fuse and wire sizing

rp3703rp3703 Registered Users Posts: 123 ✭✭

Hi Everyone, so I’ve committed to my equipment list for my off grid solar setup and now I need to figure out wiring and fusing. What I will have is 4 to 5 310 watt(37V, 8.38A) panels wired into two or three strings of two panels a piece and maybe the fifth one by itself. I need to know how best to combine, fuse and what wire gauge to use for the panels before they hit the Midnite Classic charge controller. From there it will need to be fused again going to my 24V 430AH battery bank and then after through another fuse to the inverter. I would assume 2 AWG would be fine for running from charge controller to batteries and from batteries to inverter but I don’t know how to determine the amps of the battery bank based on the AH. The charge controller will probably be about 10’ away from the battery bank and the Inverter should be around 3’ away. I have the AC portion figured out, I just need to figure out the DC. 

1860 W (6) Rensola JC310M, Classic 150, [email protected] (8) Deka DSGC15 FLA's, Victron Phoenix Multi 24/2500 Inverter
Powering-20.5 CuFt. Fridge, 1 HP Submersible water pump, UV, Washing Machine, Gas Dryer, Gas Stove, Lights and Receptacles
Off Grid Cottage on lake in Northern Ontario 46˚N 

Comments

  • mvasmvas Registered Users Posts: 359 ✭✭✭
    Have you tried Midnight Classic Configuration Tool ?
    http://www.midnitesolar.com/pdfs/Classic-String-Sizing-Tool.pdf
  • rp3703rp3703 Registered Users Posts: 123 ✭✭
    Did that but how do I use results? 
    1860 W (6) Rensola JC310M, Classic 150, [email protected] (8) Deka DSGC15 FLA's, Victron Phoenix Multi 24/2500 Inverter
    Powering-20.5 CuFt. Fridge, 1 HP Submersible water pump, UV, Washing Machine, Gas Dryer, Gas Stove, Lights and Receptacles
    Off Grid Cottage on lake in Northern Ontario 46˚N 
  • PhotowhitPhotowhit Solar Expert Posts: 5,041 ✭✭✭✭
    edited May 2017 #4
    rp3703 said:
    Did that but how do I use results? 
    I think he was being kind and not saying;

    "panels wired into two or three strings of two panels a piece and maybe the fifth one by itself."

    5 panels won't work, you will have to have another string to make 6 if you want more on the same charge controller.

    Usually the charge controller will have the 'string' fuse rating on the back or an information sheet. Pretty safe bet it's a 15 amp fuse, but might be a 20 amp, so check. 2 strings will not need  fusing for each string, 3 strings should be combined with a fuse or breaker for each string. In addition it's good to have a breaker box near a 'power center' where you have the batteries, charge controller and inverter, These all need to be close to each other. It's good to have a breaker between each element, so between the panels and charge controller, charge controller and batteries, batteries and inverter.

    Many inverter manufacturers make boxes for their inverters, and they should also suggest wire gauges and Breaker size in their information sheets.

    There are also specifically made boxes, like these;

    https://www.solar-electric.com/catalogsearch/result/?q=midnite+power+center&_antispam=antispam_532

    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
  • BB.BB. Super Moderators, Administrators Posts: 29,825 admin
    The per string fuse rating is generally on the back of the solar panel.


    - Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • rp3703rp3703 Registered Users Posts: 123 ✭✭

    I actually have 6 panels so 3 strings will be no problem but I would like to start with 4 and see how well the system operates before committing to 6. According to the results of Midnite’s array calculator, my maximum power point voltage will be 74 volts. Using the Classic’s manual, it says I will need a 50A breaker from the panels to the charge controller using 8 AWG wire. I will need a 100A breaker from the charge controller to the batteries using 4 AWG wire. So the panels themselves list “Maximum Series Fuse Rating 20A”. So should I feed each two panel string into a 20A breaker and the output from those breakers will go into the 50A breaker? The panels have 12AWG cables, so can I continue using that same gauge to the 20A breakers? I’m guessing that 4AWG wire needs to be used from the batteries to the inverter as well but I skimmed through my manual and cannot find anything about the required breaker size.

    1860 W (6) Rensola JC310M, Classic 150, [email protected] (8) Deka DSGC15 FLA's, Victron Phoenix Multi 24/2500 Inverter
    Powering-20.5 CuFt. Fridge, 1 HP Submersible water pump, UV, Washing Machine, Gas Dryer, Gas Stove, Lights and Receptacles
    Off Grid Cottage on lake in Northern Ontario 46˚N 
  • PhotowhitPhotowhit Solar Expert Posts: 5,041 ✭✭✭✭
    You don't need breakers for 2 strings, but will for 3, they are to prevent over powering/back feeding a short in a string, and string of the same size isn't a problem but 2 might be...

