Meters

[diegokid]

Is there any disadvantage with having the ampmeter vs a voltmeter?

[Bill D]

No real advantage. But you have to be careful of your alternator rating. It can't exceed the gauge's rating.

[Jim Harding]

This subject comes up often, and there are some pro's and con's with either meter. The biggest con using an ammeter is that you must insert it in series with the positive lead of the battery in order for it to give you accurate indications. (you do not want it to see starter current however, so care must be taken to properly install it). This will require a larger gauge wire to hook it up. Depending on the amount of current requirements in your car, it could be as small as 12 gauge or as large as 6 gauge cable. There are "remote sensor" type ammeters that avoid the larger gauge wire to the ammeter. But unless it is calibrated correctly, it's meter readings could be inaccurate. In reality, the meter will only indicate the charge current going into the battery when the alternator is spinning. Usually it indicates a higher + current just after starting the engine, and will taper off to just a few amps after the battery charges up. With the engine off (alternator not spinning) the ammeter will show -, the current being sucked from the battery if you're running a lot of electrical load, i.e. lights, radio, fans, heated seats :-). The ammeter could read many amps, hence the need for the large gauge wiring.

A volt meter on the other hand can be installed with 16 gauge or smaller wire as there is hardly any current required to operate the voltmeter.

Here's a 'cut and paste' from a post I did sometime ago that dealt with alternator sizing.......

The amp meter on the dash will tell you if the alternator is up to its job. If it is reading 'negative', it tells you that the battery is being called on to supply some of the current needs of the car. If its reading 'positive' it means the alternator is doing it's job and re-charging the battery. A volt meter is not so intuitive. It will measure somewhere around 12.6 volts at rest (engine not running), and should peak to around 14.6 volts when the engine is up to speed. What it doesn't tell you is where the voltage threshold is when the battery starts to supply some of the load. It can be safe to assume that if the volt meter indicates something over 12.6 volts that the battery is not discharging.

[diegokid]

Thanks for the info, someone told me that fires had been started from ampmeters but these cars don't draw that much amperage.

[Jim Harding]

Thanks for the info, someone told me that fires had been started from ampmeters but these cars don't draw that much amperage.

Under "normal" circumstances I'd have to agree..... but "things" happen, like a short circuit or other high current demand for example. A lot of current can flow. Combine this with too small gauge wire, a fuse with the capacity to handle more current than the wire, and you'll have this 'glowing' wire somewhere under your dash. That's why I mentioned that the right sized wire for the current demands you'll expect, plus a nice margin for safety, and you shouldn't fall victim to a fire.