Alternator draing battery

robzombie

Well-Known Member
I'm having issues with the battery draining every couple of days if I don't drive the car.

There is a slight hum coming from the alt [KOEO] and I can barely hear it unless I put my ear near the alt.

I've changed alternators and still have the problem. If I unplug the field wire it stops humming and is fine when I go to start it days later. I just have to remember that I unplugged it and plug it back in which is a pain in the butt.

Is there a way that the field wire is shorting out the rectifier or something else in the alt ? The alt charges between 13.8/14.2 when running with the two alts that I tried.

Is the field wire the problem or the alt ?
 

turbo87adam

Active Member
If you have a meter that measures dc amps you can perform a parasitic draw test. Then you can isolate the problem circuit by pulling fuses or disconnecting electrical loads on your car.
 

robzombie

Well-Known Member
That would only work if I new what the draw was or wasn't supposed to be.

I could test the field wire and see what it is but would also have to know what it's supposed to put out if anything.

Thanks for the input but I think I just need to isolate that circuit.

If I'm off base on this point me in the right direction.
 

gunzandgearz

gearzandgunz
Turbo87adam is on the right track with what he said, what you can do with these older cars, not so much the newer ones as they have computers and things that stay awake for a while after key is off but with your car you can disconnect the negative battery cable and hook a test light between the cable and the negative post (key in off position), if the light is on, it should not be, start by pulling fuses one at a time and watch for light to go out when you pull a fuse (or any load under hood) might start with alternator wire since you are pulling it and it doesn't kill the battery, when light goes out that is the circuit to chase.It does sound like you've got a bad new alternator with what your explaining though draining your batt. and this trick will tell you,if you unplug it and light doesn't go out wiggle the field wire and see if it turns out test light hopfully this will lead in right direction and you can visually see with test light.
 

gunzandgearz

gearzandgunz
Turbo87adam is on the right track with what he said, what you can do with these older cars, not so much the newer ones as they have computers and things that stay awake for a while after key is off but with your car you can disconnect the negative battery cable and hook a test light between the cable and the negative post (key in off position), if the light is on, it should not be, start by pulling fuses one at a time and watch for light to go out when you pull a fuse (or any load under hood) might start with alternator wire since you are pulling it and it doesn't kill the battery, when light goes out that is the circuit to chase.It does sound like you've got a bad new alternator with what your explaining though draining your batt. and this trick will tell you,if you unplug it and light doesn't go out wiggle the field wire and see if it turns out test light hopfully this will lead in right direction and you can visually see with test light.
 

davelostmissing

Senile Member
I had/have a similar problem on my "other brand" truck. traced it down to a partial grounding where I should have had an open in the alt wires thru the ignition.
I didn't have another ignition switch but I did have a relay so I open the circuit when the ignition is off via relay. Been like that for a few years now, truck has lasted longer than expected...
 

robzombie

Well-Known Member
I had/have a similar problem on my "other brand" truck. traced it down to a partial grounding where I should have had an open in the alt wires thru the ignition.
I didn't have another ignition switch but I did have a relay so I open the circuit when the ignition is off via relay. Been like that for a few years now, truck has lasted longer than expected...

That sounds realistic to me as I know it's on a dedicated circuit and have seen a bad ignition switch do some really crazy stuff.

My diesel suburban gave me fits until I traced it to the ignition switch. Start, wouldn't start, cut off randomly, damn thing had a mind of it's own.

I will check the switch and see if that is the problem. It may be a week or so till I work on my car as I'm painting a 68 stang for a customer right now.

If I can get to it sooner I will but when I find the problem I will post it so others might not have to go through this crap!
 

czimpel

Boost...gotta get some!
I've been tracing a drain on mine. Pulling fuses didn't find it, I'm going to try the alternator.
 

robzombie

Well-Known Member
I've been tracing a drain on mine. Pulling fuses didn't find it, I'm going to try the alternator.

The fuse method doesn't always work as you've found out.

Let me know if switching the alt fixes it for you. It didn't for me but hey I might have two alts that work but have an internal short somewhere.
 

robzombie

Well-Known Member
I just checked it and no noise after plugging in the field wire from alt now.

I started it and let it run for a few minutes and checked it again. Still no noise.

It has been an intermittent problem that comes and goes.

I will have to just keep an eye on it and when it happens again I'll start eliminating things one by one.
 
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