ZoraC3

Here is the course of events. I have had the car for approximately 6+ years.

Mechanic changed my power steering rack and power steering pump a few months ago. I drove the car home, Ran well. I did not drive the car for a couple of months (too hot down her in FL). I go to start the car and the battery is dead.

I looked and the battery was replaced in the past 9 months. I took the battery back to Interstate batteries and they said it had a bad cell. They replaced the battery under warranty.

I put the new battery in the car and drove approximately 50 miles. I park the car for 2 weeks and went to start the car. The battery was dead. I assumed I had a bad alternator or voltage regulator. I pull the alternator off and take it to Advance Auto Parts. They check the alternator and voltage regulator on their machine and say they everything checks out as good.

I then try to charge the battery and it will not charge. The auto parts store tries to charge to charge the battery and they say that it has a bad cell.

So, this is the second new battery that has a bad cell after being in the car for a very short period. The alternator and voltage regulator have been tested and check out as good.

What is the next course of action? Could it be a bad ground for the negative battery cable causing the alternator to continue charging the battery and kill a cell? I know everyone is going to suggest checking the connections with a multi meter. Sadly, I do not have access anymore to a shop and lift like I did in Atlanta.

What is your guess? Where to check next?

69427

Check for a parasitic current drain. It's easy to kill a battery if it's drained down to nothing and held there for a long time.

ZoraC3

When the battery was checked today, it was down to 10 volts. That should not be low enough to kill the battery.

I am thinking that overcharging is what killed the cell in the battery.

sparky77

Easy to check if the system is over charging ,start the engine and take a voltage reading across the battery should be about 14 volts.If the the battery is dead after setting for a week than as stated above it's a slow drain ,could be something like you're under hood light is staying on.

Andredechimpansee

Best to unhook the battery when stalled for more than a week.
strange you never had this problem before. Or was this the first time you stored the car for months?
When charging use a quality charger. Especialy when trip charging for longer periods.
When fast charging check out the max charging Amp for your battery. Best to keep at least 1A under.

Ydnar44

I encountered same battery drain, checked for drain, lights staying on etc. Installed disconnect on ground at battery, when going from open to closed I heard a distinct relay click from console, was the alarm relay triggering, removed relay, been good since. I do have an AIM for my 80, I was as able to use that to determine what was under the console first

4SPDL81

Maybe you got two defective batteries in a row....?

jb78L-82

I have had a GM CS-144 140 amp alternator on my 78 for years and it charges at 14.4 volts with no battery issues. As other have stated, check the charging rate when the car is running. Also, you should have a battery quick disconnect like I have for over 20+ years and always cut the battery voltage to the car if the car is going to sit for more than a few days...battery will last a VERY long time...my last Costco battery lasted 14 years.

https://www.paragoncorvette.com/p-35...ct-switch.aspx

I would get an interstate or Costco/kirkland battery..............

ZoraC3

I have never had a parasitic drain, since I have owned the car. Sometimes would sit for 2+ months and would start right up. (My 1963 had a parasitic drain and I was lazy and put a battery cut off, in my younger years)

I understand a parasitic drain could develop, if the alarm relay, etc has recently gone bad. I have purchased a battery cut off this week. I plan on using it, even if I find a parasitic drain and cure it. I know how to check for drain, with a meter on the negative battery terminal. I plan on looking at that soon, but I do not think it is my problem with new batteries being killed and having to be replaced. (Please notice I did not say that my new batteries have been drained and not starting the car, my charging system is killing cells in the new batteries) A parasitic drain should not kill a cell in a brand new Interstate battery twice in a row, after driving the car once and sitting for a week or two.

A parasitic drain, pulling the volts from 12 to 10 over a 3 week period should not be able to kill a cell on a new battery. The only thing I can think of is that the alternator and voltage regulator are good, as bench tested, but the voltage regulator is overcharging the battery, due to a bad ground for the alternator or a bad ground for the battery.

Or, can a voltage regulator pass a bench test, but fail intermittently? The bench test does not appear to take the alternator to a high rpm. Can a VR work at low rpm and fail at a high rpm, therefore overcharging the battery?

Hammerhead Fred

More likely your field or sensing wire going to the alternator is broken/weak and fails to allow the regulator to properly charge the battery.

ZoraC3

HH Fred, my field and sensing wires are not in the original clip that connects to the alternator. They are wired separately. The way I checked that they are hooked up correctly was to switch them and see if the generator light turned on. The generator light on the dash came on with the way it was wired when the batteries were killed.

Any other way to check that they are connected correctly?

Richard454

If you are "positive" there is no parasitic drain-

Overcharging- depending on the voltage- it's likely to be burning out bulbs and you would see the bulbs going brighter.

