × V = I ^ 2 × R.
The last one is Joule–Lenz law.
« Last Edit: January 18, 2020, 11:02:19 pm by Vovk_Z »
 

Offline Vovk_Z

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Re: Reistor Rating
« Reply #3 on: January 17, 2020, 10:10:12 pm »
And you can use 1 R resistors there, but it will lead to other changes.
 

Offline Rolf98Topic starter

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Re: Reistor Rating
« Reply #4 on: January 17, 2020, 10:35:07 pm »
Oh god. Like i said i had a case of the dumbs today. Thanks for your help guys. Sometimes you just cant think in a straight line anymore. Had me stuck for like the last hour or more. so i just gave in and asked.
Thank you very much for your Help
 


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