High Ammeter Reading

[Duffman]

My ammeter is reading a constant +15 to 20 at idle or while I drive. I have a 60 amp alternator with an internal regulater and Arne's upgrade. When I turn on my afternarket AC, the reading drops close to 0, back up to +15 to 20 when I turn it off. I am thinking the installation of the AC has something to do with it, but have checked the connections and can't see anything wrong. I just installed a stereo and it doesn't seem to have any impact on the reading. Was living with this for the last 2 months, but now the battery was drained this am. Any ideas?

[DeesZ]

I was going to suggest checking the voltage regulator, but with a drained battery today, you have other things to address. A failing battery may have required all of the charging that you reported, and it finally failed. Or perhaps there is a drain that has caused a low (now dead) battery? I am discounting the stereo because you said that you "just" put it in. Simple things first: check the battery cables - are they cleanly connected at both ends, and are they in very good shape overall? Are all of your grounds good and clean? Have you charged the battery to get it up to capacity? If not, try doing so with clean connections and see what the electrical system does. If still a problem, you will have to start testing and eliminating components (or take it to a shop to have a diagnostic of the charging system performed to determine where the problem originates). Just my late-night $0.02.... I'm certain that others on the board will come up with some other great suggestions as well.

[Six_Shooter]

First thing is get rid of the ammeter, or at least don't use what it is showing you as any type of "proper" reading.

Grab a DMM, and test what the voltages are, battery, key on engine off, engine running, at the battery and the fuse panel, etc.

The ammeter can show a charge even if it's not really charging.

In my '73 it would show on the charge side, even though the voltage was barely 13V, a true charge requires minimum 13.6V on a 12V system.

[Zs-ondabrain]

First.. The stock alternator only put out 40 amps, max. The ZX internally regulated alternator puts out 60 Amps, Max. That's 15 to 20 amps more than stock. That's the 15 to 20+ increase that you're seeing. No big mystery there.

DeesZ, you can't check the VR because it's now internal. good suggestion though, on a stock 240z alternator, not the case here.

If the stereo system is fairly new to the Z, don't dismiss it. If it's a large system like mine (800 watts) a newer battery and larger power wires are almost Required. I personally run 2 gauge battery wires from the battery to the distribution block and to the ground. From there, I run 4 gauge to the starter and to the amps. GROUNDING cables are more important than most people think. Great connections from the battery to the block, frame and ground cable on the engine harness are VERY important.

I would personally enlarge the cables, upgrade the battery, refresh the grounds (clean them and make sure they are bolted down properly). THEN....

Loosen the ground terminal on the battery, remove it from the battery. wait 1 minute, make sure the doors are closed and everything is off, then slowly bring the terminal close to the battery post. Watch for even the smallest spark upon touching the terminal to the battery. If you see a spark, something is on and you need to address it. Use the old "process of elimination" by disconnecting electrical items and retest with each removal.

You can also use a volt meter between the battery and the disconnected battery ground terminal. just remember that the internal clock and memory on your stereo has a very small draw and should be ignored. Make sure the stereo and amp(s) (if any) are well grounded and powered with the proper size power wires.

Back to the original question. The ammeter will fluctuate more than before due to the increased amperage. Think of the ammeter as a mid-valve. If power is being drawn from the battery side, the meter will swing to the positive and if you're drawing from the fusebox, your needle will swing to the negative.

Hope some of this clears things up a bit.

just another 2 cents in the pot.

Dave.

[Duffman]

Thanks, John, Chris and David. As always, good insight and sage advice!

I have hooked my battery up to a charger to get a full charge and will follow thru with the above suggestions.