Voltage Drop Problem

[ltmark]

I have had a problem, for some time, with voltage drop when my '85 coupe sits for a week or so. After reading several forum questions, I hooked up my volt meter, in series, with the red battery wire. With doors closed, no accesoreis on, etc., the meter reads 12.89 volts. I read that hooking up a simple test light in the same manner should only show a dull light due to a radio clock, etc. and that the light would brighten if the door was opened, etc. My light was pretty bright with nothing supposedly drawing current. When the door was opened, the light did brighten further.

Question....Should the meter have read 12.89 under the conditions above, or am I not testing correctly? I pulled each fuse, one by one, with both the light and meter, with no change in the voltage reading OR light brightness?

Any help would be appreciated.

 

[Edmond]

How old is the alternator? The battery?

 

[ltmark]

The battery is brand new and the alternator is about 6 months old.....The reason the battery is new is becaue since rtirement, my wife doesn't drive it that much and it's eaten 3 batterys just sitting arouns a going dead on me

 

[G Winter]

Try unhooking the alternator and check the voltage. could be a bad diode or a short in it. Just a little food for thought .

 

[WhalePirot]

Fully charged, each cell is 2.2vdc. Six cells multiply to 13.2 vdc, fully charged. It CAN be overcharged, BTW. There is not need to connect your voltmeter in series, unless you are measuring current draw. Is there an issue starting the car after it sits? Maybe you need to enjoy more of the non-rush-hour driving in the sunshine!

Another alternative is to use a battery maintainer. The solar powered types can be found for $20-30 and will keep the battery up to snuff. Similarly, a plug-in type can be permanently mounted or not and NAPA sells a good quality unit for about $30.

Ya see, the electronics in the new cars slowly drain the batteries. It adds up over weeks to ruined batteries. I heard once that a discharged battery loses 30% of its capacity after going dead.

 

[WhalePirot]

Try unhooking the alternator and check the voltage. could be a bad diode or a short in it. Just a little food for thought .

NOT RUNNING, of course?

You can check alternator output with either your dash voltmeter or your hand held. After starting, it will read 14.5vdc or so, then slowly reduce to about 13.5 as the battery is recharged; assuming daylight, lights off.

 

[G Winter]

:duh I should have added to check for a current draw with alt. unhooked and not running. What the mind thinks don't always end up on the page. Thanks for making that a little more clear Whalepirot.