Battery charging problem?

[thomashoebus]

The last 2 months my battery was empty (8 volt) after 2 hours of sailing. During sailing i had autopilot and frigo on.
The battery is a 1 year old mastervolt 160 ah. Since the battery was under warranty the seller of the battery came to check things out. He told me my battery charger was broken and that it should be replaced. He tested the battery and said that it was fine only it was flat. This is strange since i always have my battery charger on when in port. He also told me that the few hours that we use the engine in the weekend was not enough to charge the service battery with the engine. One thing is very odd when in port the battery charger is able to supprort lights frigo etc... so i really wonder if it is broken.
Has anyone an idea what could be wrong?

 

[aluijten]

Very simple:

Hook up your boat to the shore power, switch on the charger and measure the voltage across the battery. Anything below 13 volts (after approx 1 hour of charging) points towards the charger. Either the wires to the battery are faulty, the fuse in the charger is blown or the battery charger has no supply voltage (indicator lights?). Or the unit is simply broken of course

Cheers,

Arno

 

[Mal113]

I would be interested to know how he tested a flat battery? Can you check if the charger is giving an output, is there an ammeter on the charger or can you place one in series with the charging circuit possibly using a shunt to reduce the current measured at the meter. It seems strange that the shore power can supply the power for all your needs while in the marina and yet it is not charging. If you had a damaged cell in the battery you would get a similar result as the battery would have a high resistance which it turn would not allow the battery to be charged. How about using a cheap motorcar-charging unit to see if that will charge the battery, that will show if the charger is really the problem.

 

[lw395]

The battery will need at least 13.8V to charge at any real current. When fully charged it may be maintained by a float charger at about 13.2 to 13..5 V. It may be that your shore charger is only putting out a float charge voltage, which would still be enough to run all the lights etc.
A poor connection can cause the charger to deicde that the batt is fully charged and switch prematurely to float.
Get a dvm on the battery and check the charger is doing what it should.
It could be as simple as someone unplugged your shore power last week of course! (not me guv!)