battery charging

[KREW2]

I think my alternator on my VP2002 may be dying.
Just motored all the way back from Alderney and there was never any more than 12,9 volts at the battery terminals. I was running a fridge and the usual nav aids for nine hours, the state of charge on the battery was 82% when I left, at the end of the trip it was still 82%.
This suggests that the alternator was just keeping the batteries in a state of equilibrium, usually after such a long run I would have expected my batteries to be at least 90% state of charge.
Does this indicate that my alternator is goosed, or is there anything else I should check.

 

[charles_reed]

I think my alternator on my VP2002 may be dying.
Just motored all the way back from Alderney and there was never any more than 12,9 volts at the battery terminals. I was running a fridge and the usual nav aids for nine hours, the state of charge on the battery was 82% when I left, at the end of the trip it was still 82%.
This suggests that the alternator was just keeping the batteries in a state of equilibrium, usually after such a long run I would have expected my batteries to be at least 90% state of charge.
Does this indicate that my alternator is goosed, or is there anything else I should check.

Diode bridge gone - have the unit off and the bridge replaced - should cost less that £10.

 

[KREW2]

Thanks, is that the thing on top of the alternator that looks like a fuse bank but only has one terminal on each side?

 

[charles_reed]

Thanks, is that the thing on top of the alternator that looks like a fuse bank but only has one terminal on each side?

No, it's usually on the end, opposite the pulley - it's about the size of a 2€ piece. It varies from alternator to alternator, but that is where it is on Bosch and Hitachi alternators though it's totally hidden on Magnetti Marechal and Lucas.

 

[VicS]

I think my alternator on my VP2002 may be dying.
Just motored all the way back from Alderney and there was never any more than 12,9 volts at the battery terminals. I was running a fridge and the usual nav aids for nine hours, the state of charge on the battery was 82% when I left, at the end of the trip it was still 82%.
This suggests that the alternator was just keeping the batteries in a state of equilibrium, usually after such a long run I would have expected my batteries to be at least 90% state of charge.
Does this indicate that my alternator is goosed, or is there anything else I should check.

The alternator may be faulty .

It may be a faulty rectifier as Charles-reed suggests or it may be a faulty regulator.

Charge the battery and satisfy yourself that the battery is good. Start the engine and monitor the volts with it running at fast idle, or better taken for a short trip, with no load on the system. The volts should soon rise to 14 + .

If you cannot get up above 14 suspect the regulator.

If you get above 14 put as much load on the system as possible. If the volts then drop suspect the rectifier.

I cannot say if a DIY repair to the alternator is simple or not. Some are easy to do. Some need some heavy soldering to be done.

If in doubt about the alternator or your repair skills take it to an automobile electrician for testing and repair.

 

[VicS]

Thanks, is that the thing on top of the alternator that looks like a fuse bank but only has one terminal on each side?

If both wires are 1.5mm² red wires then ITYWF it is in fact a fuse bank!

 

[ghostlymoron]

If you have doubts, I would take it to an auto electrician straight away rather than faffing about. I've found their charges are usually reasonable and they have test equipment that can test it in a few minutes.

 

[PaulRainbow]

If you have doubts, I would take it to an auto electrician straight away rather than faffing about. I've found their charges are usually reasonable and they have test equipment that can test it in a few minutes.

:encouragement: Very big +1

Any decent place will test in a minute, doubt they'll charge if there is nothing wrong and will likely have parts to repair.

 

[William_H]

I agree with all that has been said however other possibilities might be a slipping drive belt or simply motor running at low speed so alternator not turning fast enough to meet the load. (not likely) I do not hold with battery charge % type indications. I am guessing it is just extrapolating battery voltage to %charge. If it is a real cumulative amp meter type then it should indicate amps as well. An amp meter should indicate just what is going on. Either an amp meter just for the alternator output which I would prefer or a total system amp meter which should always show a charge over the discharge. A failure of one diode out of the 6 fitted will give a huge drop in charge capability. This failure is often indicated by interference on radios of a whine from the alternator. (but not always) good luck olewill

 

[KREW2]

I went out to the boat armed with every tool I own to try and fix the problem.
I only needed a 10mm spanner to tighten the nut at the back of the alternator that holds on the charging wire.

 

[Champagne Murphy]

I went out to the boat armed with every tool I own to try and fix the problem.
I only needed a 10mm spanner to tighten the nut at the back of the alternator that holds on the charging wire.

That’s the problem then, you need ANOTHER tool set to keep on the boat.

 

[charles_reed]

I consider batteries consumables - 5 years good service and replace after 7 years. That on a liveaboard boat mostly at anchor.
Sealed batteries have a much more limited life than properly maintained open-cell ones - the last open-cell one I got in Corsica lasted 10 years. One of the advantages of open cell is that, as they wear out, their water consumption increases, so you have a clear handle on life-expectancy. It's best to budget for regular battery replacement..
Every Greek town has a local auto-electrician - as long as he doesn't have to come out to the boat alternator-testing will usually be free - if he does the mending. He'll also be the cheapest for replacement batteries - about €1/amp-hour as a budget price. It will take him 2' to test and diagnose an alternator - you two days (if you know what you're doing). And then there's the cost of the plasters, the risk of exsanguination!!!