Solar Panel Cable Branch Connector and fuses

BilljustBill
BilljustBill Solar Expert Posts: 219 ✭✭✭
Off Grid System with a 24v, 880ah battery bank.

To save on wiring, if I am were to put two panels in parallel, I see that you can buy a Y-connector. I was wondering when two panels are wired with these, wouldn't you want to fuse each panel rather than one fuse for two panels? I would be wiring two Kaneka 60v/60w panels together in parallel, with 20 Kaneka panels for a 24v system and MPPT controller. Here's an example:

http://cgi.ebay.com/MC3-Y-M-F-F-Solar-Panel-Cable-Branch-Connector-/290525431321?pt=LH_DefaultDomain_0&hash=item43a4aa4619

Second question: If wiring three 12v, 135w Kyocera panels in a series, would you put a fuse between each panel before going to a breaker in a combiner box? I would be wiring three panels at a time with a total of 12 panels on a second 24v MPPT controller.

If you do protect each panel with a fuse, what type and what type of holder for each type of panel? The fuses would be in line for the Kaneka panels and on the roof rather than a combiner box near the ground, how do you know if one fuse opens without going up and hand checking each set of three?

Thanks for you help,
Bill

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    Re: Solar Panel Cable Branch Connector and fuses

    If you have one or two parallel strings, no series fuse is required.

    For three or more parallel strings, there should be one fuse per string, no matter how many series connected panels are in the string.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BilljustBill
    BilljustBill Solar Expert Posts: 219 ✭✭✭
    Re: Solar Panel Cable Branch Connector and fuses
    BB. wrote: »
    If you have one or two parallel strings, no series fuse is required.

    For three or more parallel strings, there should be one fuse per string, no matter how many series connected panels are in the string.

    -Bill

    Thanks for answering, Bill. Help me understand a bit more, if you would, please.

    Wire Sizes and Fuses:

    I also saw some other 30amp connectors where one leg of each of 3 parallel panels are connected with a 4-way "+" and the 4th leg is the out connection to the combiner box. So, are you saying that each parallel string only needs a single fuse/breaker between the panels and the combiner box? I don't have to worry about fuses between panels of each parallel set/string?

    And when I wire the three 135's in SERIES, I don't have to worry about a fuse in between those panels either? Just 1 breaker on each string in the second combiner box mounted on a pole array. The pole will be about 60' from the MPPT controller using #6 strand wire..

    The conduit on the roof mounted Kaneka panels will run to the outside wall mounted combiner/breaker box 6' from the ground. The longest run to the combiner/breaker box of the 60v Kaneka roof panels would be 50' and the shortest run would be 20'.

    I have a 500 ft. reel of single run, #6 copper wire that is made up of 18-strands. Do you think that it is fine enough wire and large enough to carry the 60v Kaneka panel array or the Kyocera 36v string array?

    For the Kaneka roof panels, the run between the outside combiner box to the inside MPPT controller should be about 6'. The distance between the controllers and battery bank is 6'. Using 2/0 copper welding cable should be ample, don't you think?

    I've gathered all my materials and now I'm ready to start building my system. All help is appreciated.
    Bill
  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    Re: Solar Panel Cable Branch Connector and fuses
    Wire Sizes and Fuses:

    I also saw some other 30amp connectors where one leg of each of 3 parallel panels are connected with a 4-way "+" and the 4th leg is the out connection to the combiner box. So, are you saying that each parallel string only needs a single fuse/breaker between the panels and the combiner box? I don't have to worry about fuses between panels of each parallel set/string?
    I am not quite sure I understand the question... Let me try some quick drawings about your options:
    [FONT=Fixedsys]
    |--P--P--P--"+"no fuse
    |------------"-"
    
    |--P--P--P--+--"+"no fuse
    |--P--P--P--|
    |
    |--------------"-"
    
    |--P--P--P--fuse--+---"+"
    |--P--P--P--fuse--|
    |--P--P--P--fuse--|
    |
    |--------------------"-"
    [/FONT]
    

    Each wire should be rated (minimum) to carry the Fuse Rating (i.e., 15 amps, 14 awg).

    When the wiring combines, the wiring needs to be able to carry 3x Fuse rating (i.e., 3x15a=45 amps in case #3).
    And when I wire the three 135's in SERIES, I don't have to worry about a fuse in between those panels either? Just 1 breaker on each string in the second combiner box mounted on a pole array. The pole will be about 60' from the MPPT controller using #6 strand wire..

    Yep.

