1979 battery problem--need some help

[72and86]

I picked up a 1979 thats been sitting in the seller's driveway. I have several issues that need to be addressed before it can see the road...
First, is the battery (thats in excellent condition). It holds a charge and starts the car, but unless I disconnect it after an hour, the battery is dead. (once the car is started I can disconnect it and the car is fine... For now it is driveway-bound till I can solve this & a few other problems.)
Whats killing this battery and where do I start? :huh:
Thanks in advance...
Steve

 

[jeffn]

1)Take the bulb out from under the hood. 2)Is your power antenna always running?(does it operate properly?) 3)Does your anti theft system work?..4) Does the plunger switch work when the hood closes?......These are a few things to look at right off the bat.....Any one of those items can drain the battery overnight..........Do this first...Take a look at the car in a dark garage and look for light .It could be something as simple as your interior light switch being in the on position.....If none of that is the problem......we'll go to plan B.......

 

[72and86]

1)Take the bulb out from under the hood. 2)Is your power antenna always running?(does it operate properly?) 3)Does your anti theft system work?..4) Does the plunger switch work when the hood closes?......These are a few things to look at right off the bat.....Any one of those items can drain the battery overnight..........Do this first...Take a look at the car in a dark garage and look for light .It could be something as simple as your interior light switch being in the on position.....If none of that is the problem......we'll go to plan B.......

Will do tomorrow. I dont believe there is a hood bulb, there is no power antenna and there is no after market anti-theft system. This is a bare bones Vette, almost NO options. It even has manual windows. Is there a factory anti-theft system?
Thanks

 

[72and86]

1)Take the bulb out from under the hood. 2)Is your power antenna always running?(does it operate properly?) 3)Does your anti theft system work?..4) Does the plunger switch work when the hood closes?......These are a few things to look at right off the bat.....Any one of those items can drain the battery overnight..........Do this first...Take a look at the car in a dark garage and look for light .It could be something as simple as your interior light switch being in the on position.....If none of that is the problem......we'll go to plan B.......

The battery also dies while the engine is running too. I takes about an hour to die.
I tested the battery on DCV while the engine was running and seemed to get a reading of 14.3 DCV. The battery not hooked up tests at 12V.
Then I switched to ACV and got random numbers flashing which made no sense but it seemed to settle on 0.001. Im not used to the digital multimeter.
Now what?

 

[Vettehead Mikey]

Don't use any AC (alternating current) settings on your multimeter, only DC (direct current).

Try reading battery voltage with the engine running, but with all the electrical accessories turned on- headlights, brake lights, blower, rw defroster etc. If you don't have 14 volts or so your alternator is weak and not really charging.

If OK, you have power drain somewhere. Disconnect the battery, then remove all the wires from the alternator and cover the exposed terminals with insulating material. Attach the battery again and see if the battery still discharges. If so you probably have a bad diode set in the alt.

 

[72and86]

I tested the battery w/everything i could running, fan, lights, wipers and got 11.3 DCV reading.

 

[Vettehead Mikey]

Ah-ha!. Sounds like a weak alternator. Take it off and have it tested by a car parts store to confirm. If this is the original unit for your car, I would hang on to it and have it repaired. If not trade it in on a new or rebuilt, they're not too expensive.

I'm rebuilding two of my spares right now with kits off eBay.

 

[72and86]

How hard is it to rebuild?

 

[vetteboy86]

You could have a week battery draw, that is causing the battery to die. Especially with the week alternator problem.

To track down a battery draw, this is what I have done in the past.

Use the multimeter to measure current. Disconnect either side of the battery(whichever is most convenient). Then complete the circuit using the multimeter. This will allow you to measure current. You should get a reading if you have a draw on the battery.

Now, with the meter hooked up, write the nominal value down. Then remove one fuse at a time from the fuse cluster. If the value drops when you remove a fuse, there is a draw in that circuit. Sometimes it is tricky because you need to have the door open, and that would case interior lights to come on. However, I have done it many of times. You will also be able to get a nominal reading with the door open. It will be higher than when the door was closed. However, you can still track a battery draw with the door open. Write the number down with the door open. Pull one fuse at a time, and if the current recording goes down, same scenario, battery draw is in that circuit. Remember off course that when you pull the fuse for the interior lights it will decrease.

