YJ charging problems

[JD770]

I have a good 16V give or take comming out of the alternator, and when read at the Noid on the firewall or at the battery its a litle less than 12 running.

Before I start ripping out wires and replacing them, anyone have anything sinilar happen so I can narrrow it down? The alternator is new.

[bobbo27]

I thought 12 was normal?

[White 92 YJ]

What's the condition of your battery?

[wcjp]

New doesn't always mean good. That being said have you had the battery load tested? How old is the battery. Also, the output voltage should be in the neighborhood of 14.7V. Too much higher and the battery will be damaged. The battery will continue to charge until you get around 13.3V. Lower than 13.3V the battery isn't really charging. My guess is a bad cell in the battery. The bad cell is putting quite a load on the alternator. If not taken care of soon you'll need another new alternator. The tricky thing about bad cells is they can be intermittent. They'll test ok now and bad 5minutes later. While the vehicle is turned off the battery voltage should be around 12.6V. This represents 2.1V per cell.


If the battery and alternator test ok than you're looking at a short in the vehicle. With the key turned off and all accessories and lights off pull the Positive cable off the battery. Connect one lead of your multimeter to the battery and the other to the disconnected lead. The multimeter should be set to read amperage. Amperage can only be tested in series. If everything is off the amperage draw should be less than one amp. Ideally, the draw would be less than .5 amp. There will be some draw representing the computer and clock. If the draw is any higher start pulling fuses from both fuse blocks. When the draw goes way down you've found the power drain.

[JD770]

the battery tests fine, Load tested, I Work with batteries alot so I am familiar with cell damage and the like. swapped in another battery just to be sure.

Running, the amp gauge and or load tester sould show between 13.5 and 15 volts at the battery. Mine reads 11.67.

The POS stock gauge reads just below 8.

[wcjp]

Not as common is corrosion in the battery cables. Sometimes the corrosion is inside the sheath. Check the resistance of the cables. If this looks ok reattach the cables. Use jumper cables in addition to the stock cables. The stock cables may look ok with an ohm meter but unable to pass any amperage.

Did you check for a draw and/or short yet?

[JD770]

-=- originally posted by wcjp -=-
Not as common is corrosion in the battery cables. Sometimes the corrosion is inside the sheath. Check the resistance of the cables. If this looks ok reattach the cables. Use jumper cables in addition to the stock cables. The stock cables may look ok with an ohm meter but unable to pass any amperage.

Did you check for a draw and/or short yet?

No, thje jeeps at home and I'm not.

Does the alternator run through the stock gauge and then to the battery?

[JJinVA]

What year is your YJ? Older YJ's like my 90 have fusible links on the wires coming from the alternator to the stater and battery areas. I had a similar charging issue and finally tracked it down to two fusible links that had the insulation peeled off and were corroded green. Check those. Newer YJ's and TJ's have an extra fuse box under the hood and don't have the fusible links. Mine were located under the battery at the firewall where those cables all merge on a post there.

JJ