Roughly 12/27/03 21:47, Tibur Waltson's monkeys randomly typed:

> Today I load test the alternator by an instruction in an aftermarket repair
> manual. The instructions says to turn on headlights, defoggers, fan, radios,
> cigarrete lighter, etc and measure the voltages. It reads 13.6V at 2000 rpm
> or 11.2V at 750 rpm. It's within normal range according to the book. But the
> headlight seems a bit weak unless rpm is above 1300 rpm or sometimes it just
> too weak for the starter. We hardly drive in the highway. It has an alarm
> system. Is the alternator fine?

It looks like the alternator is OK, but the battery itself
may be on its way to failure.

You may want to try AutoZone or Sears for a quick check of
your charging system and the battery itself.

First make sure that all of the battery connections are
squeaky clean and tight. If the cable posts are loose
inside the battery might as well head to the battery store.

You can load check the battery itself with similar test as
above.

With nothing connected, the battery should read 12.4 volts. If
below that, it isn't charged fully or is defective. If you
have a battery charger, try it.... but replace any battery that
can't hold 12.4 volts or higher with no cables connected.

Then make sure the battery isn't just taking a surface charge
by giving it a load, then check the open circuit [no cables]
voltage again. Turn on your headlights [with battery connected]
for 15 minutes, then turn them off and wait 5 minutes. The
battery should still show at least 12.4 volts. If it can't,
it is getting old and is only taking a surface charge.

With no-load and the headlight 15 minute load test, rough battery
voltages for charge are:
12.0 volts = 25% charge
12.2 volts = 50% charge
12.4 volts = 75% charge
12.6 volts or more = 100% charge

If the battery is 5 years old, swap it anyway if it is a premium
model. If not a premium model, derate that to 4, 3, 2 years.


--
Fan of the dumbest team in America.