Kensmith

Ok, I have been told the battery meter is actually a volt meter which makes sense since I never heard of a battery meter. Some refer to it as an amp meter but obviously it's not since it measures volts. So I would thing the 12 o'clock position is somewhere near 12 volt reading? Mine runs just a hair toward the right side of this position except at idle where it is pretty much at 12 o'clock and just to the left if I turn on the A/C at idle. Does this sound right? Or is straight up 12 o'clock something other than 12 volts?

62Jeff

It's measuring the voltage differential between the horn relay and the starter. Straight up 0 means the two reference voltages are the same - so the charging system is fully charged and the voltage regulator is keeping things at an even state.

Kensmith

Ok so that would indicate 12.5 volts or a fully charged battery.

MikeM

Put a hand held volt meter on your battery while the engine is running and reference your car's volt meter. Shut the engine off and repeat. Then, you'll know what it means.

Kensmith

Well, I already know the battery should hold approximately 12.5 volts and the alternator should charge at approximately 14-14.5 volts. But I'm am questioning the gauge. Want to make sure it reads correctly so if it is slightly to the right of 12 o'clock it would be showing the battery is receiving 14.5 volts and if to the left, it is being used by electrical components at a rate more than the alternator can put out to maintain 12.5 volts at the battery? A typical voltmeter gauge in modern day cars show what the alternator puts out, not the battery volts. Correct?

MikeM

If the alternator is putting out 14 volts while the engine is running, you should be able to read 14 volts at the battery cables while the engine is running. When you shut the engine down, the reading at the battery will slowly settle from the flash charge to it's true level. Or, you can turn the headlights on for a few seconds, then turn them back off and do the same thing.

When the charging circuit is working, everything in that circuit has the same voltage.

jim lockwood

Ken, what you have been told is true, but it is misleading if you don't have some understanding of electric circuits..... Corvette charging circuits, in particular.

Yes, it's a Voltmeter, but no it's not measuring the battery charging Voltage.

It is measuring the Voltage drop and polarity of the drop along a length of wire that connects the horn relay to the large starter terminal. This Voltage drop and polarity is a proxy for whether the battery is being charged and, on a relative basis, the rate at which charge is flowing into (or out of ) the battery.

If the Voltage at the horn relay is greater than the Voltage at the starter terminal, as it would be if the battery is being charged, the needle on the battery gauge will swing to the right. The converse is also true.

Jim

Kensmith

"if the battery is being charged, the needle on the battery gauge will swing to the right. The converse is also true."

Jim

Thanks Jim, that was what I was looking for.

66BlkBB

Mine reads the same as yours. It is correct. I get a little past center to the "+" side when running and right at the center mark when idling. If you crank on the starter for quite some time you will notice that as soon as the engine starts the meter will read to the "-" side for a short period of time until the battery charges up to its previous voltage.

magicv8

IMO that's correct. I haven't looked a a schematic, but thats what my new Equinox seems to do. My Sting Ray does it too, but I have installed an 8volt to 16volt voltmeter mechanism in place of the factory galvanometer.

JohnZ

It should read the other way after a lot of cranking - when it starts, the needle will go to the (+) side (indicating charging) for a few minutes, then gradually move back to center (or very slightly +) as the battery is recharged.

Bill Dearborn

What you are describing is a voltmeter being used as an ammeter. That is how all ammeters work no matter where they are used. An Ammeter is a voltmeter with a known resistance across its leads through which a current flows. I (current) =V (volts)/R (resistance). The voltmeter reads the voltage polarity and level across the known resistance and the needle moves to a certain location on the face of the meter which is marked in amps. Same type of circuit that my 69 and 71 Corvettes had. When the pointer is to the left of the 0 the battery is discharging (current flowing out of the battery), at 0 there isn't any readable current flowing and when the pointer is to the right current is flowing into the battery.

The Corvette's first use of a voltmeter as a true voltmeter was in the 77 Corvette when they updated the C3 instrument panel.

If you knew the resistance of the wire being used you could calculate the delta voltage drop across that section of the circuit by multiplying that resistance by the current reading on the ammeter. A little tough since they didn't provide a lot of resolution of the current. You are lucky you got + and - 40 amps printed on the face. That still wouldn't give you the voltage being applied to the battery.

Bill

jim lockwood

Yes, I'm fairly confident that's what I said.

Jim

mashinter

I found that the "ammeter " in my '65 (measures potential difference between the battery and the alternator) freaks out when I suck current straight from the battery for my electric fans; I disconnected the ammeter so I wouldn't fry it. I don't think an ammeter (voltmeter that indicates actual current flow through the meter; solid axles) would respond to that additional load at all.

jim lockwood

The "Ammeter" is wired in such a way that any time the battery or anything connected directly to it is drawing current from the alternator, the gauge will indicate a charging condition.

Jim

67*427

What Jim said....

If you are going to put any significant current consumers in the car like AC or radiator fans, the power for them needs to be taken from the tie point on the horn relay or the large terminal on the alternator. Then the ammeter will still read correctly.

Steve

MikeM

That goes back to what I was saying in post #4.

magicv8

IMO you guys are missing the definitions

A galvanometer (Sting Ray BATTERY meter) is a device that may be calibrated for use as a volt meter or a ammeter.

It normally measures difference of potential (volts) and can be calibrated (sometimes with a known series resistance) to provide specific volt readings. The Sting Ray version is not calibrated, and has no resistance other than the wire in the winding.

If the same galvanometer has a parallel resistance (shunt) across it's terminals it works as an ammeter. Most ammeters come with a shunt from the factory that allows the amp values to be defined and limits it range. Some suppose the wiring harness and the (often corroded) terminals of the Sting Ray serve as a shunt and make it an ammeter without a scale. Fine.

With either view, needle to the right shows higher voltage supplied to the horn relay with current flowing to the battery, and needle to the left shows higher voltage at the starter solenoid battery cable with current flowing from the battery.

mashinter

My fans pull 40 amps. No way am I going to run 40 amps through the factory wiring.

Kensmith

You could but I wouldn't turn the lights, radio, or anything else on