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Strange goings on - charging
speedyxjs - 8/12/09 at 09:09 PM

Battery voltage when engine off is 12.2v

Start engine, battery voltage starts climbing after about 1 minute up to 12.3v.

I was always told that it should be around 14v across the battery when the engine is running so how come it seems to be charging the battery?

JohnN - 8/12/09 at 10:14 PM

It should be just under 14v, else it isn't charging the battery.

Ben_Copeland - 8/12/09 at 10:35 PM

Yep, appears you have an alternator problem/wiring problem

Should be near 14v

AdrianH - 8/12/09 at 10:38 PM

Have you checked you volt meter is accurate, or it does not have faulty leads?

speedyxjs - 9/12/09 at 07:15 AM

quote:
Originally posted by AdrianH
Have you checked you volt meter is accurate, or it does not have faulty leads?


Yeah, its fine. This is really bugging me now.

If i want to check its wired properly, can i attach the multimetre to each pin on the alternator to see which one is putting out the right voltage or is that likely to screw it up?

02GF74 - 9/12/09 at 08:11 AM

Depending on which alternator you have - you are keeping that secret, right? - you need to rev the engine a bit, say 1200 rpm for the alternator to "kick in" - self-energise and produce output.

for meaning ful measurements, put multimeter across the battery terminals and run engine at 2,000 rpm.

If you are seeing 12.3V, then that is simply not good enough.

All cells in you battery seem ok as you are seeing over 12 V.

Does you ignition lamp go out when engine is running?

Grimsdale - 9/12/09 at 08:24 AM

i presume you haven't got an ecu controlled alternator?

speedyxjs - 9/12/09 at 08:30 AM

No, not ecu controlled. It is from a mk 2 fiesta. I blipped the throttle but that just made the number increase faster.

britishtrident - 9/12/09 at 08:40 AM

Charging voltage depends on a few things including ambient temperature, battery condition and other loads.

Cold weather can knock 0.5 volts off the battery voltage.
You can't test the the charging voltage if the battery is in a partly discharged state or has dead or gassing cells.

Best way to test charging voltage is

1 Charge battery for a few hours.
2 Leave battery to stand for at least an hour -- over night is better. Check battery voltage should be 12.5v to 12.8v depending on temperature.
3 Do a cranking voltage test should be over 10v -- under 9v indicates battery problem ie dead cell
4 Start engine and warm it up
5 Measure charging voltage at a steady 2,000 rpm with electrical loads (head lamps & heater blower) on and off should be at least 13.4v but less than 14.9v and voltage should not jump when load is switched on and off.

Modern cars tend to charge at the top end of the voltage range.

jollygreengiant - 9/12/09 at 09:42 AM

And just to be certain its the alternator and not a connection/wirring problem, check the alternator voltage output AT the alternator.

[Edited on 9/12/09 by jollygreengiant]