Alternator giving low voltage

[Roberto Conigliaro]

Thanks everyone for your comments and advice.

I just swapped the alternators and the results are quite unexpected :

now the domestic alternator (the one that only gave 12.8v / 13.0v max) is wired to the starter battery and when the engine is running gives me 14.35v. The starter alternator (the one that gave 14.2v) is now wired to the leisure batteries and gives 13.75v 

If I voltmeter directly the batteries when engine is on I get : Starter 14.25v, leisures 13.30v

 

Basically now both alternators seem to be working fine. Any idea of what might be happening? if the belt was the problem I should still get a low voltage on the starter battery but it's not happening.. or am I missing something? 

[nicknorman]

As I explained, the propensity to slip is related to the load on the alternator which is related to the size and state of charge of the battery. So it seems that the pulley that was slipping badly, is now spinning ok despite being worn and polished, as the load is minimal. The one that was previously not loaded and hence not polished and worn from extensive slipping, is for the time being working better. Did you tighten the belt at the same time? Anyway, I would get a new belt and stay on top of keeping it correctly tensioned. Clean off the black dust. If it recurs this indicates the belt is slipping.

[Roberto Conigliaro]

3 minutes ago, nicknorman said:

As I explained, the propensity to slip is related to the load on the alternator which is related to the size and state of charge of the battery. So it seems that the pulley that was slipping badly, is now spinning ok despite being worn and polished, as the load is minimal. The one that was previously not loaded and hence not polished and worn from extensive slipping, is for the time being working better. Did you tighten the belt at the same time? Anyway, I would get a new belt and stay on top of keeping it correctly tensioned. Clean off the black dust. If it recurs this indicates the belt is slipping.

I see, thanks for the clarification! I am gonna get a new belt and have a look at how to replace / tightening it, since I have never done it before. In the meantime, can I just leave them swapped temporarily or the Amps difference between them might cause some problems (one is 90A the other one 60A)?

43 minutes ago, nicknorman said:

As I explained, the propensity to slip is related to the load on the alternator which is related to the size and state of charge of the battery. So it seems that the pulley that was slipping badly, is now spinning ok despite being worn and polished, as the load is minimal. The one that was previously not loaded and hence not polished and worn from extensive slipping, is for the time being working better. Did you tighten the belt at the same time? Anyway, I would get a new belt and stay on top of keeping it correctly tensioned. Clean off the black dust. If it recurs this indicates the belt is slipping.

I see, thanks for the clarification! I am gonna get a new belt and have a look at how to replace / tightening it, since I have never done it before. In the meantime, can I just leave them swapped temporarily or the Amps difference might cause some problems (one is 90A the other one 60

 

Okay, actually managed to tighten the belt  (quicker job than I thought), swapped the alternators back to their original and now I get a sound 14.2v coming from both alternators.. it took me 2 full days to figurate it out (thanks to you guys) and it was the easiest of the problem to solve..  God knows for how long the alternator was underperforming and I noticed it only recently after the batteries are pretty much dead.. they are 7 years old anyways I guess - time for the hybrid Lifepo4 / Lead Acid now. Cheers everyone!

[Tony Brooks]

Deleted because the OP's question about alternator outputs is now redundant. (He has fixed it.)

Edited February 1 by Tony Brooks

[BEngo]

1 hour ago, Roberto Conigliaro said:

time for the hybrid Lifepo4 / Lead Acid now. Cheers everyone!

Before you go LiFePO you need to sort the belt out so there is better wrap on the pulleys, or do what I suggested and swap the travel power alternator out with one the same size but 12V and wire that in to feed the domestics.

LiFePO batteries pull consistently high currents until nearly full and will cause rapid belt wear on your present set up.

 

N

[Roberto Conigliaro]

20 hours ago, BEngo said:

Before you go LiFePO you need to sort the belt out so there is better wrap on the pulleys, or do what I suggested and swap the travel power alternator out with one the same size but 12V and wire that in to feed the domestics.

LiFePO batteries pull consistently high currents until nearly full and will cause rapid belt wear on your present set up.

 

N

Thanks for the advice, I will try with a new belt firs - for the moment the alternator gives the right voltage, but the belt sounds quite squeaky. 

If it keeps wearing rapidly I'll try to install the travel power one, although I don't know if still works and how to install a new alternator but in guess I'll find out!