Dimmed battery dashboard light

Hi!

For some days I have been having the battery light on the dashboard staying on, dimmed (not fully on, like when you just turn on the dashboard and not the engine). It may turn off, or may stay on, while driving. I checked with a voltmeter for voltage on the battery when the light is in this condition and, in idle, voltage is around 14 V, while it raises to 15 V and more under acceleration (checked with the car stopped by pulling the accelerator linkage on the carburettor).

Can this be a failing alternator or something else? I suspect the alternator should work if the voltage is that high, but who knows... Thanks!

Ciao,

complimenti per il tuo inglese!

It could be the diode pack in the alternator that is failing or a loose alternator belt.

Most non Japanese 12 volt charging systems should regulate between 13.7 and 14.3 volts. If yours is going over 15 volts then your alternator is working.

The fault will probably be with the voltage regulator. If your problem relates to the 1100 or 2400 in your username, then I think they had a separate regulator fixed to the bulkhead or inner wing in which case, the problem could also be the wiring between the alternator and regulator or the regulator earth connection.

Dave.

I suppose you meant "not working"?
The car I am referring to is a Tempra, so the regulator should be installed directly on the alternator. Will wait some days for checking what happens, for example if the light turns on brighter, then I will have the alternator checked by a technician.

Thank you very much for your appreciation of my written English, unfortunately I am not so good in speaking it as I am in writing

It seems you are right and it could be the diode pack, or regulator, because Davren says the voltages are a bit too high The belt is properly tensioned, since it was checked about a week ago when I had the water pump replaced.

No..... I meant what I posted "If yours is going over 15 volts then your alternator is working". It's the regulator that's not working. As you didn't say in your original post which car it was, I assumed it was one of the cars in your username, both of which have external regulators.

If your alternator is made by Bosch, Lucas or some types of Magneti Marelli, the regulator will be fitted on the back of the alternator and is easy to replace. Some Magneti Marelli alternators have the regulator inside and are difficult but not impossible to replace.

Dave,

Well, in the Tempra section I thought it was obvious I was speaking of a Tempra-related issue
Excuse me for the misunderstanding, but I use to consider the alternator as a whole, including the rectifier, and so reading first that > 15 V were OK and later that it should work between 13.7-14.3 V made me make some confusion. Didn't think that the AC voltage was OK and the DC one NOT!

It is a Magneti Marelli unit, I already had the rectifier section overhauled a couple of years ago, since then it won't charge the battery at all, so I suppose it can be replaced or rebuilt if needed.

Thank you!

Hi Daniele,

For a dim alternator light, that may go out sometimes, the first stop is the belt tension. Then check the connections are clean tight on the alternator especially the field connection, thats the smaller wire of the two to the alternator, it occasionally can work loose or corrode.

The next point that usually causes this problem is the alternator brushes, they wear reasonably quickly and also they cut "grooves" in the alternator slip rings. In all my alternator problems its has been the brushes and never once the regulator. I keep a spare alternator to replace the ones on our two 1.9TD's, it sitting under my desk now just waiting for the brushes to go on one of the cars.

Is the car a TDs or petrol ?, the alternator on petrol cars is easier to replace, the TD's is space limited making getting the alternator out a difficult job. However it can be repaired ON the car from underneath.

Disconnect the battery and leaving the alternator in place dismantle it from the cowling end after removing the cables, the end housing will come off so the brushes can be renewed and re assembled, but be careful as the new brushes need to be held back in the housing until they are over the slip rings, then released. Reassemble and test, I've done this several times. If the slip rings have deep grooves its best to replace the rotor / alternator as the grooves may not match the new brushes. Slip rings can be resurfaced if the grooves are not too deep (<1mm, 2mm max).

Parts for the Magnetti Marelli units are available on the web from Wood Auto Supplies but you need the alternator part # of the alternator, The brush unit is combined with the regulator and is replace as one, Wood's part # for this is on a 1.9TDs is VRG3667, I need to get a new one my self, this posting has reminded me, thanks.

I can do photos of a stripped down alternator if required.

Mike
mike@soemtron.org
www.soemtron.org

How can it be any of these things when he's getting "15 volts and more under acceleration" from the alternator?

The only thing that will allow a 12 volt, non Japanese alternator to charge at over 15 volts is a faulty regulator.

Dave.

It's not charging, the alternator light does not go out only dims, in spite of the voltage readings, there is not enough current being produced, amps not volts. Duff brushes result in less field exitation current in the rotor, resulting in not enough magnetisation to produce current in the stator. I have had this with worn out brushes on a Tempra, more than once over 15 years.

If perchance it is the regulator, changing the brushes will fix the regulator as well, as the regulator and brushes are one assembly, changed as one piece.

There is one other fault that could produce a dim charging lamp with high voltage output and that is a duff diode in the rectifier pack, again giving a low current output, effectively one half of one phase is missing (alternators are rectified multiphase AC units), you get the volts but low current. However I have never seen this on a Magnetti Marelli unit, but I have on Lucas.

I'd still go for the brush pack first, cheaper too, a rectifier stack is more difficult to change requiring a big soldering iron, the brushes WILL be worn anyway.

Regards.

Thanks for your replies, I don't have the necessary equipment for working safely underneath the car, even if it is petrol and so easier to work on, so I will have the alternator checked by a specialist soon. Will ask him about what issues he will find!

If its a petrol car, Eg 1.6IE, the alternator is a lot easier to get out and can be done totally from the top. You will probably find alternators are easier to find / have repaired over there in Italy than here in the Uk. Tempra alternators were common over many Fiat brands.
Buona fortuna !.

Just an update, even if after a while...
The problem disappeared: after some days, the dashboard light started to stay off (as normal) and I could measure about 14.2 V on the battery with the engine at idle or accelerating.
Probably something had moved inside the alternator/regulator with the changing of the water pump and belt re-tensioning, and corrected itself after some time of use.

I had this problem to mate some times its all ok then some times a light a be on the dashboard, have you checked all the connections? it may be a defective diode pack in the alternator.