    8 amps over 60' one way run (some calculators use 1 way run, others use round trip distance), using a voltage drop calculator, would be 0.5 volt drop.
    • 0.5 volt drop / (3x17.6 Vmp) = 0.009 = 0.9 % voltage drop
    So the 6 awg is well within the 1-3% voltage drop we try for.
    The conduit on the roof mounted Kaneka panels will run to the outside wall mounted combiner/breaker box 6' from the ground. The longest run to the combiner/breaker box of the 60v Kaneka roof panels would be 50' and the shortest run would be 20'.

    Double check the 60v Vmp kaneka panels--Those may not be possible to place 2 in series for the typical 150 VDC max. Voc MPPT charge controller.

    You may only be able to stay with one panel in series unless you are in the Caribbean or somewhere else that does not get very cold.
    I have a 500 ft. reel of single run, #6 copper wire that is made up of 18-strands. Do you think that it is fine enough wire and large enough to carry the 60v Kaneka panel array or the Kyocera 36v string array?
    Fine Wire, such as used for cords or welding cables, are actually a pain to use... It is very difficult to use standard binding screws. The fine wires just do not make make solid connections in NEC type wire holders).
    For the Kaneka roof panels, the run between the outside combiner box to the inside MPPT controller should be about 6'. The distance between the controllers and battery bank is 6'. Using 2/0 copper welding cable should be ample, don't you think?
    What controller (brand/model)? What voltage battery bank and current rating do you want to carry?

    Have fun!
    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BilljustBill
    BilljustBill Solar Expert Posts: 219 ✭✭✭
    Re: Solar Panel Cable Branch Connector and fuses
    BB. wrote: »
    I am not quite sure I understand the question... Let me try some quick drawings about your options:
    [FONT=Fixedsys]
    |--P--P--P--"+"no fuse
    |------------"-"
    
    |--P--P--P--+--"+"no fuse
    |--P--P--P--|
    |
    |--------------"-"
    
    |--P--P--P--fuse--+---"+"
    |--P--P--P--fuse--|
    |--P--P--P--fuse--|
    |
    |--------------------"-"
    [/FONT]
    

    Each wire should be rated (minimum) to carry the Fuse Rating (i.e., 15 amps, 14 awg).

    When the wiring combines, the wiring needs to be able to carry 3x Fuse rating (i.e., 3x15a=45 amps in case #3).



    Yep.

    8 amps over 60' one way run (some calculators use 1 way run, others use round trip distance), using a voltage drop calculator, would be 0.5 volt drop.
    • 0.5 volt drop / (3x17.6 Vmp) = 0.009 = 0.9 % voltage drop
    So the 6 awg is well within the 1-3% voltage drop we try for.



    Double check the 60v Vmp kaneka panels--Those may not be possible to place 2 in series for the typical 150 VDC max. Voc MPPT charge controller.

    I didn't plan to wire the Kaneka panels in series. With the Kaneka panels, I would be wiring three postive wires from three panels on one of those "+" 4-way connectors and three negative wires on another of the same connectors. In parallel, the 60 volts stay the same, but the amps for the three panels would be 5.7amps
    You may only be able to stay with one panel in series unless you are in the Caribbean or somewhere else that does not get very cold.


    Fine Wire, such as used for cords or welding cables, are actually a pain to use... It is very difficult to use standard binding screws. The fine wires just do not make make solid connections in NEC type wire holders).


    What controller (brand/model)? What voltage battery bank and current rating do you want to carry?

    The 24 volt bank is eight L-16hc, 6 volts, from U.S. Battery. Each array has it's own Outback 80 amp FlexMax controller.
    Have fun!
    -Bill

    Thanks for your help. I put the answers to your questions in red.
    Bill
    Bill
  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    Re: Solar Panel Cable Branch Connector and fuses

    I am a little confused. How big of arrays are you planing on?

    80 amp outback controllers are probably good for almost 3,000 watt arrays each on a 24 volt battery bank.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BilljustBill
    BilljustBill Solar Expert Posts: 219 ✭✭✭
    Re: Solar Panel Cable Branch Connector and fuses
    BB. wrote: »
    I am a little confused. How big of arrays are you planing on?

    80 amp outback controllers are probably good for almost 3,000 watt arrays each on a 24 volt battery bank.

    -Bill

    Like you have said, the problem with the "bargain" of the twenty 60v Kaneka panels is that I bought an individual Outback controller just for them. But, the total cost (including shipping) of the 20 new panels and the Outback controller was $1,450.00 for 1,200 watts. The same cost wouldn't ship four 135w Kyocera panels totaling 540 watts.

