warm AGM batteries

[tpb]

Hello,
I would be grateful of information and advice regarding problems with overcharging batteries. We have 3 Victron AGM batteries 100 amp hours each on our yacht. They are now all 6 years old. We have had no problem with them sailing down the French Atlantic coast, Biscay, Northern Spain, Portugal or last summer in Lanzarote. However, this year in Arrecife and now in Tenerife, the battery monitor is regularly displaying 14.7 V and 2.7 Ams when connected to shore power and the Mastervolt battery charger is on. Additionally, there have been occasions this year when the batteries have felt very warm to touch, particularly the middle one of the 3. If the wooden cover is left off the battery compartment, thereby increasing the ventilation, the batteries are not hot to touch but the voltage and amps are still 14.47V and 2.7 Amps despite the battery being 100% charged. The Mastervolt charger appears to display the bulk charge indicator light permanently regardless of the voltage.
Any thoughts appreciated.

 

[matthewriches]

Start of a potential failure. Disconnect all into individual batteries and have someone put a battery tester on or try the charger on each one individually. This will show which 1 (or more) are sucking it up and converting to waste energy.

 

[tpb]

Thank you Matthew for your very speedy reply. This was very helpful.
Trevor

 

[VicS]

It might be worth checking the operation of the battery charger against its specification and possibly altering the settings , until you can replace any failing batteries, to reduce the absorption voltage perhaps gettting it to go into float mode sooner.

The voltages you quote for absorption ( 14.47, esp 14.7) seem a little high but I do not know what model charger you have

Reducing the max % state of temporarily would be preferable I think that "boiling" one of the batteries .

 

[A_8]

Its more often the batteries and from what you are saying one beeing warmer it very likely needs replacing. An easy test would be to disconnect the warm one and see if it changes the charge status/current.

 

[tpb]

It might be worth checking the operation of the battery charger against its specification and possibly altering the settings , until you can replace any failing batteries, to reduce the absorption voltage perhaps gettting it to go into float mode sooner.

The voltages you quote for absorption ( 14.47, esp 14.7) seem a little high but I do not know what model charger you have

Reducing the max % state of temporarily would be preferable I think that "boiling" one of the batteries .

 

[tpb]

Thanks for advice Vic.

 

[tpb]

Thanks for advice.

 

[Ian_Edwards]

14.7 V and 2.7 amps, is just shy of 40 watts, and is less an 1 amp per battery, the three batteries will weigh close to 100kg and will have a reasonable surface areas, that's not a lot of power to make the batteries warm.

Do the batteries cool down when the charger is disconnected and the batteries bank is isolated so that there is no current being drawn?
I ask because I had a problem at the start of this season, where one battery developed a partial short circuit, this allowed the other batteries in the bank to discharge through the faulty battery making it heat up to the point where the acid boiled.

If this isn't happening, I'd check the battery charger, if it's not going into float mode, after a long uninterrupted charge (say overnight), then the the prolonged high charging voltage might be causing the problem.

It could also be that all the batteries are developing a slight internal short circuit, or high internal rate of discharge, which wouldn't be surprising given that they are 6 years old. This could happen if they have been regularly discharge below, say 50%, which would have significantly shortened their service life.

 

[VicS]

looking at several Mastervolt charger instruction manuals I find absorption stage voltages of 14.25 often with a time limit ( 4-6 hours) on the absorption stage .

With the more sophisticated models these settings ( and others) can be user altered. If might therefore be worth while looking into these settings.

 

[tpb]

looking at several Mastervolt charger instruction manuals I find absorption stage voltages of 14.25 often with a time limit ( 4-6 hours) on the absorption stage .

With the more sophisticated models these settings ( and others) can be user altered. If might therefore be worth while looking into these settings.

Vic, I have an instruction manual for the charger and it refers to the absorption stage voltage of 14.25. There is, however, no mention of settings other than the three jumpers. I questioned the ambiguous comments about the jumpers with Mastervolt and I have had a reply to say that all three jumpers should be inserted which they are. They advised me to try disconnecting all sources from the charger and reconnecting to see if the charger would re-set itself from what seems to be bulk charge. This made no difference. Someone local is coming on Thursday or Friday from a marine electronics company here in Santa Cruz, Tenerife. I notice that your home port is in Kent. We were in Ramsgate. Thanks.

 

[dom]

There is/(are) no sense wire(s) on this system per chance?