[Mgs] Battery/Alternator question (Non-MG)

[Richard Ewald]

It could be a battery, a draw or the alternator. (I'm assuming the cables
are clean and tight.)
Turn everything off, lock the car and remove the negative battery cable.
 Hook a test light between the cable end and the battery post.  If the
light lights, you have a draw, find it and fix it.
Then let the car sit for at least 4 hours (or overnight even better) with
everything off.
Measure the voltage at the battery before starting the car, and you will
have a good indication of the state of charge of the battery
12.6V or above = fully charged
12.45 = 75% charged
12.25 = 50%
12.00 = 25%
Below 12 Dead player
The alternator is not designed to charge a dead battery, it is designed to
keep a fully charged battery fully charged, or charge a mostly charged
battery.  If the battery measures at 12.25V or below, you need to put it on
a battery charger.
After you charged the battery (if needed) measure the standing voltage
start the car wait about 10 seconds and measure voltage at the battery with
the engine running.  It should be in the 13.5-14.5V range.
If it is above that range you have a bad regulator (built into the
alternator), if it is below you either have a bad alternator, or a voltage
drop in the cables.
To check for a voltage drop, with the engine running and the headlights on,
place one end of your voltmeter on the case of the alternator and the other
end on the battery (-) terminal.  You should measure 0.2V or less.  Above
that and you have a bad ground.  Could be the battery cable, or it could be
the small ground cable from the alternator to the engine block (blue in
color)
If that test is OK, repeat the test going from the alternator output
terminal to the battery (+) terminal.  Again you should be below 0.2V.
If the alternator tests good, and there is no draw, it is probably a bad
battery.
Hope this helps.
Rick

On Sat, Jun 23, 2012 at 10:31 AM, Joseph Cianciotti <jmc987 at verizon.net>wrote:

> This morning my non-MG vehicle (1993 Volvo 240) wouldn't start. It cranked
> a
> couple of times and then died. I measured 12+ volts at the battery. Hooked
> up
> the charger/starter to the battery, waited a couple of minutes and the car
> started right up. I measured 13.88v at the battery. Let it run for about a
> 1/2
> hour, the turned it off. Let it sit for another half hour and it started
> right
> up (though it was warm this time). I have a new Bosch alternator in the
> car.
> The battery is a few years old (I really can't remember). What do you guys
> think? Time for a new battery?
>
> Sorry to ask a non-MG question. But you're the best group of mechanics I
> know.
> Thanks in advance for your sage advice,
>
> Joseph Cianciotti
> 1967 MGB Roadster
> 1993 Volvo 240
> 2004 Subaru Forester
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