Over winter battery charging question

[Norman_E]

My boat has four batteries as follows Engine Start 105 AH
Domestic Batteries 2 X 110 AH and Windlass/bow thruster battery 125 AH. Total 460 AH.

When I leave the boat over winter all electrics will be switched off but I can leave the 25 AMP charger, which charges all batteries at once, connected via a timer.

If I set the timer to run the charger once a week, how many hours should it run just to maintain the batteries against internal losses?

 

[ex-Gladys]

The general idea is to have 10% of your AH as your charger rating... so you would need 50A (round numbers). Using a smart charger would be better than a conventional charger on a timer, because the conventional will not take any notice of the battery state

 

[Guest]

I have a lower pwoer charging supply .. so assuming we are at same relative levels .... I set my timer to do 2 hrs for 4 days out of a weeks 7. That meant batts rested for 3 days ...

Later when I had boat at home .. I reduced it to 4hrs every other day ... still I reckon over the amount really necessary.

Now the boat is sitting waiting for me to fix the injector pipes ... in Yacht Club ... and I have my timer set to 6hrs each third day ...

Really I think the matter to pay attention to is not to over-heat or gas of the batterys ... so that is why I have rest days inbetween charge periods ...

Oh and I also use a standard unregulated charger via a Maplins Charge splitter ... so both my batts are fed from one charger.

There are also plug in battery keepers .. low ampage charge blocks that plug into wall and are designed for indefinite battery maintenance.

 

[Norman_E]

Sorry, I did not say it, but it is in fact a "smart" charger, and in practice seems to re-charge the batteries quickly enough. What I am trying to get at is how many hours per week will be needed to maintain the battery bank if no 12 volt equipment is turned on.

 

[john_morris_uk]

[ QUOTE ]
The general idea is to have 10% of your AH as your charger rating... so you would need 50A (round numbers). Using a smart charger would be better than a conventional charger on a timer, because the conventional will not take any notice of the battery state

[/ QUOTE ]He is asking how long to leave the charger on for a 'maintenance charge' not to recharge a discharged battery bank.

If it's a smart charger, it is not critical. The charger will work out that the batteries are fully charged and go to 'float mode'.

 

[Boathook]

I just use an ordinary car charger and plug in when I am down on board. Most decent batteries seem to/will hold charge for a few months which also happens to my batteries !!

 

[Guest]

This would work at my home pontoon ... but as most boats despite best installations do leak electric along the way ... stray bits here and there - IMHO based on environment more than anything ... a float charge / timer based system is actually a good way to cover it - certainly sorted my boat out ...

I used to leave my boat in UK for months while over here in Baltic. Putting a charger on when I got to UK wasn't good enough ... it meant that I had to go direct to boat from airport ... when all tired and wanting to get home - plug in charger etc.
Putting the Maplin splitter, charger and timer combo in was the best thing I ever did ! Never saw a flat battery again.

In fact so good - that even with boat at house pontoon - I still use it - fit and forget basically. As soon as mains lead is plugged in - it all fires up again. Doesn't matter that timer is out of time synch - so what !!

 

[Hoolie]

It would be best left on continuously on float since switching on and off with a timer will trigger boost mode and hence overcharge.

 

[aluijten]

If your batteries are in good shape, I would recommend to switch it on 1 day per month. That should be more than enough.

Batteries don't lose much charge at low temperatures.

On the other hand the most 'risky' moment for gear failure (charger failure) is at power-up phase. So from that perspective, with a smart charger, keeping the power on all the time is not a bad idea.

Arno

 

[Norman_E]

Thanks everybody. Some good ideas here. My smart charger is perhaps not as smart as I would like as it charges to over 14 volts before switching to float mode. The boat will be left from late October to the following March or April so I need to set up something. The winter in Turkey is warmer than here so there will be some battery voltage drop if left too long. I think I will look in Turkey for a small automotive smart charger and a 7 day time switch and give it a few hours each week.

 

[halcyon]

Over 14 volt, thats what you want, charging to 13.6 volt over winter will kill the batteries. You need the14.4 volt phase to stir it up.
As long as the charger does not have a fixed time equalization charge your ok, as it will just drop to float charge, and you run for 2 hours. If it has a fixed time, run it for say 15 / 30 minutes a week, the high charge rate will kick in anything you loose, and the short time will minmise gassing.

Brian

 

[Anonymous]

If it is a decent modern smart mains charger (which it sounds like since it goes to over 14V then falls back) then provided you set it up for the type of batteries you have (read the manual carefully and call the maker if not completely clear) then I would leave it on all winter. OK, it does waste electricity, I and if that is your concern then a solar panel or windgen with smart controller would be the way forward.

 

[Norman_E]

Thanks to you and Halcyon. Trouble is I don't have a manual, so I think the idea of giving it 15 or 30 minutes a week is the way forward. I am in Turkey for 7 weeks starting on Tuesday, and will be able to experiment to see how long I can charge for without the batteries gassing. For my last few days there the boat will be put on the hard and there will be very little 12 volt use so I will be able to monitor battery voltage drop carefully then, and see how long it takes for the charger to bring the batteries back up to full charge, and hopefully set up the timer correctly.