How to test a C3 ammeter?

[Charles P.]

Is there a simple and safe bench test for battery gauges (ammeter) for C3's. It would be nice to know before installation. I did a quick archive search and didn't see a lot on this.

[Philip P.]

Re: How to test a C3 ammeter?

http://scienceshareware.com/how-to-measure-DC-current-with-a-dmm.htm

Take a look at the above.
THe ammeter is a series device and you could hook your meter outside the car
Battery pos to ammerter pos- ammeter neg to a load(ie headlight) other contact on light to neg side of battery the meter should read a current deflection of the draw, about 5 amps for a 60 watt lamp.
P=IE 60Watts = 5 amps X 12 volts.
This will vary depending on the voltage that you use and the lamp itself.
Hope this does not confuse.
Phil

[Jack H.]

Re: How to test a C3 ammeter?

The ammeter used in dash is NOT an ammeter. If it were, the wires that connect it to the electrical system would have to be the size of battery cables!!!

The meter is an el cheapo voltmeter. It connects to different points in the car's electrical system where the resistance of the wiring between those points is known and controlled. Therefore, the voltage difference between those points varies in lock-step to the magnitude and polarity of charging current supplied by the alternator. Hence, the voltmeter's face scale is graduated in current versus voltage.

The typical 'swing' for a C2-C3 dash ammeter with +/-40A scale is approximately 0.7 VDC. Use of a 1.5V battery to 'exercise' the ammeter should drive the pointer needle beyond its dynamic limits. So, IF you go this route to perform a gross operability test, only connect the external battery momentarily.

I use my regulated lab bench supply set for 0.5V output to exercise ammeters. I expect good ones to read just a hair below their 40A limits in response.

[Philip P.]

Re: How to test a C3 ammeter?

Being an old guy I missed the C3 part and do not have any informtion on wiring for that type of car.
I was in the C1 era where an ammeter is an ammeter.
Sorry for any confusion.
Phil

[Troy P.]

Re: How to test a C3 ammeter?

Are you sure C1 ammeters really measure amps?

[Philip P.]

Re: How to test a C3 ammeter?

Yes, the load circuits are in line with the meter, the battery is conneted to one side of the meter and the loads are connected to the other side. It is not conneted across the battery as you would have with a voltmeter, if that is what you are wondering about.

[Jack H.]

Re: How to test a C3 ammeter?

Ought to be easy to test your hypothesis...

The typical DC ammeter will have an input impedance that's darn near zero ohms (allow the max current flow freedom) while the typical DC voltmeter wants to a high impedance device, expect mega ohms, to thwart artificially loading the circuit under test.

[Philip P.]

Re: How to test a C3 ammeter?

Its an ammeter.
In terms of external connections Ammeter (used to measure current) is connected in series of the circuit (through which the current flow need to be measured) and voltmeter (used to measure voltage) is connected in parallel to points in circuit (across which voltage needs to be measured).