Tracing down a Battery drain

[Joe Lickey]

Ive got a slow battery drain that seems to have gotten worse recently and I am trying to track it down. Does anyone know of a digital meter that measures DC current this way I can put it between the battery and the cable and one by one remove items to see which one is causing the drain and how much it is drawing. I know the typical drains are stereo memory, EFI computer, I have a Dakota gauge that has a clock and a computer that I'm guessing has a small draw. Other then that I'm not sure of anything else that will draw power with the key off. My old yellow top optima (3 or 4 years old) wont seem to keep a charge for more then a day I replaced it last night with a new one and hopefully it will last 2 or more weeks of sitting and still start. My thinking is that it should last for months with just memory loads on it. Am I missing something?

[ntsqd]

Re: Tracing down a Battery drain

Just need a voltmeter btwn the post of the battery and the cable. Pull fuses one by one until you get to the one fuse that causes the voltage to go to zero.

[904Bronco]

Re: Tracing down a Battery drain

Just need a voltmeter btwn the post of the battery and the cable. Pull fuses one by one until you get to the one fuse that causes the voltage to go to zero.

You could even use a test light if that is all you have... Voltmeter is much better.

[CityHick]

Re: Tracing down a Battery drain

The $5 digital voltmeter from harbor freight should be in the glove compartment of every eb. They work well and who cares if it gets lost or stolen.

I have chased many a gremlin with one of them. Put it on the negative side of the battery between the post and ground cable, set it to amps, and start pulling fuses one by one.

[JimGo]

Re: Tracing down a Battery drain

I use meter set to read amps between negative cable and terminal.

[Joe Lickey]

Re: Tracing down a Battery drain

Thank You. I have good meters just better at AC then DC

[DirtDonk]

Re: Tracing down a Battery drain

The ones that measure more than 10 amps of current draw are the more expensive ones of course. And if your drain is more than 10 amps, your small inexpensive meters might blow their internal fuses if you test for more than a couple of seconds at a time. It's not the end of the world, but they don't always make the fuses easy to replace either.

If you disconnect the battery and let it sit overnight and it still drains, it's just the old battery. That would be one indicator your Optima is on it's way out. If so, there are some tricks you can do to see if it will come back.
Not all will come back of course, but with a nice expensive battery like that, it'd be nice to at least give it a few chances before retiring it. I've had good luck with the deep-cycle Blue Tops coming back from the dead.

If it does not go dead in the same period of time while disconnected, then a common culprit to check next is the charging system itself. You have a stock 1G with external regulator? Or maybe a newer 3G internally regulated unit?
Either way they can start to pull a battery down and if its the alternator itself can do it in very sort order. Overnight is a piece of cake for a failing diode-array in an alternator.

Good luck.

Paul

[1968u15]

Re: Tracing down a Battery drain

I have seen a lot of alternators get skipped as part of the diagnosis for a key off draw condition. Many times they will still make the running volts required but their max. amps is also low. I use an inductive current pick almost daily at work. There is also a new diagnostic aid that measures the actual load through a fuse, but they cost about a hundred bucks. A little steep if you're not using it everyday. All the guys above are right, like Paul said don't forget to check the alternator. Good Luck, David

[CityHick]

Re: Tracing down a Battery drain

I forgot about the alternator drain, my first 3g did that to me.
I've decided that my bronco is always going to have a drain, but the drain that I have now takes a couple of months to actually be noticeable, and I'm trying to drive the bronco often enough that it's never a problem. I also bought a battery tender which I'd recommend to anybody who lets a vehicle sit.

[Joe Lickey]

Re: Tracing down a Battery drain

I'm running the 3G alternator and it dale it's testing at 14 volts. How do I test it otherwise? Put a load on it like the headlights and see if the voltage drops a lot?

[1968u15]

Re: Tracing down a Battery drain

It is difficult sometimes to get a full load on an alternator these days with just vehicle loads, as most make well over 100 amps.(I remember when a good alt. was 35 amps) You're alternator should maintain 14.2v with ALL lights on at 1500-200 rpm. The best way is to load the alternator is to load it at 1500-2000 rpm with a carbon pile(such as a VAT-40) that will drop the voltage to about 13.6 volts and then read the amperage out put. Compare that to the spec.s for your alternator. Not everybody has access to one of those machines. I believe that some parts stores have the ability to bench test an alternator. If you have a good DVOM you can set your volt meter to ac and read the voltage ripple caused by leaking diodes. These days I believe that is less than .5 volts. A lab scope can do the job as well.(set to dc ) With a lack of tools, the home garage test of charging the battery , then reading the voltage, noting it, then disconnect the alt(all wires). Re-read the voltage after leaving it set with the key off for a day or two, and compare. There should be no significant drop in voltage. This same procedure can be used in a process of elimination to trace down any key off draw as long as you are certain your battery is in good shape. All that said, batteries hate to set stagnant, especially with less than a full charge. I too, recommend some type of maintainer installed. I went so far as to build one into my battery box. There are some very small but capable maintainers on the market. Best of Luck, David

[welndmn]

Re: Tracing down a Battery drain

Here is a good how to
http://www.popularmechanics.com/cars...attery-drains/

But if it's draining over night, it's a very large drain, are you sure the battery is even good? Have that tested at an auto parts stores.
On an EB, I'd start with alt's and aftermarket radios when looking for a drain.

[ntsqd]

Re: Tracing down a Battery drain

Taking a voltage reading right after charging will result in a high reading. Let the battery sit for a couple hours, or even overnight before taking a reading. Then let it sit disconnected for 24 hrs before taking another voltage reading.

A large drain isn't like the headlights are on. I had a drain on the 4rnnr that would kill a battery overnight, it was just a tiny ignition lock illuminating light. Was so faint in daylight that I had a hard time deciding if it was actually on.

[DirtDonk]

Re: Tracing down a Battery drain

A reading of just 14 while running is a tiny bit low. Could be the gauge is half a volt off of course, but it could also mean that your alternator is getting tired of working in the sweatshop conditions.
But at 14, it's not the lack of charging that is causing your battery to go dead overnight. It's still a drain doing that.
So have you disconnected the negative terminal overnight yet? Did the battery still go dead?

Paul