alternator dead ??? Options

[SirAndy]

my volt-meter dropped to ~10V while driving, dead battery i thought ...

i measured the battery with the car turned off, 12.5V on the terminals.
i started the car, 11.5V on the terminals. checked at the alternator, 11.5V ...

alternator dying ???
(IMG:http://www.914world.com/bbs2/html/emoticons/confused24.gif) Andy

[JoeSharp]

Andy: Check voltage before the regulator, should be more than batterie.
:PERMAGRIN: Joe

[SLITS]

Es ist tot meine Furher...................

[dmenche914]

12.5 is a bit low for a battery. I'd first try charging the battery overnight, (disconected from car) and see if it gets up to about 13-14 volts if it still remains at 12.5 volts, then i would think the battery is on its way out.
I'd do this first, cause it is easy, just set it up over nights, and see what yu have in the morning.

Strange that it dropped so much when you ran the car, does it drop even more when head lights are on? changes with higher rpm?

A drying battery can pull down teh voltage, as one cell of the six may be shorted. This prevents full voltage in a charge

. If battery is good, before chucking the alternator, make sure the connections including the ground strap is good.

you could also swap a known good battery in today if you don't want to wait overnight for a charge, and see if situation is fixed with that. (I assume most 914'ers have spare cars for a spare battery source) Be sure to swap out teh battery, not just jumper it to the existing one, casue if teh existing one is shorting, it will also draw down teh voltage on the other battery.

good luck

[lapuwali]

I disagree. 12.5v for a battery w/o the alternator charging is perfect.

[dmenche914]

Per offical VW manual 1970-1978 for Bug Ghis, etc...

section 8, subsection 4.3:

".....In normal charging, the battery is considered fully charged when it is gassing freely and the voltage of the individual cells has risen to 2.5 to 2.7 volts each (about 15 volts for the battery). An hour or so after you have switched off the charging current, use the voltmeter /tester to determine the rest voltage of the battery. This should be 2.1 to 2.2 volts per cell, or approximately 12.5 to 13.0 volts for the battery."


So 12.5 volts is on the low end for the rest voltage, and much too low for a battery that has just come off charge.

note it is not totally clear to me on: "use a voltmeter tester" if the test is under load or not, the "tester" pictured in fig 4-1, captioned; using voltmeter to test total voltage of battery" shows a meter with a load attached. An extra load on the battery will drive down the voltage.


Sir Andy: is the battery voltage you meaured with the battery connected, or disconnected to the car? If connected the lower reading may be ok, if there is drain on it (radio, short, alarm etc....) If disconnected, and just after you charged it, then the read is low. If still connected, and/or it has not been recently ran (ie charged) then 12.5 may be just fine.

Just be sure to check all the groundstraps before chucking the alternator, bad ground straps can cause chronic under charging.

good lcuk

[SLITS]

A charged battery will see 12.5 volts...if checked immediately after charging..maybe a 0.5 volt more.

With the car started, it will see less than 12.5 if the alt isn't working because the ignition and fuel circuit all take power.

Any alternator system that is working will see about 14 volts at the bat terminals when the vehicle is running......unloaded.

A VOM only tests for voltage...unless you have shunt (resistor coil) for placing a load on the battery/alternator and then it would have to have AMP capacity readout.

[r_towle]

Andy,
Go to Sears and have them put an AMP test on your battery. It is called a battery load test.

A volt test will not tell you the real condition of the battery under load. Usually the test is free.

I would not trust the volt meter in the car either...I think its a rough guess and is meant to alert you to a change in condition.

If your battery test out fine, follow the wire from the alternator to the relay board...
Stick a volt meter tester on the alternator side of the relay board..you have to leave it plugged in while doing this...
My dad taught me a great trick for this...
Take two pin (sewing pins) and push them through the insulation of the wires...then you can test the alternator while the car is running. It should produce alot more than 12 volts...I am not sure of the spec.

If that tests ok, and you are still getting less than 13-14 volts at the battery while running, its is a bad voltage regulator...

I'll give you Dad's laymans terms...how he taught me...

The battery is designed to hold 12.75 volts. in order to obtain that voltage, you must pour more than that into the battery all the time while charging...
So, your charging circuit should always be above what your battery is in a standing state, in this case 12.5-12.75 volts.

I have found that all I needed to do sometimes is take the voltage regulator off, clean the terminals, and put it back, bingo, all is well again...

Take a look, mine was all green and corroded.

Rich