Voltage Meter Questionable?

I've had my HMMWV for less than a week now and am curious about the gauge indicating the health of the charging system. When I got the truck the gauge read about two needle widths into the green when running down the highway (just north of yellow).

It seems to be about one needle width in now (but I'm not burning down the highway either). When first starting the truck the needle is at the high end of the yellow. Under load it moves to the green.

The alternator is a 200Amp model installed recently. What should I be looking for? Is this potentially just a calibration issue?

Thanks,

Michael
aka - Heavydrop (ask me to explain when you get an extra 10 minutes)

First, have your batteries load tested to see if they are good, bad, or ugly.... The gauge could be 100% dead accurate, and your batts are not functioning properly...

Aha - and the learning begins! Thanks Emmado!

ya. grab a DVM(voltmeter) and check out whats really going on. you should see your voltmeter swing for about 30 seconds after a cold start. that indicates your glow plugs cycling after startup.


If you really do have low voltage and it's the alt causing it you might can adjust it. I've got the 100A on my hmmwv and mine's not adjustable. the 60's are so maybe the 200's are too. I've got one here but I've not yet installed it.

You also want to be sure you have the additional grounding harness as the hmmwv's have had issues with grounds not being very good.
Basically you want to add a #8 from the alt to the PCB to the rear of drivers cyl head then down to the starter then to the battery.

If the voltage meter is properly calibrated and your charging system is adjusted properly, then the needle should be right on the little tick mark in the green zone once the engine is warmed up and the glow plug system stops cycling. I don't think there's any adjustment available on the panel voltmeter, though, so I heartily agree with the suggestion of using a good digital voltmeter (DVM) to verify and adjust the charging system voltage.

By the way: on at least some alternator designs, the adjustment screw is HOT with respect to ground! Since this screw is generally accessed by removing a pipe plug and then inserting a narrow screwdriver blade through a hole in the grounded metal alternator housing, you should wrap the screwdriver blade with electrical tape to avoid shorting stuff out.

Charging system ranges on gauge.

From that label, it should be in the middle of the green when running, checking with a voltmeter should give you ~28v.

FYI: check with a good meter....every truck I have owned appears to read high on the dash gauge....slightly into the red. You will also get the pulse (as noted) from GP cycling- Sometimes up to a couple minutes depending on which control box you have.