PV array mismatch.Help

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mbu
mbu Registered Users Posts: 7 ✭✭
in PV Installers Forum - NEC, Wiring, Installation #1
I have 250 w 24v x4 and 150w 12v x6. I have a 48 v battery bank of 800ah and mppt 60A 250v limit and a 48v kv inverter. zI need help with the pairing of the panels ad the voltage of the 12v panels in seried doed noy match the voltage of the 24 string
and i wanted to connect the 2 strings in parallel
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  • mbu
    mbu Registered Users Posts: 7 ✭✭
    #2
    sorry mppt is 60A 150v
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,135 ✭✭✭✭✭
    edited April 2018 #3
    Your 250 watt panels aren't likely 24 volt.  12 volt panels have 36 cells. 24 volt panels have 72 cells. Your panels are probably 60 cells. These 60 cell panels have a lower voltage than a typical 24 volt panel, making it difficult to mix and match with 36 or 72 cell panels.

    Your best bet would be to get more 250 watt panels to pair up with the ones you have. For a 48 volt system you definitely want either 3, 6 or possibly 9 panels series wired in 3 panel strings. Three in series is really the only string size you can use to get the voltage high enough, but not too high  for your controller.

    Can you describe your battery bank? That's a very large battery and a 60 amp controller at full output is not going to give you enough charging current to properly maintain an 800 Ah battery.  If you do, in fact, have an 800 Ah. battery and already have a 60 amp controller then you might consider the previously mentioned 9 panel set up AND another controller for the 6 150 watt panels.

    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,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

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  • mbu
    mbu Registered Users Posts: 7 ✭✭
    #4
    Thank you for the advice my bank is 200ah 12v gel batteris connected in series thus making it 48v system. Now that you mentioned it ive realised that it is a 200ah bank because the batteries are not in parallel. Currently only the 12v x6 amerisolar panels are connected to the mppt in series giving a Voc of around 117v and a current of about 8.5 amps. With a 4 gauge wiring to inverter
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  • mbu
    mbu Registered Users Posts: 7 ✭✭
    #5
    4 batteries
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  • mbu
    mbu Registered Users Posts: 7 ✭✭
    #6
    the voc is 36.8 and I want to connect them in series but im a bit uneasy because the total Voc is 147V because of the 150v limit of mppt so ill do 3 strings of 2pv in parallel
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  • mbu
    mbu Registered Users Posts: 7 ✭✭
    #7
    2strings
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,135 ✭✭✭✭✭
    edited April 2018 #8
     Problem with that plan is 2 in series isn't high enough voltage to charge a 48 volt battery. 3 of those panels in series is only 110.4 Voc. you're fine with 3s2p wiring.  As mentioned earlier, those aren't 24 volt panels. Keep in mind also your MPPT controller wants higher than nominal voltage to operate as designed.

    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,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

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