    How big are the Arrays?

    1,200 watts for the Kaneka panels (Roof Mount)
    1,620 watts for the Kyocera panels (Tracker Mount)
    1,120 watts for used panels and China made panels (tracker Mount)
    3,940 total watts in theory.
    Bill
  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    Re: Solar Panel Cable Branch Connector and fuses

    BjB,

    Sorry, you said that before--I should have remembered (I thought so, but I was not sure).

    Anyway, assuming that you have three controllers with the following configurations (just taking some guesses here--It is too late for me to look up all the specs. And I don't have any idea what the 1,120 array is. :p ). Assuming 6 awg wire 30' one way length:
    • 1,200 watts for the Kaneka panels (Roof Mount) (20 panels in parallel; 60w, 60v Vmp, 1 amp Imp)
    • 1,620 watts for the Kyocera panels (Tracker Mount) (12 panels; 135 watt, 17.6v, 7.67a)
    • 1,120 watts for used panels and China made panels (tracker Mount) (12 panels; 93 watt, 17.6v, 5.3a)
    First set of Keneka:
    • 20x 1 amp = 20 amp Imp @ 60 volt Vmp
    • Voltage drop = 0.6 volts / 60 volts = 1% array wiring drop
    Second Set of Kyocera panels... Assume 4 in series, 3 strings in parallel (your choices may be different):
    • 4x17.6 volts = 70.4 volts
    • 3x7.67 amps = 23.1 amps
    • Voltage Drop = 0.7 volts / 70.4 volts = 1% array wiring drop
    Third set--Assuming that this are 17.6 Vmp panels and you can arrange as 4s*3p connections:
    • 4x17.6 volts = 70.4 volts
    • 3x5.3 amps = 15.9 amps
    • Voltage Drop = 0.5 volts / 70.4 volts = 0.7% array wiring drop
    If you can combine #2 and #3 arrays behind one controller (assuming 4x17.6 volt Vmp and add the current from the two above arrays) and still using 1x pair of 6 awg run for both arrays:
    • 4x17.6 volts = 70.4 volts
    • 23.1 amps + 15.9 amps = 49 amps total
    • Voltage Drop = 1.4 volts / 70.4 volts = 2.0 % array wiring drop
    Of course, you can still use 2x pair of 6 awg and run each pair to the combiner for the single FM 80 controller.

    Wiring from the Controller to the battery bank... Assuming worst case of #2+#3 arrays combined of on 6' one way run of 2/0 cabling:
    • 1,620w + 1,120w = 2,740 watts total
    • 2,740 watts * 1/29 volts charging * 0.77 derating = 73 amps
    • Voltage drop = 0.08 volts / 29 volts = 0.3% voltage drop
    Now, the voltage drop from the charge controller to the battery bank is not really so much of a % drop issue--It is how accurate the charge controller can hold the battery bank voltage while charging...

    For a 24 volt battery bank, I would guess that less than 0.2 volt drop is OK, and less than 0.1 volts is even better. Yours, on the 2,740 Watt controller (highest power) would be 0.08 volt drop--so that is great.

    Remember for a 12 volt battery bank that ~0.1 volt change in voltage represents around ~10% different in resting voltage... So, keeping the voltage error less than 0.1 volts (and prefer 0.05 volts) for a 12 volt battery bank would help ensure that you are pumping full current into the battery bank without the voltage drop of the cabling causing the charge controller to enter Absorb (current limited charging mode) to soon.

    Your configuration--I took a guess at it--but this is how I would attempt to configure a system given what I know here.

    Regarding fusing--Look at the fuse rating for each series connected string of panels--And use that fuse/breaker rating for that string... Some strings may use a 15 amp fuse, others may use a 5 amp fuse (for many panels, Ifuse is roughly equal to 2xIsc rounded up or down to nearest standard fuse size).

    For the battery bank, assume two parallel strings of 420 AH at 24 volt battery bank for a total of 840 AH at 24 volts.
    • 3,940 Watts * 1/29 volts charging * 0.77 = 105 amps nominal charge current
    • 105 Amp / 840 AH = 12.5% rate of charge
    So--Assuming everything works as planned--You have a nicely paneled battery bank (we recommend from 5-13% rate of charge and ~10% minimum rate of charge for "tall batteries").

    I hope the above makes sense.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BilljustBill
    BilljustBill Solar Expert Posts: 219 ✭✭✭
    Re: Solar Panel Cable Branch Connector and fuses

    Bill,

    Thank you for your time and insight. I know it took time and thinking to understand this DIY solar project. Now, at the point of planning the wiring and mounting, help is needed even more as I proceed....

