Amp meter vs Volt meter, Which one to use? Options

[nola914]

I'm close to starting up my 2.0L out-of-body. I'm going to plug in a few basic guages to keep an eye on what's going on. In my parts bin I have an old Amp meter (old - but never been used). But I got to thinking... the 914's use a volt meter, as do newer cars. I suppose that there is a reason for that.

Seems to me, and this is a very simplified way of looking at it, the amp meter is providing info about the alternator's operating efficency, while a voltmeter is showing the battery's condition. Am I thinking correctly?

In my case, with a new battery, but an old alternator that hasn't been turned in 4 years, to get a reading on the system, should I use the amp meter or look around for a volt meter? Or both?

[chris914]

A battery always has a voltage difference that can be measured even when there is no current draw (unless it is dead). It is the condition of the battery that is important to starting your car and keeping it running. It is only important to know if the alternator is working or not, hence the little idiot light in the dash.

An alternator is not always charging the battery. It charges the battery when the battery falls below a certain voltage. When you car is running it draws almost no current from the battery. Your car could run for days before the alternator would need to charge it again. The starter is the biggest draw of current on your battery.

If you had an ammeter in you dash you would have to run a big a$$ wire from the alternator to the gauge and back again. Look at the wire that is there now. The copper is like a quarter inch in diameter. The amount of current running in that wire can kill.

A voltmeter measures voltage in parallel and an ammeter in series to the circuit.

So yes a voltmeter tells you the condition of the battery and an ammeter tells you the working condition of the alternator, that took me long enough to say, lol. (IMG:style_emoticons/default/blink.gif)

Do you need one? Depends on that you want.