Have you checked the AC ripple coming from the alternator- AC more than .5 volts can be a problem- and the battery trying to rectify the AC ripple will cause problems.

Test at the output of the alternator - turn on the headlights and run engine to 1800-200orpm to see what AC voltage is present.

Richard

Hammerhead Fred

Looking from the back of the alt (as if sitting in the driver's seat) there are two terminals. I'd use left & right but your alt clocking may not necessarily have these terminals between the 10-2 o'clock position.
So; These terminals are just clockwise from the +BAT positive wire connection point.
The terminal closest to (just to the right of) the +BAT alt positive wire is the field terminal and the smaller brown wire goes there. The larger black w/Wh stripe wire goes to the other terminal AKA the sensing wire. The sensing wire monitors and prevents battery overcharging.

mrvette

Locate and toss all them stupid 'curTOSSY lights in any car....not needed.....let alone in a vette.....take a DVM in current mode to the battery, in series with one of the posts, don't matter which....see ANY current draw on a non computer car....gotta find it, old as these cars are, first place to look is for water/moisture damage on the fuse block, down LO where it's a bitch to get to much less SEE the damn thing.....

pull fuses one at a time till you get the correct one, that is the circuit with the drain.....could be power windoze, door locks, wipers, even headlights due to a bad switch assy.....

wonder about the brake light switch...see that it's working right....ON AND OFF, not some silly failure......

OH, I need to add.....on the back of the alt, as viewed from driver location the MOST CLOCKWISE and if a replacement connector is used it is the RED wire.....stock vette was some other colors....that MOST CLOCKWISE connection is always hot....the one with the white wire/lesser clockwise is switched.....that stock vette wiring is silly and very confusing because the wires look the same, and anyone replacing the connector can easy reverse those wires, and cause a drain on the battery.....revealed when you unplug the thing with a DVM in current mode as suggested above.....



Need any help...PM me......GENE

Garys 68

Yes, a 4 wire alternator can be ok for bench testing and overcharge in the vehicle.
The sensor wire controls the amount of voltage put out. If there is a drain downstream in that circuit, the voltage will look low at the alternator, but could overcharge the bsattery.
Put a voltmeter on the battery terminals while driving, turning lights, radio, etc on.
These cars get wiring mods from every owner. Who knows how stuff is hooked up any more.
An intermittent diode in the rectifier can also result in AC current output, resulting in high voltage, but you would see that on the dash voltmeter.

diehrd

Alt is bad ..

ZoraC3

Here is the UPDATE........

Interstate batteries charged my battery and said that it was marginal, but to put it back in the car and then check the charging system.

I decided to go to Napa this morning and get a "new" alternator. No harm in replacing an old alternator for $60.

I install the alternator and battery. With the key in the ignition, the gen light is on. The car starts fine and the gen light goes out. The alternator is putting out 13-14 volts at idle and 14-15 volts at 2000+ rpm, per the gauge on the console.

I turn off the car and remove the key. With the key in my pocket, the gen light is on. I pulled the field/sensing wires on the alternator and the gen light goes out.

I have been reading on CF and other websites. The gen light illuminates if the voltage is different on the 2 inputs. My first thought is that the ignition switch is keeping the circuit open. (Note:No accessories function, with the key out) The ignition switch was replaced last year, by a reputable corvette shop. Maybe it has come out of adjustment?

Most threads suggest that a diode is bad in the alternator, keeping the light lit, with the key out. I know a "new" reman alternator could be bad, but the charging system is working and the gen light is out, when the car is running.

I don't want to tear into the column, if someone thinks this is not the problem.

Thanks again for all of your help.

Hammerhead Fred

I wonder if your Alt is grounded properly to the motor and/or via the harness.
You're not using powder coated brackets are you?
Try this.
Hook the sensing & field wires back up to the alt.
Run a separate ground (temp) wire from the battery to the alt body and see if the gen light goes out. (good temp wire for this is a jumper cable.


Also: verify that the battery connections are connected correctly (+ to starter & - to frame below box) and not the wrong way round.

FYI: response 2 on this thread has perfect photo of rear of alt with field/sensing wire arrangement.
Verify you have the same.
https://www.corvetteforum.com/forums...ubba-wire.html

ZoraC3

Thanks for the response, HH Fred.

On my alternator, the small brown wire is on the #1 post on the alternator. All good there.

I will try to hook up a wire from the alternator to the negative battery post, to ground they system, to see if that is my problem. I will post the results.

ZoraC3

Since I had to evacuate for the hurricane, I haven't tried to ground the alt to the battery. Next weekend I will work on it.