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Old 02-10-2011, 12:47 PM   #1
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Battery Drain


My truck had a battery that was app. 5 years old. Sometimes it would crank after setting 1 to 2 weeks, other times it would be too low to start in two days.
I bought a new battery and I have the same problems.
I know that automotive electrical problems are a whole different animal from most electrical work, so I am going to start by checking for battery drain--often.
I am aware that electrical components are energized during shutdown.
How can battery drain be checked with a voltmeter?

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Old 02-10-2011, 01:20 PM   #2
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Battery Drain


Did you clean the connections when installing the new battery?

You can use an ammeter to see if any current is being drawn due to a bad switch or a dome light left on. If you don't have an ammeter, a lamp from a flashlight may prove cvurrent usage crudely although depending on the lamp and the current draw the lamp may burn out.

Do not connect an ammeter or flashlight lamp between positive and negative. Remove one cable from the battery, turn off as many circuits as you can, and connect the ammeter between the battery post and the cable end.

Modern vehicles with electronic dashboards will draw a minute amount of electricity all the time but I think it is insufficient to light a flashlight lamp.

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Old 02-10-2011, 01:35 PM   #3
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Battery Drain


Yep, you need to connect a meter in series with the battery lead. Turn everything off, pull fuses one at at time until the current draw is gone (or very low as in a few milliamps). If the draw goes away when you pull a fuse, then that is the circuit you need to check for a problem.

Since at least 9 out of 10 times when this problem occurs, the cause is the alternator (diodes either shorted or leaking), you might want to first check the alternator. The test that they do for free at the autoparts store is NOT a good test for this problem. You should use a battery charger and charge the battery to a full charge, disconnect the alternator, leave it that way for as long as you want for the test. Then try to crank it. If the battery held the charge, replace the alternator.
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Old 02-10-2011, 05:02 PM   #4
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Battery Drain


What about starting the engine, disconnect the battery, and if the engine dies then the alternator is certainly bad. If it doesn't die, the alternator could still be bad...just not real bad.

Would this be a sufficient test for the alternator??
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Old 02-10-2011, 06:39 PM   #5
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Battery Drain


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Originally Posted by jlmran View Post
What about starting the engine, disconnect the battery, and if the engine dies then the alternator is certainly bad. If it doesn't die, the alternator could still be bad...just not real bad.

Would this be a sufficient test for the alternator??
In the old days before electronics that was the norm. It could cause electrical spikes taking out the ECU.
The "pull the fuse one at a time" is simple.
Giles, what make and model truck is it?
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Old 02-10-2011, 06:39 PM   #6
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Battery Drain


I agree with the monitoring of current draw while the engine is off. Pull fuses one a a time until you find the one (or more) that is drawing excessive current.

My last battery drain escapade was on my 2001 BMW. Saw it was pulling 7 amps for 10-20 seconds, dropping off to <1 for around 2 seconds, then back to 7, etc. Found out is was the AC/Heating system's blower which was running while the engine was off. After I identified the culprit as the blower circuit, I put my ear to the vent and heard and felt the blower running a little. (Bad blower resistor pack.)
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Old 02-10-2011, 06:48 PM   #7
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Battery Drain


Quote:
Originally Posted by Know It ALL View Post
In the old days before electronics that was the norm. It could cause electrical spikes taking out the ECU.
The "pull the fuse one at a time" is simple.
Giles, what make and model truck is it?
Old days, huh?
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Old 02-10-2011, 08:13 PM   #8
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Battery Drain


Quote:
Originally Posted by Know It ALL View Post
In the old days before electronics that was the norm. It could cause electrical spikes taking out the ECU.
The "pull the fuse one at a time" is simple.
Giles, what make and model truck is it?
I agree with you about damage that can be done by disconnecting a battery cable while engine is running.
The truck is a 2001 Ford 4X4 Ranger 4L---86K miles with "o" problems.
I am just curious as to how much amperage draw would be normal--I guss I will just take some measurments a see.
With today's battery quality-- the new battery may very well be defective also.
I just don't want to return the battery for exchange and then find out I have an electrical problem.
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Old 02-10-2011, 08:57 PM   #9
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Battery Drain


Old days, pre 1974.
I would not think the amp draw would be more than 0.2 amps. A simple check is to turn on the headlights before cranking and see if they get brighter after it is running. An alternator is a 3-phase AC device. If one phase were to fail it will still produce enough power to run the engine during the daytime. When the lights and other power hungry switches are thrown the battery dies. Normally it's the regulater that dies. Never try to charge a dead battery with your alternator unless you are stranded. You really need a volt meter to fully understand how it's performing. This mostly pertains to deep cycle batteries, but has some great info. http://www.phrannie.org/battery.html

Here is a shot in the dark. http://www.explorerforum.com/forums/...light=amp+draw

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