How do you test for a draw on your car battery?

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lerto
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How do you test for a draw on your car battery?

Post by lerto » Mon Dec 04, 2006 7:57 pm

First let me say hello to all. I am new here and have been checking the site and love it. I apologize if this topic has been covered already, but I couldn;t find it.
I have a 1993 Dodge Dakota. If I dont start it for 2 days, it wont start and the battery dies. I CANT REMEMBER HOW TO TEST FOR A DRAW ON THE BATTERY. It's been a while since I've done this. I have a new battery in. It charges to 12.5 V and while running it charges at 14.2 V. But if I dont run it for 48 hours, it is dead. I have no hood light, no interior light, the glovebox light is off. My stereo is off, etc (all the usual suspects) It is getting frustrating as I am trying to find another problem ( no brake lights) but everytime I have time to try to find that problem, the truck is dead.
If anyone could give me a refresher on how to draw test, I would greatly apprerciate it.
I am pretty sure you use a digital amp meter. Unhook positive battery post and place leads between battery terminal and cable end. Positive lead to battery post and negetive lead to cable end. But I cant remember for sure.
Thanks alot!

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Post by Gorgon » Tue Dec 05, 2006 12:54 am

Digital or analogue, you use an ampmeter on the highest range, normally 10ADC. Loosen one pole(+) on the battery and put the meter between like you said.

If your generator has a diode bridge, I would check out the diodes in this for reverse current leakage. This happens from time to time.

Another possibility is the car computer, ex. a bad capacitor.

TOK ;)
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Chris Smith
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Post by Chris Smith » Tue Dec 05, 2006 8:12 am

Also ensure the alternator is putting out the required amps, and not just the voltage at one setting.

If AC is leaving the alternator because of bad diodes this will also discharge the battery.

A simple AC volt meter on the Battery will show if this is the cause, as well as loading down the battery with everything in the car and then testing the voltage at mid range rpm.

If you use the hi beam, heater, Ac etc [ and a extra load preferably] and the voltage is still not high in the range [well into the 13 volts] the alternator is not keeping up with the draw and the battery will drain.

At static the battery will return to the 12 volt range giving you the false impression.

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haklesup
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Post by haklesup » Tue Dec 05, 2006 8:17 am

Checking for a large load when the car is off is a logical step but in my experience, everytime I have seen a battery die frequently it is because it needs to be replaced. If it is over 5 years old, this is a very likely situation. (how many of us have replaced a regulator or alternator only to find out it was the battery all along, at least once in their life - I have)

While you may be able to put a charge into the battery (enough for 2-3 days of standby power), it's capacity appears to be significantly reduced which is the typical way car batteries end their life.

Putting a fuse in series with the measurement that has a value lower than the range of the meter can spare you from replacing the fuse IN the meter if the load is very large (like if your helper tries to start the car when all you asked for is to turn on the lights (this happened to me)

Falling temperatures at this time of year can push a weak/marginal battery into the grave. Batteries don't really like the cold. Many auto parts stores and most service stations can do a load test on it as well for you.

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Chris Smith
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Post by Chris Smith » Tue Dec 05, 2006 8:53 am

If your going to load test the battery, you must know if its been fully charged either by the alternator, or an external charger.

To test just the battery with out knowing this to be a fact is useless.

A dead battery will show up dead with out telling you how it got there.

Also don’t do any ammeter tests except in the off position of the car with your small ammeter, and only to see if you have a excess draw when it parked.

Anything else requires a proper ammeter to check for a heavy draw.

Your only looking for small draws that are larger than accepted, at rest or off, not running and not under full load. That requires special equipment.

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lerto
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Thanks

Post by lerto » Tue Dec 05, 2006 9:53 am

Thanks alot everyone. This is great advise. I am glad I came here.
I have tried all above suggestions, and had charged battery to full charge with a benchtop charger before beginning.

I went to do the milli amp test but when testing my meter first realized the fuse must be blown,(As I get OL in the the test mode)

I learned working on cars back in the times of test lights (which I dont have anymore) and if I remember correctly, we used to remove NEG cable, attach the test light to cable end and ground. If light went on, we would pull one car fuse at a time until the light went out, then trace our draw to that fuse circuit. (ex. If radio fuse pull caused the light to go out, trace the radio wiring)
I guess cars have changed alot since those days.

I was able to test in the 10A mode - Not sure if this test really did anything- (as my 300ma fuse is shot) and it showed amps, and I pulled 1 fuse at a time to see if there was any DROP, and no fuse pull caused any drop (Leading me to believe NO draw)

I probably should mention the NEW Battery I bought is (as I have found from posts on this site) a NEVERSTART Wallyworld battery. Maybe is just a bad battery?

I guess I should replace the fuse in my meter and do the ma test, as well as return the Wallymart battery and get a better one, no? Otherwise I am flying blind, right?

Thanks everyone! This place is great!

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Post by rshayes » Tue Dec 05, 2006 11:01 am

If a good battery is being discharged in 48 hours, the discharge current must be on the order of an amp or so. This might be enough to deflect a compass held near the battery cable. One of the tail lamp bulbs could also be used as a test lamp in series with the battery.

