Charging System Checks

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E_T_V
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Joined: Thu Jan 29, 2009 9:38 pm

Charging System Checks

Post by E_T_V »

If you suspect problems then a multimeter is an invaluable tool. You can typically pick up one for under a fiver at the likes of maplin etc and you'll find loads of uses for it once you have one!

With the engine off a healthy battery will be in the region of 12.5 volts.
With the engine running the voltage across the battery should be 13.5-14.5 volts. (Too high indicates a faulty voltage regulator on the alternator - these can often be replaced separately to the alternator itself. Too low and more checks are needed.
If you then turn on the heater, heated rear window and headlights, the voltage should remain above 13 - 13.5 volts. If not then more checks are needed.

If the voltage is low for any reason then check the security of the battery terminals. If loose then secure them. Also check the security of the earth straps as they are known to fail. There is one to the chassis then onto the gearbox. And another to the front "slam" panel which the bonnet closes onto. These are a common failure point.
Check the cable from the alternator to the starter-motor/battery. Check that the alternator connector is clean and secure and the same goes for the other end of the cable too. Check it hasn't melted or shorted out on anything too.

If the voltage is still low and the battery is known / tested to be good then the alternator is the prime suspect.

If the battery light glows when the ignition is turned off but goes out when the engine is running then the diodes in the alternator have failed and it needs reconditioning.
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