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I've noticed in my '69 Z28 that my battery gauge is doing something lately that I haven't seen it do before and was wanting to know if there could be a problem starting to happen. Each time I start the car the needle on the gauge goes to the 3/4 mark then about five seconds or so later it comes down to about the second little mark to the right of the middle mark. This is where it stays and it doesn't go back where it was until I turn it off and start it up again. I may be wrong, but I was thinking that a couple of marks to the right of the middle was normally where it should be under normal driving with no lights on or anything. Can anyone explain what could be happening and if there's something I can check? Thanks, Donnie...
 

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Mine goes up to the 3/4 mark right after starting and then comes back down to about 1 mark to the right of center within a minute or so, and then stays there as long as the car is running. Doesn't seem to matter much if the lights are on or not. Even though the gauge is labeled as an ammeter, it isn't one. It's a millivolt meter designed to show the direction and magnitude of current flowing in the No. 10 AWG wire between the battery and the horn relay terminal. As long as you alternator can keep up with the cars electrical load the meter should be pretty stable with a slight amount of current going to charge the battery. It shouldn't really matter if the lights, and heater and wiper are running (except at idle or slightly above) as long as the alternator is in good shape as all of these loads are powered directly from the alternator.

Of course if you've added loads directly to the positive terminal of the battery (like an amplifier or electric fan) then more current will flow towards the battery and the meter will read more of a charge (needle towards the right) being supplied to the battery to keep it at 12V.


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Mark Canning
1969 Indy Pace Car
350/300HP RPO Z11
My 69 L48 - 350/300HP Engine


[This message has been edited by Mark C (edited 04-30-2002).]
 

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Discussion Starter #3
Mark, Has yours been doing this for a long time and never noticed any problems? I was thinking of a couple of things I have done to my car lately that could have caused this to happen, but I'm not sure. The only things I have done lately is replace the low fuel indicator, which is working fine, and disconnected the wires on my column that control the backup lights and ran the wires to a toggle switch. I disconnected the toggle switch and hooked the wires back at the column thinking that was doing it for some reason but it didn't make a difference. I guess as long as it's coming back down where it should be maybe it'll be alright. A friend of mine that rebuilds alternators said it wouldn't be good if it stayed on the 3/4 mark all the time because then it could be over-charging possibly. He also said that I could be having a problem with my voltage regulator. If yours has been doing this and you haven't had any problems, then hopefully mine will be alright also. Thanks, Donnie.
 

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Mine has done this for as long as I can remeber. These gauges are not know for their accuracy, or being able to compare one to another as they are made up of commercial parts with 5% tolterance components. The biggest variable with this circuit is the #10 gauge wire run between the horn relay and the positive terminal post in front of the battery. This is because the gauge is actually measuring the voltage drop through this wire from the horn relay to the battery caused by the current flow in the wire. An increase of .001 ohms will affect the meter reading quite a bit. If you have a #12 wire, or if the #10 is old, or if the terminals are dirty and corroded you will get a higher resistance thru it, and a larger swing of the ammeter needle for the same current flow in the wire because the resistance of the wire is slightly higher. These gauges are only meant to show charge or discharge, and give a relative idea of the magnitude of charge or discharge, not to be able to tell that you have 2 amps or 3 amps going to or flowing from the battery. In otherwords they are better than an idiot light but only marginally.

As long as the gauge indicates from center to the right of center, and your battery voltage doesn't exceed 14.5V with the car running I wouldn't worry about over charging the battery.

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Mark Canning
1969 Indy Pace Car
350/300HP RPO Z11
My 69 L48 - 350/300HP Engine
 

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I'll concure with Mark on this. Mine (after resolving all other charging problems) swings to the right when starting and takes about 30 seconds to find itself leveled out kust to the right of straight up. It does it just a bit more if the car has sat a couple weeks between starts.

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...Dennis
"The '69, the '96 & the club"
 
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