Can Alternator Cause Battery Drain?

Yes, it's possible that a marginal diode can cause battery drain. I think your idea of pulling fuses is a good idea. Connect a meter to to the battery to measure current, determine how much draw there is, then start pulling fuses, one at a time.

Note that stereos with clocks will always draw some power, as will an alarm system. Be careful what you disconnect, since some alarm systems need a complete reset if power is lost. The ignition / fuel management systems on some vehicles are also affected by power loss. Check your owner's manual first!

Alternator Draining Battery

the surge when shifting into drive sounds like an entirely independent problem. Often this can be caused by low Automatic Transmission Fluid. If it hasn't been run in a while, it takes a second for it to heat up so it fills the torque converter completely. Before it lurches, it probably seems like it's needing to have high RPMs to go a low speed. If it makes a really loud slamming noise, it's possible something in the transmission itself is a problem, but usually it sounds more like grinding, as if the gears didn't quite catch. If the car starts, runs and has 14.x volts on the battery, then your ground isn't a problem. Make sure though you have the actual ground strap grounded to the car. Occasionally the positive cable to the starter is wrapped in black which can lead to problems and a shortly dead battery if you ground it to the chassis. But that's probably not the problem for you. Like other people have said, short circuits can cause a rapid battery drain. If you're leaving it for a week and the battery is dying, I wouldn't worry too much. The car I'm working on right now, (1986 BMW 325e with 1991 525i engine) loses enough power over the course of a week if it's not run so that even the electric locks don't work, much less start. My friend's 1989 325is seems to run dry fast too. Point is, some cars just are big battery wasters and if you don't drive it often, it'll lose its charge surprisingly quickly. Hope I've been helpful, and good luck solving your problem!

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RE:

Can Alternator Cause Battery Drain?

Hi my first visit

I have been having problems with battery drains lately. Overnight the voltage of my car battery drops from 12.4 to 11.8 and if I leave it more than 3 days it will not start (11.5 to 11.2). On idle and load it is near 14.2. So I feel alternator is charging well.

I am...

full charged battery's are 12.4- and up not 13.8 only, that guy sounds like a rude know it all. and yes it can, there are allot of thing inside the alternator that can go bad and drain the battery. if you want to do it the easy way get it tested at an auto parts store, they can tell you. if you would rather do it your self, use to volt meter and pulling fuses, but I suggest putting it on the amps setting and use and use the ground post and terminal. because if you accidentally ground out the positive side you could blow fuses, cause shorts, other kinds of damage, or get shocked. but of you ground the ground.... well you'r grounding a ground and nothing happens lol. and don't let people tell you that you have to go to collage to change it or rebuild it. if you look the info up and just put you'r head into it there is no reason you can't do it or at least try. people that tell you that are just smart mouths and the world is full of them. my brother didn't go to school to weld and he is the best welder in this town and my uncle is a very respected mechanic and he didn't go to school for that either. I'm the first man to go the collage in my family and i still have to ask the older people around for advice allot. all school is, is a way to get a peace of paper, take it from me, there was some people in my class that would do more damage then they fixed. and they graduated too. anyways Hope you get it fixed.

First to stop some bad information. 12 volt car batteries are 13.8 volts at full charge. This is why the Alternator puts out about 14.2 volts to fully charge it. To solve your problem buy or get a VOM meter. You can get for 25 dollars at Radio Shack or Lowe's. Then remove negative battery terminal connection. Then attach the meter between the battery terminal and the cable with the red or positive wire on the cable and the black or negative wire on the battery post. Have the meter set on amps. The meter will display the current in the car. New computer controled car use about 35 to 40 Milli amps to keep the computers in the car active. Anymore than that you have to remove fuses and watch the meter to see where the problem is at. It takes time but is not hard to do.

your car has a divided fuse box, for items that are always on and items that are on only when the ignition is in the start position....

So the items that are always on could be the problem, like cigertte lighter, glove box, dome light, trunk\hood light.

Chances are if your battery is over 4 years old, the battery, just can't keep a charge. There is a computer in the car that is using power at extreamly low voltage; but if your battery is old, then just get a new one from Sears (Die Hard).

No, an alternator can only charge, or fail to charge your battery... the starter is the only other thing that will use your battery at high levels.... In cold weather, your starter requires more power.

Yes the alternator can cause a drain. I would recommend taking to a shop who has someone who is good with electrical diagnosis. Parasitic drains can be difficult to track down. It will be a lot more cost and time effective to have a professional do it.

yes it can the voltage regaulter can stick but it can be a number of things i had a thunder bird and it had a rear defroster on it that cut off after it was on for a while all cars are the same and it would turn on by it self and run the battery the horn relay or brake sencor there is a number of things it cold be try these things first i would try to un hook the horn first and then rear defrost the easyest way to see what is draining the battery un hook something make sure all lights are off pullbattery cable off and touch it back to post if it sparks that not it un hook something else and repeat until it dont spark when it dont you found your problem

This may not be the cause of your drain but The alternator can cause a drain due to bad diodes. Keep pullin fuses if you can pull the big wire off the back of the alt while checking for draw