Battery testing problem
Thread Starter
Instructor
Joined: Apr 2014
Posts: 179
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From: NJ
Battery testing problem
I have a one year old battery, after a week or two, the battery acts weak, and it has lost some charge, too much for the newly rebuilt clock to be the cause.
I disconnect the battery negative, put my test light between the battery minus side and the disconnected cable, and the light goes on. (Same if I open the door). I've tested most everything, from lights in the dark, to fuses out, to alternator and regulator disconnected, I still get the test light on in all cases.
My old multimeter has no fused 10amp setting, so I bought a new multimeter with fused 10 amp yesterday. I put the new meter in place (I know how to use it, I think), I get 0.0 when I put the leads between the battery negative post and the negative cable (disconnected), and I get 0.0 even when the door is open. Am I doing this test correctly? [Negative cable off, meter red to cable, meter black to battery post, meter set to 10amp setting (and meter probe in the correct 10amp slot)]. Meter fuse is not blown.
Help!
Mark
I disconnect the battery negative, put my test light between the battery minus side and the disconnected cable, and the light goes on. (Same if I open the door). I've tested most everything, from lights in the dark, to fuses out, to alternator and regulator disconnected, I still get the test light on in all cases.
My old multimeter has no fused 10amp setting, so I bought a new multimeter with fused 10 amp yesterday. I put the new meter in place (I know how to use it, I think), I get 0.0 when I put the leads between the battery negative post and the negative cable (disconnected), and I get 0.0 even when the door is open. Am I doing this test correctly? [Negative cable off, meter red to cable, meter black to battery post, meter set to 10amp setting (and meter probe in the correct 10amp slot)]. Meter fuse is not blown.
Help!
Mark
Race Director
Joined: Apr 2015
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From: Fresno California
It sounds like you're using the proper technique, but choosing the wrong scale on your DVOM. Your test light indicated a voltage draw. Your amps scale should work, but it sounds too coarse. You could switch to milleamps, or try switching it over to 'volts' and re-test. If you turn on the headlights, you should get a 12 volt draw. Ideally, you want less than a half a volt draw with everything turned off. Very small amperage draw, like half an amp or less, IIRC. If you get a voltage draw with everything off, that's when you start disconnecting accessories or pulling fuses to isolate the circuit that has the parasitic draw.
Le Mans Master
Joined: Jan 2000
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From: New Hill NC
It sounds like you're using the proper technique, but choosing the wrong scale on your DVOM. Your test light indicated a voltage draw. Your amps scale should work, but it sounds too coarse. You could switch to milleamps, or try switching it over to 'volts' and re-test. If you turn on the headlights, you should get a 12 volt draw. Ideally, you want less than a half a volt draw with everything turned off. Very small amperage draw, like half an amp or less, IIRC. If you get a voltage draw with everything off, that's when you start disconnecting accessories or pulling fuses to isolate the circuit that has the parasitic draw.
Team Owner
Joined: Jul 2006
Posts: 22,162
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From: Kannapolis NC
Forget about the 12v draw part, that's not what happens. Put your test light on the way you mentioned. When the light lights up, pull the fuse for the clock and radio. If you have an aftermarket radio with station memory and clock, it can draw the battery the way you stated. If the light stays on with the clock fuse out, start pulling other fuses until the light goes out. If it still doesn't go out, disconnect the plug to your alternator, it may have a current leakage in the diodes. You didn't say what year car you have, but they aren't very electrically complicated. It could be as simple as your glove box light staying on.
As far as your ammeter, something is not working correctly because if there is enough current to light the light it should not read 0.0. As said, see what other ranges you have to choose from besides 10a.
As far as your ammeter, something is not working correctly because if there is enough current to light the light it should not read 0.0. As said, see what other ranges you have to choose from besides 10a.
Race Director
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From: northern california
C2 of Year Finalist (track prepared) 2019
Jim
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Joined: Apr 2014
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From: NJ
It's a 65, sorry.
The new multimeter can't be right, I'll just bring it back for a replacement. I will try all the fuses next. I only tried the heater fuse, I had been working with that. It is not that circuit. I also tried the alternator and regulator, light still lights. I took out the glove box light, not that. I also checked all three interior lights, none of those stay on with the doors closed.
