Charging System Problems

[1980_Cj7]

Since we redid the alternator mounting the other night, the alternator doesn't seem to be putting out. The voltmeter has dropped as low as 10 volts, but most of the time runs about 12 volts. The weird part is when the Jeep is sitting idling, the voltmeter kicks up to 13 volts, but when you are running down the road, it drops back to 12.

We stopped at and Advance Auto (I know, not the best place, but the only place open) and had them hook up their diagnostic equipment. They said the battery is good, although low on charge, and the alternator seemed to be working, but was only putting out 28 amps at idle, and it dropped down to like 18 at 2,000 rpms. Same with the voltage, it drops off at higher rpms.

The alternator is a new Powermaster. The test tag tag says 104A at idle, 152A at highway speed, and 14.8V. The good thing is it is still under warranty. I was worried because the Jeep has been sitting for 10 months with all our engine problems, but it's good til 8/11/07.

I did some tests that were shown in the paperwork that came with the alternator. One was checking voltage between the alternator case and the negative battery post. It says if you get more than .1 volts, it's a bad ground. We got .24 volts. But, I held a temporary jumper from the negative battery post to the alternator case, and the output on the voltmeter didn't go up, but stayed at 12 volts.

Oh yeah, double belts and they are plenty tight.

Any ideas?

[82Waggy]

http://oljeep.com/gw/alt/edge_Alternator_Theory.html

[jeepsr4ever]

You will have 3 wires coming off your alternator. 1 is brown and goes to your charging guage and the other two go to your selenoid. If these wires are broken or not connected then thats the issue but if they are fine then its your alternator.

[1980_Cj7]

We slow charged the battery overnight, and changed nothing else, and now the alternator is putting out 14.8 volts.

Don't recall anything, like the lights, being left on that would have drained the battery. It's a fairly new Optima yellow top. Guess we'll just keep our eye on it and see what happens.

Love the Taurus electric radiator fan, and it's working great, but it sure is an amp hog. Wondering if that has anything to do with it. It continues to run for a good while after the engine is shut off.

[82Waggy]

We slow charged the battery overnight, and changed nothing else, and now the alternator is putting out 14.8 volts.

Don't recall anything, like the lights, being left on that would have drained the battery. It's a fairly new Optima yellow top. Guess we'll just keep our eye on it and see what happens.

Love the Taurus electric radiator fan, and it's working great, but it sure is an amp hog. Wondering if that has anything to do with it. It continues to run for a good while after the engine is shut off.

As you probably read in the link I posted above, if there is not enough battery voltage available to excite the alternator coil it will output nothing.

Sounds like the fan running after engine shut down is the likely culprit - bringing your battery voltage down too far.

You might consider wiring in a relay so that the fan is shut down with the ignition off. I know electric fans in newer cars are thermostatically controlled and continue to run after engine shut down but since the engine circulating pump is not running I'm not sure what the benefit of this really is - other than maybe helping to keep the paint from blistering off the
hood.

Or, install a higher Amp Hour capacity battery.