amp gauge reading

[GMCMAX]

Any one have an idea why the amp gauge barely shows charge even with a partly low battery? This is on my neghbor's 68 K20. The battery is fresh, the alternator and reg were replaced for a different reason, have checked the 2 fuses on the fenders. If you watch closely when it starts it shows barely towards discharge, then barely moves to charge when it starts, my 68 sometimes goes halfway to charge side after it cranks and starts, why the difference? His truck looks showroom fresh, been restored, and this gauge really drives him nuts, so I told him I'd ask (can't get him near a computer).
Sorry for the run on, thanks, Max

[pjmoreland]

I don't know if this is correct, but based on looking at the wiring schematic it appears to me that the amp gauge indicates whether current is flowing from the alternator to the battery (needle deflects to the right) or whether the voltage regulator has shut off the alternator, and current is flowing out of the battery to power the electrical system (needle deflects to the left).

I just replaced the two fuses in my harness last night and the needle moves about half way to the right for just a moment after I start my truck, and then it moves back to just barely to the right of center. If I turn my engine off, but put the key in the "on" position, the needle points slightly to the left.

I think when the needle is pointing to the right, it indicates that the alternator is working to charge the battery. When the needle points to the left, the alternator is not charging the battery.

[GMCMAX]

Anyone know what makes this thing tick?

[roger0080]

You should see more activity on the amp guage other than it ever just moving a hair either way.

I have had trucks over the years that the amp gauge worked correctly, others just as you describe it.

It is "normal" after startup to see it move to the right a good part then snap back to just right of vertical.

If the battery is low on charge/not holding a charge the amp guage should move to the first mark to the right at least while running.

If the battery is discharging, like your altenator belt broke and you are driving with your headlights on, you should see it discharging to like the first mark to the left. This is what tipped me off that something was wrong and when I looked -- the altenator belt was gone!

I don't know how to test the guage itself. I'ld try looking at a guage replacement if you are sure of the correct wiring, no fuse problems, circuit board problems.

[Robert1970C20rstbukt]

I kept trying to get the ammeter on my truck working for months. Turned out a wire had been pinched for years and finally corroded in half. Put a new piece of wire in there and it worked. When I start the truck, the needle drops about halfway to the left, and when the engine cranks up and the alternator starts charging, it jumps way over to the right and moves back to the left, and stays about 1/8" to the right of the center. One thing he might check is if the bulkhead connector for the gauge cluster is pushed in all the way and making good contact. If the gauge does move, it's probably something else and not the gauge.

[GMCMAX]

Thanks

[KFreddy]

Amperage is a measurement of "rate" or "drain," the amount of energy being used from the battery.

Wattage is this "rate" converted into output, ie headlamps, car stereo, windshield wipers.

Voltage is available constant, or force.

The conversion is simple;
watts divided by volts = amps (55w/12V=4.58A) or
amps * volts = watts (4.58A*12V = 55w) or
watts divided by amps = volts (55w/4.58A = 12v)

The lower your battery is the more the "drain" or the amperage will be. A 12 volt battery powering 55watt headlamps will "drain" 4.58 amps, same battery at 9 volts with 55watt headlamps will "drain" 6 amps, same battery at a proper 14.3v will draw 3.8 amps. As you can see the higher the voltage ie, a well operating charging and battery system places the least amount of "drain" or strain on the electrical system. Hence you will see only small variations of needle movement on an amperage gauge if the system is up to snuff.

To better see the effects of amperage; turn on all the accessories in your truck then lastly turn un your hazzard lamps, you will certainly see your amperage gauge keeping pace with the hazzards, then turn off all of your accessories but leave the hazzards on, the amp needle will barely move. If your also have a voltage gauge or a multimeter you will notice that the voltage will remain constant or close to constant when you do this. If your lucky you might even blow a fuse or fry an old wire or two... On second thought don't do this test, I don't want to feel guilty for someone having an electrical fire

The best indicator of your battery is a voltage gauge, the best indicator of the alternator or charging system is an amp gauge... They tell you different things.


-Fred
"The Great State of Florida"