Lazy alternator

[iainbluk]

My alternator on my Volvo penta d2 55 (Bav 38) takes around 15 mins to start charging. Meanwhile the warning light and warning horn work as normal. I understand that the light forms part of the excitor circuit and so would appear to be working normally. Its a fairly consistent 15 mins before it gets going. Anyone got any suggestions of a fix before I let Volspec loose on it (and my wallet!!)

 

[Talulah]

Take off the alternator. Look at the brushes. My money is you'll find one a lot longer than the other. Indicating a sticking brush that is barely making contact.

 

[VicS]

Are you saying that the light goes out promptly but no charging is registered by the ammeter?
That's a bit odd. it is quite common for the light to stay on until the revs are increased a bit.

I would want to confirm what is happening with another ammeter if possible, or to connect a voltmeter up to the alternator to confirm that it is 15mins before the output rises to a level at which charging will start.

As suggested a good first thing to check would be the brushes and to compare their length with the specified length for your alternator. Beyond that who knows? Regulator playing up?

You are right that the warning light plays an essential part in the operation of the alternator. It is the current flowing through the bulb that provides the initial field current. Once that alternator is producing it provides its own field current of course. As the volts produced rise the light dims and it is finally extinguished as they reach the battery voltage. Normally that all happens so quickly that it appears that the light simply goes out when the engine starts.

If you have to get it checked try to find a local automotive electrician who will test and repair the unit.

 

[Guest]

How do you know it is not charging?

Do you have a VSR or automatic battery combiner in the system. If so it will not charge the house bank until the starter battery is up to voltage. You could also have a delay in the Alternator regulator and a soft start. These could all add up to 15 minutes. The state of the starter battery would determine the time.

 

[William_H]

As Vic says remove the brushes and inspect. On some alternaors the brushes are mounted on the regulator which is plastic box screwed with 2 screws to the end of the alternator. (opposite end to the pulleys)
The box nay have wires connected to it.You will be able to view the slip rings through he hole. They should be smooth and shiny for good contact by the brushes which should appear to give similar pressure onto the slip rings. Unless you have a dead diode there is not much else goes wrong with alternators.

You probably can't do this inspection without removing the alternator as I imagine the front of the engine is the accesable part and the brushes are on the back of the alternator. in which case if you can't see anything wrong take it to an electrical shop for testing.

If the bruses are bad then it often requires replacement of the whole regulator (not expensive for cars) If the slip rings are bad they can be turned down smooth by removing the rotor and turning in a lathe or you might be up for a new rotor. (possibly cheaper a new or rebuilt alternator) good lcuk olewill

 

[scarlett]

My alternator on starting, has always needed a blip of the throttle to get it going from tickover but stays going when back to tickover.

 

[VicS]

[ QUOTE ]
My alternator on starting, has always needed a blip of the throttle to get it going

[/ QUOTE ] As I said that is fairly common.

Theorising a bit but i suspect that in those cases the current supplied by the warning light is not quite enough to get the alternator output up to the point where it can supply its own field current at very low revs. Blip the throttle then that gets it going and it is then able to continue to power its own field even when the revs drop back again.
Maybe in those cases a higher wattage bulb as warning light would get it charging sooner