Need advise about Batteries how big a battery and what voltage.

Submitted: Wednesday, Jul 06, 2011 at 13:18

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Scoof

Need Help with battery choice .I need to replace the batteries in my boat.At present I have 2@ N70 deep cycle Batteries, and could do with a bit more storage power at times, I have enough room so should I go for 2@ 6 volt Deep Cycle batteries(a bit bigger in size) with a AH of 245 each battery or go for 2 @ 12 volt Deep Cycle batteries 100 AH each battery.
The batteries will be charged by 80watt solar panel most of the time and when travelling by the outboard motors.
Why I ask is if I go with the 6volt batteries, OK they can store more power but will they get enough charging from the solar panel to cope with charging them to fully charged??The boat only get's used on some weekends.Hope I have supplied enough info.

Cheers
Scoof

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Reply By: Battery Value Pty Ltd - Wednesday, Jul 06, 2011 at 18:18

Wednesday, Jul 06, 2011 at 18:18

Hi Scoof,

so you need the 80W panel to keep the batteries topped up and supplying small loads like lights while not travelling.
And when out and about the power demand exceeds the panel output thus you want to draw from the outboard's 12V system?
Does the outboard have a regulated 12V supply, similar to alternator/regulator in a car, or is it just an unregulated magneto type setup?

cheers, Peter

AnswerID: 459314

Follow Up By: Scoof - Thursday, Jul 07, 2011 at 10:27

Thursday, Jul 07, 2011 at 10:27

Hello Peter,
Thanks for your reply,
At the moment the solar panel keeps the batteries N70's fully charged easy.
But if I went to the 2 @ 6 volt would the 80 watt panel be able to handle the job.
Also if it could not handle the job of fully chargeing the 6 volt batteries would they be damaged being not fully charged.
The outboard motors charge the batteries quickly because if they are down on power we just start the outboards for say 30 to 40 minutes and we have enough power to run the water pump for a few more showers.This is only happened when we have had 6 or 8 people using the shower and lights.
The outboards are alternator charging.
Hope I have anwered all your questions Peter.

Cheers
Scoof. :-)

FollowupID: 732907

Follow Up By: Battery Value Pty Ltd - Thursday, Jul 07, 2011 at 11:34

Thursday, Jul 07, 2011 at 11:34

You're welcome Scoof,

note the batteries aren't the limiting factor in a solar system. The question is, is the panel large enough to supply enough juice to power all the loads over a longer time span.
The batteries are just there to fill the gaps in power supply if no sunshine.
They also act as high energy buffer, as they're capable of churning out lots more amps for a short time, than any solar panel.
By the looks of it your solar panel keeps the N70ies charged easily, so you could just as well use bigger batteries which can store more energy, saving you a bit of outboard motor run time.
Batteries only get damaged if you discharge them more than the solar panel can supply over a few days, so just keep an eye on their voltage which should be 13.6~13.8V for much of the time.
A good solar regulator will let this voltage increase in a controlled way, depending on how deeply the battery gets discharged at night.

cheers, Peter

FollowupID: 732909