Troubleshoot to isolate which line has short. Battery drain

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  #1  
Old 05-07-09, 05:53 PM
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Troubleshoot to isolate which line has short. Battery drain

The problem:
Car that has a short somewhere that causes the battery to drain when parked overnight.
(With cable disconnected, the battery stays charged. No lights or radio left on, fans running, relays buzzing, etc.)

For now I simply want to isolate to which line the problem lies.
I would think one way to troubleshoot this is to disconnect one battery cable, connect an ammeter in series (between the battery post and disconnected cable), see if it's drawing current, then (assuming the problem lies with one of the lines protected by the fuses in the fusebox; not the alternator or similar) pull one fuse at a time until one causes 0 draw or, at least, a significant drop. I haven't done this as 10ADC is the top range of my vom and I assume a car battery would blow the meter. True?

Could I instead, following the same fuse pulling procedure, use the voltmeter from empty fuse clip to ground?

If not, what is a better method for troubleshooting?

Thanks!!
 
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  #2  
Old 05-07-09, 06:14 PM
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You have a good method. I think you are confusing volts with amps. If it is rated at 10 amps, nothing you have hooked to it except the starter and headlights would come close to pulling that much amps. Not sure where I got it, but I have an amp draw meter with a double angle piece on the back that you lay across a wire. If there is any pull, it will indicate it. Probably got it at an auto parts house. But, as stated, your method is probably the best trial and error one, since you don't have any obvious items causing the drawdown.
 
  #3  
Old 05-07-09, 07:33 PM
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No, I'm not confusing volts with amps.

My thinking was that the meter is rated at only 10 amps. A battery can put out many times that. I'd be measuring an unknown.
The unknown may be over, maybe under. It'd be a crapshoot. If I gamble and that unknown is drawing more than 10 amps, I guess I'd lose my meter...which I'd rather not do.

It's probably true that nothing else but the starter or headlights come close to pulling that much current under normal conditions but what if, for example, something like a shorted or stuck relay is involved? Could it draw more than 10A? I don't know.

But now your volts & amps comment got me thinking..
I don't really need to measure the exact value of the draw; only know that there is or is not a draw on each circuit. So, why couldn't I use the same procedure described but instead of an ammeter, use a voltmeter safely set in the 20vdc range since the voltage will never exceed 14vdc or so?

(By the way, thanks for that super speedy response!!)
 
  #4  
Old 05-07-09, 07:38 PM
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You know there is a slow draw down, right? It isn't the capacity of the batteries amp rating, but the amount of draw on a particular circuit. You will be safe using the ammeter. You know, also it isn't a 10 amp draw. That would kill your battery in a mater of minutes. Since it is an overnighter, the draw could be in milliamps.
 
  #5  
Old 05-07-09, 08:16 PM
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Hi AC, Chandler has the right idea as the overnight drain should be something like one amp or less. Just don't turn on the lights.

If you want to use the volt meter, wire in something like a tail light bulb in series where you would have placed the current meter. If it is drawing some current, you will be able to measure a voltage across the lamp, it may even glow a bit. If it is too low to create a voltage, then you can use your amp meter and know you are safe.

Your thinking is correct from there on.
Good Luck
Bud
 
  #6  
Old 05-07-09, 09:31 PM
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That makes sense.

I guess what I didn't think to mention is that I don't really know that it's an "overnighter" or "slow draw". Yes, I did say "overnight" because it was the following morning that I noticed a dead battery but since I didn't monitor the draining process, I really have no idea how long it actually took; it may've taken all night or occurred in the first few minutes. I really don't know. After the 2nd time I just got into the habit of disconnecting the battery.

Anyway, thanks to you both for your help. I'll do as you suggested but I'm still curious; wouldn't the voltmeter from fuse holder to ground also have worked?

Thanks again!
 
  #7  
Old 05-07-09, 09:40 PM
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If you check off the battery, make sure to disconnect the hood light and wait 30 minutes for everything to shut down. Be safe, G
 
  #8  
Old 05-08-09, 07:18 AM
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batt drain

If you put a voltmeter in series any draw will show full batt voltage. So you wont know if you have a mili amp or 5 amps. A light bulb in series will do the same thing. Your ammeter would be your best bet. Yes you could use the ammeter to jump the fuse on each circuit. Going to ground with a volt meter will only tell you if you have power to the circuit. Good luck. RW
 
  #9  
Old 05-08-09, 08:20 AM
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I would put a 5 amp fuse in series with the VOM lead.
Just a fuse and duct tape should do.
If real woried about metere then put 10 ohm fuse in the series circuit also.
I am sorry I do not understand your idea of the voltmeter to find draw.
 