    It's been a quite a quest just to get this far, hunting panel bargains, low prices on new deep-cycle battery prices, satellite dish mount parts, heavy copper wiring, large and long lengths of 1/0 aluminum wire, and searching every night for Internet sites with closeouts and sales of Outback inverters and controllers....

    Funding this project with garage & flea market sales, flea market finds, and the sale of garage sale silver/gold jewelry finds has taken over a year....

    With 3.94Kw in panels, after the 30% IRS tax credit, I will have $8,500 in this Off Grid system. Do you have any insight as to how I could have spent less?

    Thank you, again, for your help and the help & reflections of the members like "Saw Mill" I've met on this Forum!!
    Bill
    Bill
  • BB.
    BB. Super Moderators, Administrators Posts: 33,439 admin
    Re: Solar Panel Cable Branch Connector and fuses

    Bill,

    You are very welcome--Let us know how it works and if you want, feel free to document the system for the next "newbie".

    Regarding saving money--I sounds like you have done all the things that you can. Sometimes, trying to get smaller/used panels to fit into and existing string or mixed with new panels may become more effort that it is worth (second controller, wiring, mounting, etc.)--but that is a personal decision.

    And you are paying for the systems with savings/earnings/scrounging instead of an equity loan--I am a very big fan of getting out of debt and staying out of debt instead of financing Solar PV systems.

    There are instances where Solar Power can make economic sense--but adding the cost of loans on top of the costs (and maintenance costs) is difficult (for me) to justify.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Solar Panel Cable Branch Connector and fuses
    Thanks for answering, Bill. Help me understand a bit more, if you would, please.

    Wire Sizes and Fuses:

    I also saw some other 30amp connectors where one leg of each of 3 parallel panels are connected with a 4-way "+" and the 4th leg is the out connection to the combiner box. So, are you saying that each parallel string only needs a single fuse/breaker between the panels and the combiner box? I don't have to worry about fuses between panels of each parallel set/string?

    I'm a little confused by your wording. Just to be straight, a string is a set of modules connected in series. For more than two strings connected in parallel with each other, each string gets a single fuse at the positive voltage point of connection (combiner). The value of that fuse is the Isc of a single module times 1.5625 (1.25 twice), rounded up to the next fuse size.

    It "sounded" to me as if you were referring to a set of modules connected in parallel as a "string". Strings are always series connected modules. It is possible, however, to have a string length of 1, i.e., a single module. The same rules apply; if more than two in parallel, each gets a fuse.
  • BilljustBill
    BilljustBill Solar Expert Posts: 219 ✭✭✭
    Re: Solar Panel Cable Branch Connector and fuses
    ggunn wrote: »
    I'm a little confused by your wording. Just to be straight, a string is a set of modules connected in series. For more than two strings connected in parallel with each other, each string gets a single fuse at the positive voltage point of connection (combiner). The value of that fuse is the Isc of a single module times 1.5625 (1.25 twice), rounded up to the next fuse size.

    It "sounded" to me as if you were referring to a set of modules connected in parallel as a "string". Strings are always series connected modules. It is possible, however, to have a string length of 1, i.e., a single module. The same rules apply; if more than two in parallel, each gets a fuse.

    Getting my correct terms down seems to be a problem. If panels are hooked positive-to-negative forms a "Series STRING". What is the correct term for panels wired in Parallel?

    If more than two panels and each gets a fuse, how does one know if the fuse opens when the wiring is under the rooftop panel array?

    I found this company that makes wiring harnesses to fit the layout of panels. Since I have 20 Kaneka panels wired in two........ runs...of ten panels..... I have asked them for a cost of connectors/wire in making a harness for each run of this rooftop array.....

    http://www.win-solarllc.com./

    Does anyone know anything about this company's product?

    Thanks,
    Bill
  • ggunn
    ggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Solar Panel Cable Branch Connector and fuses
    Getting my correct terms down seems to be a problem. If panels are hooked positive-to-negative forms a "Series STRING". What is the correct term for panels wired in Parallel?
    Two modules (panels) wired in parallel is two strings of length 1.
    If more than two panels and each gets a fuse, how does one know if the fuse opens when the wiring is under the rooftop panel array?
    You put the fuses on the other end of the wire where you can get to them, usually in a combiner box. Also, not every module gets a fuse, every string does. That's because no matter how many modules you have connected in series, the current anywhere in the string is the same as that of a single module.