Ammeter guage

[Snakebit]

What should the guage read with fully charged battery at idle? Should the guage read to the negative side or the positive side if everything is working properly?

[Ron61]

With no draw such as lights and etc. the gage should read right at center. With lights or any accessories on it will most likely show just a minor negative reading at idle. I used a voltmeter in my car, but the other one had an amp meter and it read as I stated above. And if you have to crank the car over several times to start it, the gage will most likely read a high positive for a few minutes as the alternator recharges the battery.

Ron

[wtm442]

About the only thing you can determine from an ammeter gauge is when something with a big current draw kicks on, like temperature controlled fans.

What Ron said is correct, but most ammeters are not that accurate.

If you put a voltmeter across the battery terminals, a good battery with a full charge should be about 12.8 volts with the engine off. With the engine running and the alternator working properly, the voltage should be more than 12.8 volts ... something like 13.5 to 14 volts (with all high draw accessories off).

[GreenSnakeDoc]

Ammeters are good at indicating when a battery cannot accept a good charge. For example, if the battery is "down" and you need a jump to get the engine started, you watch the amperage when driving or fast idling. It should take many minutes at a high charge rate to fully charge a battery if the battery is good. If the ammeter shows the charging amps getting lower fairly quickly, the battery can't take a good charge and should be replaced. Sorry I can't be more specific on times and charging amps, but it's been many years since I was a college student on a tight budget. Is "ammeter" the correct spelling, or should there be a "p" in there?