| Nichrome wire test from GMC photo site [message #369740] |
Sun, 22 May 2022 07:03 |
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RF_Burns
Messages: 2276
Registered: June 2008
Location: S. Ontario, Canada
Karma: 3
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Senior Member |
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I found this test of the nichrome wire heating on the GMC photo site.
http://www.gmcmhphotos.com/photos/nichrome-wire-test/p6663.html
It seems to show that a 25 volt and 12 volt source where connected in series to obtain 37 volts. The nichrome wire in a GMC harness was connected across the 37 volts and tested to determine the amount of heating. It was determined that it did not warm enough at that level of voltage to melt the plastic insulation even over a period of time.
However.... I note that he is reading a current of 1.8 Amps through the 10.0 ohm nichrome wire. From ohms law that is only 18 volts across the wire.
1.8 amps through 10.0 ohms = 32.4 watts of power dissipated.
At 37.4 volts shown on the voltmeter across 10.0 ohms = 3.74 amps of current and 140 watts of power dissipated. That would easily melt plastic in short order.
So obviously there is some additional resistance in the circuit limiting the current to 1.8 Amps or the voltmeter was not connected directly at the nichrome wire while the load was present. I can see the positive lead of the voltmeter is connected at the 25V power supply. Also the white jumper cable does not look very heavy.
So the observed experiment was likely at 18 volts across the nichrome wire resulting in 1.8A of current flow and the much lower 32 watts of power dissipated.
But that's just me.
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
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