If one amp of current is actually flowing, I would expect some sparking when the battery cable is disconnected.

There may be some loads that are not fused, such as the starter circuit. Pulling the fuses will not break the circuit if the problem is in the wiring harness between the battery and fuse block.

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Post by Gorgon » Tue Dec 05, 2006 11:06 am

Replace the fuse first. This fuse is only protecting the low mA range shunt. The 10A range has normally a separate shunt.

If you can't find the leak when removing the fuses, try to remove the positive lead from the generator, starter, clock and computer if installed.

TOK ;)
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lerto
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Problem SOLVED!

Post by lerto » Tue Dec 05, 2006 1:33 pm

Thanks everyone. The problem is solved!
I appreciate the help.
Turns out the problem was not in the fuse line but a direct problem (as was suggested here!)
I used the 10A test and had a draw of .40
Then eliminated the starter, the alternator, clock with no change. Still .40
I then unplugged the last black cable that was left, and down to zero.
Traced cable to the relay/fuse box located under the hood of the truck, started pulling realys -nothing. Then, there are 2 fuses in there besides the relays, pulled one, and down to zero! Fuse was for 'battery draw'. It was supposed to be 5A but previous owner mixed that up with the fuse next it and had a 20A in there (20 A is for the next slot for hazaard lights) The truck has NOT has hazaard lights since I bought it a few weeks ago. Now the fun part. I decided put the 20A fuse in the hazaard slot where it belongs, and like magic, I now have hazaard lights. I then put the 5A in the Battery Draw slot where it belongs and still drawing ZERO! Problem solved. (Well, mostly draws zero, with a .01-.05 intermittent reading which I believe is for the radio clock/station memory)

Anyways, enough babbling!
Thanks to all.
I will come here often, asI hope I can be of help to others as they have helped me.
Thanks and Happy Holidays!

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jollyrgr
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Re: Problem SOLVED!

Post by jollyrgr » Tue Dec 05, 2006 3:10 pm

lerto wrote: {SNIP}
Fuse was for 'battery draw'. It was supposed to be 5A but previous owner mixed that up with the fuse next it and had a 20A in there (20 A is for the next slot for hazaard lights) The truck has NOT has hazaard lights since I bought it a few weeks ago. Now the fun part. I decided put the 20A fuse in the hazaard slot where it belongs, and like magic, I now have hazaard lights. I then put the 5A in the Battery Draw slot where it belongs and still drawing ZERO! Problem solved. (Well, mostly draws zero, with a .01-.05 intermittent reading which I believe is for the radio clock/station memory)
First, what is "BATTERY DRAW" for on a car. I've worked on many cars and never recall seeing this type of fuse. Second, the 5A fuse is likely blown. If you swapped the 20A and the 5A and got a zero draw and working hazzard lights then the 5A fuse is bad. It is POSSIBLE that the hazzard lights would have worked on the 5A fuse (not likely very long) but if they did not work at all then the fuse is bad. Placing the blown fuse in the circuit you removed the 20A fuse would then be like removing the fuse. This means something is not working and is now disabled because of a non working fuse.

Still, I'd like to know what a BATTERY DRAW fuse is for.
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Chris Smith
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Post by Chris Smith » Tue Dec 05, 2006 3:43 pm

Battery draw could be for accessories like the cigar lighter looking device used to power such things like lap tops, cell phones, and external lights.

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Post by haklesup » Tue Dec 05, 2006 5:02 pm

I'm glad you fixed it but it's puzzling because just swapping the positions of two fuses should not have changed the loads on those branches. fuses do not regulate loads only limit them.

Perhaps you had a mechanical short or leakage in the fuse block which you cleared by manipulating the fuses. Or maybe the 5A is now blown and that load is now open. That makes sense because the hazards previously did not work but now they do and all you did was replace the proper 20A fuse. (BTW lamps is cars are tpically high current and would likly blow a 5A fuse under normal conditions). I suggest you check the 5A fuse again and determine if you need the devices on the battery draw branch and what they are (i've never heard of this label either)

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lerto
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Post by lerto » Wed Dec 06, 2006 2:06 pm

OK, the 5A is for what is called the "IGN. OFF DRAW" (Inside the relay cover just says Batt Draw, but manual states the correct name above)

And I can not explain it, as the 5A fuse is NOT blown, yet the draw on my battery is gone.

I have hooked the meter up again and tested, and when I put the 20A in, the draw returns. Is a mystery to me as well! But just by putting the wrong fuse in the IGN OFF DRAW, I get a severe battery drain.

Since I swapped them, my battery holds steady at 12.38 even after 30 hours of not being started. (Would have been dead by now) So I am confident the problem is solved.

Thanks again to everyone for their input! It is greatly appreciated

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lerto
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Post by lerto » Wed Dec 06, 2006 2:06 pm

Must have hit send twice. Had 2 identical messages. Sorry. Thanks again

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Post by Joseph » Sat Dec 09, 2006 7:14 pm

It sounds like ignition off draw would be for things like radio memory power and the clock.

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