Battery or Alternator? - Alfa Romeo Bulletin Board & Forums
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post #1 of 17 (permalink) Old 06-11-2019, 05:56 AM Thread Starter
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Battery or Alternator?

I normally keep my '84 GTV-6 on a charger (have a two-year old Optima Red Top), but have not for the past week. The car started fine Saturday morning; pulled it out of the garage to wash/wax, turned it on/off several times for better placement in my driveway, then left it for the afternoon. Went to start it and nothing; it would crank but not turn over. Attached the Optima charger and left it overnight, started right up Sunday morning. Tested battery w/ a meter Monday evening after leaving car sitting for 24 hours without charger attached:

Cold - 13V
Idling - 12.5V
Idling w/ lights on - 12.25 (no flickering)

Reattached charger Monday evening (last night) and tested again:

Cold - 13.5

Shouldn't I get a minimum reading of 14V?

I've gotten 8-10 years out of Optima batteries when used with their chargers, so I'm wondering if its the alternator? Or maybe the attached voltage regulator? Thanks!
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post #2 of 17 (permalink) Old 06-11-2019, 06:05 AM
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A sound 12v battery should test at about 12.4 - 12.6 volts. If the battery was on a charger, the "top charge" will need to be removed before checking voltage. The alternator should charge the battery at about 13.5 - 14 volts. Have you checked for a current draw at the battery? A simple "test light" works best for this.

ALFA ANDY
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post #3 of 17 (permalink) Old 06-11-2019, 06:09 AM Thread Starter
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Thanks Larry. Exactly how do I use a test light to check for current draw? Also, haven't tried the "disconnect the positive battery cable while car is running" trick to see if car dies...
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post #4 of 17 (permalink) Old 06-11-2019, 06:55 AM
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Originally Posted by VaiVeloce View Post
Thanks Larry. Exactly how do I use a test light to check for current draw? Also, haven't tried the "disconnect the positive battery cable while car is running" trick to see if car dies...
Don't do that! The battery acts as a stabilizer/damper for the electrical system and you can damage components that way (think ECU).

Charge and test your battery as suggested and check for parasitic drains, and if that's OK, you either have either an under-charging alternator or a voltage drop somewhere that is preventing full electrical system voltage.

I have been living with some slight voltage drops in the wiring of my junkyard special '81 GTV6, but I know that some day I will need to replace the wiring between the alternator and fusebox. But you can start by checking and cleaning all major positive and ground connections in the engine compartment and at the battery.
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Chris A: '81 GTV6 rescued from junkyard, "GT" car/'86 Porsche 944 Turbo track/street car/'73 BMW 2002tii fun street car/'74 Jensen Healey Lemons Rally car!
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post #5 of 17 (permalink) Old 06-11-2019, 07:15 AM
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@cda951 is correct. Never disconnect either battery cable while the engine is running. To check for current draw: Engine off, all accessories off, doors closed, etc. Remove negative cable from battery and install the test light between the negative battery cable (end) and the negative post on the battery. If the bulb in the test light illuminates, touch the negative battery cable (end) back to the negative battery post (while the test light is still connected and illuminated) for just a second and then pull it away. If the bulb is still illuminated, you have a current draw.

ALFA ANDY
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post #6 of 17 (permalink) Old 06-11-2019, 07:23 AM Thread Starter
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Thanks! I was wondering about disconnecting the battery because I've read/seen differing points of view. I'll check for the drain tonight...
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post #7 of 17 (permalink) Old 06-11-2019, 07:32 AM
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You should be getting better than 14 volts when the engine is running, 14.2-14.4 would be great. I would test at something above an idle, 1700rpm maybe. There should be zero difference between the reading at the alternator and the battery. .1 volt at the most.
I disagree with what seems like the entire population about the battery tender thing. Batteries are by their very design are a storage medium for electrons. It's what they want to do. Battery tenders just keep pushing volts in and you have no idea if there are too many volts being forced into the battery which would cause the battery to gas out water. Once a portion of the water or whatever in there leaves your battery is toast. Better in my mind to just monitor standing battery voltage, like once a month or three weeks and throw a real battery charger on it when volts drops down to 12.0 for a couple hours.

