To Steve, Bob, Theo, etc.
Been extra busy this week and didn't have time till now to get in on this
discussion.
>Theo wrote:
>As Bob alluded to earlier, the amount of heat generated in a resistance is
>given by the square of the current (in amps), multiplied by the resistance
>value in Ohms. Components do not "cause" resistance to the wiring, and I
>completely agree with Bob that while the symptom you had (hot connections
>apparently originating at a poor junction near the alternator) can be
>explained (just on the basis of the bad connection), the fact that the hot
>connection went away when you removed the ammeter is kind of a mystery to me.
I have some experience that could be related to this
situation. Last year, while driving at night, my 50 amp Ammeter froze in a
discharge position. I was concerned at first but no problems occurred and
no other symptoms developed so I drove home. I purchased the ammeter from
Rick at SS and simply bought another one along with a matching
voltmeter. I suspect these are Mo-Ma productions, but I haven't confirmed
this with Rick. In any case, I changed out the meter and everything was
fine. Some time later, I took the "bad" ammeter apart to see what I could see.
What I found was interesting and I'd guess that it would be
classified as a design failure, but I'm getting ahead of myself. The meter
consists of two steel studs a U shaped Cad plated steel (I'm guessing here)
stamping attached to an insulation board. At the bottom of the U the
section is punched with two small rectangular slots centered on a round
hole. A pin is swaged into this hole holding another small U shaped piece
of steel (I think), with the legs of the U protruding perpendicularly
through the slots. These small U legs carry some "signal" related to the
current passing through the larger U. On the pin is the balanced aluminum
indicator needle on a plastic bushing with a concentric donut shaped
magnet. The poles of the magnet must move in accordance with the "signal"
giving the analog needle reading.
My meter developed a resistance in the contact between one of the
studs and the larger U shaped stamping. This is evidenced by the darkened
insulator material (yeah, it got hot) adjacent to this stud connection. A
very small gap between the head of the stud and the U stamping can also be
seen under the microscope. The stud partially melted the stepped case
insulator washer and transferred enough heat down it's leg of the U to
partially melt the plastic needle bushing causing it to lock in one position.
This explains why everything kept working except the ammeter
movement. Since this is not the only occurrence of ammeter problems, It
relates to the base design. A simple soft solder of the studs to the U
would have avoided this failure. How this could relate to Steve's hot
charging wire, I leave for others, but this was not an external connector
problem. Tom
>My guess would be that at least one third of the 'hot' ammeters encountered
>by Margaret at Mo-Ma are due to bad (loose or corroded) connections at the
>ammeter. Another third would be caused by wiring accessories directly to
>the positive terminal of the battery (or on the Tiger, by wiring accessories to
>the batt connection of the starter solenoid), which requires the ammeter to
>pass a lot more current than just what is required to charge the battery, as
>well as giving false indication of the charging process. Only a third or
>less probably have any genuine issues that are not caused by
>nut-behind-the-knob mistakes.
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