Alternator Output Voltage

Safeman · Aug 14, 2007

Hi Everyone, Having recently fitted a new alternator to my P38 4.6HSE I was wondering what the voltage should be if checked across the battery terminals with a volt meter and with the engine running. Anyone Know? This is my first post on this site.

Dorset VogueSE · Aug 14, 2007

With the engine running it should be around 14.5 Volts across the battery and a fully charged battery should be around 12.2 volts with the engine off.

Hope this is some use

Nigel

redrange · Aug 14, 2007

Dorset VogueSE said:
With the engine running it should be around 14.5 Volts across the battery and a fully charged battery should be around 12.2 volts with the engine off.

Hope this is some use

Nigel

you sure?
i thought with engine off the voltage would be nearer 13.2volt!
6x wet lead acid cells each producing 2.2 volt = 13.2v.
(unless you have a drain somewhere in which case you prob wont start up tomorrow)

Dopey · Aug 14, 2007

[FONT=Arial, Helvetica, sans-serif] A good battery, after a full charge, should read approximately 12.8 volts (open circuit with nothing connected to battery) or pretty close. Float voltage @20C (voltage with the alternator charging the battery) should be about 13.6 volts. These voltages vary more than you would think with temperature and battery chemistry (the type of battery e.g. gel cell, flooded, AGM). A few tenths of a volt is the difference between a "good" battery and a "bad" battery. Low open circuit voltage on a fully charged battery = inability to deliver any substantial current. Use the manufacturer's tables and a GOOD voltmeter (millivolt resolution and accuracy). Manufacturers of high quality batteries will be able to provide the voltages, maximum charging current and charge times, With cheap batteries you will be pretty much on your own. Batteries of a given type, such as all flooded lead-acid batteries, will have roughly the same characteristics so you might be able to "fudge" by using the data from a different manufacturer.

Warning: cheap batteries are no bargain[/FONT]

Safeman · Aug 14, 2007

For reference the new alternator is a Denso 120amp/hr and the new battery is an Exide 75 amp/hr . Both these were changed due to the vehicle failing to start if not used for 2/3days. I would also add that the Rf Receiver was changed to YWY500170 after reading various posts on this forum about battery drain

I have now tested as suggested and with the engine running at 1500rpm the voltage was 13.85 volts. With the headlights on at the same time the reading fell by about 0.50 volt.With the engine turned off the battery showed a reading of 13.20 volts

Dopey · Aug 14, 2007

Seems about right?

did the Rf Receiver fix your draining problem? seems to have sorted mine out, the + is i can lock the doors etc form more than 5m away now getting used to it is another thing though, i still walk right up to it and unlock it on the fob, i can lock/unlock it from over 5 meters away now

Alternator Output Voltage

Safeman

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Dorset VogueSE

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redrange

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Dopey

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Safeman

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Dopey

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