    Typical installation would be to run the strings to a combiner box, where they would be combined. In the combiner box they would have fuses or breakers for each string if needed. From the combiner box to the charge controller you would want wire heavy enough to carry the amperage with a minimal voltage drop. You can use a "DC voltage drop calculator" to get figures depending on how far you want to run the wire. The breakers Midnite is talking about would be just before your charge controller. My run from the combiner box to the powercenter/breaker box is about 12 feet and I used 4 gauge wire, I think 6 gauge was what met my minimum voltage drop, but I had 4 gauge on hand.

    The size of wire and breaker between your inverter and battery, will depend on the size of the inverter, the distance between the battery and inverter and the desired minimum voltage drop. You will likely want a thicker wire than 4 gauge, unless you have a very small inverter very close to the battery. I think I used 2 gauge for a 1100 watt inverter 2 feet from the Breaker box in a 24 volt system. It might be too small! I used 2/0 wire from the battery to the Breaker box and it's 4-6 feet away and my large inverter is 1800 watt / 24 volt. I really should have 4/0 with the potential of both inverters.
    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
  • rp3703rp3703 Registered Users Posts: 123 ✭✭

    Ok, so after thinking about it, it makes no sense to not use all six panels, especially since the panels will be responsible for trickle charging the batteries while we are not there 11 months out of the year. So with 6 panels, I will have 12 AWG wire running from each string to three 20A breakers in a combiner box. Those breakers will feed a 50A breaker using 6 AWG wire and that same gauge wire will run to the charge controller. We are in agreement with Midnite that from the charge controller to the batteries, there needs to be 100A breaker and even though It states 4AWG, I will probably use 2AWG since my batteries will be about 10’ away. 

    I ended up getting a 2500 watt Inverter and I plan to place it around 3’ away from the batteries. So with a peak wattage of 6000 watts at 120V, should I just use a 50A breaker between batteries and inverters since that would be the max amps the inverter should be allowed to put out? Am I figuring that correctly even though I am talking in AC terms and the inverter will be pulling DC from the batteries?

    1860 W (6) Rensola JC310M, Classic 150, [email protected] (8) Deka DSGC15 FLA's, Victron Phoenix Multi 24/2500 Inverter
    Powering-20.5 CuFt. Fridge, 1 HP Submersible water pump, UV, Washing Machine, Gas Dryer, Gas Stove, Lights and Receptacles
    Off Grid Cottage on lake in Northern Ontario 46˚N 
  • littleharbor2littleharbor2 Solar Expert Posts: 1,451 ✭✭✭✭
    edited May 2017 #10
    You're talking more like 250 amps @24 Vdc and 4/0 cable

    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, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

  • rp3703rp3703 Registered Users Posts: 123 ✭✭
    So you're dividing 6000W by 24V to get the 250 Amps. Makes sense. So with the 4/0 are you talking copper or aluminum?
    1860 W (6) Rensola JC310M, Classic 150, [email protected] (8) Deka DSGC15 FLA's, Victron Phoenix Multi 24/2500 Inverter
    Powering-20.5 CuFt. Fridge, 1 HP Submersible water pump, UV, Washing Machine, Gas Dryer, Gas Stove, Lights and Receptacles
    Off Grid Cottage on lake in Northern Ontario 46˚N 
  • rp3703rp3703 Registered Users Posts: 123 ✭✭
    Sorry, you were obviously talking copper.
    1860 W (6) Rensola JC310M, Classic 150, [email protected] (8) Deka DSGC15 FLA's, Victron Phoenix Multi 24/2500 Inverter
    Powering-20.5 CuFt. Fridge, 1 HP Submersible water pump, UV, Washing Machine, Gas Dryer, Gas Stove, Lights and Receptacles
    Off Grid Cottage on lake in Northern Ontario 46˚N 
  • HorseflyHorsefly Registered Users Posts: 368 ✭✭✭✭
    If you are really sizing for the 6000W peak:

    6000W / 24V /0.85 (inverter efficiency) = ~300A

    @littleharbor2 is right, you need #4/0 cable to your batteries for that kind of current.
    Off-grid cabin: 6 x Canadian Solar CSK-280M PV panels, Schneider XW-MPPT60-150 Charge Controller, Schneider CSW4024 Inverter/Charger, Schneider SCP, 4 x Vmax XTR12-155 12V, 155AH batteries in a 2x2 24V 310AH bank.
  • rp3703rp3703 Registered Users Posts: 123 ✭✭
    But everyone is in agreement on my breaker and wire sizes from panels to the batteries, right?
    1860 W (6) Rensola JC310M, Classic 150, [email protected] (8) Deka DSGC15 FLA's, Victron Phoenix Multi 24/2500 Inverter
    Powering-20.5 CuFt. Fridge, 1 HP Submersible water pump, UV, Washing Machine, Gas Dryer, Gas Stove, Lights and Receptacles
    Off Grid Cottage on lake in Northern Ontario 46˚N 
  • mcgivormcgivor Solar Expert Posts: 3,205 ✭✭✭✭✭
    edited May 2017 #15
    Current is inversely proportional to voltage, if for example the inverter can supply 10 A at 120V,  the DC input would be 120A at 12V, 60A at 24V, 30A at 48V approximately. So 50A at 120 output, the input current  would be ~250A DC, using 24V input, but the important thing to remember is, the overcurrent protection device is to protect the conductors, not the device downstream. For intermittent peak output, cables can carry higher loads at the expense of voltage drop, circuit breakers and time delay fuses can accept higher currents for short durations. But remember the inversely proportional rule, as the battery voltage sags under peak demand, the current will increase. Using conductors with an overrated capacity is the best to avoid voltage sag, overcurrent protection can be smaller but not larger than the conductors rating.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • EstragonEstragon Registered Users Posts: 4,303 ✭✭✭✭✭
    Could be wrong, but I don't think 2ga wire will fit in the output terminal of the classic. IIRC, I used a short length of 4ga from classics to buss bars. Using a box like an e-panel with buss bars to hold breakers and mount gear makes for a cleaner installation IMHO. It gets hard to make good connections to battery posts with more than a couple of cables. From the buss bars to bank (~8') I used 4/0.

