Amp Gauge 'Adjustable'?

[Alpine 1789]

...If anyone cares, SS does sell a voltmeter that more closely matches the rest of the gauges.

I never noticed that Rick had one, but one of the TEAE members sells a very close voltmeter for $105. http://teae.org/forum/viewtopic.php?f=9&t=3206 I bought one of them for my SV (he also has a SIV version) and the only difference I can see is that the lettering is a little heavier than the rest of the gauges; almost like Bold vs. a normal font. I doubt I will ever notice the difference going forward.

 

[Jay Laifman]

Two things.

First, on re-reading Tom's longer email, I see that I missed what he said about the ability to read a voltmeter.

Second, putting my money where my words were, I bought the voltmeter. Thanks Jim for the reference. So, now I will need that training on how to read a voltmeter better.

 

[RootesRacer]

Guys, the ammeter is very simple. As Mike Hartmann noted (assuming the ammeter is wired in correctly) simply shows the current flowing into or out of the battery, except it does not show current going into the starter.

With the key off, ALMOST no current is going to or from the battery. But note that there is possible current even when the key is OFF. Anything connected to terminals 1 or 2 on the fuse box are NOT wired thru the ignition switch. That means the headlights and taillights, and Map light as well as likely the clock, radio, or other accessories could be drawing current even with the key off. I believe the negative reading that Mike sees when all is off is simply a mechanical offset in the pointer. He can easily verify that by disconnecting the battery and confirming that it still read slightly neg. But if there is a difference between battery disconnected and key off then he can be sure that there is some small current actually flowing out of the battery even when the key is OFF-. Clock? Radio? Some keep alive circuit in the radio? Alarm?

Either an ammeter or a voltmeter can be used to monitor the battery and charging system. I see no difference in capabilities that makes one better suited for Alternator vs Generator. For some people, the ammeter is better: simpler to interpret - if the gauge is reading Plus you are charging and if reading Neg you are discharging the battery. But the biggest point against an ammeter is that if it fails into an open circuit you lose all power. For some people the voltmeter is better because it is in parallel with the battery and if it fails open it simply stops telling you about the system but does not disable the power. But the interpretation of the state of your charging system is a bit trickier with a voltmeter as you need to understand what level of voltage it SHOULD show under various charge conditions.

Tom

Just read this Tom, wish I had read this before I wrote nearly the same exact words...

With regards to (if it fails open), how about opening the ammeter and removing the shunt, install an equivalent shunt right at the solenoid then using smaller gauge wire, reconnect the shuntless ammeter across the remote shunt.
All the functionality of the ammeter system without the liability and fire hazard of pushing 100% charge current through the firewall and out again.

 

[Tom H]

Jay said:

So, now I will need that training on how to read a voltmeter better.

Paul wrote a pretty good explanation below:

For most of us it will be a reading around 13.5 or 13.6 volts after startup. The following is from GM:

"Cold, the alternator puts out 14.7 volts and because of the 0.3 volts drop across the ignition switch contacts, the dash voltmeter will read 14.3 volts. As the alternator gets warm its output drops 1 volt to 13.7 volts and the dash will read 13.3."

As long as your voltage reading is around 13v or higher your alternator/generator is charging and your system is functioning as it should. If while the engine is running the voltage drops below approximately 12.5v the charging system should be checked.

 

[Tom H]

Rootes said:

With regards to (if it fails open), how about opening the ammeter and removing the shunt, install an equivalent shunt right at the solenoid then using smaller gauge wire, reconnect the shuntless ammeter across the remote shunt.
All the functionality of the ammeter system without the liability and fire hazard of pushing 100% charge current through the firewall and out again.

That's a possible solution. In fact I think that is how the ammeter in my 1981 Dodge van worked. I think it may have actually used the resistance of a fusible link as the shunt. It was not a very accurate ammeter, but that's not really important, as all you really are looking for is Plus or Minus and a little or a lot.

The difficulty in trying to do this on our Alpines would be twofold. First, finding an "equivalent shunt" is difficult. You'd want a shunt resistance of about 0.010 Ohm, or less. Yes, that's 10 MILLIohm!, and even with that small a resistance you still lose 0.3 V from the charging system when it is putting out 30 A. Second, I don't think you could use the stock Alpine ammeter with an external shunt. In looking at pictures others posted on this thread, I am 95% sure that the "shunt" in our ammeters is actually a short loop or two of heavy copper wire that actually provides the magnetic field to move the needle.

Looking at the design of the Alpine ammeter, I am pretty confident it will not fail, so I will stick with stock! But a voltmeter is also OK.

Tom