How to check Alternator for function

[MudRunnerTD]

Hi Gents,

After our recent snow trip and winch recovery where i fried my cranking battery (End of life i think) i recharged the battery and got a week out of it before it left the wife stranded. RACV sorted her out. I swapped out the battery for an old new battery (bought new for the GQ but sat in the shed a couple of years and recharged for maintenance a couple of times) and she got 3 days before having a flat battery again.

She called me yesterday as she was nearly home to tell me a number of dash lights and come on (Sub tank, Glow, and a couple of others) while driving. She got home and parked it. When i got home i checked the battery and it was reading 12.1v. I have had it on charge all night and it shovel be good to go.

I think the lights coming on suggest the Alternator is gone? can anyone suggest otherwise? Note the car has 275k on it and this is the first alternator so I've had a good run.

Can someone explain how i go about checking the Alternator for function? Do i just rev the car and see the voltage output on the battery terminals or do i need the check the back of the Alternator? If i need to check the Alternator what and where am i checking and what settings on the multimeter and i looking for please.

Anyone got a good price on an Alternator for a 2005 TD42Ti

Thanks in advance.

[4bye4]

Side of the road quick check; with the engine stopped put a volt meter across the cranker battery terminals and check the reading. If the battery is good you should see 12.4 or so volts. Start the car and at idle read again, the voltage should be 12.4 or better. Rev the engine and watch the meter, you may need help or have very long leads or legs, the voltage should increase with revs to a max of about 13.5 to 14 volts, then stabilise. If the volts go above 14 volts and keep increasing, stop the car. The regulator is stuffed and it will cook your brand new battery. If the alternator is faulty the battery voltage will just decrease from the static voltage you read first. Hope that makes sense. Incidently, odd combinations of dash lights or all dash warning lights is nearly always an indication of a stuffed alternator.

[PeeBee]

I would say that a good battery condition is 12.68 - 12.72 with a charge rate at idle of circa 13.8 - 14.0, and fast idle of 14.2 - 14.3, with a boost voltage to top up straight after crank of say 14.5- 14.6. Above this, as 4bye4 has stated its getting into damage territory for the battery and the electronics I understand. Further than that I head to the auto elec as he is skilled better than I am to trouble shoot. Hope this fills in a piece of the puzzle.

[MudRunnerTD]

Thanks gents, Just took it off charge and the battery held 13.7v. I started the car and it dropped to 12.4v. Revved the engine for no discernible change at all. It would seem there is Zero signal from the alternator.

[Softy]

On the alternator there will be the "thick" post on the rear of that, that wire is the one that runs to the battery to charge it.. Hook the multimeter up to that with the motor running.. Just be aware of the fan belt etc because they can quickly eat fingers or said multimeter if you not paying attention. lol

[jff45]

It's a good idea to check the output at the alternator post to be sure that the connection between alternator and battery is not broken.

[MudRunnerTD]

Helpful thanks guys, when i revved the engine there was not even a tickle of change, not a flicker on the Multimeter reading to 2 decimal points. I thought that a little odd even for a dead alternator. I will have a good look and see if i can find a broken wire thanks guys. Missus has the car now.

[GQtdauto]

If the alternator really shits itself it can and will drain power , peebee is spot on with his voltages , as for new alternators try either Patrolapart or auto8 .

[Hodge]

It's a good idea to check the output at the alternator post to be sure that the connection between alternator and battery is not broken.

This +1 .
Always check alternator volts at the alternator. I found out the hard way when I had similar issues with my Navara. What had happened, the alternator was charging fine, but the cable between the Alt and battery was so annealed, it was letting very few volts through, giving me a false reading at the battery end.

[MudRunnerTD]

This +1 .
Always check alternator volts at the alternator. I found out the hard way when I had similar issues with my Navara. What had happened, the alternator was charging fine, but the cable between the Alt and battery was so annealed, it was letting very few volts through, giving me a false reading at the battery end.

How did you find that Eric?