Simply said, current flow causes heat, end of story.
Brad Hogg <----also a qualified electronics engineer.
Winnipeg, Manitoba
http://www.nybclub.org/bradhogg/index.htm
1990 Chrysler Imperial 4-door Sedan (the KImperial)
1978 Chrysler Newport 4-door Hard Top (the Newporker)
1976 Chrysler New Yorker Brougham 4-door Hard Top (the Black Beast)
1968 Chrysler Newport Custom 4-door Sedan (Grand-Dad's car)
----- Original Message -----
From: "Dick Benjamin" <DickB@xxxxxxxxx>
To: <mailing-list@xxxxxxxxxxxxxxxx>
Sent: Monday, September 16, 2002 11:24 PM
Subject: Re: IML: What causes heat in conductors?
You're playing on my turf here, so if I may, I'd like to add a comment to
"chrysler1978" 's statement:
Heat is generated in conformance with the expression P=I(squared)R, or in
English, the power disippated is equal to the square of the current times
the resistance, for a purely resistive circuit. So for a given current flow
through any path, the heat generated will be directly proportional to the
resistance of the circuit. If a switch contact develops significant
resistance due to crud, loose contact or corruption, the current will be
reduced somewhat, but the increased resistance will cause some localized
heating at the point of resistance, and at a particular range of values for
the resistance, there will be a very high heat generated at the point of
resistance. The maximum heating is when the value of the introduced
resistance of the switch contact equals the resistance of the design load,
but anything within a factor of 10 will cause enough heat to do damage to
the insulator that holds the contacts. Anyone who has had to replace a
fried blower switch on our beloved 81-83 coupes will be very familiar with
this phenomenon.
Neil's problem with his dash rheostat, however, is more likely to be a
situation where the nichrome wire of the rheostat has become coated with an
insulating layer of oxide or some other crud, which will go away if the knob
is rotated 187 times with the lights on. Do this at night where you can
notice the dash lights flicker when there is momentary contact through the
offending layer, and work with that spot, exercising the rheostat knob back
and forth; you'll see the good spot expand slowly, until finally the dash
lights will work like new again. This is true of any dash light control
for any year, if it is the type that controls the gauge illumination by a
rotary knob on the headlight switch.
Dick Benjamin (who has a 46 year old sheepskin somewhere which says I'm
qualified to speak on this subject.)
(I'm sorry to be thick, but "fruit bat impression"? OH! Hanging upside
down - Ding! I get it!)
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