TDI 130 Alternator problems

Hello, I have a Seat Ibiza TDI 130 Sport from '03 which has started to behave a bit strangely. It has a dashboard mounted voltmeter standard from the factory, and from the
day it was new it always reported 14v with the engine running, no problems there. However, in March this year, it started reporting 12V or less when the engine had just started, and will not reach 14v until the engine reaches 2000rpm almost exactly, everytime. It's like the alternator does not switch on until 2000rpm is reached. When the car returns to idle it stays at 14v.
I reported it to the dealer, and they initially thought that the alternator needed replacing, which they did, but the problem is still there and now they're claiming this is normal - although it clearly isn't because the car never used to do that.
The alternator has been replaced, a new one is clearly visible, as is the rear-section of the alternator, which is where I believe the rectifier is? Any ideas what's causing this problem? The revs required to turn it on are gradually increasing, and I'm worried it'll leave me stranded one day.
Cheers ~
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I would have thought the voltage meter is battery voltage rather than the charging rate.
it could be that the battery has extra load such as any aftermarket add-ons or needs replacing in the near future
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snipped-for-privacy@abbeycrossSPAM.co.uk says...

Glowplugs? Early March was *very* cold IIRC. I was at Center Parcs (Lake District) and when I went to pick the car up from the carpark ~3rd March, the temperature gauge was showing something like -8, and I'm pretty sure it reads a few degrees high!
Pete.
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Still doing it, and it's 20 degrees today.
I hadn't thought about the glowplugs though - is it possible that they're being left on after the engine starts, and this is draining current (hence lowering the potential?) only switching off when the engine reaches 2000rpm?
Unlikely, but I have no idea how to explain what I'm seeing.
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The glowplugs remain on for upto 2 minutes after the engine has started (helps lower emissions), or until the engine has been revved above aprox. 2k for a few seconds, which would explain the low reading until the engine has been revved. Plus it could be that the battery is slightly weak, meaning that the alternator is struggling to bring the battery voltage back up as well as power the glow plugs.
If you restart the car while it's hot, does the voltmeter behave the same way?
If not, I'd ignore it.
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Ah - this does indeed sound similar to my symtoms. But why did it suddenly start doing this in March? Previously, the voltmeter went straight to 14v in any circumstances.

Yes it does, it behaves like this whatever the situation straight after starting.
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The alternator output is hard wired to the battery, so battery volts alternator volts. And anything over about 13.5 volts means the battery is being charged.
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does the alternator warning light work ?
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No warnings lights are showing, and I'll check that the warning light is actually working tomorrow (good idea). However, once the engine has revved over 2k rpm, the alternator appears to be working fine, voltage only dips a bit when the fan comes on.
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the warning light is usually essential for proper operation. if it is not working then it will self energise if you rev high enough.
mrc
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Hmmm....distinct absence of a warning light on my dashboard. The manual (03 Ibiza TDI 130) says all models have one in the bottom-left hand corner, but there's nothing!

Can you explain this in more detail please?
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On most cars the warning light gives the signal/energising current to the alternator so that it can start charging. If there is no warning light then usually they can get themselves going if you rev them to a high enough speed (sounds like your symptoms)
mrcheerful
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mrcheerful

Some that excite the field via the warning light have a resistor in parallel with it so if it fails the alternator still works.
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This does indeed sound like my problems, however, I have just spoken to a better informed person at the garage who says that the alternator is an LED on the circuit board that controls charging. If the circuit board fails, then the LED does not light and presumably the engine enters 'safe mode' until 2k revs are reached.
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Hmm...
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the
LED
Even with no excitation provided by the charge warning lamp, *some* alternators will begin charging of their own accord anyhow- but not until its spun to a much higher rpm.
Tim..
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Check glowplugs and make sure they're switching off. If the engine is at operating temp, they shouldn't switch on.
JOhn

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