Very annoying. But thanks all.
The new multimeter can't be right, I'll just bring it back for a replacement. I will try all the fuses next. I only tried the heater fuse, I had been working with that. It is not that circuit. I also tried the alternator and regulator, light still lights. I took out the glove box light, not that. I also checked all three interior lights, none of those stay on with the doors closed.
Very annoying. But thanks all.
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Thread Starter
Instructor
Joined: Apr 2014
Posts: 179
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From: NJ
A little discharged. I think. That's why I am testing. I am also checking the battery charge after it sits a while, I'll do that in an organized way.
Le Mans Master
Joined: Oct 2002
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From: Las Vegas - Just stop perpetuating myths please.
Forget about the 12v draw part, that's not what happens. Put your test light on the way you mentioned. When the light lights up, pull the fuse for the clock and radio. If you have an aftermarket radio with station memory and clock, it can draw the battery the way you stated. If the light stays on with the clock fuse out, start pulling other fuses until the light goes out. If it still doesn't go out, disconnect the plug to your alternator, it may have a current leakage in the diodes. You didn't say what year car you have, but they aren't very electrically complicated. It could be as simple as your glove box light staying on.
As far as your ammeter, something is not working correctly because if there is enough current to light the light it should not read 0.0. As said, see what other ranges you have to choose from besides 10a.
As far as your ammeter, something is not working correctly because if there is enough current to light the light it should not read 0.0. As said, see what other ranges you have to choose from besides 10a.
Yes remove fuses one at a time to isolate the load. If u have to u can start lifting wires starting with the batt pos to find/isolate location. It could be a short to ground through a worn insulation. Usually problems are found in the last area of car that was worked on.
U need to move the red multimeter lead over to the "amps" socket to measure amps - the socket for volts/ohms wont measure the amps/current. I u are lighting incandescent bulbs with the circuit u have current flow if only a few millamps. BTW u should be using the milliamps (ma) setting rather than the amps setting.
Good luck.
Racer
Joined: Feb 2012
Posts: 253
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From: Kingston, TN, Denham Springs, LA & Agoura Hills CA
Disconnect the Bat +lead and measure resistance
Disconnect the hot cable off the battery and using the DMM measure the + cable resistance to chassis. Change the meter sensitivity if required to get an accurate resistance #. Current is equal to volts divided by resistance. The clock should be the only load drawing current unless a security system is connected. The resistance should be over 10K ohms unless the clock internal coil sw is closed.
Thread Starter
Instructor
Joined: Apr 2014
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From: NJ
I am using the test light until I can get a replacement test meter which has working amps.
Starting from the bottom, I took out the lowest fuse, 15a for Courtesy, Stop and License lights. The test light, which had been pretty bright before, is dim to the point of not being able to see it. So I think this is the culprit. (Or a culprit). I took out the bulbs for all 3 courtesy lights and for the glovebox light. (Although none of them light up with the car off.) Still bright when the fuse is in. License lights and stop lights are not lit.
Wait, my diagram shows the clock on the same circuit as these lights, I guess that's next. The original clock was refurbished about 6 months ago, runs and looks great, so I am dubious of that.
Wait, one more thing: When we redid the dash cluster, the red wire to the cigarette lighter was never plugged in. I recently noticed it was hanging, I just taped it up. That looks like it interacts with the blk/orange wire which goes to all the bulbs associated with the fuse which is a problem. How could that cause this draw? (I'd plug it in, but I could not find the obvious place it goes)...
thanks,
Mark
Starting from the bottom, I took out the lowest fuse, 15a for Courtesy, Stop and License lights. The test light, which had been pretty bright before, is dim to the point of not being able to see it. So I think this is the culprit. (Or a culprit). I took out the bulbs for all 3 courtesy lights and for the glovebox light. (Although none of them light up with the car off.) Still bright when the fuse is in. License lights and stop lights are not lit.
Wait, my diagram shows the clock on the same circuit as these lights, I guess that's next. The original clock was refurbished about 6 months ago, runs and looks great, so I am dubious of that.
