Batterys, chargrs and panels

halfcrazyhalfcrazy Solar Expert Posts: 720 ✭✭✭
I have a friend who is off grid i dint install the system but have since been trying to repair it. The system consists of 16 6v 220ah interstates wired 24 volt for 880ah bank. 12 shell sq 160 panels wired 10 into a mx60 at 48v and 2 into a c60 at 24v. An outback fx2024 inverter and finally a trimetric meter. Also have a 5000w honda gas generator.
Now his batterys appear to have served there usefull life they spent 2-3 years outside literally not even a piece of carboard over them here in central maine and where only being charged by 2 of the sq panels and an old trace dr 1500 watt inverter so i believe they have been cronically undercharged.

A quick example the other day we ran the generator and performed an equilization and when done we turned off all pv inputs and waited 30 minutes then took a specific gravity reading of 1.280 and reset the trimetric to 0
24 hours later we rechecked the sg and it was 1.17 voltage was 23.8 and trimetric showed -274ah so really looks bad for these they are now 5 years old

Ok so on to question 2 money is a big factor here and he is leaning towards the interstate l16's 6v400ah now i said no more then 12 he would like 16 but i am afraid they are going to be undercharged again without the addition of a second inverter or more panels figuring a 1200ah bank the minimum would be 60 amps and prime would be 120 amps if my math is correct and 16 would be 1600ah so now we wold need a minimum of 80 amps and prime being 160 amps Recomendations?

Also he has poor morning sun so his winter production is pretty low thats where the generator comes in and the little fx struggles to put out 50 amps continuisly i did put a turbo cover on it witch helped


  • crewzercrewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: Batterys, chargrs and panels


    16 each L16 batteries wired 4 x 4 would make for 24 V x 1,600 Ah. Targeting a 5% charge current (80 A) and assuming 85% effective system efficiency (real word PV performance wiring and controller losses), the array spec would be 29.6 V x 80 A / 85% = ~2,800 W STC.

    The 12 x 160 W = 1920 W STC array should be able to deliver ~55A, or ~3.4% of the desired battery bank capacity. 3.4% should be able to charge new batteries under ideal mid-day conditions. However, less than ideal environmental conditions, less than optimal array alignment, leas than clean PV module glass, day time loads on the system, and gradually aging PV modules and batteries will challenge the systems ability to fully recharge the batteries.

    Assuming an average daily discharge of ~240 Ah (~15% of summer battery capacity), the combination of the inverter an the PV array (~110 A total in bulk stage) should be able to fully recharge the batteries as long as day time loads are not too high. However, low winter insolation and/or shade/shadows will reduce the PV array’s output.

    If he’s committed to the big battery bank, and if buying another inverter is an option, how about selling the 2024 (with the Turbo, I think it’s now a 2524) and buying a VFX3524? The 3524 should be good match for the 5000 W generator, and its 85 A charger would be a good match for the 1,600 Ah battery bank.

    Jim / crewzer
  • halfcrazyhalfcrazy Solar Expert Posts: 720 ✭✭✭
    Re: Batterys, chargrs and panels

    Crewzer that was pretty much my logic i was going to try to sell the fx for him and go with the vfx. but i think staying with 12 of the l16s is still best maybe. The pv panels are not aligned optimal they are losing morning sun witch in the winter kills us here in maine.
    gives us something to think about and the batterys are now in a nice warm home setting in the battery box witch is part of the house so it has radiant heat in the floor and everything stays right at 70F.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Batterys, chargrs and panels

    how's the wiring and such? could be some losses in there enough to make a small difference.
  • halfcrazyhalfcrazy Solar Expert Posts: 720 ✭✭✭
    Re: Batterys, chargrs and panels

    well we actually tried to do that right. I moved the system from the shed to the new house when i built it 2 years ago thats when we added panels etc i have 4 runs of #2 copper thhn going to the combiners on the roof probably 30-35 ft from combiner to outback dc box then i used 10-2 tray cable to go from each set of 2 panels wired at 48 v to the combiner longest run there 15 ft. then of course everything inside is neat and close the battery box is directly under the outback unit etc.
    He has his neighbors trees on the morning side and it kills him in the winter will keep everyone posted
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