Hi guys,

I know this is off topic but since we're into the volt checking mode, I need some advise on my daughters 1998 Ford explorer charging (or in this case, perhaps discharging) system. Her battery was about 6 years old and would not hold a charge for more than a day, so I replaced the battery back in August. It seemed ok but now if the car is not driven every two days, she will go out and it will not start unless jumped. After charging for 30 to 45 minutes it will last another 2 days.
I'm thinking it's either a short somewhere draining the battery or perhaps a defective battery. This morning after letting it run for an hour, I took out my multimeter, disconnected both cables and put the probes of the multimeter on the postive and negative posts. Held them on for 15 seconds and got a reading of 12.52 keeping in mind that the temp outside is 25 degrees. I then reconnected the cables, started the car and put the multimeter probes on the pos and neg posts. The reading fluctuated between 14.23 and 14.24V. It appears the alternator is fine.
What I'm doing now is disconnecting both cables and will let it sit overnight. Then I'll repeat the battery Volt check and see what I get. If the volt reading (with the battery disconnected) drops significantly say, to around 12.20, would that indicate the battery is not holding a charge and is defective?

I guess if it does not drop, I clearly have a short somewhere which can be a nightmare to find. I've checked every inside and outside light (hood, glovebox etc) I can think of and see nothing that remains on. What's the best way to check for a drain, or short using the multimeter?

Thanks all,
Jim

 

to test the system on an explorer you have to wait for all the modules to go to sleep I dont rember what the timer is but is should be about 30min. once a sleep you need to test for amp draw. sound like you have some thing with a draw draining the system. this is really not the right spot for this concern. there is a different section of the boards for explorers.

 

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Thanks, understood. Checking for a battery draw will be part 2. Concerning the part where I fully charge the battery, immediately remove the cables and wait 24 hours then recheck the volts. If it drops from 12.50 to say 12.20 or lower, would that in itself indicate a bad battery that's not holding a charge?
Thanks again.

 

NO that does not make a failed battery. A battery is just under 2v per a cell so 11.8 is were it would sit and still be normal. But that still is not a good test. If you take the battery down to like autozone and have it load tested that is a test of a battery.

 

There are clearly onboard systems that keep the memory alive, and of course radios etc too. The way you can try to find it is to disconnect the battery, use a senstive ammeter and run one lead to the battery, one to the terminal you disconnected and then note the current draw. Then one at a time, start pulling fuses noting which ones go where, see if any one of them has a big draw, that could localize it a bit. Also you may want to try disconnecting the wire to the alternator, the see if the amp draw gets better in case there is a faulty diode plate creating a reverse current.. That's a start. If you see a draw on one, then you can see what's hooked to it and start hunting it down to the component. Clearly, if you have a bad battery that won't hold a charge, that could cause this too.

 

On FORDs with the "smart" PCM? that turns off things like interior lights, etc. after a certain interval, doing the test as you suggested will show a very large current draw until "it" decides to turn it off.

So the trick is to get the readings after it settles down.

There is a very small drain at sleep mode... it is tiny.

The drain here is far greater to drain the battery overnight.



Suggest that the expedient solution is to get a new battery and see how it does --- then worry about expensive diagnostics if that bombs.

 

Thanks for that Cabinman. I'm keeping my fingures crossed that I don't have to go through that but if I do, I appreciate that help. To cheezit's point regarding the proper volts on a battery there seems to be a gross difference of opinion. I called Autozone to ask when a good time to bring in the vehicle and we had a discussion regarding battery volts. The gentleman was adamant that each battery cell provides 2.1 volts per cell and gave me the following run down on the battery charge percentage:

12.68 100%
12.45 75%
12.24 50%
12.06 25%
11.89 0%

After a full charge and disconnecting the cables I showed 12.48%. I checked after 2 hours and it showed 12.35. The battery appears to be losing it's charge and it will be interesting to see what tomorrow shows. I'll keep you posted and sorry for going of topic on the thread.

Jim

 

That tells you nothing and is normal drop after you disconnect the charger.

The issue is never just voltage, but whether it "load tests".

That can only be determined by having a load tester that puts a resistive load across it, and then measure the voltage drop.

Take it to Walmart, or Autozone, or any like shop... they do it for free.

 

and yes I am wrong its not 1.8... its 2.2 what was I thinking when I typed that crap. sorry.
Didnt remember what it was. doooooohhhhhh

 

The big variable is temperature:


See:


Chapter 5: Discharge Methods


Lead-acid battery cold performance

 

This is a topic I happen to know fairly well. I have been working with lead acid batteries on campers and RVs for many years. You really cannot make a good judgement on the health of these batteries based on unloaded voltage alone providing the voltage is higher than 11.25ish. Below that value, and you most likely have a dead cell. Above that value, the actual voltage is so dependant on temperature, specific gravity, surface charge density, and other factors, only a good load test is accurate enough. The chart you have listed is the scientifically correct one for a certain temperature and chemistry status. It's not as accurate in real life.

One thing that works fairly well for me is to connect a 50 watt headlamp to the battery and leave it on for about 2 hours. That equates to roughly an 8 ampere-hour load event. Not enough to harm the battery much but enough to tell you if the overall capacity is good or not. If the voltage remains above 11.5 for the two hours you have a good battery. If not, you might have a bad one. A bettery that can't hold up to an 8AH load is probably too weak or self discharging anyway. Good luck!

 

Yes absolutely, have to have a reliable source. If they are good, and you have done a load test that's a start.
What you really need at this point is to figure out where the draw is though. Audio amps are bad for staying alive after the stereo is off. A solution is to use a diode placed into the trigger feed lines of amps to keep them from back feeding and keeping each other alive. This usually only occurs with a problem or multiple amps, although it shouldn't ( but it does ).. So if you have a draw, start pulling fuses on those audio amps if you have one or more because they kill batteries all the time, then move on down the line.

 

Well, I just got back from having the battery checked at Walmart where we bought it 6 months ago. It has been certified as good. Got the computer read out. On the checking for a short. If anyone can provide the "juvenile version" of how to start, would be much appreciated. I have a multimeter. The alternator is charging at 14.30 volts steady.

Thanks.

 

1st, think back to before the problem began to occur...what was different, what have you changed with regard to accessory add ons, mods, lighting, etc... anything is fair game...if it consumes juice...then it should be suspect. Check every possible ground you can find...check both alt and starter for short to ground or short to power. Ad cabinman stated....let her go to sleep (sometimes as much as 20 minutes) pull fuses one at a time until you find the one thats draining your power then track down what that fuse supports. As you pull the fuses...don't put them back until you're all finished. Just pull one, note where it went then move on. There are several web sources that break it down (parasitic draws). Good luck...this isn't a quick task by any means.

 

Thanks for all the tips! Tomorrow I'm going to dive into checking for the battery drain. Will fully charge the battery and then wait about 40 minutes to insure that the computer has "gone to sleep". I'll start by removing the positive battery cable and attach my multimeter to the positive cable, then to the positive post.
What would be an acceptable reading with no significant parasitic drain? Once I identify an unacceptable drain, I will pull fuses one at a time until I hopefully discover the problem circuit. I have attached a picture of my multimeter. Can someone tell me what I should set it at and what are the readings I should be looking for?

Thanks!