Wait, one more thing: When we redid the dash cluster, the red wire to the cigarette lighter was never plugged in. I recently noticed it was hanging, I just taped it up. That looks like it interacts with the blk/orange wire which goes to all the bulbs associated with the fuse which is a problem. How could that cause this draw? (I'd plug it in, but I could not find the obvious place it goes)...
thanks,
Mark
Race Director
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From: Fresno California
Mark, sounds like you are getting there. An open wire won't cause a draw. Can't....it's open circuit. No load can pass. It sounds to me like your clock/circuit is the issue. Bear in mind that pretty much all new cars have considerable parasitic drain due to keep alive memory computers and accessories. If they sit a month they will be dead or nearly so. So, how much of a drain do you really have? Is it slow to crank if you drive every week? If not, I would use a battery tender and not worry about it if indeed it is the clock. JMO....
Racer
Joined: Feb 2012
Posts: 253
Likes: 21
From: Kingston, TN, Denham Springs, LA & Agoura Hills CA
Just measured + pow cable resistance 1965 Conv
Mark, sounds like you are getting there. An open wire won't cause a draw. Can't....it's open circuit. No load can pass. It sounds to me like your clock/circuit is the issue. Bear in mind that pretty much all new cars have considerable parasitic drain due to keep alive memory computers and accessories. If they sit a month they will be dead or nearly so. So, how much of a drain do you really have? Is it slow to crank if you drive every week? If not, I would use a battery tender and not worry about it if indeed it is the clock. JMO....
Thread Starter
Instructor
Joined: Apr 2014
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From: NJ
Thanks. I knew that an open circuit should not cause this...doh. OK, the car will generally start fine, even after one or two weeks. It's just that 2 weeks ago, after about 2-3 weeks of non-use, on a rainy humid day, it did not start. I think the battery was turning decently, but not sure if it was the battery... I am pretty OCD about things, I just wanted to get to the bottom of it, and with the test light being bright, it make me wonder...I will open the clock access, disconnect the wire plug, see about the test light in that case and get back.
Thread Starter
Instructor
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From: NJ
We'll see what I find....
Thread Starter
Instructor
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From: NJ
Maybe I found the real problem? I went to the rear of the car to look at the license plate and stop lights. When down there, I noticed that the ground wire to the fuel gauge sender was hanging. We had replaced that sender a few months ago, the ground was obviously not put on tight enough (or at all, I didn't do the final work). Ground is on now, test light barely registers, fingers crossed that this was the problem...but also surprised that the fuel gauge worked at all, which it did.
Thread Starter
Instructor
Joined: Apr 2014
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From: NJ
What was wrong: I made two changes to fix it ---
a. The ground to the fuel sender had fallen off. It is on now. Once I put it on, the test light in series to the battery went very very dim. (My ammeter must have blown the amp fuse).
b. The voltage regulator was clearly bad -- it was the second one too, old design, rebuilt. I bought and installed a new cheap Duralast VR-715 from the local store, battery now charges right (old regulator was putting out between 14.9 and 17.2 volts, depending on how it felt, new regulator puts out 14.2 volts all the time).
My mechanic had a quick look: Dim light is because there is a 5 millivolt draw somewhere. No problem. (When the clock charges, every few minutes, it jumps to much higher for a second). We also put on a quick disconnect, since the car sits for a week or two sometimes --- also a small anti-theft deterrent.
Car starts well, runs well, battery is fully charged now all the time, it tests excellent, since it is only 1 year old. I am happy. All's well that ends well.
Mark
a. The ground to the fuel sender had fallen off. It is on now. Once I put it on, the test light in series to the battery went very very dim. (My ammeter must have blown the amp fuse).
b. The voltage regulator was clearly bad -- it was the second one too, old design, rebuilt. I bought and installed a new cheap Duralast VR-715 from the local store, battery now charges right (old regulator was putting out between 14.9 and 17.2 volts, depending on how it felt, new regulator puts out 14.2 volts all the time).
My mechanic had a quick look: Dim light is because there is a 5 millivolt draw somewhere. No problem. (When the clock charges, every few minutes, it jumps to much higher for a second). We also put on a quick disconnect, since the car sits for a week or two sometimes --- also a small anti-theft deterrent.
Car starts well, runs well, battery is fully charged now all the time, it tests excellent, since it is only 1 year old. I am happy. All's well that ends well.
Mark