Alternator question

Hi all,

Let me begin with this info - 1990 740 wagon 130K on B234f engine.
Battery checked by Les Schwab's and found to be OK.

Last week I had to get a jump to get it going, the first time since I
replaced the battery about 3 years ago. I put a charger on it all night
and, so far, no more problem.

Question - I have a small digital volt meter that plugs into the lighter
outlet. When I start up in the morning it reads around 11.7V, as I see
it that's a net loss for the battery; once the engine etc are all warmed
up it reads around 12.9 to 13.5V, a net gain for the battery.

My feeling is that the alt. is on it's way out the door.

Any ideas?

Thanks much,

Perk >)

 

Don't know about checking the voltage at the lighter or the accuracy of
a tester that plugs into a lighter.
If you check it at the battery with the motor running you should see 14.4V.

Either something is draining the battery or the battery is toast.

A fully charged** battery should read 12.65V.
Voltage and charge states:
12.65V=100%
12.45V=75%
12.24V=50%
12.06V=25%
11.89V or less=Discharged

**Some more reading:
<http://www.batteryuniversity.com/partone-13.htm>

 

Thanks Clay, I'll check it, prob. tomorrow, and get back to you.

 

Don't forget that it takes a lot of juice to start the engine, the
battery could be a bit weak but still acceptable and drop down a bit
after starting until the alternator replenishes it.

I would be curious to see if it drops further after sitting for a few
days though, it's easy enough to measure the drain with the car off,
glove box lights in a lot of cars are notorious for sticking on and
causing battery drains.

 

Thanks James, I'll check that too.

P. >)

 

How was it tested, with a load tester? At the battery it should go to
around 14+v for awhile and back off to around 13.6- 13.8. Cables need
to be checked and they can eventualy break inside the insulation, the
ground may be bad. Why didnt the guy check alternator output when he
checked the battery. At that age cables need looking into also as it
wont charge with bad cables.