Wiring 24V Battery Bank and Solar Panels.

linnuxlinnux Registered Users Posts: 5 ✭✭

I currently have a 12V solar setup at my off grid cabin and want to remove the older 600W solar panels and replace with 6 - 250W 24V panels to supply power to my 10 battery's. The charge controller is Midnite Classic 150 and will need to buy combiner box, breakers and 24V inverter. Everything inside the cabin is very energy efficient and at night the the battery bank only drops 2-3% - using a TriMetric battery monitor. 

I'm wanting to change the 12V battery bank to 24V, but not sure about wiring. I have attached diagram of 24V setup, would this work? 

Also about wiring the 6 - 250W 24V panels, could you wire 2 panels in parallel using mc4 t branch connector that each run 30V into the combiner box? Would require MNPV6 breaker box and 3 - 20 amp breakers.. The distance from the panels to charge controller is 15-20 feet. The panels maximum power is 250W - Vmp 30.10V - Imp 8.32A - Voc - 37.5V - Isc 8.87. 
Any help would be greatly appreciated.




  • littleharbor2littleharbor2 Solar Expert Posts: 1,481 ✭✭✭✭
    Sounds to me like you should SERIES wire 2 panels at a time and bring the 3 series wired strings into the combiner box (which then parallel's your 3 strings). You could also series wire 3 panels at a time for higher voltage but if you have a 3 string combiner already you might want to stay with the 2s3p for better efficiency.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Welcome to the forum,

    I don't see the diagram you attached.  You have 10 batteries and you want to reconfigure them to be a 24 volt bank... what batteries are they?

    As littleharbor mentioned, 2 of those panels in series is the correct configuration for a 24 volt system.

    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • oil pan 4oil pan 4 Solar Expert Posts: 766 ✭✭✭✭
    What's wrong with the old 600 watt panels?

    Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.

    Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.

  • linnuxlinnux Registered Users Posts: 5 ✭✭
    edited April 2016 #5
    Two panels 24V in series would work, but would make the power going from panels 48V? This would be going into 24V bank would this configuration work better? 

    The batteries are Everstart 29DC wet cell some of the batteries are going on 6 years old, but I never drain them below 80-90% and use a BLS desulfator. Reason wanting to replace 600W panels for the lack of power to charge the 1,200 ah battery bank and is only capable of doing this on very sunny days - charging the batteries 3-4%. I hope by adding 1.5KW or 2KW panels would charge the battery's 12-18% day this would allow for those overcast days. Would like to get Trojans, but have to much invested for now. 

    Thank you for your help and sorry about the diagram not showing. Below is the 24V diagram.     Image and video hosting by TinyPic
  • BB.BB. Super Moderators, Administrators Posts: 30,037 admin
    Your wiring diagram is fine (Inverter to opposite corners, charge controller to "other" opposite corners).

    My only nit to pick is that you cannot use a Clamp Meter or Shunt Based Battery Monitor to measure the "net current" into/out of the battery bank.

    In the end, "net current" to/from the battery bank is really all the battery bank "cares about". Is it getting charged/discharged/sufficiently charged every day. So the ability to measure the actual battery bank current is helpful.

    So--If you put both inverter+charger on the same terminals, you can now put a large shunt (in the negative battery terminal to battery negative bus/common connection point) and have a nicer way to monitor the actual battery current.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • linnuxlinnux Registered Users Posts: 5 ✭✭
    Thank you Bill. I have the charger and inverter on the same 500 amp shunt monitors power going in or out. 
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