breaker tripping

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Comments

  • BB.BB. Super Moderators, Administrators Posts: 30,625 admin
    Anita,

    I may have missed it, but can we have the exact Vmp/Imp of your panels... Something like:

    60 Watt panels:
    • Vmp = 17.5 volts
    • Imp = 3.43 Amps
    290 Watt panels:
    • Vmp = 30 volts
    • Imp = 9.67 Amps
    The exact numbers do matter...

    And the intent would be for each series string to have its own fuse/breaker. For each string (numbers below are guesstimates--The panel specifications should have a series fuse rating--Although, the 60 Watt panels may be old enough to not have a rating listed):
    • 60 Watt string would be ~6-8 amp
    • 290 Watt string/panel would be ~15-20 amps
    The idea is that if any one panel/string becomes shorted, then its fuse/breaker would protect it against too much current from the other parallel strings and reduce the chances of cabling/panel catching fire.

    From guesses above, still not quite sure why the 30 amp breaker should trip. Roughly 20 amps nominal Imp and a 30 amp breaker should work with 24 amps nominal load.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • VicVic Solar Expert Posts: 2,998 ✭✭✭✭
    Hi BB Bill, Thanks for chiming in ... just did not have the time this AM to post my cents worth.

    290 Watt PVs:

    Watts (PTC): 261.1 Watts
    Max Power Voltage (Vmpp): 35.9 Volts
    Max Power Current (Impp): 8.08 Amps
    Open Circuit Voltage (Voc): 44.4 Volts
    Short Circuit Current (Isc): 8.64 Amps
    Max System Voltage: 600 Volts
    Series Fuse Rating: 15Amps
    Module Efficiency: 15.11%

    Have assumed that the 60 W PVs were in the range that you, BB, guessed. There are some PVs in this power range with considerably higher voltage specs.

    Anita, so just what are the specs on the two differing 60 W PVs that you are using, including any rating for Maximum Fuse rating (or similar language).

    But, generally, EACH PV string should have a Breaker or fuse when there are three or more strings of PV modules -- there can be some exceptions. Without such protection, there can be a risk of fire in the event of a short in a PV module or its wiring.

    IMO, adding one or perhaps two combiners , depending on the location of the modules and what is the best approach if trying to use existing PV wiring, would be essential for safety.

    FWIW, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • AnitaAnita Registered Users Posts: 14
    Power58 64
    Vmp20.07 16.5
    Imp2.89 3.88
    Four 58s, two 64s
  • BB.BB. Super Moderators, Administrators Posts: 30,625 admin
    This may be approacing the land of diminishing returns.

    Using breakers/fuses to protect solar array from possible fire is always a good plan... But by the time you add the costs to protect a few low wattage strings of solar panels (and the labor)--It may be a better plan to get one or two ~290 Watt panels and sell the small panels on Craig's List or similar. And you will have new/large format solar panels too (with less wiring/connections/fuses/etc. to worry about).

    Have you verified the small panels are still working OK and do not have any impending signs of failure (water damage, corrosion, brown spots, etc.)?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • VicVic Solar Expert Posts: 2,998 ✭✭✭✭
    And, as always, BB Bill brings up a great point - you might be better served by selling your low power PVs, and replace them with a couple more 290s.

    At that point, you would probably want to change the battery breaker to an 80 A NON QO unit. This could be a MidNite MNEPV 80 A, an MNEDC 80 A, or other high quality DC-rated breaker.

    Either of the above MN breakers would need a different box (for all practical purposes) -- the MNEPV is a DIN-Rail mount and would fit in a Baby Box, or the Big Baby. The MNEDC would want the MN DC Quad box (probably).

    You might be able to get by with the existing QO 70 A breaker, by setting the Max output current of the FM CC to about 67-ish amps for a starter ... possibly higher. This output setting would depend on your ambient temps, etc.

    When thinking about adding the proposed two new 290 W PVs, it will be very important for you to consider the size of the PV wiring that connects the new 290s to the input breaker. And also consider the 6 AWG (IIRC) cable that connects the output of the CC to the breaker and battery ... believe that this is what you mentioned as the present system. Generally # 6 AWG copper cable is not really rated for 8 even 80-ish Amps, without considering any safety factor.

    For CC efficiency, it would probably be better if all of the proposed 290 W PVs be run all in parallel. This would mean that a Combiner would for four parallel modules. Depending on the location of the existing PVs you might want to have two separate runs of cable from possibly two locations, and so on ... all depends.

    One could run only two strings of two 290 PVs, but the string Vmp would be over 72 volts (at STC conditions), and with a 12 V battery, this is a bit high, and would cause the CC to run warmer or HOT, at times.

    More later. All FWIW, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • AnitaAnita Registered Users Posts: 14
    It's actually a #4 cable from the controller to the batteries; the 6 was from the combining nut to the controller.

    Don't think I will be getting more new panels in the next few years; it was a pretty big project to build the mount and get them installed this year. It would be much easier to put a breaker box on the 60Ws, and they seem to be producing enough for my need at this time. I will think about selling them next time I upgrade in ten years or so. I got the new ones this year to go with my new chest freezer, but I don't have any other new uses planned right now. Thanks everyone for all the advice.
  • SolarPoweredSolarPowered Solar Expert Posts: 626 ✭✭✭
    Anita wrote: »
    Should be under 48V, Voc is 44.4.


    44.4 VOC is an STC condition. 25C is 77F

    If the condition is hypothetically 25F that is -3.88C

    Lets assume a hypothetical VOC temp coefficient of .34%, that would be 9.81 VOC

    44.4 + 9.81 = 54.24 VOC

    48V breaker that operates + 10% means its limit is at 52.8V

    It would be better to have a 60V or 72V breaker

    8.64 ISC

    8.64 + 1.87 = 10.51 ISC

    The rating at 15 amp is still within spec, so its probably colder than usual.





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