newbie battery question

[650mark]

mark in mesa here. i just set up a small 45 watt(3 amp) solar panel array at home and would like some input on batteries. i will be using a dc>ac inverter for powering some small ac devices and need to know if one 12 volt storage battery or two 6 volt batteries would give the best longterm performance. thanks in advance for any info.

[GarrettCoMD]

It has been my experience that (2) 6v batteries (in series) are better than (1) 12v battery. The 6v batteries are usually 200+ amp hrs @ 20hrs while the 12v batteries are 100 amp hrs. - Go with the (2) 6v.

[icarus]

IMHO, it all depends on the batteries. With multiple batteries in series, you can have differing resistance in the cabling that you won't have in a (good) battery. Amp/hours are amp ours if you are comparing apples to apples.

You could make the argument that if one battery fails you only have to buy one new one instead of a whole new string. The problem there is that any new batteries in a string will quickly "take on the age" of the oldest one.

Icarus

[niel]

it really makes little difference which battery setup you go for, but please make sure you have enough pv to charge the battery(s) as it should fall within the 5-13% charge range of your pv(s) unless the manufacturer would state otherwise. 5% of 100ah = 5a charge rate. you have 3a of pv so that would be good on a 60ah to 23ah 12v battery. a3% rate of charge your 3a pv will give to a 100ah 12v battery is pushing the limits, but if you are patient and careful it may workout.

[Wayne from NS Cana]

Just to help you understand the 5 to 15 % thing - - you need to get the batteries backup to full charge ASAP after use, so as to avoid sulphation. (or sulfation if you prefer)
Like Niel said, if you are careful, in that you only use a little power from the batteries between charges so they can be brought back to full charge in a couple of days, things might work out. It will be harder though, to do an EQ on the batteries if they require it, because of the smaller PV.
Also take note, I would expect that most days, you will not see 3 amps delivered from the panel.
Not in any way trying to discourage you, rather it's our desire to see you not set up for a disappointment if we can help it. Just trying to get you off on the right foot, so your solar experience will be a good one and you will continue on into a solar future.
Cheers and all the best
Wayne

[650mark]

thanks wayne. yesterday my solar array was in full sun for 7 hours straight here in mesa arizona(it was 114 degrees!). i checked the output of the panels several times and they were at 2.2amps almost the whole time. i'm thinking that should be enough to recharge a 12 volt deep cycle battery rated at 48 ah, given that we think we'll use about 12 amps overnight to run a small evaporative cooler. sound about right? thanks again for the info.
mark in mesa

[niel]

for clarification that is 5-13% and you are close to the 5% mark with that 2.2a into a 48ah battery. you should be fine as long as you allow the extra number of hours needed to fully charge the battery for even if you got 7 full sun hours in a day, that would account for 15.4ah put back into the battery in a day. if you drained it to 50% then you need to put back a total of 24ah and you'll need another 8.6ah. if you don't exceed what the pv gives in a day for your loads you can keep the battery charged up.