  #10  
Old 05-08-09, 03:05 PM
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http://forum.doityourself.com/automo...-few-days.html

Try this....

If yours goes dead overnight..then it should be easier......

Consider all the possibilities.......
 
  #11  
Old 05-08-09, 03:57 PM
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it would seem that the fuse would blow if you've a short (assuming most fuses are <10 amps?) so your original idea is likely fine and won't blow your meter.
 
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Old 05-08-09, 05:11 PM
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It could be a slightly resistive load and won't blow a fuse. And it won't hurt the VOM.
 
  #13  
Old 05-16-09, 08:39 AM
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I told my son I hated Fords for this reason

I've been having problems with my battery dying the past month or so...And decided to look on the internet for/ and found this here forum about the problem today ....And have a question to maybe narrow down a quick way to solve it....
I've recharged to battery 3 times, the latest was Friday (yeserday)...Was told to start the car and pull one of the cables off and see if the motor still runs, which it did ..Just to make sure the alternator was ok.. If not then it wasn't....
After a long thought process from the get go ...Everytime I recharged and was hooking the battery up..I get a spark along with the horn honking when the negative touches the terminal...I was told by mouth it was a short in the car alarm..
Now I'm babysitting my sons car a'96 Mustang GT while he's in boot camp and before he left he had the alarm disconnected by a mechanic..So am I thinking maybe the horn itself has a short and draining the battery? Or was the alarm wasn't completelty disconnected ? Or do I still need to go through the process with the meter I've been reading here?
Thanks
 
  #14  
Old 05-16-09, 02:47 PM
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Not a pro on this, but if you are having to recharge the battery every few days, it sounds like your alternator is not keeping up with your day to day driving. Stop any garage or auto parts store that can test the system and point you in the right direction.

Bud
 
  #15  
Old 05-16-09, 04:28 PM
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The first time when the battery died. There's a buzzing sound that was comming out from under the hood..Even after the key was out of the ignition it just kept rattling....After looking around I noticed it was comming from the high current fuses under the hood and noticed one of the relays was vibrating (horn relay accoring to the manual)...So I recharged the battery and replaced that particular relay. Figuring the relay was bad, the current wasn't going full cycle and somehow/someway was killing the battery
So after 3 weeks and maybe drove the car 3-4 tmes in that span ..The battery was dead, totally nothing....Recharged it again, drove it around the block, left it alone untill the end of the week and it was deader than dead...not even a click....Where i go to get the battery charged up .The battery tester was rating it in the low to mid 2's
 
  #16  
Old 05-16-09, 04:49 PM
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It does sound like a load on the battery, but when the voltage drops really low, electronics, like the old alarm can do funny things. So still not certain the horn is the problem or just a symptom. They may have disabled, but not disconnected the alarm.

Do you have access to a meter and are you comfortable using one?

Bud
 
  #17  
Old 05-17-09, 08:53 AM
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This is a really odd thing but it may be your problem. I had an 89 Cherokee with that problem. Answer was the neg and pos. cables fused together somehow. Very lucky the battery didn't blow up. Good luck
 
  #18  
Old 05-18-09, 03:04 AM
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Why not save all your friggin around with amp & volt meters & buy a $5.00 12VDC test light & put it in between battery positive post & cable connection. Pull all fuses, light will be out, then start putting them in 1 at a time, when it lights bright, big draw, if it lights dim, small draw.
 
  #19  
Old 11-21-09, 08:37 AM
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Originally Posted by Mike.B View Post
Why not save all your friggin around with amp & volt meters & buy a $5.00 12VDC test light & put it in between battery positive post & cable connection. Pull all fuses, light will be out, then start putting them in 1 at a time, when it lights bright, big draw, if it lights dim, small draw.
What if you do this and the light stays on? That's the problem with this Yukin. The test light stays on even if you pull all the fuses out.
What cable connection should the other end of the light be connected to to be sure?
 
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