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how to check if alternator is charging


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Take a voltmeter and connect it to ground an + while engine is off. Voltage should be around 12 to 13V. Then start the engine - voltage should go up to approx 13.5 to 14V. Switch on lights, fan and everything else - voltage should be stable (might need higher revs).

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You need to put a voltmeter across the battery and check the voltage while the engine is running.

You should see around 13.8 - 14.2 volts when charging and about 12.5 with the engine stopped (may be less when not charging depending on age and condition of battery.)

Any less than 13.8 volts charging would suggest the alternator is U/S but there could be wiring issues that can affect it too so don't condemn the alternator straight away if it's outside of the limits above.

Edit; must type faster ;)

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disconnecting the battery with the engine running isnt wise, as it can stop the alternator regulating the voltage properly.

If the Alternator is no good it wont matter :rolleyes:

Tried it lots of times and never had a problem.

If the Alternator no good, it can't keep the engine running because it can't produce enough power to power the pump ;)

Ash :D

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Quote "If the Alternator is no good it wont matter"

Indeed it wont matter at all - however if the alternator is working properly, the unregulated output can rise to 18 volts or more and you're seriously in danger of frying the cars electrics, especially if it's a later one with various ECU's, these electronic modules can be quite sensitive to over-voltage.

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