Size of DC Breaker for Solar Panel

With54With54 Registered Users Posts: 21
What amperage breaker should I purchase for 100 watt and 120 watt solar panels?

Which Combiner Box would you recommend?

Thanks

Comments

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Size of DC Breaker for Solar Panel
    With54 wrote: »
    What amperage breaker should I purchase for 100 watt and 120 watt solar panels?

    Which Combiner Box would you recommend?

    Thanks

    How many 100 Watt and 120 Watt solar panels configured how?
    It makes a difference.

    One panel: you don't really need any over-current protection.
    Several in series: same again, as it acts as one big panel.
    Two or more in parallel: each should be fused as per NEC regulations in respect to the panels' current. In other words, 12 V 100 Watt panels with a current potential of 5.5 Amps (say) would have 7.5 Amp fuses on each. (This is not a precise calculation on my part; just for demonstration purposes.)
  • With54With54 Registered Users Posts: 21
    Re: Size of DC Breaker for Solar Panel

    6 panels - 5 are 100 and 1 at 120 watts. They are connected in parallel.
  • BB.BB. Super Moderators, Administrators Posts: 31,425 admin
    Re: Size of DC Breaker for Solar Panel

    Many of the newer panels with specify the series protection fuse... For example, the Kyocea 135 watt panel says (PDF):
    Pmax = 135 Watts
    Vmp = 17.7 volts
    Imp = 7.63 amps
    Voc = 22.1 volts
    Isc = 8.37 amps
    Vsys-max = 600 volts

    Maximum Fuse = 15 Amps

    So, my estimate would be 2x Isc and round to the nearest standard fuse (down to 15 amps in this case).

    And, you only need to fuse/breaker a solar PV array if there are more than two parallel strings (every series string then needs its own breaker/fuse--typically in the Positive lead for Negative Grounded systems).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • bobdogbobdog Solar Expert Posts: 192 ✭✭
    Re: Size of DC Breaker for Solar Panel
    BB. wrote: »
    Many of the newer panels with specify the series protection fuse... For example, the Kyocea 135 watt panel says (PDF):



    So, my estimate would be 2x Isc and round to the nearest standard fuse (down to 15 amps in this case).

    And, you only need to fuse/breaker a solar PV array if there are more than two parallel strings (every series string then needs its own breaker/fuse--typically in the Positive lead for Negative Grounded systems).

    -Bill

    Wow, you just answered my specific question. I knew if I searched long enough I'd come across this answer. Thanks Bill.
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Size of DC Breaker for Solar Panel

    actually if i miss my guess here and remember it correctly it is

    imp x 1.25 x 1.25 and rounded up to the nearest commercial value.
  • kenputerkenputer Solar Expert Posts: 27
    Re: Size of DC Breaker for Solar Panel

    I have a 30 amp Tracer solar charge control which will take up to 150 volt solar array and I was hoping someone could help me on fuse size and rating. We will have 3 -190 watt panels in series the panels are rated 45.2 volt open circuit so we would be at 135.6 volts.

    Thanks
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Size of DC Breaker for Solar Panel
    niel wrote: »
    actually if i miss my guess here and remember it correctly it is

    imp x 1.25 x 1.25 and rounded up to the nearest commercial value.
    Close. Actually it's Isc X 1.25 X 1.25 and up to the nearest std size.
  • ggunnggunn Solar Expert Posts: 1,973 ✭✭✭
    Re: Size of DC Breaker for Solar Panel
    With54 wrote: »
    6 panels - 5 are 100 and 1 at 120 watts. They are connected in parallel.
    The power is not what determines the breaker rating, it's the current.
  • BB.BB. Super Moderators, Administrators Posts: 31,425 admin
    Re: Size of DC Breaker for Solar Panel

    And you do not really need a fuse/breaker on the solar array input for the charge controller for a single string.

    What you do (usually) need is a series protection fuse per string if you have three or more panels (strings) connected in parallel. Each series connection needs its own fuse/breaker to protect against a local panel/wiring short from being fed by the rest of the panels in the array. And it usually takes three or more parallel panel circuits to generate enough current to be a "danger" if there is a short.

    By the way, Trace only made PWM controllers (from the little history I know). Why would you want ~100 volts Vmp into the controller? If you are not charging a ~60-72 volt battery bank, why would you do it with a PWM controller? Or is this a really a "Tracer" brand MPPT controller?

    Normally, for standard 12/24/48 volt battery banks, I would be suggesting a MPPT charge controller.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • kenputerkenputer Solar Expert Posts: 27
    Re: Size of DC Breaker for Solar Panel

    Thanks for the info and yes it is the Tracer 3215 MPPT controller
  • FARAZFARAZ Registered Users Posts: 1
    Dear, 

    First Of all i dont understand you are given suggestion to use more than 25% over amp breaker for Pv. My question is why I use more because if a circuit will get burn or caught fire max of 6 amp and its max amp 5.9 amp of that device. As per your calculation  i use breaker of 6.15 amp
  • EstragonEstragon Registered Users Posts: 4,494 ✭✭✭✭✭
    Not sure which calculation you're questioning.  Using deratings in some posts above, fuse would be Imp 5.9a x 1.25 x 1.25 = 9.2a, rounded up would be 10a breaker or fuse.  IIRC, some DC breakers don't require as much derating.  The derating is to ensure normal operating current doesn't cause heating in the breaker.

    The breaker should never open with normal current from the panel (or series string) it protects.  The purpose of the breaker is to prevent the current from two or more panels/strings connected in parallel with the protected panel from feeding combined parallel fault current through a short in the protected panel.

