Undercharging batteries

xp190 Registered Users Posts: 6
Hi Folks

I'm trying to improve an off-grid solar installation I put together some 3-4 years back at a cabin of mine.

Here is the setup:

3x80watt keyocer solar panels
30amp controller (Sunforce I believe but now the same units are sold under xantrex)
4 deep cycle marine batteries, 115Ah each (they are not a perfect match which compounds the problem.)

Not being able to obtain the minimum charging current from the manufacturer, how can I guesstimate it?

I'd like to replace these batts with a new set, but I don't want to buy too many and get stuck with undercharged batts which will diminish very quickly.

I also considered adding a few more solar panels and a new charge controller, what would be the formula to determine what the optimal setup would be? I'm interested in crunching some numbers for this and finding out what the best setup would be.

Any advice and suggestions will be greatly appreciated.

Thank you



  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Undercharging batteries

    i'm not too sure what it is you are really looking for here. you make no mention of what your loads are so for even the present setup i'm not sure if you are needing to reduce the battery ah or increase the pv current. as it is the pvs you have are rated for 4.73a and you have 3 of them for roughly 14.2a. this would supply the minimum recommended 5% charge rate for about 284ah of battery capacity. you have 115ah x 4 for 460ah total. 14.2a/460ah = 3.08%. the 5% minimum on 460ah of batteries is 23a. remember you can feed a battery bank up to 13% without too much problem, but is much more in pvs.
    changing the battery array can change the battery capacity if different batteries, but i suggest you try to match that battery capacity to your loads so that the batteries do not drain below 50%. from there you can see how much pv you need.