Shall I charge batteries at a higher voltage during winter?

[Doodlebug]

Hi all,

 

Its now officially winter, and so we are running our genny once a day. We don't get a huge amount of time in the day to run the genny before 8pm and so the batteries slowly loose charge over the week. I know this isn't ideal.

 

As well as that I am sure our batteries are not performing too well.

 

Our sterling has been set to the lead acid battery setting, charging at 15v for the bulk stage and then it floats at 13.5 (its a 40a version)

 

I have been trying to run the equalisation charge at weekends, but thats not always possible.

 

Is it a good idea to change the sterlings settings during the week so that it floats at 15v, so that a little bit of desulpherisation is happening, as well as forcing more power into the batteries?

 

I'll then change back at weekends and give them a longer charge.

 

Any thoughts appreciated.

 

Ps. I now have a battery monitor. It needs calibrating better so these measurements are not precise but give an idea:

 

We are using around 33ah per day

Running the genny for about 2 hours a day at 40 amps.

By the end of the week they are starting to die.

[by'eck]

You don't mention which Sterling charger you have. In many of the three output stand-alone ones an equalise cycle automatically runs once every 15 days.

 

Most of these models incorporate a temperature sensor which, if fitted, should take care of seasonal battery temp variations.

 

If left on float unattended I often just cycle the charger off/on when returning to boat, which puts it back in absorb mode for a while and livens up the plates a tad.

 

Note that bulk is the constant current not constant voltage mode.

 

By the sound of it you are unable to run the charger for long enough to adequately re-charge the batteries. Setting the absorb voltage as high as the batteries can stand will help matters to some degree, but only if it ever reaches that phase.

 

Note that battery capacity may already be shot also.

Edited December 4, 2013 by by'eck

[Keeping Up]

Just to address the precise question now that By'eck has given the useful and practical answer, the amount of temperature compensation when charging is approx -0.02v/^oC

[dmr]

If your running off a genny then I reckon you are an off grid liveaboard, in which case you will struggle to get your batteries full.

So...the charger should really never go into float, and if it does then its not really suitable for a liveaboard. Most chargers go into float much too soon.

So...if you can set the float to 15v that would be great.

If you ever run the generator for a long long time then there is a tiny chance of hurting the batteries but this would be after many many hours and your neighbours would probably have hurt you first by then.

 

Just keep an eye on the water level (inside the batteries rather than outside the boat) and it will be fine.

 

............Dave

[smileypete]

+1 to what dmr says, what charge voltage are you seeing after 2 hours genny running? If the charger is set to 15V it should rise up to that level and stay there provided you aren't running big 12V loads at the same time.

 

If it drops to 13.5V anytime before the 2 hours is up then it's going into float too early, try switching the charger off and back on as byeck says.

 

cheers, Pete.

~smpt~

[Alan Saunders]

<snip>

Ps. I now have a battery monitor. It needs calibrating better so these measurements are not precise but give an idea:

 

We are using around 33ah per day

Running the genny for about 2 hours a day at 40 amps.

By the end of the week they are starting to die.

Are you really charging at 40A for 2hrs? I doubt it - it may start at 40A but will reduce rapidly.

Opinions vary on the efficiency of recharging batteries but I like to use 70/80%.

At 33Ah/day I would only need one 110AH battery and recharging for 2hr/day would be more than adequate without any fancy charge controller.

 

This works well with new batteries but when they lose capacity, get sulphated etc. they need a lot more charge voltage/current to replace the lost charge.

Apparently, you are putting back 80Ah for 33Ah useage - 40% efficiency.

 

Every year, about now, I replace my FLA batteries, promise myself that I will look after them and every year I fail!

Replace your batteries, look after them and they will last more than a year; 2 hr charge per day and 7/8 hr at the weekend according to your figures.

N.B. Claims that batteries last ten/twelve years are not from live-aboards or apply to very expensive batteries that are fastiidously maintained.

 

HTH, Alan

 

Edited to add: observe more learned opinions above!

Edited December 4, 2013 by Alan Saunders