Alternator help

[hudlow]

I've got a little probelm with the electrical system on this old Jeep truck (pictured left) that is beginning to get me riled up.

First, I know my alternator is good. It's been tested several times. I've tried 2 different Voltage regulators and get the same results.

Here's what's up...My battery is losing it's charge overnight. The truck will not crank in the a.m. after I park it for the evening.

There are two wires coming off the back of the alternator. One is the big wire that charges the battery. The other is a smaller wire that goes to the voltage regulator.

1.) I have figured out that if I unhook the smaller of the two wires from the alternator when I park it for the evening the battery will not die overnight.

2.) If I do not hook this wire back up when I crank the truck the next day the alternator does not charge the battery and also the ammeter does not work.

I know this smaller wire reads to ground but for the life of me I can't find the short.

It's driving me nuttier.

I have figured out a work-a-round. I've bought a relay that I'll put in line with the smaller wire that I'll run through a set of N/O contacts and energize the coil when the truck is running. Then the contacts will close and the smaller voltage regulator wire will charge the battery and the ammeter will work. When the ignition is turned off the contacts will open back up and stop the battery drain.

I'd rather fix the problem instead of putting this relay in.

Does anyone have any ideas?

I thought about putting 110v. to the wire just to see where the smoke came from and find my short that way.....but I was real mad and slightly drunk at the time I'm not going to do that nor do I advocate anyone else do it, although.....

Any suggestions or condolences will be appreciated.

hud

 

[DieselPower]

For starters do you have a multi-meter?

 

[hudlow]

For starters do you have a multi-meter?

Yes.

hud

 

[randy41]

this aint gonna help you but my son had an old crown vic and he had to disconnect the negative terminal after driving. we tried to find the cause to no avail. he sold it for a little cash and an electric guitar.

 

[hudlow]

this aint gonna help you but my son had an old crown vic and he had to disconnect the negative terminal after driving. we tried to find the cause to no avail. he sold it for a little cash and an electric guitar.

For an old Les Paul or Strat I might let this Jeep go......

hud

 

[Jimbrown]

Wild guess but. Alternators have to have diodes somewhere in the line to rectify the AC to DC. If one of those diodes is going bad it will allow the curent to flow back into the alternator. So the alternator may check good and produce current but a bad diode will short to ground.

 

[hudlow]

Wild guess but. Alternators have to have diodes somewhere in the line to rectify the AC to DC. If one of those diodes is going bad it will allow the curent to flow back into the alternator. So the alternator may check good and produce current but a bad diode will short to ground.

Thanks for the guess and it was a good one.

I've had 3 different alternators on this truck and I'm hoping my luck isn't bad enough that the diodes were bad in all 3.

I guess to be sure I could physically remove the alternator from its mounts and see if I read voltage from the alternator casing to ground?????

Thanks,

hud

 

[BillyP]

Wild guess but. Alternators have to have diodes somewhere in the line to rectify the AC to DC. If one of those diodes is going bad it will allow the curent to flow back into the alternator. So the alternator may check good and produce current but a bad diode will short to ground.

I ran into that very problem on a 71 Ford LTD. As soon as you turned the key off, the alternator light would come on. Start it up and the light would go out. Bad diode.

 

[gator]

Had a problem like that on a 73 Ford F100 P/U. Ended up being the old points type voltage regulator had a couple of contacts stuck closed. Father in law mentioned to check if idiot lights on dash and gauges still register after key shut off. Sure enough did and after replacing voltage regulator no more dead battery.

 

[czechsonofagun]

There are multimeters capable of meassuring the current. I got mine from sears and it has the claw to clamp on the wire to see how much runs in it. I would get one of those and check where the amps are going over night.

Maybe a big strippers party?

 

[RonMar]

It sounds like you have something draining the battery. The clamp on or inductive pickup meters are not all that great at checking low currents. Most multimeters can measure small currents far better, but you must place them in the circuit. IE: With everything turned off remove the negative battery connection and with the meter set to read current(usually requires shifting the test leads to a different port on the meter) connect one lead to the now free negative cable connector and the other to the negative post on the battery. DO NOT turn anything on or try and start the engine. This may pull more current than the meter is capable of and blow an internal fuse in the meter. If it is a mechanicle meter(has a needle) you may have to swap the test leads to get the meter to move in the right direction(a digital will just read a negative number if connected backwards)

Now, while checking the current being drawn thru the meter, start removing the fuses from the fuse block on by one and checking the current draw. you are looking for the circuit that is pulling the current. IF you pull a particular fuse and the current stops being drawn, that is your troublemaker and you need to follow the wire to whatever it powers looking for loose and corroded connections and breaks in insulation that may be allowing current to complete a circuit and discharge the battery. Modern vehicles will always have a small current draw feeding the ECU and a clock and stereo if installed. I am not specifically familliar with your vehicle wiring. The alternator excitation/regulartion circuit may go thru the fuse panel or it may not. If you pull ALL the fuses and you are still loosing current, follow the positive battery lead(or leads)and start breaking connections along that wiring such as to the regulator or alternator till the current draw dissappears. This should lead you to the offending circuit.

Good Luck and NO arc welding!

 

[jdbower]

If you give up, I've been tempted to get this for some of my seldom-used vehicles:
Griot's Garage 1-800-345-5789 - Accessories

There are also cheap manual disconnects you can get that make the job faster and tool-less:
Griot's Garage 1-800-345-5789 - Accessories

Good luck in your quest, finding random current drain is always a painful search but RonMar's suggestions are a good way to start to isolate the problem.

