Charging Problems

FORD EXPLORER
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RAYARMOUR
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My wife was out teaching my 16 year old daughter how to drive my 2002 Explorer. 75,000 kms, yesterday when the radio went dead and the car lost power. They managed to get it around the corner safely and called me on the cell. They turned of the car and it would not start. Battery dead.

I went out and put my boat battery in the car and it started and ran fine. Got it home so I could have a look.

Voltage across the battery was 12.5v with the engine off and 14.1v when running. No warning lights, battery gauge on dash is fine.

Charged truck battery overnight and it shows 13.1v. Started truck this morning with boat battery still in it and it seems fine. Battery gauge good and no warning lights. Bulb good as it came on at start up.

Turned on lights and as many acc's as possible and no dimming.

Any thoughts as to my next step. Don't really want to start replacing battery or alternator if they are not the problem. :?:
Jan 8, 2007 at 8:24 AM
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BACKYARDMECHANIC
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You say you voltage reads were 12.5 and 14.1. I have a question was the readings taken with the alternator under a load (with all accessories on fan defroster etc). The voltage should never drop below 13.2 you got 12.5. I suspect the alternator is bad but make one more test to elimanate the battery or short. I don't like to replace parts either if they test good.You need to load test the battery but if you don't have one you can improvise by doing the following. Disable the fuel or ignition system so the car will not start. first make sure the battery is fully charged. Next connect the volt meter to the battery while and assistant cranks the car for 5-7 seconds no more. The voltage should not drop below 9 volts during the test and if it does the battery is no good. The last thing to check for is a short. You need a 12volt test lamp to conduct this test. With all accessories off (don't forget the hood light) disconnect the postive cable from the battery and connect the lamp between the postive cable and positive terminal of the battery. You should have either no light or a very dim light if there is no short. If you have a bright light then there is a short within the system. Hope this helps but from what you said so far I would bet it's the alternator. GOOD LUCK :)
Jan 8, 2007 at 10:16 AM