On Fri, 2 Feb 2007, Jimbo wrote:
[...]
I am a mechanic by trade. I am good at diagnosing electrical and
drivability. I have seen a few times that high resistance in the negative
leg of a circuit can take out components like computers, modules and even
not-so-complicated devices like bulbs and switches. What I don't understand
is why. Ohm's law states that E=IXR. If this is the case then if resistance
is high it will decrease amperage. I would tend to think that just the
opposite would happen...component would just lose power and not fry.
Dear Jimbo,
You're right that the current should drop if the total resistance
increases, since the battery voltage is practically fixed. My thought
while I was reading this was that noise in the circuit, from say corrosion
at the negative battery connection, could explain the failure of
components. Unlike any other type of device I can think of, some electric
motors can burn out if they aren't getting enough power because they cool
themselves while turning. On the other hand, incandescent light bulbs will
last a very long time if run at less than their full operating voltage
(such as a 220 volt light bulb run at 110 volts). I would also expect the
part of the circuit causing the resistance, such as a frayed cable, to get
hot and burn out in that place, since power = EI = RI^2
Yours,
Chris
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