MC4 plug recommendations ?

LANTA
LANTA Registered Users Posts: 5 ✭✭
in Solar Beginners Corner #1
I would like to hook my 6 - 150W 12V panels to a combiner box. 2 panels in parallel on 3 strings.
I'm going to need a y branch to connect the 2 panels for each string.
Does anyone have any recommendations of make or brand name of MC4 plug to buy?

Thank you!
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    edited September 2019 #2
    Just to clarify terminology, a "string" is generally a series string (+ive to -ive connected, with voltage adding).  Going into a combiner box, you would generally wire panels in series strings (eg 2 panels each for ~36v), then combine in parallel (eg 3 strings @~8a = ~24a into a controller).   Depending on distance, the controller, and bank voltage, other series string sizes might make more sense.

    This could be wired using an mc4 extention cable cut in half, leaving a male and female (+ive and -ive) mc4 end to connect to each end of the string, and a bare wire end into the combiner.

    I can't think of an application offhand where you'd want to parallel panels with a 'y' connector, then wire in series.  Are you wanting to parallel of pairs of panels into a combiner, then further parallel pairs using a combiner with fuse/breaker for each pair?
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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  • LANTA
    LANTA Registered Users Posts: 5 ✭✭
    #3
    Thank you for the reply! I am trying to connect 2 panels together in parallel and bring them into the combiner box.
    I would like to connect them in series to make a 24V string (2 panels each on 3 strings) leading into a combiner box with circuit breakers for each line.
    I would purchase a MPPT controller, to charge my 2 - 200 Ahr batteries that I would leave at 12V because i only have a 12V 300W MorningStar inverter.
    Can this be done safely?
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,107 ✭✭✭✭✭
    edited September 2019 #4
    Provided your proposed MPPT controller has a Voc. limit above your input Voc. you can series wire 3 panels and with only 2 strings. You don't even need to fuse them. You can use a Y branch  parallel connector then. It will require some extension cables. Personally I would make a simple combiner box with off the shelf parts instead.

    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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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #5
    As LH2 says above, putting the panels in series strings of 3 may make sense, provided the controller can handle voltage of over ~75v.  Many are 100-150v and would be no problem.  If it's close, you'll want to check that the open circuit voltage of the string, adjusted up for record low temps at your location is well under the controller limit.  There are string calulators online to help with this if needed.

    Doing strings of 2 panels should also work, and may allow for slightly better controller efficiency.  Depending on distance and wire size, this may be more than offset by losses on lower voltage / higher current wire from combiner to controller though.  String Voc (cold) vs controller limit should still checked, but shouldn't be a problem with most decent controllers.

    Using 2 strings of 3 panels does avoid the need for string breakers, but breakers can be handy as shutoffs for troubleshooting etc, and would be needed anyway if you ever expanded beyond 2 strings.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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  • LANTA
    LANTA Registered Users Posts: 5 ✭✭
    #6
    Guys thank you for helping me with my future plan of connecting the panels in a series for 24V's. I will be sure to make sure my controller can handle it.
    But i am going to take one step at a time so I dont stress my finances. I will take that larger step towards a MPPT controller at a later date. 
    So if I stay with a 12V, and put 2 panels on each line. Each panel has a ISC of 9,05. So do I have to double that 9,05x2=18.10, 18.10x1.56=28.236. Should equal a 30amp breaker?
    Am I right by 2X the ISC#?
    Am I right about anything? LOL
    Thanks guys!
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,107 ✭✭✭✭✭
    edited September 2019 #7
    Two 12 volt panels in series with 9.05 Isc. will still be 9.05 Isc but at the higher 24 volt nominal voltage. Another STRING in parallel will give you the same 24 volt nominal voltage but at 18,1 Isc. So If you go with 3 strings you will get 27.15 amps Max @ 24 volt nominal. Your Imp. will be lower of course and Will vary with the amount and angle of the sun hitting the 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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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #8
    Assuming you're referring to string breakers in a combiner box, there should be a maximum string breaker/fuse size spec'd by the panel maker (often 15a).  If you use the same size (or larger) mc4 extension wire as the wire used on panel leads, I'd go with the spec size.

    In the series strings voltage adds as you add more panels to the string.  After you combine the strings in parallel current adds as you add more strings, so you may want to use bigger wire and a larger breaker between the combiner and controller.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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  • LANTA
    LANTA Registered Users Posts: 5 ✭✭
    #9
    Yes you are right! On the back of my panel it says "Max Series Fuse Rating 15A". 
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  • LANTA
    LANTA Registered Users Posts: 5 ✭✭
    #10
    Thank you for your help!
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #11
    You're quite welcome.  Eveyone here at one time had to learn.  Feel free to pay it forward.
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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  • billybob9
    billybob9 Registered Users Posts: 141 ✭✭
    #12
    Here's a cool little combiner box I got from either Amazon or Ebay.
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,107 ✭✭✭✭✭
    edited September 2019 #13
    billybob9 said:
    Here's a cool little combiner box I got from either Amazon or Ebay.
    That looks more a transition box being there isn't any combining being done the way it sits and there doesn't look to be any fusing/breakers for the 4 strings. Also the empty output terminals need to be wired to some type of Buss or combiner block which combines the 4 strings and output's with a larger single pair of wires that would go on to the charge controller. 

    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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  • billybob9
    billybob9 Registered Users Posts: 141 ✭✭
    #14
    littleHarbor2
    You can't see the bar in the middle that connects the 4 solar inputs. So with one output per 4 inputs your just combining 4 panels or strings. That bar is the buss. I think it was called a 4 string combiner but without all the bells and whistles. It was cheep but I couldn't find it again. 
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,107 ✭✭✭✭✭
    #15
    Combining 4 strings would require fusing in all 4 strings. That was the first thing that I noticed. They do make MC-4 based fuse holders but IMO they aren't cheap.

    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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  • billybob9
    billybob9 Registered Users Posts: 141 ✭✭
    #16
    Well I ran out of combiner pictures to show so I'll just show my Racking tool that is pretty kool. The perfect 90 degree to make the perfect rectangle. Goes 30' easy.
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