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post #8 of 17 (permalink) Old 06-11-2019, 08:50 AM
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The previous post is incorrect.
Current from the charger will drop to zero when the battery voltage equals the charger voltage.
Volts are not "forced into a battery".
13.5 volts is normal for a 12 volt lead acid battery.

I have been responsible for industrial battery backup systems where the batteries are always on charge and they have a life of well over 10 years.

Ed Prytherch
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Last edited by alfaparticle; 06-11-2019 at 09:06 AM.
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post #9 of 17 (permalink) Old 06-11-2019, 08:55 AM Thread Starter
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post #10 of 17 (permalink) Old 06-11-2019, 09:05 AM
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Quote:
Originally Posted by andylarry View Post
@cda951 is correct. Never disconnect either battery cable while the engine is running. To check for current draw: Engine off, all accessories off, doors closed, etc. Remove negative cable from battery and install the test light between the negative battery cable (end) and the negative post on the battery. If the bulb in the test light illuminates, touch the negative battery cable (end) back to the negative battery post (while the test light is still connected and illuminated) for just a second and then pull it away. If the bulb is still illuminated, you have a current draw.
What exactly is happening when you perform this test? I would expect the bulb to light if it is placed between the negative cable end and negative terminal. Touching the cable end to the negative terminal effectively removes the bulb from the circuit momentarily so I would also expect it to go out. Pull the cable away and the bulb illuminates again, same as the first condition. How does that show a current draw?

Spending my kids' inheritance one mechanic at a time.
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post #11 of 17 (permalink) Old 06-11-2019, 07:35 PM
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You should be getting better than 14 volts when the engine is running, 14.2-14.4 would be great. I would test at something above an idle, 1700rpm maybe. There should be zero difference between the reading at the alternator and the battery. .1 volt at the most.
I disagree with what seems like the entire population about the battery tender thing. Batteries are by their very design are a storage medium for electrons. It's what they want to do. Battery tenders just keep pushing volts in and you have no idea if there are too many volts being forced into the battery which would cause the battery to gas out water. Once a portion of the water or whatever in there leaves your battery is toast. Better in my mind to just monitor standing battery voltage, like once a month or three weeks and throw a real battery charger on it when volts drops down to 12.0 for a couple hours.
There are numerous modern "smart" trickle chargers on the market (CTEK, etc) that automatically stop charging when the battery is fully charged, and begin to trickle charge again once the battery voltage drops below a certain level. Dozens of my customers use these with great success. They need to be connected directly to the battery terminals to be 100% accurate, which is a challenge in the modern cars with battery current monitors built into the negative terminal, but not in an old Alfa!

Chris A: '81 GTV6 rescued from junkyard, "GT" car/'86 Porsche 944 Turbo track/street car/'73 BMW 2002tii fun street car/'74 Jensen Healey Lemons Rally car!
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post #12 of 17 (permalink) Old 06-11-2019, 09:45 PM
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Buy one of the ciggy lighter socket plug in volt/amp digital displays to get an accurate idea of what the alternator is doing, and how well the battery is charged. I have one, and it works great.

I also use one of the little trickle chargers to keep the battery up in our less used 1994 164LS. Works well to keep the battery where it should be, confirmed by the little volt/amp plug in meter.

Del

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previously owned since 1964:

62 Morris MiniMinor 850, 67 Austin 1275 Cooper S (Downton 3/4 race), 64 Giulia Sprint GT (1st red one made), 72 Fiat 128 Sedan, 75 Alfetta Sedan, 78 Alfetta Sedan, 78 GTV, 81 GTV6, 86 GTV6
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post #13 of 17 (permalink) Old 06-13-2019, 05:14 AM Thread Starter
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Haven't been able to test further, but I plan on finding the time over the next couple of days. Will report back...
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post #14 of 17 (permalink) Old 06-13-2019, 05:20 AM
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Just take the car to NAPA or any other auto parts store. They will run a test on the battery and charging system for free.

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post #15 of 17 (permalink) Old 06-13-2019, 05:26 AM Thread Starter
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A good friend (and vintage BMW/Alfa mechanic) is stopping by either tonight or tomorrow; we'll figure it out...
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