goblinish15

So i got a new alt. Then i hooked it all in. It charged at 14.3 off the alt. and battery read the same. Then i took a drive and kept it running. I checked once again and it charged at 12.53 from the alt. and at the battery. Is that normal? i was using the heater all the lights were on, and my stereo. I turned all the accesories off. And it stayed at 12.5. Is that right? i feel like its off by 2 volts?

goblinish15

bumpage

belvedere

The 12.5 does sound low, especially with no electrical loads on. Was the engine idling? If so, what happens if you increase the rpms?

salad

12.5 is low indeed. The charging system needs to run at 14V. You've checked this with a real multimeter right?

Also +1 belvedere's suggestion. Belt re-tightened?

Firestorm500

Voltage drops as amp load increases. Ohm's Law.

I have been told that the ECM/PCM regulates alternator charging. Maybe 12.5 volts with accessories off is all your Jeep needed at the time to maintain battery charge.

mike mike

Make sure all the connections between the Alt. and battery are CLEAN and tight.

salad

Please don't randomly quote electrical laws without understanding them or the context they're applied in.

Post-Renix alternators are indeed regulated by the PCM. The Jeep's electrical system Is specified as a 14V charging system. The 6-cell 12-volt lead acid battery requires this voltage to keep a charge. Supply voltage from the alternator will not drop below the regulated level until load exceeds its nominal capacity (96 A for example)

This is always a good idea! All connectors on the alternator and the grounds should be cleaned up too.

The Rooster

just curious after you turned your jeep off and say used it today... does it still have 12.50?

goblinish15

it stays at 12.3 now. And with load it hits like 11.3. It keeps slowly getting lower and lower! connections and grounds are now all tight and clean!

Firestorm500

Either the battery is going bad, or the new alternator is defective sounds like.

The Rooster

i agree with this statement...

tjwalker

My experience is that with a healthy charging system and battery, you should see approximately 13.5 to 14.0 volts measured with a meter at the battery at engine idle.

If you WERE at this voltage after new alternator installation and you're NOT there now, the odds are high that your alternator died prematurely. It is not at all uncommon to have early death with alternators nowadays.

I'd take it off and take it back to where you bought it.

wrenchhead82

12.6 volts is the correct voltage for a fully charged 12 volt battery with no loads and the engine off. If your voltage is below 13.3-13.4 with no loads, your charging system has a problem. Your alternator is not charging at all. You are draining the battery every time you start it up. Check all your fuses, you could have blown the charge fuse. If not the fuse, recheck all alternator and battery connections. Check alternator belt. If all checks good, you most likely got a bad alternator.