# drich5

Registered Users Posts: 7 ✭✭
I have 8 x 155ah 12v agm batteries I would like to put into service(new condition).  At present, I have 12, 100w, 12v panels(Vmp: 17.4v, Voc: 21.6v, Imp: 5.75a, Isc: 6.32a), & 4, 140w, 12v panels(Vmp: 17.8v, Voc: 21.7v, Imp: 7.87a, Isc: 8.6a).  I intend to buy Morningstar MPPT 30, 45, or 60 C.C., or a combination of any of the three, to charge my 12v battery bank, connected in parallel, for a total of 1240ah.  My question is, what would be the best wiring configuration of my solar panels, into which of these Charge Controllers?  Yes, I did try Morningstar's String Calculator, yet I couldn't figure out how to configure the string array into which, or how many of these particular C.C.s.  They say(mm-hmm), these batteries should last 10-12 years, with proper care & charging.  Any reply or help is greatly appreciated.  Thanx.

## Comments

• Super Moderators, Administrators Posts: 30,737 admin
Assuming you have the battery bank wiring and proper AGM batteries figured out:

http://www.smartgauge.co.uk/batt_con.html

Along with breakers/fuses for the bank--Designing for the battery bank capacity (solar array sizing):
• 8 * 155 AH * 14.4 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 1,159 Watt array minimum
• 8 * 155 AH * 14.4 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 2,319 Watt array nominal
• 8 * 155 AH * 14.4 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 3,015 Watt array "cost effective" maximum
So--1,200 Watts of panels does meet the minimum recommended 5% rate of charge. The minimum size of MPPT charge controller would be:
• 1,200 Watts * 0.77 panel+controller derating * 1/14.4 volts charging = 64 amp minimum recommended charge controller
You will not damage your MPPT MorningStar charge controller at 60 amps--You will just have a bit more current limited output (normal MPPT controller operation) on cold/clear days.

Typically, the optimum Vmp-array rating is ~2x battery charging voltage--So, placing your panels in 2x series * 4 parallel would be the typical answer.

If, you have a long wire run from the array to the battery bank+charge controller, you could also go with 4x series * 2x parallel (Vmp-array~72 volts Vmp). The charge controller will be a little less efficient with the higher Vmp-array voltage.

Note, with a large battery bank and array--A 1,240 AH @ 12 volt battery bank will require pretty large wiring (for low voltage drop)--It also limits you to ~1,200 Watts on a 60 Amp MPPT MorningStar controller.

If you where to do a 24 volt battery bank, then you could run almost 2,400 Watts on the 60 Amp controller (620 AH @ 12 volt battery bank) and install more panels later with the same charge controller.

Anyway--That is the basics.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Registered Users Posts: 7 ✭✭
Okay.  I figured out how to use the string calculator on MS.  The best course seems to be:  8 x 100w on the ts-mppt-60;  4 x 100w on the ts-mppt-30;  and my remaining 4 x 140w panels on the ts-mppt-45, w/room for 1 more 140w, which I will buy, for a total of 700w into the 45.  Here, dyslexia sets in again:  According to the S.C. I can achieve  the max. wattage by wiring my panels in series, or parallel, or series/parallel.  Do the controllers react better, output-wise, to one configuration over the others?
• Super Moderators, Administrators Posts: 30,737 admin
Roughly, the "most efficient" Vpanel working voltage is ~2x the battery voltage. So, charging at ~15 volts would be Vmp-array~30 volts.

If you run at a higher working voltage (not sure in the MorningStar case, but as I remember, Vmp-array~100 VDC would be the rough maximum for colder climates with Voc~140-150 VDC max for the controller input), then the controller is a bit less efficient.

See page 34 (file page #) of a TS 60 MPPT controller:

http://www.morningstarcorp.com/wp-content/uploads/2014/02/150V-TS-MPPT-Operators-Manual.pdf

The lost efficiency is just about a "don't care" in overall system electrical design (I.e., 97% vs 93% eff)--However, from a hardware point of view, that is 2x more heat for the electronics to dissipate (between Vmp~18 volts vs Vmp~96 volts). Hot electronics (and thermal cycling) are killers (shorten equipment life).

-Bill

Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Registered Users Posts: 7 ✭✭
Thanks, Bill.  Got it.
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