Alternator starts charging after reaching 3000 RPM

Thread Starter

Alex Radu

Joined Nov 22, 2018
1
Hello all,

I have a 2004 Seat Ibiza and I decided to change the alternator because it was worn out. The old alternator started charging past 2000 RPM. After reaching 2000 RPM, even when coming back to idle, the alternator was charging. Idling for hours will just drain the battery.

After changing the alternator, the behavior is the same with only a difference: the trigger is now at 2800 RPM.

Now I suspect that the Field wire can't hold 2A because the wire might have thinned in time due to a design flaw (wire is touching somewhere or the connection at the ECU is faulty).

I need to know if I can directly connect 12V to Field. Has anyone done this?
 

drc_567

Joined Dec 29, 2008
1,067
Possibly you are right ... but often the problem is an old or worn out battery. Is your battery in good condition, with freshly cleaned cable clamps? What is the voltage between the battery terminals? Is there a parts store near you that will test the new alternator in order to verify its operation?
... If the factors mentioned are not an issue, then something unusual is occurring.
 

drc_567

Joined Dec 29, 2008
1,067
... The alternator performance is likely controlled by an I.C. regulator ... so the field will not be readily accessible from an external terminal. Check the alternator fuse, the ignition fuse, and the gauge fuse. These fuses have to be intact.
 

bwilliams60

Joined Nov 18, 2012
1,381
I am going to assume the alternator is internally regulated. Have you done a voltage drop test on the battery positive and battery negative cables to the alternator? Have you load tested the cables? Was the pulley changed at all on this unit, Is it loose or oversized? Does it have an idiot light in the dash and if so, does it go out and at what RPM? Are your belts all good and tight? Any belt tensioner issues? Has the battery been load tested?
Often when you have an alternator with late turn-on, it is to do with the magnetic field of the rotor not inducing voltage into the stator or an issue with the regulator. This unit should turn on around 1000 RPM or less.
Do not full field this unit and leave it like that. You will regret it. Answer the above and we can figure this out.
 

MaxHeadRoom

Joined Jul 18, 2013
22,373
One advantage of the alternator over the older DC generator is the alternator is capable of full output at Very low RPM.
Feeding the field on a typical alternator with full 12v can produce in excess of 50v -60v.
Max.
 

cork_ie

Joined Oct 8, 2011
428
Hello all,

I have a 2004 Seat Ibiza and I decided to change the alternator because it was worn out. The old alternator started charging past 2000 RPM. After reaching 2000 RPM, even when coming back to idle, the alternator was charging. Idling for hours will just drain the battery.

After changing the alternator, the behavior is the same with only a difference: the trigger is now at 2800 RPM.

Now I suspect that the Field wire can't hold 2A because the wire might have thinned in time due to a design flaw (wire is touching somewhere or the connection at the ECU is faulty).

I need to know if I can directly connect 12V to Field. Has anyone done this?
The short answer is no, you cannot connect the field directly to 12V, if you do you will likely have no voltage control and do damage.
The 2004 Seat Ibiza either petrol or diesel is fitted with a Bosch or Valeo Alternator. Neither of these is connected directly to the engine ECU. The Bosch is fitted with an F00M series regulator and the warning light pin on the regulator provides a negative path to the warning light circuit that is removed once the alternator starts to charge. The Valeo alternator operates in a similar manner. The cut in speed (when alternator starts to charge) should be around 700 engine RPM . Typically alternator speed is about 2-2.5 times engine speed depending on pulley ratio. I have no idea why the alternator is not charging below 2,800 RPM but if correct it is either a faulty alternator or an incorrect pulley ratio.
I suggest that you retrace your steps and check that you have the correct alternator fitted and that it is charging properly. If you need help please post the alternator part number and the engine code of your car (AWY, AZQ, BBY are popular engine codes) it will be on the white label fitted in the spare wheel well.
 

gerty

Joined Aug 30, 2007
1,298
Another thing I would consider is pulley diameter. If the pulley is much smaller than the one on the old alternator you would need higher revs to produce a charge.
 
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