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Old 07-02-2010, 09:45 PM   #12
texcarguy
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Join Date: Jul 2010
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Default Re: Ammeter vs Voltmeter

I just went through this exercise with my '59 Jaguar saloon. I recently added airconditioning. This required an electric cooling fan for the radiator, as well as a secondary small auxiliary heater radiator (with fan) to keep the old beast cool under the hood as well as in the cabin.

Problem was, running at night... headlights, A/C compressor, dual blower motors, electric fan, and aux radiator fan... the new 60 amp alternator was pumping some 35-40 amps, and all of it trying to go through a 50 year old 30 amp-max ammeter. The gauge got so hot I could hardly touch it, and melted a bit of insulation off the incoming wires.

My solution: re-wire the primary ammeter supply wires to a larger gauge, and totally eliminate the ammeter from the circuit. The car came stock with an "ignition" (idiot) light for gross reporting of a catastrophic charging failure.

I didn't want to muck up the look of that beautiful wood dash with a NAPA voltmeter hanging underneath in a plastic housing, so I found a very small, thin, digital voltmeter display on eBay (LED), and fabricated a polished aluminum housing, accommodating a momentary push-to-light button so I wouldn't have that display on all the time at night.

It works great, and gives me the opportunity to monitor system performance under all conditions. The voltmeter requires only 18-20 gauge wire, so no issue passing current. I'm definitely sold on the value of voltmeter information vs ammeter.
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