Dead battery

[Butch2112]

91 Ranger 4.0 supercap automatic. Battery died I hooked a small 10 amp charger to it. Went inside to get a drink when I came back out the charger was red hot! It was connected the right way, I figuared it just died I got a new battery and installed it rane fine the first day next morning It sounded like it was a low battery but it started when I turned on the lights it died and wouldnt start is there anything other than replacing the alternator to check? Thanks

 

[engdept]

Sounds like your voltage regulator in the alternator is bad. Remove the alternator and take it to a local auto parts store to have them check it.

 

[shadetree]

You can check for a voltage drain with a common test light. Remove the negative battery cable, and connect the test light in line with the cable, one wire to the cable, and the other end of the light to the negative battery post.

Close all doors, glove compartment, unplug the underhood light, and ignition switch off. If you have a drain, the light will illuminate. Disconnect the large wire from the back of the alternator. If the test light goes out, the alternator is bad. If the light stays lit, then the voltage drain is from another source. You can then try pulling fuses to see if one of them causes the light to go out, and you can then diagnose that circuit.

It could also be that the alternator is not shorted, but isn't generating any voltage, and running the truck runs the battery down.

A check at the battery with a voltmeter across the battery terminals will tell you if the alternator is charging the battery. You should get 13.5 to 14.5 volts at idle if the alternator is chargin.shady

 

[MAKG]

Shady, it's not just an open charging circuit. The charger is also putting out far too much current. SOMEthing is shorted to ground. It can be inside the alternator, any of the hot-all-the-time circuits, any energized load, or even the battery itself.

You can test for the last one by disconnecting one of the battery cables and then trying to charge the battery again. If it still draws ridiculous current, it's fused. It can happen with very rapid discharge (such as an unsecured battery hitting the hood), or even by repeated shock.

Though I suspect it's more mundane like a "hot" cable that has fallen apart and shorted to ground.

Note that a discharging battery might take other things with it.

 

[shadetree]

Shady, it's not just an open charging circuit. The charger is also putting out far too much current. SOMEthing is shorted to ground. It can be inside the alternator, any of the hot-all-the-time circuits, any energized load, or even the battery itself.

This is not testing for an "open charging circuit," it tests for shorts. The test light will tell him this. He will do this with the charger disconnected. It's a common method of testing. If it is a large current short, there will be smoke and burning, and possibly the truck will not start. But he says he drove the truck after installing a new battery.

 

[Ranger5.0]

so, rather then use a test light today may be a good day to learn more about a multi meter. perform the same test as stated with the light but use a meter set to amps. See what kinda ampdraw there is. If its high, over one amp, then youhave huge problems.

 

[shadetree]

so, rather then use a test light today may be a good day to learn more about a multi meter. perform the same test as stated with the light but use a meter set to amps. See what kinda ampdraw there is. If its high, over one amp, then youhave huge problems.

If the test light illuminates, amp draw is too much. Knowing the exact amperage is not necessary, at this point. Normal draw is in the milliamp range, very small, not near enough to cause the lamp to illuminate. If he has a meter, and knows how to use it, it can be subbed for the light. Light is easier for initial checks. I only get the meter out for more complicated problems.shady

 

[MAKG]

Also, if it's draining as fast as I suspect it might be, a "positive" will be a loud POP and a dead DMM. Hopefully just the fuse, but sometimes a 10 cent fuse is protected by a $50 meter.

The "clamp on" types can handle more (but cost more); almost all the inline DMMs have 10A fuses.

I agree; the test light may be a blunt instrument, but it's adequate here. It can get a bit hard chasing down very small drains, but I really don't think this one qualifies.