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Alternator charges for 2 minutes, then stops, unless over 3k revs

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bigngroovy

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Location
cannock
Car
06 cdti tour-nav-hft
Hi all, my 2.2cdti battery was dead this morning, (clickclickclickclickclick when trying to start).put the noco jump starter on it and started no problem. Put the meter on the battery and was showing 12.6v whilst running, so not being charged by alternator. Saw that rise to 14.4v when revving over 3k revs, but straight back down when idling. Changed battery over for new and started car no problem, left idling and showing 14.4v on meter, (so alternator charging)... All of a sudden after almost exactly 2 minutes the meter reads 12.2v,so alternator no longer charging. Turned car off then back on, alternator provides 14.4v for 2 minutes more then drops to 12.2v. Tried again and again, always charges for 2 minutes then stops charging. No battery light on dash during any of this. Any idea what's going on? Thanks.
 
Check relays in the fusebox by tapping them with a hammer.

I once had a fault with another car where the glowplug energiser circuit would come on due to damp in the temperature sensor.

On an older car I also had a faulty cigarette fob, just under the fuse trip current.
 
0
antdad said:
Belt tension/wear perhaps, has it had the conversion to shorter serpentine?
Click to expand...

Hi, thanks, not had the shorter belt conversion. Bought a voltage displaying wotsit that plugs into the 12v socket and done some testing whilst driving. At constant revs driving, (say around 1700rpm),the voltage drops to 12.7v. As soon as I back off, the volts go over 14 for a short time then drop below 13 again. Accelerate and get same situation. When driving at constant revs, the volts drop but if I place a demand on the electrical system like lights or blowers, volts go to over 14v and stay there until I turn off the lights/blowers, then it drops below 13 again. No idea if this is normal... I'm thinking not, and that it should constantly read over 14v while engine is running.
 
My old alternator acted quite similar several years ago

It showed 14v whilst the engine was running but then it suddenly died after 5 mins or so.
Turned out to be the alternator.
They are easy to change, you just need a special long arm tool to release the tensioner and remove the aux belt.

What Noco jump starter model have you got that jump started the Ictdi engine?
Was thinking of getting one
 
Thanks, i changed the alternator about 4 years ago as it wasn't charging at all and alternator light was on dash. Had to get a socket and grind it down from both ends, then got a couple of strips of 2mm steel, welded it all together and have a great tool to release the belt tension.
Reading on the net, the alternator appears to be connected to an ELD in the fuse board (electrical load detector), which decides how much electrical generation you need at any given point, which in turn operates a clutch on the alternator pulley (in a similar way to an a/c compressor pulley clutch?). this is all for the sake of fuel economy, so if no electrical power is required, then the alternator would freewheel to save fuel.
Can anyone confirm this theory?

I have been using the car regularly for commuting and short distances and the battery hasn't gone flat yet, so that's a good sign.

If anyone (who is experiencing no issues) could get a voltage displaying wotsit for the 12v socket and see if they get the same result i'd appreciate the confirmation.

Regarding the noco, i have the boost XL (GB50). it's awesome, would start a fleet of V8 monsters no problem. (cost just over £100 from Halfords with trade card) money well spent i think.
 
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