Hi,
What would be the symptons if my alternator was failing, (other than not charging the battery).
I'm trying to determin wether my alternator is faulty or if the battery is no longer holding the charge. Is there a way I can find out.
If the alternator was weak, would it affect the car whilst driving in any way.
Cheers
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Have you tried recharging the battery using a charger? If it holds its charge this way then you know its the alternator at fault.
Also worth checking the voltage across the battery when the engine is running which should show you the charging voltage. Can't remember the sort of figure you should expect but IIRC if its outside 14.2-14.6v then there's problems. I'm sure someone will correct me with the correct charging voltage range.
When I had a failed alternator the headlights were very dim while driving along, which wasn't pleasant as it happened at night in the middle of nowhere (or Wales as its otherwise known ;) ). Whereas with a dodgy battery and a good alternator you would expect the headlights to light reasonably well.
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And the car is??
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If the alternator is not charging the battery, then driving with lights on, heated rear window on, lowering an electric window etc should dim the lights, plus the battery will go flat quickly - possibly the "no charge" warning lamp will light too. As has been mentioned, check voltage across battery terminals with car at idle, then when revving the engine. If you don't have a voltmeter, take it to local auto electricians.
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You need a voltmeter which can read in the range 10 volts to 15 volts in 0.1 volt increments.
After the car has stood for at least an hour after a run, check the battery voltage with no load (or charge over night then leave to stand for 2 hrs). It should be 13.2 volts if the battery is fully charged. 12.6volts is ok, but if it's as low as 12.2 the battery is virtually flat.
Start the car and check the voltage with the engine idling and no loads turned on. The voltage should be at least 13.5 volts, preferably nearer 14.5 volts. Now switch on as much load as you can and raise the revs to 2000. The voltage should still be at least 13.5.
Pull the fuse from the fuel pump, release the remaining fuel pressure and disable the HT. Crank the engine for 30 seconds with the throttle fully open. The voltage should not fall below 10 volts after this time.
These simple tests should give you the clue you're after.
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Winter time shows up faults in connections. Before you do anything technical check your terminals are clean and the clamps are tight. Then check the earth connection to the body or maybe the gearbox, is also clean and tight.
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Might be showing my age a bit here but nobody seems to check for voltage leaking across the top of the battery, fundamental stuff from my H**e T***e days which has paid off countless times. Get your voltmeter, and place the 'pos' probe on the 'pos' terminal, now here comes the tricky bit... place the negative probe near to the '-' terminal, not touching it and note the reading. If the top of the battery is all horrible and clarty you might see as much as 11 volts! this is sufficient to flatten a battery in a short time as the battery is actually shorting across all the crud and dampness on top of the battery. Move the probe slowly across the battery near to the filler plugs and look for any sudden voltage changes. Cure is to spray the top third of the battery with WD40 then clean with a dry cloth paying particular attention to the terminals. Any electrolytic corrosion on the 'pos' terminal can be washed off with boiling water then treat with grease or petroleum jelly.
Andrew
Simplicate and add lightness!!
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