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?

[Dave_Darling]

I think Chris may be overstating things, but he is at least partly right.

The voltmeter gives you an indication of the current condition of your charging system, including the battery. The ammeter tells you how much draw your car is putting on the system versus how much your alternator is putting into it.

The main reason cars don't have ammeters these days is the wiring. Ammeters need big wires, and those are a little expensive (particularly for long runs like in a rear-engine'd or mid-engine'd car!) and a little difficult to work with, and pose a not-insignificant risk of "letting the magic smoke out" of your car.

I'd use the voltmeter, because I'm used to it. For out of the car, the ammeter might be worth a look...

--DD

[914-8]

The voltmeter gives you an indication of the current condition of your charging system, including the battery. The ammeter tells you how much draw your car is putting on the system versus how much your alternator is putting into it.

I have both in my car.

Dave's explanation in the paragraph above is the best, most clear one.

In real life, I'd take the voltmeter if I had to choose between the two. The most impt info, overall, is the condition of your charging system, including the battery. In addition, it seems like the voltmeter, to some extent, also does tell you the net draw that is being put on the battery. For example, when I turn on my AC, my voltmeter drops a bit.

All useful info to help quickly see the most common failures, particularly alternator or regulator failure.

The ammeter never moves. The only time I found it even slightly helpful was when my starter seized up. When I turned the key, the starter would not turn, but the ammeter showed a huge draw on the system.