23 replies to this topic

[Milo1997]

wondering if anyone can help , every morning i go out to my car go to start it and nothing not a sound no light nothing , so i go and jump it off and fires up straight away after letting it charge for a while id turn it off but when i come back half an hour later again there's nothing no sound no lights anything ive put the multimeter on the alternator and that's putting out about 13 volts anyone got anything else ?

[KernowCooper]

13v is not enough to charge the battery, the regulator in the alternator is normally 13.7-14.3v if its not making between those voltages at 2000rpm+ its not charging. Do the tests in the FAQs on the charging circuit here http://www.theminifo...ng-basic-tests/

[Milo1997]

thanks will try tomorrow , but would the battery die so quickly ?

[Milo1997]

would the car not even have enough life in the battery even to show a light on the dash ?

[KernowCooper]

If its dead flat and not charging then jumping it and let it charge wont charge it, in its current charge rate 13v is way to low, a flat battery with a good charging system takes many miles to fully charge, Once a battery is dead flat then its sulphated and will never give 100% again.

[Milo1997]

by dead flat do you mean 0.0 volts or just low voltage ?

[KernowCooper]

You mention no light nothing in the morning so that battery is flat and might have a very small voltage, but if the 12v 2.5w ignition light wont power thats flat Milo

[Milo1997]

so what do you think i should do , go about diagnosing if the alternators at fault ? 

[CityEPete]

Id try running it for a minute without the battery attached, see what voltage you are getting at 2000 rpm, if the battery is buggered it might be skewing the result, might just need a new battery.

[KernowCooper]

Hang on a minute, running with the battery removed is not good the alternator wont like it, if its not faulty it is now, the method is fully charge the battery let it stand 4hrs test the voltage

 

12.65v is 100% charged

12.45v is 75%

12.24v is 50%

12.06v is 25%

 

If you see 12.45v your battery is sulphated and wont be at its best during cold cranking, replacement is immenent

If you see less the battery is heavily sulphated and needs replacement

 

If you do see 12.65v the battery is now suitable for a load test which a tyre/battery company can do for free

 

Either way you either come back with a battery which has either passed or a new one.

 

Install the battery and carry out the alternator tests

[Milo1997]

think there might be a drain on the battery i set my multimeter to 10 ohms removed negative clamp put one end on the clamp and one end on the terminal and its showing around about 7ohms but when i remove second fuse down in fuse board under the bonnet it drops to 0.00 any ideas ?

[CityEPete]

I'm only talking about running it for twenty seconds to test the alternator output.

[KernowCooper]

The instant you remove the battery the Alternators finished, with no capacitor ( the battery) between the + and - terminals the alternator voltage spikes to around 200v, this is outside the range of most diodes (approx 50v) and the diode pack is blown at best most likely the voltage regulator as well.

[CityEPete]

Well I have never seen one blow like that, in an instant. Running with a dead shorted battery or one that has no circuit would be just the same, ive seen cars showing a few volts at 2000 rpm with a good alternator as the damaged battery is making the readings go to pot.

[cal844]

The instant you remove the battery the Alternators finished, with no capacitor ( the battery) between the + and - terminals the alternator voltage spikes to around 200v, this is outside the range of most diodes (approx 50v) and the diode pack is blown at best most likely the voltage regulator as well.

I change batteries with the car running