If a battery is charged up to 15V and the next morning that battery is down 12.7V. Is this the sign of a weakening battery?

 

are you load testing or with a volt meter?after charging it is normal for the volts to drop or normalize (i made that word up)but it should stay close to 13 volts with out use,at least for a couple of days...a battery in storage will lose a small amount of voltage over time...i dont remember just how much but a few weeks shouldnt be a problem.....load test and use a hydrometer to get a real idea of the batterys condition........tao

 

No I'm not load testing it, I'm just measuring it with a voltmeter.
My alternator makes the whining sound when I turn the lights ON or the rad fan is ON. The voltage drops from 14V to just below 12V and then the alt starts whining up and down with the RPMs. Seems to get louder when hot.
I replaced the old 20 yr old alt with a newly rebuilt one, still whining.
Got the new alt tested at the parts store where I bought it, checked OK.
Got the battery tested at the the same store, checked OK.
Still whining.
Change alt belt, the old one was done, still whining.
Now trying to find a short, but lights and rad fan are on separate circuits. Unless there's a short in both circuits, I don't know where to turn to.

 

if you disconnect the negitive battery cable and hook a test light bettween the cable and the post you will be able to see if there is a draw(the light is on)if there is start pulling fuses until it goes out...dont forget to disconnect the radio (clock memory ect.) hope this helps.....tao

 

I didn't get the test light to go ON but I did get my meter showing a 6.2mA draw. This of course was with the ACC fuse out, so no clock, no dome light or anything. Once I pulled the Hazard Light fuse out, I got 0mA.
That's not enough draw to make the alt whine.

I did a test to see how much juice I was drawing from the battery without any charger.

Ign OFF, Battery was at 14.34V
Ign ON (not RUN), drop to 13.56V (-.078V)

Test #2
Ign ON (not RUN), battery @ 13V
Turn Rad Fan ON, drop to 12.37V (-0.63V)

Ign ON (not RUN), battery @ 13V
Turn Headlights ON, drop to 12.32V (-0.68V)

Ign ON (not RUN), battery @ 13V
Turn Rad Fan + Headlights ON, 12.00 (-1V)

I was wondering if these voltage drops were normal?

Anyways, I'll take the car out for a test drive this weekend, it should stop raining here in Eastern Ontario. Thanks for your help!

Rob

 

they sound reasonable....ive seen a voltage drop as far as 10.23 when engaging the starter on a tight eng....good luck....tao

 

the squeeling will be seperate from the battery, and probabaly a problem. A rebuilt alt could be faulty, but i'd remove the belt from the alt if you can, to see if it's something else that's squeeling. If it's definately the alt (belt too tight?), then exchange it. It won't have a long life either way.

your voltages sound right, I wouldn't think you have a short or drain or anything.. When you go out to the car in the morning, it's not a dead battery every time right? So I wouldn't think there's a drain. I'd go to the parts store, and say, "hey, my new alt is whining!", take the guy out and show him, then rip out the alt and give it back to them, exchange for another one, and put it in, in their parking lot. (Love the rain eh?) That'll probably fix the whining problem.

 

I replaced the alt because my old one was whinning and thought it was the bearings. But while trying to take the pulley off to check the front bearings, the alt fell down off my vise and cracked on the cement floor. Anyways, decided after 20 yrs of use, this alt maybe due for a change. I bought this new exact 98A model from Canadian Tire, and it whined just the same. I got the battery tested, it checked out OK, I returned the alt, it also checked out OK, I changed the belt, still whining. I checked for shorts, the only thing I found was my Hazzard lights were pulling 6.2mA off the battery.
Now this whining only becomes noticeable when the engine is warmed up and when I turn on the rad fan, or I turn on the headlights. If I take the plug out of the alt (field and sensing) the whining stops, so it's not the belt. What I'm thinking, is the alt is working but perhaps working too hard. It will recharge the battery back up to 14V when the RPMs are up to 2500 or if I turn everything off at idle (which is not an option) but maybe it's an amperage problem the battery is lacking of. Hey! thanks for the advices.
Rob

 

If a battery has been drained dead once too many then it can start to self-discharge.. I once had a 10.5 years old battery that started drawing heavy charging currents. In the end I had to have the engine at 2000 rpm to get full voltage, and the battery would get hot from the continous 40A current. Still I was able to start the next day, but not after 3 days. After a resting period, 12.75V is regarded as 100% and 12.00V is 0%.
Even at a fast idle the generator should be able to keep 14.4V with the headlights on, but won't be able to deliver a full 98Amps until around 2000 rpm's. It should not whine. That could be an indication of one (or two) of it's three phases that's shorted or open. It would then be down to 66 (or 33) Amps capacity, but would still be able to retain the Voltage (but at corresponding lighter loads). You would be able to determine this if you had access to an oscilloscope.

 

I do have an oscilloscope. Do I take the reading from the Bat terminal on the back of the alt? Then should I look for 3 DC phases or 3 half positive cycles coming out? I should also check the diode trio and the coils with a meter?

 

Sorry for late reply.. Compliments to having an oscilloscope, not many do!
Yes, hook oscilloscope to the bat (B+) terminal on back of alt. Set the input to AC so you can use 0.1V/cm or something sensitive like that. Look for continous bumps with no flats in between. If there's 2 positive bumps and then a flat (or a negative bump) before 2 more positive bumps then the main rectifier is gone. If one of the bumps are much higher than the others then the small diode trio may be gone. This small trio may not be present in all alternator designs. If it's there then the alt has a D+ terminal that goes to a charge lamp in the dash, and you can scope it too expecting similar bumps.
If you suspect any of the diode trios you must disconnect them from the coils in order to check them with a meter. There's 6 diodes in the main rectifier and 3 in the small.

 

Well as I suspected, no bad diodes. I plugged my oscilloscope and got all half positive sine waves, although a little bit of noise but otherwise OK. I called the shop who tested my alt and they assured me if there would've been any bad diodes, the test would've failed. Although I'm using a manual choke, my choke heater relay buzzes whenever I pull the FP Fan fuse out. Only after pulling out the Gauge fuse out as well that the relay stopped buzzing. The choke relay uses the field sensing wire from the alt. So after disconnecting the choke heater circuit out of the instrument panel, the relay doesn't buzz anymore and the choke heater relay and its circuit is dead. GOOD!
However, my problem is still not gone. After checking the ground on the alt and the Rad Fan motor, I know the alt, the belt and the battery are all good, I'm wondering if the ECM might have something to do with this. Since everything has been replaced, the engine, the distributor and everything is back to old school hotrod, I'm thinking maybe I'll take the Eng Cntl fuse out.