If nothing happens, then possibly the batter draw is on the interior light circuit. The readings should be in the milliamperes, unless you have something really pulling some juice!

Clear as mud?

 

[Vettehead Mikey]

How hard is it to rebuild?

Rebuilding a GM/Delco alternator

 

[72and86]

Rebuilding a GM/Delco alternator

awesome! Now the eBay link please...:eyerole

 

[LLC5]

Make sure your alternator belt is tight, if you can spin the pulley with your fingers using the pulley fan on the alternator (with the engine off of course, key out of the ignition), then it is too loose and the belt is probably worn also. Fully charge the battery also and have it load tested to make sure it is good.

 

[72and86]

Make sure your alternator belt is tight, if you can spin the pulley with your fingers using the pulley fan on the alternator (with the engine off of course, key out of the ignition), then it is too loose and the belt is probably worn also. Fully charge the battery also and have it load tested to make sure it is good.

Thanks. I will check that too.

 

[73shark]

Most auto parts stores can test your alt and batt on the car. So if you can drive to a close one, you won't have to remove them.

 

[72and86]

Yeah, i cant drive it yet w/o risk of getting caught. No registration.

 

[Vettehead Mikey]

awesome! Now the eBay link please...:eyerole

Here is a link to the seller:

eBay Canada Seller: s-and-d-repair: Automotive, Home Garden on eBay.ca at low prices

look for kits to repair a 10SI series alternator. You want the ones that contain both bearings, the rectifier, regulator, diodes and brush holder with brushes. This guy even includes a little tool to hold the brushes back so you don't need to look for a paperclip. Mixture of US and offshore parts.

 

[72and86]

Thanks for everyone's help. Many of you have pointed to the alternator. So I bought a NEW one on eBay for $31. It wasn't worth rebuilding for $31.
So I will keep everyone posted once it's installed.
Steve

 

[Mr. Chuck]

The battery also dies while the engine is running too. I takes about an hour to die.
I tested the battery on DCV while the engine was running and seemed to get a reading of 14.3 DCV. The battery not hooked up tests at 12V.
Then I switched to ACV and got random numbers flashing which made no sense but it seemed to settle on 0.001. Im not used to the digital multimeter.
Now what?

A reading on the meter set to AC volts at the large alternator (output) terminal would indicate that one or more of the diodes on the rectifier block inside the alternator have failed (are open) and needs replacement. This results in an varying DC voltage output, which will in time damage your battery and any other electrical component that requires only DC power, like the radio. Things like lamps are typically not negatively affected by the variable DC, other than you may see the lamp brightness varying if the serveral diodes have failed. I had this problem on a 1970 Mavrick and went through two batteries before identifying the bad diodes in the alternator (noticed the flicking glove compartment lamp), replace the diode block, problem solved.

 

[72and86]

A new Alternator solved the problem. Now I can leave the battery hooked up w/o it dying...:laughing:
Thanks to everyone for your help...

 

[Mr. Chuck]

A new Alternator solved the problem. Now I can leave the battery hooked up w/o it dying...:laughing:
Thanks to everyone for your help...

One potential problem laying in wait is un-seen internal battery damage caused by the alternator / diode failure. Technically, a battery is recharged by applying a reverse direction current, this chemically changes the lead sulphate (created during discharge) back to lead peroxide, resulting in a charged battery. The defective diodes, i.e. varying DC voltage causes the battery to rapidity go from re-charge to non-re-charge states. Bottom line, this cause the battery to get hot, even very hot to the touch, a secondary negative effect is that the lead plates begin to flex and this speed up the lead plate material flacking off process.
Batteries normal dis-charge and re-charge process causes plate flacking, but at a much slower rate over a longer period of time. Battery designers allow for this process and build-in valleys at the bottom of the battery to collect the loose flacks so they don't create electrical shorts across the bpttpm of the lead plates. Eventually the flacks pile-up and shorts out the repective battery cell & a dead battery. A shorted battery that remains connected to the alternator power wiil over heat, causing battery bulge, then rupture. Worst case is major damage from leaking acid or even cause a fire.
The hot touch test is quick, plus a visual inspection of the battery for case bulging could prevent major damage / repair cost and should be part of ones normal periodical fluid level inspection.