Testing alternator
Discussion
Test the voltage at the battery. It should be between 12 and 12.5 volts with the engine off, assuming the battery is reasonably well charged, and should be higher with the engine running. Increase the revs steadily with the engine running; the voltage should rise to maybe 14.5 volts or so, but should not exceed 15, and should not fluctuate wildly.
This will test whether the alternator is charging or not. If the charge warning light is still flickering despite the alternator charging ok, it is either a bad connection somewhere, or the voltage sensing circuitry inside the alternator is playing up.
This will test whether the alternator is charging or not. If the charge warning light is still flickering despite the alternator charging ok, it is either a bad connection somewhere, or the voltage sensing circuitry inside the alternator is playing up.
Edited by Sam_68 on Thursday 6th July 21:26
Just tested as you said..
Think i might need a better multi-meter
it reads to the end of the scale in all cases (end of scale is about 14v poss 15v) or does this mean it's had it ??
Have had the battery on charge for a couple of Hrs as need the car a.m. for a short journey. The charge light didn't come on though
Think i might need a better multi-meter
it reads to the end of the scale in all cases (end of scale is about 14v poss 15v) or does this mean it's had it ?? Have had the battery on charge for a couple of Hrs as need the car a.m. for a short journey. The charge light didn't come on though
If it reads that high with the engine off, then your voltmeter is screwy!
...unless you had been running the engine just before taking the first battery reading. If a battery has been on charge (whether alternator or battery charger) it takes a while to settle down to its normal level of voltage.
Leave it another hour, then take a reading of the battery voltage before starting the engine. If it is still reading off the scale, there is a problem with your voltmeter (or the way you are reading it).
If the voltage of the battery when the engine is not running is ok when it has been standing a bit (12 to 12.5 volts), but it rises off the scale when the engine is running, then the voltage regulator on the alternator is faulty.
In any event, no offence, but if you are having trouble with something as simple as taking a voltage reading, my advice would be to take it in to a garage - kwik fit type places will usually do a check free of charge.
Alternatively, Gunsons (who I would not normally recommend for anything, 'cos most of what they sell is appalling, cheap tat) do a little gadget called a 'Start Check' which is pretty much numpty-proof. Simply connect it to your battery and the little row of LEDs light up to tell you whether the battery is ok and, with the engine running, whether it is overcharging.
...unless you had been running the engine just before taking the first battery reading. If a battery has been on charge (whether alternator or battery charger) it takes a while to settle down to its normal level of voltage.
Leave it another hour, then take a reading of the battery voltage before starting the engine. If it is still reading off the scale, there is a problem with your voltmeter (or the way you are reading it).
If the voltage of the battery when the engine is not running is ok when it has been standing a bit (12 to 12.5 volts), but it rises off the scale when the engine is running, then the voltage regulator on the alternator is faulty.
In any event, no offence, but if you are having trouble with something as simple as taking a voltage reading, my advice would be to take it in to a garage - kwik fit type places will usually do a check free of charge.
Alternatively, Gunsons (who I would not normally recommend for anything, 'cos most of what they sell is appalling, cheap tat) do a little gadget called a 'Start Check' which is pretty much numpty-proof. Simply connect it to your battery and the little row of LEDs light up to tell you whether the battery is ok and, with the engine running, whether it is overcharging.
Edited by Sam_68 on Thursday 6th July 21:51
Sam_68 said:
Test the voltage at the battery. It should be between 12 and 12.5 volts with the engine off, assuming the battery is reasonably well charged,
12.5v is MINIMUM for a charged battery, 12.3v is a 'click, click, click' FLAT battery for most cars
Sam_68 said:
. Increase the revs steadily with the engine running; the voltage should rise to maybe 14.5 volts or so, but should not exceed 15,,
With the engine running at idle , newer cars will put out 14.5volts rising to 14.8 at higher revs. Older cars (pre '96 approx) will put out 13.5 at idle & 14.5+ at higher revs.
Max volts is about 15.5,
if the charge light is dimly on then it usually means one phase has gone the car will work for some time
but the alternator needs replacing
have the car running with all electrics on if the voltage is less than non running electrics off value then the battery is discharging higher voltage then it is charging
but the alternator needs replacing
have the car running with all electrics on if the voltage is less than non running electrics off value then the battery is discharging higher voltage then it is charging
splatspeed said:
if the charge light is dimly on then it usually means one phase has gone the car will work for some time
but the alternator needs replacing
have the car running with all electrics on if the voltage is less than non running electrics off value then the battery is discharging higher voltage then it is charging
but the alternator needs replacing
have the car running with all electrics on if the voltage is less than non running electrics off value then the battery is discharging higher voltage then it is charging
Thats better 
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