Good Luck and NO arc welding!

Awww, what fun is that?

 

[hudlow]

It sounds like you have something draining the battery. The clamp on or inductive pickup meters are not all that great at checking low currents. Most multimeters can measure small currents far better, but you must place them in the circuit. IE: With everything turned off remove the negative battery connection and with the meter set to read current(usually requires shifting the test leads to a different port on the meter) connect one lead to the now free negative cable connector and the other to the negative post on the battery. DO NOT turn anything on or try and start the engine. This may pull more current than the meter is capable of and blow an internal fuse in the meter. If it is a mechanicle meter(has a needle) you may have to swap the test leads to get the meter to move in the right direction(a digital will just read a negative number if connected backwards)

Now, while checking the current being drawn thru the meter, start removing the fuses from the fuse block on by one and checking the current draw. you are looking for the circuit that is pulling the current. IF you pull a particular fuse and the current stops being drawn, that is your troublemaker and you need to follow the wire to whatever it powers looking for loose and corroded connections and breaks in insulation that may be allowing current to complete a circuit and discharge the battery. Modern vehicles will always have a small current draw feeding the ECU and a clock and stereo if installed. I am not specifically familliar with your vehicle wiring. The alternator excitation/regulartion circuit may go thru the fuse panel or it may not. If you pull ALL the fuses and you are still loosing current, follow the positive battery lead(or leads)and start breaking connections along that wiring such as to the regulator or alternator till the current draw dissappears. This should lead you to the offending circuit.

Good Luck and NO arc welding!

Thanks for your help.

I'll follow the advice you have given me to see if I can find the bad circuit.

I'll try to get a progress report when I have a chance to work on my old truck.

Again...thanks!

hud

 

[hudlow]

If you give up, I've been tempted to get this for some of my seldom-used vehicles:
Griot's Garage 1-800-345-5789 - Accessories

There are also cheap manual disconnects you can get that make the job faster and tool-less:
Griot's Garage 1-800-345-5789 - Accessories

Good luck in your quest, finding random current drain is always a painful search but RonMar's suggestions are a good way to start to isolate the problem.



Awww, what fun is that?

This truck doesn't get driven very often. It's just a project, more or less. But it's a pullin' 4x4 gas hog son of a gun if I need it.

I do like the looks of that manual disconnect, for my problem and because I leave this truck in some not-so-secure places sometimes.

Maybe just a little welding.....?

Thanks for your help.

hud

 

[tommu56]

I suspect a low current drain my wifes Wrangler had one (turned out to be under hool light)
I would pull all the fuses in fuse block and leave it set if it still has the problem it is in the un fused curcuits. its ok with fuses out put one back in at a time till you find curcuit.

The other way to do it is remove battery lead off battery put fuse holder ~5 amps in line then multi meter set up for dc amps. If there is a current draw pull one fuse at a time till it go's away. Then you have to find were the load is on that curcuit. The fuse in line limits the current to meter to save it.

tommu56

 

[pappy19]

If you need questions answered regarding alternators or starters, call the guys at DB Electrical. They also have the best prices around.


DB Electrical - Alternators, starters, generators and electrical parts

 

[George2615]

Ron's info is very helpful. You could also use a 12V test light between the disconnected negative post and the battery. If you have something drawing power the light will be lit. Then start pulling fuses until the light goes out. Another thing to check is the top of your battery. If the top is not clean you can have voltage leaking across the top of the battery. To test, take a DC volt meter and hold the negative black lead to the negative terminal. The touch the red lead to any spot on the battery surface. If you get a reading you have voltage leaking across the battery top. Clean or neutralize with a mixture of baking soda and water then hose off.

 

[Shimon]

Leave the small wire attached (key switch off) and see if the alternator gets warm (make sure it's cold before you start) and also see if the alternator is magnetized (put a screwdriver near the pulley nut). If it's magnetized then the alternator is being energized by the voltage regulator when the key is off so you need to find out why...bad regulator? or miswired? If the alternator is warm then you have a blown diode which can drain the battery (producing heat). You can also run the truck and test for AC ripple voltage at the battery post on the alternator. Anything over about 1V AC also means blown diode. How did you test the alternator and voltage regulator?

 

[hudlow]

How did you test the alternator and voltage regulator?

I've used 2 different voltage regulators with the same results - again I'm hoping that both are not bad.

The alternator(s) was tested on the vehicle at two different auto parts stores with their roll out battery charging tester machine they all seem to have.

They said it was OK.

hud

 

[Shimon]

Did this problem just show up? Did it always do this? Was any wiring changed or messed with prior to this problem?

Since you said the problem goes away when disconnecting the small wire from the alternator it sounds to me like the alternator is being energized by the voltage regulator (field/excite wire) or a diode is blown (did you try an AC ripple voltage test like I posted below...what was your reading?)

What year is the vehicle? Does the voltage regulator look like any in these photos: link? It could be that the key-switch wire which turns the voltage regulator on could have constant 12v on it instead of 12v with the key-on-only. If you have 4 wires on the voltage regulator: one should go to the alternator (that small wire), one should be a voltage sense wire (goes to a battery terminal or post), one should be ground and the last should be the "turn-on" wire from the key-switch. If you can figure out which is the last wire then see if it has constant 12v with the key-switch off. Or it may be reversed with the voltage sense wire. If you could take a photo of the voltage regulator and wiring that may help.