74 CJ5 charging problem

Hi all,

IHA 74 CJ5 w/ AMC 232 in line 6. Installed a new Painless Wiring harness last year and was running great. However, in the last 4 months the battery (new) is going dead. It started when the contacts on the back of the Alternator (also new) fell off. It drained the battery. After correcting the issue and verifying there was a good charge going to the battery form the alternator (13.95 v being pushed from the alt and 12.13 showing at the batt) it was charging and running fine. However after sitting for five days it is dead again. The battery is less than a year old. The cells have fluid. The voltage regulator and alt are new. Where is the problem? Also, when I pulled the original alt last year, there was a capacitor attached on the back I was told that needs to be there. I don't remember where it connected on the back of the alt and is it necessary? This is a Motorola alt. so I do not know what each blade connector represents only that they go to the voltage regulator.

Thanks!

 

Capacitor is to prevent radio interference I believe.

Your local parts store should be able to load test the battery for you.

If you have a multimeter, use the amps scale to check if there is a drain on the battery while everything is supposed to be off. Disconnect battery, look for current between the disconnected cable and its post.

Welcome from Boston. We like pics here.

 

Ok. I have a Fluke voltmeter. It was an indispensable tool when installing the wiring harness. What amperage reading should I see when testing?

Thanks!

 

If everything is off (ie no clock, radio display, meters etc) it should be zero. I would not worry about a few milliamps of leakage, but I'd wonder where it comes from.

You can figure the time it should take to discharge the battery for a leakage of some value from the amp-hours rating of the battery. Say you have a leakage of 20 mA, and a battery of 30 A-H, then 30/0.02 = 1500 H or 62.5 days. If you can't account for the discarge due to some leakage, then either the battery is self-discharging, or the alternator isn't charging the battery.

 

Sounds like the problem is that you have too much of a voltage drop between the alternator and the battery. It could be caused by quite a few different things, but you shouldn't see much more than a half a volt drop.

 

Try reading voltage at the battery terminals with the engine off. You should see ~ 12 volts. Next start the engine and read again. It should read ~13-14 volts DC. If it still reads ~ 12 then the battery is not charging.

 

Ooh! Ooh!

Motorola alternators are notorious for popping diodes. I think there are two (full wave? maybe 4) so if you pop one, the alternator will be weak. You used to be able to get the diodes across the parts counter, but today it may be cheaper to replace the entire alternator with a reman unit ... or better yet, a Delco.

<edit> Just looked at the manual - actually there are 3 diode assys (each with 3 diodes in parallel) - pos, neg and field. You can probably get the parts, but I would dump the Motorola alternator if it were mine.

 

You are not getting correct voltage at battery for proper charge. Should be reading 14.2-14.6 approx voltage (regulated) even with headlights pulled on and at idle or above idle slightly. You indicate a near 2 volt loss between Alt output and Battery. This won't do the job. Charge the battery to full charge and install in jeep with only the Bat. wire disconnected from back of alt and let set for few days if you don't need it. This tells you all wiring in jeep is not shorted or draining power to ground. (look at alt problem) Otherwise follow Tim's and others suggs.