Unusually high voltage

[Murflynn]

My little 'lectric cruiser has a bank of  six 12v 110Ah leisure batteries in parallel. 

I have them on charge regularly out of season, using a PACO 20A 7 stage charger that is sold specifically for keeping caravan batteries charged up and maintained over the winter season.

The charger has been very reliable for 4 years and is also used for overnight charging when I am on a cruise; the maximum  voltage recorded when the charger goes into maintenance mode is 14.6v.

Two days ago I removed two batteries that had obviously outlived their usefulness - their voltage dropped to 9v within a couple of days with no load - and I put the remaining four on charge again.  

Within an hour the charger had progressed to maintenance mode and I noted a reading of 16v on both of the boat's voltmeters.  

I took the batteries off charge and the volts dropped to 12.8v and then down to 12.1v within 8 hours.*

Today I put them on charge again - again the charger soon reached maintenance mode and the meter showed 15.3v when I observed it and took the batteries off charge.

To check the condition of the remaining four batteries I plan to charge each battery separately and then monitor the voltage over a few days, and to do a load test with a 55watt car headlight bulb over 8 hours.

 

My main concern is whether the charger has failed in some way by apparently supplying an unusually high voltage.  Any suggestions?

 

* EDIT: it's been off charge now for 6 hours and battery voltage is holding at 12.8v this time.

 

 

Edited December 6, 2019 by Murflynn

[Detling]

It may be applying a temperature adjustment if the batteries and charger are in a cool place. or doing an equalise period.

 

[Murflynn]

11 minutes ago, Detling said:

It may be applying a temperature adjustment if the batteries and charger are in a cool place. or doing an equalise period.

 

I would be surprised if the charger was that sophisticated, but it's worth following up. 

thanks for the suggestion.

[nicknorman]

I did initially think about temperature compensation but that would only take it up 1/2 volt or so. Definitely not up to 16v. But I would check it with a digital multimeter before getting too excited - analogue voltmeters can be pretty inaccurate (if that is what you were using).

[Tony Brooks]

and if it is a digital meter make sure it has a new battery in it (ignore if its an on boat instrument).

[Murflynn]

23 minutes ago, nicknorman said:

I did initially think about temperature compensation but that would only take it up 1/2 volt or so. Definitely not up to 16v. But I would check it with a digital multimeter before getting too excited - analogue voltmeters can be pretty inaccurate (if that is what you were using).

I have 2 digital meters on the boat, one is between the solar charger (not in use) and the batteries, and one is in the remote switch panel serving the minor loads, both reading as stated.

 

I found a detailed spec for the charger which states that over-voltage protection is set at 17.5v.   

 

I guess the question is - will a maintenance or float voltage of 16v do any harm to the batteries over a period of a few hours - is there any risk of the batteries 'boiling' at that voltage?

Edited December 6, 2019 by Murflynn

[nicknorman]

12 minutes ago, Murflynn said:

I have 2 digital meters on the boat, one is between the solar charger (not in use) and the batteries, and one is in the remote switch panel serving the minor loads, both reading as stated.

 

I found a detailed spec for the charger which states that over-voltage protection is set at 17.5v.   

 

I guess the question is - will a maintenance or float voltage of 16v do any harm to the batteries over a period of a few hours - is there any risk of the batteries 'boiling' at that voltage?

Depends on the type of batteries but probably not too much if they are cheapo type wet lead acid with lots of calcium. If they are sealed then there is a risk of drying out a bit. If open, they can be topped up. 16v in cold weather for a few hours won’t be catastrophic, but it’s not something to be repeated often as there will be some plate corrosion and loss of plate material.

 

16v possibly not good for some devices connected to the boat’s electrics though.

Edited December 6, 2019 by nicknorman

[Murflynn]

20 minutes ago, nicknorman said:

Depends on the type of batteries but probably not too much if they are cheapo type wet lead acid with lots of calcium. If they are sealed then there is a risk of drying out a bit. If open, they can be topped up. 16v in cold weather for a few hours won’t be catastrophic, but it’s not something to be repeated often as there will be some plate corrosion and loss of plate material.

 

16v possibly not good for some devices connected to the boat’s electrics though.

OK, thanks.   I think I can relax a bit and charge them about once a week over the off-season with the PACO charger.  There are no devices connected over the winter.   During a summer cruise when connected to the mains overnight the float stage isn't usually reached until about 6am and I would disconnect the charger at that time of day.  The batteries are not the sealed type, they are easily accessible and I can keep them topped up no problem. 

 

But I assume something in the charger circuit must have failed if the float voltage is now 15/16v when previously it was always about 13.6v, so I wonder if I may need to replace the charger next year.