How to check for battery drain?

65 fastback · May 9, 2004

How do I check my electrical system for a battery drain? I have my battery in the trunk and I seem to have a drain or a short in the system. How do I check for a drain?

Tim

car noob · May 9, 2004

Put a test light in series with the positive cable, or put a DMM on one of the cables

gingerbreadman · May 9, 2004

car noob said:
Put a test light in series with the positive cable, or put a DMM on one of the cables

and if it lights up when theres supposed to be NO battery draw you have a short... make sure the interior light is off and ignition off..... then start unpluggin things as a process of ilimination... such as start with the fuse box then unplug the alternature... etc.....

-gbm-

ForceFed70 · May 10, 2004

Use a DMM (Digital Multi Meter)

A test light isn't accurate enough. Some drain is normal..but a test light won't tell you exactly how much drain you have.

65 fastback · May 10, 2004

OK, I've got a Volt meter (is that basically a DMM?).
Where do I actually take the voltage reading?
Do I read right off of the positive battery terminal?
Do I leave the battery grounded or remove the ground connection?
Will a short verses a drain regester differently?

Thanks, I just need a little more guidance with electrical issues.

Tim

gp001 · May 10, 2004

You need to measure the CURRENT between the negative post of the battery and the disconnected negative lead. Your volt/ohm/current meter should be rated for 10 to 20 amps DC current. IIRC 10-30 milliohms for items like radio, clock, etc that are always connected. If you have an alarm or other items that have a constant connection you may see up to 120 or so milliohms. If it is radically above that then you have a short.

Hope this helps

ForceFed70 · May 10, 2004

What GP001 said, except replace "milliohms" with "milliamps"

A normal current draw for a classic would be about 0.2 amps (200 milliamps).
A Classic with a bunch of electronics (aftermarket stereo, alarm, etc) could be as high a 0.8 amps. You should definately see a drain of less than an amp, and preferably less than 1/2 of an amp.

Like GBM said.. start pulling fuses until you see the current drain take a large drop. This way you limit the problem to a single circuit.

gingerbreadman · May 10, 2004

70_Nitrous_Eater said:
Use a DMM (Digital Multi Meter)

you got mail

-gbm-

65 fastback · May 10, 2004

Thanks all. I'll post my results after this weekend.

Tim

gp001 · May 10, 2004

70_Nitrous_Eater said:
What GP001 said, except replace "milliohms" with "milliamps"

Ooops! Thanks for the save

Cantedvalve · May 10, 2004

Or you could hill-billy it.

Pull the positive cable with the car in a garage that can be darkened completely. Then touch the cable to the post. If you see a spark, you have something draining. This wont tell you how big the drain is, but will tell you if you have a draw.

Myfirst67 · May 11, 2004

Ok after i find out where the short is how do i fix it?

gingerbreadman · May 11, 2004

Myfirst67 said:
Ok after i find out where the short is how do i fix it?

tottaly depends on what is shorting out..... let us know and we can help....

could be some broken insulation, could be a bad alt,starter etc... i had a ranger i had to replace the alt on cause it was shorting out.....

-gbm-

ForceFed70 · May 11, 2004

Cantedvalve said:
Or you could hill-billy it.

Pull the positive cable with the car in a garage that can be darkened completely. Then touch the cable to the post. If you see a spark, you have something draining. This wont tell you how big the drain is, but will tell you if you have a draw.

That might not work so well. In my car I have alot of stereo equipment with alot of capacitance in the electronics. In this case, lots of current is needed for a split second, then very little is used at all. I literally flinch every time I connect the main power or ground cable, yet my car doesn't have a power drain problem.

vobraman · May 12, 2004

Do you leave the battery cable on all the time ? For some reason when you move the bat to the rear this happens. I had this problem with my last car. I put a turnoff switch on one of the cables, it has a wire so it hold memory for radio, clock and that type stuff. After that my problems were cured. No more drain problems.

any pics of how you mounted the battery in the rear of your car ?
thanks, hope the info helps
brian

How to check for battery drain?

65 fastback

car noob

New Member

gingerbreadman

Only half-baked

ForceFed70

That's why they call it "dope"

65 fastback

gp001

ForceFed70

That's why they call it "dope"

gingerbreadman

Only half-baked

65 fastback

gp001

Cantedvalve

Myfirst67

New Member

gingerbreadman

Only half-baked

ForceFed70

That's why they call it "dope"

vobraman

New Member

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