    The maximum size of the string fuse/breaker is given in panel specs, often 15a. 

    With one or two panels/strings in parallel, no breaker is needed (but can be handy as disconnects), because combined fault current would generally be under the max string fuse size.
    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
  • TecnodaveTecnodave Registered Users Posts: 418 ✭✭✭✭
    On the issue of derating the breaker......The NEC requires that the breaker bi sized at 125% of maximum current in the circuit. That is for "non-continuous use" with a breaker rated for "non-continuous use." For continuous use using a non-continuous breaker rating is maximum current times 1.25 times 1.25 or 1.56 times maximum current.

    However not all breakers are "non-continuous use"  The breakers sold by MidNite, the MNDC and MNEPV breakers are "continuous duty use" I.e. ARE RATED 100% DUTY CYCLE  Therefore with these breakers the required breaker size is maximum current times 1.25. These breakers are magnetic/hydraulic and do not generate heat.

    Most  Carling Switch breakers are 100% duty cycle as are many from CBI Circuit Breaker International. As well as many industrial breakers. 

    Most if not all thermal breakers are not 100% duty cycle, nothing you will find at Home  Cheepo will be rated "continuous duty" as is required for anything operating for more than 2 hours continuously as in solar where the bulk of the loads will require a "continuous duty rating" or the 1.25 X 1.25 derating factor
    2 Classic 150, 2 Kid, 5 arrays 7.5 kw total  2ea.  2S6P Sharp NE-170/NE-165, 1ea. 12P Sanyo HIT 200,  2ea. 4/6P Sanyo HIT 200, MagnaSine MS4024AE, Exeltech XP-1100,  2 Banks L-16 battery, Rolls-Surette S-530 and Interstate Traction, Shunts with whizbangJr and Bogart Tri-Metric, iCharger i208B  dc-dc buck/boost converter with BMS for small form lithium 8S 16650 or LiFePO4,
  • kewl0069kewl0069 Registered Users Posts: 4
    I am trying to figure out the best way to put a breaker in my system.i will list all the specs of everything on board it's very big portable system. Battery bank 12 crown CR-235 6v deep cycle batteries 4/0 cable ties series and parallel total 1410 AH 12V  next I have a 500 watt 3 phase wind turbine 3/6 awg cable goes into 100 amp throw switch then to 100 amp 3 bridge ac to DC rectifier then to dump control board and solid state relay
    And a 300 watt 3 ohm resister bank for resistive braking. Solar controller EPEVER 100 amp 200v mppt controller hooked to four 300 watt solar panels voc 39.85v isc 9.71 15a fuse rating. Each. These are wired with 8 awg mc4 cables less than 10 ft from controller .series tie 2 panels then parallel both to combiner box built out of copper bus bars 250 amp each pole side has disconnect switch and 100 amp ANL gold fuse holder  on positive bar.then 1/0 cables for negative and positive PV input to controller the controller is connected to the battery bank with 5ft of 2/0 cables. Second solar array 6 100 watt grape solar panels voc 21.9v isc 6.13 and 10 amp fuse rating in 3 suitcases 200 watt each case total is 600 watt 120v series no parallel to EPEVER 80a 200v mppt controller through a disconnect switch and 30 amp ANL fuse. Next 2 18 inch stroke 12v linear actuators for tilt goes to remote switch box so remote controlled and 3 ton HYDRAULIC ram for back array lift that's manual. So is the wind turbine tower it's a prototype telescoping tower that folds down and Jack's up with 30 inch 6k pound jack.like a crane. Its bolted down to a 1/2 thick steel plate 12 inch with grade 8 5/8 bolts and welded to a customer 1/4 steel tube frame underneath trailer.  Equipped with a 6k lumen flood lights on top under turbine. And also under solar array lights and equipment box lights inside . A power bright 6000-watt continuous 12k max msw inverter 30 amp RV receptacle box hardwired  and 4  4/0 cables to battery bank fused with 400 amp gopower slow fuses. Then 3500 watt puresine 7kmax inverter hardwire 30 amp RV box 4/0 cables and 400 amp gopower fused to bank. A samlex 80 amp dual bank marine charger for use with generator or shore power for rapid charging bank and also a 12v bank desulphinators . And a backup renogy rover 40 amp mppt controller fused with 60 amp breaker.. what I want to know is what would be a good way to build a din rail breaker system to cover the 100 amp controller and the 80 amp controller and both solar arrays? I want 4 breakers that fit on the same din rail what would u all recommend for this?
  • kewl0069kewl0069 Registered Users Posts: 4
    Oh and I also have 4 cooling systems installed using drok temperature controlled relay boards 4 of those and inline blower fans high speed 12v 4 of those too those are fused with 5 amp fuses each ..my temperature stays at about 28 to 30c on very hot days and in winter time I use heat lamp box and tubes filled with glass marbles and use relays as heater controller relays that turns it on to keep temperatures to 50 deg f at all times uses very low power only 200 watt hours total.
  • salakoshinasalakoshina Registered Users Posts: 2
    What size of breaker should I use between two 170w solar panel and 30amps controller and between the controller and 100amps battery. connection is in parallel
  • salakoshinasalakoshina Registered Users Posts: 2
    Vpm 28.2v
    Imp 9.34
    Voc 21.8v
    Isc 10.27a
  • PhotowhitPhotowhit Solar Expert Posts: 5,543 ✭✭✭✭✭
    Read the back of your panel or look up it's specs.
    It should have a series fuse rating for the panel listed, this will be the correct fuse or breaker for a single panel or string of panels;


    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
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