Alternator Pulley size

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plg422d
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Alternator Pulley size

Post by plg422d »

I have just fitted a new alternator from Bull Motif. The new pulley is smaller than the old one.

It is charging, based on the Volt meter but doesn't seem to be charging as fast as the old one did. Will swapping the pulley over solve the problem?

Thanks
mogbob
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Re: Alternator Pulley size

Post by mogbob »

Are you happy that the fan belt is tight. The implication of your post is that it was a straight swop ... alternator for alternator.. is this correct ? ( not swopping a dynamo for an alternator ).
What DC charging voltage did you get on you Multi meter with the engine running ?
Bob
plg422d
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Re: Alternator Pulley size

Post by plg422d »

Thanks Bob.

Yes it was an alternator for alternator swap. I was basing my comments on the voltmeter fitted in the car.

Not sure where/ how to measure the voltage output. Can you advise?

Thanks
greendefender123
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Re: Alternator Pulley size

Post by greendefender123 »

A smaller pulley will charge quicker as it has to spin more so is spinning faster.
oliver90owner
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Re: Alternator Pulley size

Post by oliver90owner »

The voltmeter does not tell you anything about the charging rate other than if the battery voltage is low (or high). The ammeter measures the charging (or discharging) rate.
mogbob
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Re: Alternator Pulley size

Post by mogbob »

Testing an Alternator with a Multimeter to see if it is charging correctly : -

Set the Multimeter to Volts DC , up to 20 volts setting. On a cold engine ( not run recently i.e the battery has settled ).
Record battery voltage , Black probe on " - /negative battery terminal " and Red probe on " + / positive battery terminal "
A fully charged 12v battery should give you a 12.6 / 12.7 volts reading. Note /record.

Place the Multimeter between earth and any convenient battery connection , such as a Brown wire at the fuse block. Start the car and rev the engine. The reading should rise from 12.6 volts to greater than 13.5 volts. This is a good indicator that all is well and the Alternator is charging.
If satisfactory test , a belt and braces check is : - after switching off engine , put on the headlights for about 10 minutes. Repeat the test , double checking that 13.5 volts + result is the same. If not , there is a problem with the Alternator.

Oliver90owner's comments are correct , IF either a Voltmeter or Ammeter is fitted to a car. That is , a Voltmeter indicates the state of charge for the battery and the Ammeter records the rate of charge or discharge.
Bob
plg422d
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Re: Alternator Pulley size

Post by plg422d »

Thanks all for the advice and information.

The Alternator is putting out 14v when the lights have been left on and charged the battery to 13v.

Previously the voltmeter in the car would show 13v when the car was running normally but is only registering 12v now, a separate Multimeter is giving the results above. I am beginning to think the Voltmeter has stopped reading correctly, which is a co-incidence but they do happen!
mogbob
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Re: Alternator Pulley size

Post by mogbob »

Good result. WELL DONE !
Might be worth disconnecting the battery for a moment and check the tightness of the connections at the back of the Voltmeter and that they are clean metal. ? Just a thought before you condemn the voltmeter.
Bob
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