1996 4.0 Overcharging

[Jim Oaks]

A while back my 1996 Ranger 4.0 had a problem on the trail with the battery smoking from being overcharged.

I replaced the alternator with a used one.

Recently the problem happened again. The Ranger wouldn't restart when I shut it off and the battery was boiling from being overcharged.

It seems like there has to be something other than just a bad alternator causing this since it's happened again.

I need to figure out what it is instead of just getting another alternator and frying another battery.

Anyone have any suggestions?

 

[Jspafford]

Are you sure it is overcharging and not grounding out on something?

Have you verified the alternator is putting out the proper voltage?

The alternator is the only thing that charges the battery. The voltage regulator is built into the alternator. I would check the voltage output from the alternator with a meter both at idle and at 2K RPM. It should be no higher than 14.5 or so volts.

 

[engdept]

or just take the alternator to an auto parts store and have them test it

 

[Quiksurf]

you are missing the most important part, the alternator does not sense the volatge on the b+ feed, check for key on engine off (KOEO) battery light illumination, the check the violet/white wire a the alternator for battery voltage. if you have a lower voltage than the battery should have it will increase the feild output of the alternator creating more voltage. possibly the cause of your issue or just another junk part

 

[Will]

I agree with Quiksurf--you replaced a good alternator. The alternator is sensing a low voltage and trying like hell to charge the battery that is already charged.

On these alternators the regulator looks at a voltage at the A terminal on the alternator. That wire runs into the power distribution and probably has a 15-amp fuse or breaker. Mine is Yellow/White. Make sure your wire is intact. Read that voltage while the truck is running and compare it to the battery voltage. If it's a lot different, there's higher than normal resistance in that wire and that's a problem.

The idiot light senses voltage and it could be in the normal range and still be overcharging the battery.

This truck has a remote battery doesn't it? What did you change when you moved it? Is there a solenoid or something added somewhere?

Keep in mind this truck probably has a lot more of an alternator than TRS-1, and that 2 batteries can absorb a lot more current than one. You might not notice the overcharging with 2 batteries but one battery could quickly become fried. And with probably 2x or more the alternator of TRS-1, just because the way you have it set up on the old truck doesn't mean it will be acceptable on this one.

 

[Bob Ayers]

you are missing the most important part, the alternator does not sense the volatge on the b+ feed, check for key on engine off (KOEO) battery light illumination, the check the violet/white wire a the alternator for battery voltage. if you have a lower voltage than the battery should have it will increase the feild output of the alternator creating more voltage. possibly the cause of your issue or just another junk part

According to my schematics for a 1997, the wire from the alternator "A" terminal is a YEL/WHT, and is fused with fuse #6 (15A) in the engine compartment fuse box.

 

[Jim Oaks]

I'm set up for (2) batteries in the bed, but there is only one in there. The other is in the other Ranger.

My truck has the factory charging gauge and it's in the normal range.

My battery is dead. I didn't want to put another battery in because I didn't want to fry the only battery I have left.

 

[Will]

The alternator is fine, that's why the gauge is reading normally.

The alternator is being given a false input so it cannot properly adjust it's output--but it's not putting out a voltage outside the expected range.

It's not capable of burning up your battery by connecting it and running the engine for a few minutes. Get a real voltmeter ready, start it and test the battery voltage. It's going to read 15-16V probably because it thinks the battery is discharged. Then poke the A terminal and it's going to read something less than 13V I believe. Then turn off the truck because you know what the problem is.

Then trace that wire and see what is causing the resistance. I would unplug it, pull the fuse and put your ohmeter probes on each end. Or jump it straight to the hot side of the starter relay and start the truck again. If there is a problem, the voltage will now be very similar between the A and the B+.

 

[Jim Oaks]

Ok.

I replaced the voltage regulator. No change.

I checked the 'A' terminal. It has 12 volts and there isn't any loss through the line with an ohm meter.

 

[Will]

12.0v with it running? What was the output to the battery with it running? How different were they?

 

[Jim Oaks]

Alright.

I'm starting to think this alternator is putting out exactly what is suppose to.

According to my Chiltons book, it should be putting 14.1-14.7 volts out at the battery when it's running.

I didn't check the 'A' running.

 

[Will]

I just started mine and I got 14.6 off both. I would run a jumper right to the terminal if you can and see. Poke a jumper wire right down in the back of the connecter on the alternator.

 

[Bob Ayers]

Alright.

I'm starting to think this alternator is putting out exactly what is suppose to.

According to my Chiltons book, it should be putting 14.1-14.7 volts out at the battery when it's running.

I didn't check the 'A' running.

Put a UDP on it Jim, that will bring that charging voltage down!!

 

[Jim Oaks]

OK!

Back to the original problem.....

The battery was boiling and went dead from what I thought was overcharging. Could the battery have taken a dump from all the vibration being shook around off road? The battery is 8-years old.

 

[Bob Ayers]

OK!

Back to the original problem.....

The battery was boiling and went dead from what I thought was overcharging. Could the battery have taken a dump from all the vibration being shook around off road? The battery is 8-years old.

Either that, or you developed a "short" somewhere in your electrical system, and the battery was boiling from being discharged.
8 years out of a battery is outstanding!