rodgling
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| posted on 26/3/12 at 07:07 PM |
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Battery or alternator?
Took the car out for a good long run (over an hour) at the weekend, but now it's struggling to start unless I charge it for ten minutes first.
What's the best way to test if this is the battery or alternator at fault?
cheers
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AdrianH
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| posted on 26/3/12 at 07:17 PM |
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With the engine on a slightly higher then tick over rev. Put a multimeter across the battery terminals on Volts and you should be seeing the voltage
at around 13.8 to 14 Volts.
That would indicate the alternator is charging.
What I would also do if you have a meter that will measure current at say a few amps, switch everything off on the car, lights anything.
Take off the connection to the positive terminal and put the meter temp in between the positive terminal and any wire you put on there. Check there
is no current drain out of the battery, caused by say a duff diode on the alternator or some other device that is slowly discharging your battery. Do
not switch anything on or attempt to start the engine with your meter in series.
If you find the first charging volts OK and no slow discharge buy a new battery would be my answer.
Sorry if telling how to suck eggs.
Adrian
[Edited on 26-3-12 by AdrianH]
Why do I have to make the tools to finish the job? More time then money.
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daviep
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| posted on 26/3/12 at 07:19 PM |
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Check the voltage across the battery terminals with the engine running - should be more than 13.5volts if the alternator is charging. If less you need
to do a bit more to identify the problem, not nessecarily the alternator but this is the simplest check to start the process.
Cheers
Davie
EDIT: Damn my slow typing
[Edited on 26/3/12 by daviep]
“A truly great library contains something in it to offend everyone.”
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britishtrident
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| posted on 26/3/12 at 07:25 PM |
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If the alternator is ok it will charge the battery at anywhere from 13.4v to 14.9 volts at anything over 1500 rpm ---- less than 13.4v then no
charge at all goes into the battery >15v will blow bulbs, overcharge the battery and potentially damage all the electronics in the car.
First check the charging voltage without any load them switch the main beam on and check the charging voltage then take the rpm up to 3,500 and
switch the lightsback off while looking at the voltmeter at all times the voltage should not be outside of the 13.4 to 14.9 volt range
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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rodgling
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| posted on 26/3/12 at 07:59 PM |
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Thanks guys, that's useful info. It did spend about an hour idling while I faffed around looking for air leaks so maybe the battery got drained
while I was doing that - didn't realise it wouldn't be charging at idle.
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britishtrident
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| posted on 26/3/12 at 08:12 PM |
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quote:
Originally posted by rodgling
Thanks guys, that's useful info. It did spend about an hour idling while I faffed around looking for air leaks so maybe the battery got drained
while I was doing that - didn't realise it wouldn't be charging at idle.
But idling doesn't drain the battery the alternator will still be pushing a few amps in.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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