ligwyd: Design my the perfect system

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Comments

  • PhotowhitPhotowhit Posts: 4,600Solar Expert ✭✭✭✭
    ligwyd said:
    Would you guys turn down 19 strand and wait for 7 strand PV wire or is it not that big of a deal? Don't want to break any wires terminating. Most of the suppliers up here all are quoting me 19 strand and thats all most of them can get. I would think MC4 connectors would like the 7 strand better as well? If 7 is the way to go (don't really need the increased flex of 19 strand) then I will wait for it and get on to something else in the meantime. I have a roll end of each and they both feel comparably manageable. My aim also is to keep the OD to min. (non-direct burial non double jacket etc)
    7 Strand is a PITA to crimp connectors on, I much prefer 19 strand! I get a good crimp without a lot of hassles. With 7 strand, I've had enough problems that at time, I'll clip one strand then half crimp and guide 3 strand into each side of the crimp! Seriously!
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
  • EstragonEstragon Posts: 2,440Registered Users ✭✭✭✭
    The way I would (and did) do the pv wiring, is to get premade mc4 wire about 2x long enough to reach from each string to a weatherproof junction box located somewhere relatively easy to access and work on, with as little weather/sun exposure as possible.

    The premade wire has a male and female end on each end. Zip-tie or tape the mc4 to the mating string mc4 (DON'T connect it), run it back to the junction box in a loop. Cut the loop at the junction box, which gives you a + and - pv string wire. Establish the polarity, and mark wire accordingly.

    At the junction box, you'd connect your 19 strand wire, if that's what's available, for the run to combiner box. You should be able to get a decent splice, but better it be in a box rather than swinging around in the wind and the sun.

    At the combiner, you might want to crimp ferrules to the ends. In any case, check and retorque all connections a day or so after. This should be done anyway, but I've found the more finely stranded stuff especially squishy and prone to loosening.

    This avoids having to make mc4 connectors at all, and keeps splices/crimps in boxes.
    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
  • PhotowhitPhotowhit Posts: 4,600Solar Expert ✭✭✭✭
    If you do it @Estragon's way, be sure to start with the longest runs, and do all the clips and fasteners before you trim the wire. This will ensure you have the shorter wires for the shorter runs.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, ForkLift battery. Off grid for @13 of last 14 years. 1000 watts being added to current CC, @2700 watts to be added with an additional CC.
  • EstragonEstragon Posts: 2,440Registered Users ✭✭✭✭
    @Photowhit - good point, it really sucks ending up a foot short when everything's done!
    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
  • ligwydligwyd Posts: 39Registered Users ✭✭
    Great info guys. Ever soldier the ends before terminating or is that not a good idea? I will also look for crimp on ends for the 19 strand.
  • BB.BB. Posts: 27,560Super Moderators admin
    Not usually a good idea to solder dip the ends before terminating... Some people do do it and swear by it. My issues:
    • Good grimp connections have enough PSI compression to make a hermetic seal between the terminal and the wire. There is no reason for solder to protect against air (oxygen) or fluids in connection. Trying to solder a connector after a proper crimp should not get any solder into the crimp itself (hermetic seal). Other issues in some of the following bullet points also apply to issues with post crimp soldering.
    • Crimp connections are typically just a little bit larger than the wire itself... Wires that have a lot of strands (finer strands) can be difficult to fit into crimp connections (air gaps between strands takes up more space than coarse strands or solid wire). Adding solder may make more difficult to insert wire into connector for crimping.
    • Coating with solder generally needs some sort of flux... The flux goes up the wiring between the strands. Use a flux made for electronic circuits (plumbing flux will corrode over time). Cannot really remove all flux between strings/under insulation when cleaning--Electronics flux may still increase corrosion...
    • When you solder/tin the stranded wiring... The place where the solder stops wicking up the cable provides a fulcrum point. Any bending/flexing of the cables will "focus" stresses at the end of the solder "joint". This will work harden copper wire and greatly reduce the "flex life" of the cable. A good crimp connection will not have a "focus" for flexing... And many crimp connectors will also provide further stability by clamping on the wire insulation.
    -Bill "in my opinion" B.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ligwydligwyd Posts: 39Registered Users ✭✭
    No solder it is! Agree with you Bill. Thank you for the detail.
    John
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