Alternator Draining Battery?

[RJRENTON]

When I took the alternator to the shop a few weeks ago when this first happened, they said it tested good and I asked if that includes the diodes and they said yes. But I really wonder if they would check for such a small drain. Do you think if I leave the battery disconnected between driving, it could still lose voltage? I will try it. Also, I noticed, after driving 11/8, the battery was at 12.77 on 11/9, at 12.7 on 11/11 and dropped to 12.0 on 11/15 (4 days later). That's a big drop in only 4 days. I need to monitor it some more. Thanks for your help!

I would have been specific as to what tests were performed and the results of those tests. "It tested good" really does not say anything without any specifics. Such as: forward resistance of the diodes; the reverse resistance of the diodes (each diode tested separately); resistance of the the stator windings (each phase separately and each to ground). The round back alternator has an internal capacitor connected to ground from the positive diode common connection and the output stud to ground. Capacitors develop leakage to ground over time, similar to what you are experiencing. This capacitor can be disconnected without any problems.
Yes....disconnect the battery and see what its voltage drops to over a few days. IF the battery's terminal voltage drops significantly, it is POSSIBLE that the battery has a bad or sulfated cell, causing the voltage to drop. Sulfation can occur any time and is not time dependent. If possible, measure the specific gravity of the electrolyte in the battery....the cell with the lowest specific gravity is the sulfated cell. If not possible, perform a load test of the battery.
BOB RENTON

 

[khryslerkid]

I have a battery that's in a car that sat for over a year. It's a five year battery and only two years old.

I slow charged it for a day and it came up to 12.7 volts. Let it sit for a day and it was down to 12 volts. The next twenty-four hours it dropped to 11.5 and so on.

I shook the battery, tilted it from side to side, then slow charged it again for twenty-four hours. Disconnected the charger, let the battery settle and the voltage was 12.7 again. Three days later it was still 12.7

Make sure the battery has the proper level of electrolyte in it. Try what I did to stir up any sediment on the bottom that can short the cell plates and give it a slow charge. I've even given them a hot charge for a small period of time then slow charge for twelve hours or so to revive them.

Your local parts store should have a meter to detect a short in the battery also. A hydrometer will show a bad cell if the top of the battery has removable caps. Call and ask.

 

[RJRENTON]

I have a battery that's in a car that sat for over a year. It's a five year battery and only two years old.

I slow charged it for a day and it came up to 12.7 volts. Let it sit for a day and it was down to 12 volts. The next twenty-four hours it dropped to 11.5 and so on.

I shook the battery, tilted it from side to side, then slow charged it again for twenty-four hours. Disconnected the charger, let the battery settle and the voltage was 12.7 again. Three days later it was still 12.7

Make sure the battery has the proper level of electrolyte in it. Try what I did to stir up any sediment on the bottom that can short the cell plates and give it a slow charge. I've even given them a hot charge for a small period of time then slow charge for twelve hours or so to revive them.

Your local parts store should have a meter to detect a short in the battery also. A hydrometer will show a bad cell if the top of the battery has removable caps. Call and ask.

Your comment: "Try what I did to stir up any sediment on the bottom that can short the cell plates" ....the sediment you refered to, is the result of the sulfate formation (lead sulfate) formed by the natural degradation process of a lead acid storage battery. Again, IF the specific gravity of the electrolyte can be measured, it is the best determination of the battery's condition. 1.260 - 1.270 specific gravity (corrected for temperature of the electrolyte) is the ideal range and the number decreases as the battery discharges. Sometimes, long slow charging over several days can be beneficial to reduce the sulfation effect (re-soluablization of the lead sulfate back to lead & lead dioxide and sulfuric acid) and can result in extending the battery's useful life... sometimes...
BOB RENTON

 

[Ed Martin]

Ed, I think you are reading the meter correctly.
0.0000022 amps is close to nothing.
@Ranger16 might be correct, maybe as simple as a bad battery.
A .7 Volt drop over 4 days from that low of leakage current doesn't jive.

Thanks Don. That's exactly what puzzles me. Such a small current backflow through the alternator should not cause this. I wonder, if it's a bad battery, would it drop like that when disconnected? I am trying to monitor that for a while.

 

[Ed Martin]

I have a battery that's in a car that sat for over a year. It's a five year battery and only two years old.

I slow charged it for a day and it came up to 12.7 volts. Let it sit for a day and it was down to 12 volts. The next twenty-four hours it dropped to 11.5 and so on.

I shook the battery, tilted it from side to side, then slow charged it again for twenty-four hours. Disconnected the charger, let the battery settle and the voltage was 12.7 again. Three days later it was still 12.7

Make sure the battery has the proper level of electrolyte in it. Try what I did to stir up any sediment on the bottom that can short the cell plates and give it a slow charge. I've even given them a hot charge for a small period of time then slow charge for twelve hours or so to revive them.

Your local parts store should have a meter to detect a short in the battery also. A hydrometer will show a bad cell if the top of the battery has removable caps. Call and ask.

Interesting … I will have to see if I can get it checked out at the store. Thanks

 

[Ed Martin]

Your comment: "Try what I did to stir up any sediment on the bottom that can short the cell plates" ....the sediment you refered to, is the result of the sulfate formation (lead sulfate) formed by the natural degradation process of a lead acid storage battery. Again, IF the specific gravity of the electrolyte can be measured, it is the best determination of the battery's condition. 1.260 - 1.270 specific gravity (corrected for temperature of the electrolyte) is the ideal range and the number decreases as the battery discharges. Sometimes, long slow charging over several days can be beneficial to reduce the sulfation effect (re-soluablization of the lead sulfate back to lead & lead dioxide and sulfuric acid) and can result in extending the battery's useful life... sometimes...
BOB RENTON

Thanks Bob. I will check the specific gravity with my hydrometer.

 

[451Mopar]

I would verify the test meter can actually measure current. It may have blown the current protection fuse inside the meter.
Do the same test on the 10 Amp scale, and open a door so the dome light comes on. A single #1004 dome light should pull about 1-Amp of current.
You can also place a test light between the battery and battery cable to see if current is flowing.
I would still suspect the alternator diodes.

 

[khryslerkid]

Your comment: "Try what I did to stir up any sediment on the bottom that can short the cell plates" ....the sediment you refered to, is the result of the sulfate formation (lead sulfate) formed by the natural degradation process of a lead acid storage battery. Again, IF the specific gravity of the electrolyte can be measured, it is the best determination of the battery's condition. 1.260 - 1.270 specific gravity (corrected for temperature of the electrolyte) is the ideal range and the number decreases as the battery discharges. Sometimes, long slow charging over several days can be beneficial to reduce the sulfation effect (re-soluablization of the lead sulfate back to lead & lead dioxide and sulfuric acid) and can result in extending the battery's useful life... sometimes...
BOB RENTON

Learned all of that back in the sixties when batteries were batteries. Now days they can be like light bulbs, one time they work, next time they won't. And most will fail right at their rated "year of expectancy".