Voltmeter or Ampmeter

One of todays posts motivated me to ask this question.If you could only have a voltmeter or a amps gague on your dash what would you pick? and why. Myself voltmeter no question

I think a voltmeter is best also. It is easier to install and you can see how well the battery is doing.

Agreed. A voltmeter can tell you if your battery is charged or not. A reading of 13.5 to 14.8 or else an upward trend to those numbers after starting or idling in traffic is good to see. A varying voltage reading under various conditions requires interpretation from the driver and not all can deal with this so we have ammeters and red lights.

Disagree. An ammeter will show you the condition of your battery. As batteries age, they begin to draw more current even when fully charged. As this amperage increases, the closer you are to needing a new battery. A volt meter won’t tell you that you need an new battery until you can’t get your car started. As far as I’m concerned, a voltmeter is pretty useless.

I choose the ammeter. A battery near the end of its life should still give you about the same voltage readings as a fresh battery.

I’d like to have both, as a voltmeter can help gauge the alternator’s performance while an ammeter can tell you how the battery feels. Both together give a pretty good picture as to the health of the electrical system, and one may indicate a problem where the other might not.



I agree with the conclusion of the article at this link, but if their ammeter requires you to route the full current flow from the alternator through the dash, it is a pretty funky ammeter. The field sensor should be under the hood, with just a signal wire from the sensor back to the gauge in the dash.

ampmeater to verrify the state of cc in your batt.

I’ll take the voltmeter every day of the week. Besides, there’s enough wiring inside the dash without running a couple of high current leads in there also.

volts follow amps.

resistance changes amps,and in the end the voltage changes also.

so voltage gauge.

‘resistance changes amps,and in the end the voltage changes also.’

This is defeated by the voltage regulator. As the amp load changes, the voltage regulator will adjust to keep the voltage flat. I like to dual gauge idea.

Not under load. A voltmeter will show the voltage drop.

just as I stated.

RE-READ slowly.

thanks anyway.

for your knowledge of the above stated .


yes I understand the diode ripple ,but not common,and was a great way to sell a ridiculous tool for 4k.

paper or plastic sir?


OHMS LAW,refresh your mind.

Ohm’s (so-called) Law does not apply here. We are talking about a voltmeter to measure the voltage across the btty and/or a current meter to measure the current into (or out of) the btty. The relationship is not linear. There is no “resistance”; indeed, the ideal btty would be a constant voltage no matter what the current.

In case anybody is thinking about the btty’s “internal resistance”, that is only an approximation of the change in btty voltage that will happen for moderate changes in btty current. The internal resistance varies with the current. Again, it’s not linear and Ohm’s (so-called) Law does not apply.

(In fact, although Ohm’s Law applies for many conductive materials for wide ranges of currents and voltages, it is only an approximation.)

Can we draw a conclusion about alternator output if we are able to maintain a voltage reading (13.4v-14.1v) with all accesories on and 1500rpm. What I am getting at is with a voltage gague we can make conclusions about alternator output (in amps) not a max figure,just adaquate or not

I vote for battery light. As long as the alternator’s charging, why does the driver need to know volts or amps?

 "Ohm's (so-called) Law does not apply here. "

You do not understand Ohms Law. It always applies and it is not an approximation. There are just a lot of variables and unless you understand all of them, you will have problems with Ohms Law.

So the answer is no or yes. Can we draw conclusions about alternator output if battery voltage is maintained above a “working” level? I reviewed my charging system texbook. What my earlier post described is a loaded charging system test It states at 2000rpm with all accessories on output should be about(their words)0.5v above battery open circuit voltage,system pass. What part of "Not understanding Ohm’s Law are you getting at.Stupid people are the ones that dont ask questions.I think that what is going on is some people are basing their response on being able to determine battery condition and some are responding in regards to alternator condition. For me I determined battery condition with a load test a conductance test and in an earlier era a specific gravity test.I dont expect to be able to draw a CCA based upon an ampmeter reading,but maybe you can. I’m listening

I understand Ohm’s Law perfectly. But, in the dynamic operation of the car, neither the Voltage, Amperage, or Resistance is a constant. The voltage regulator manages the POWER delivered from the alternator by dynamically changing it’s internal resistance to maintain the voltage. As the power demand increases, the amps being delivered increases, but the voltage regulator keeps the voltage within a tight range by changing it’s internal resistance. You do notice a flick in the needle when a high-powered load is turned on, but this is a slight delayed reaction of the voltage regulator. Using this method, the battery is simply another load-demand on the system, no different than the headlights. The volt meter tells you nothing about the state of the battery.

The ammeter is attached between the charging wire from the alternator, and the top post of the battery. It specifically measures the amps flowing either to or from the battery. This monitors both the battery and alternator by showing the overall power flow in the charging system. If the battery is in a constant state of charging, then it may be bad. If it is in a state of discharge, then the alternator is bad. If it is in a state of charging when first started, but moves to the neutral position, all is fine.