RMS or average current to determine resistoring heating?

mook Johnson · 2008-03-16T02:21:45+00:00

RMS has always been described to me as the AC current level to create the same amount or heat in a resistive load as a DC current. This as always been with sinusoidal currents.In this case I have narrow 50uS pulses of current at 5 amps with repetition rates of 500uS.If I calculate the RMS current vs. the average current there is a sizable difference. the average current is 0.5A the RMS current(from spice simulation) is 1.6A.Which if the two should be used when determining the heat generated by a power resistor.Assume the resistor chosen can handle the instantaneous power during the current spikes.I'm more concerned about the heatload this will add to the heatsink.There is a 10X difference in power between the two.thanks

Mar 16, 2008 24 Replies

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Phil Allison 18 years ago

"Mook Johnson"

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- see ABSE under " Glow Plug Regulator ".

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....... Phil

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Fred Bloggs 18 years ago

Really? And you call this "dramatic," like there has been some kind of current amplification effect taking place there, the battery supplying one current and the glow plug seeing another? Since the current is the same everywhere in the circuit, the battery and glow plug currents are the same. The battery supplies 0.5A average, and the glow plug receives

0.5A average, and conversely, in order for the glow plug to receive 5Arms, the battery must supply 5A,rms. Where is the miracle there? In any pulsed current system, Iavg=Ipk*D, and Irms=Ipk*sqrt(D) so that Irms/Iavg=1/sqrt(D) which is always >1.

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