    I would use 10ga from panels to combiner. From the inverter to bank or buss bars I would use the biggest wire that will physically fit in the inverter, and the breaker sized recommended in the inverter manual. To me, cheaping out on wire is false economy.

    The classic has a setting called something like "skip days". By default, I think it's disabled, but if you leave the system unattended for extended periods you may want to set this to 5 days or so. This will make the controller only go to float voltage for 5 days, then do a bulk/absorb cycle. Leaving it set to bulk/absorb daily isn't necessary, and if flooded batteries, they could run low on water and expose plates.
    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
  • mcgivormcgivor Solar Expert Posts: 3,205 ✭✭✭✭✭
    Sizing for the peak load is going a little overboard IMHO, conductors rated for the rated output would suffice, the peak load capacity is probably only for a very short duration and would you ever approach such demand ? Most likely not if off grid.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • HorseflyHorsefly Registered Users Posts: 368 ✭✭✭✭
    mcgivor said:
    Sizing for the peak load is going a little overboard IMHO, conductors rated for the rated output would suffice, the peak load capacity is probably only for a very short duration and would you ever approach such demand ? Most likely not if off grid.
    I mostly agree. If it was me, I'd put a 300A blue sea fuse on the pos battery terminal, like this one: 
    http://www.iboats.com/Terminal-Fuse-Block-Blue-Sea-Systems/dm/view_id.730173

    Then I'd put a breaker sized for the 2500W nominal:

    2500W / 24V / 0.85 (inverter efficiency) * 1.25 (NEC breaker factor) = ~150A

    Off-grid cabin: 6 x Canadian Solar CSK-280M PV panels, Schneider XW-MPPT60-150 Charge Controller, Schneider CSW4024 Inverter/Charger, Schneider SCP, 4 x Vmax XTR12-155 12V, 155AH batteries in a 2x2 24V 310AH bank.
  • rp3703rp3703 Registered Users Posts: 123 ✭✭
    So something like this for the 150A breaker?
    https://www.solar-electric.com/mr60ampdccib.html

    1860 W (6) Rensola JC310M, Classic 150, [email protected] (8) Deka DSGC15 FLA's, Victron Phoenix Multi 24/2500 Inverter
    Powering-20.5 CuFt. Fridge, 1 HP Submersible water pump, UV, Washing Machine, Gas Dryer, Gas Stove, Lights and Receptacles
    Off Grid Cottage on lake in Northern Ontario 46˚N 
  • HorseflyHorsefly Registered Users Posts: 368 ✭✭✭✭
    I suppose that would work fine. I think lots of folks use the marine-rated stuff where you can mount it all on a plywood backboard. I'm more familiar with din or panel mounted breakers, but unless you have a panel to mount them in, they are not handy.
    Off-grid cabin: 6 x Canadian Solar CSK-280M PV panels, Schneider XW-MPPT60-150 Charge Controller, Schneider CSW4024 Inverter/Charger, Schneider SCP, 4 x Vmax XTR12-155 12V, 155AH batteries in a 2x2 24V 310AH bank.
  • nickdearing88nickdearing88 Registered Users Posts: 96 ✭✭✭
    Estragon said:
    Could be wrong, but I don't think 2ga wire will fit in the output terminal of the classic. IIRC, I used a short length of 4ga from classics to buss bars. Using a box like an e-panel with buss bars to hold breakers and mount gear makes for a cleaner installation IMHO. It gets hard to make good connections to battery posts with more than a couple of cables. From the buss bars to bank (~8') I used 4/0.

    I would use 10ga from panels to combiner. From the inverter to bank or buss bars I would use the biggest wire that will physically fit in the inverter, and the breaker sized recommended in the inverter manual. To me, cheaping out on wire is false economy.

    The classic has a setting called something like "skip days". By default, I think it's disabled, but if you leave the system unattended for extended periods you may want to set this to 5 days or so. This will make the controller only go to float voltage for 5 days, then do a bulk/absorb cycle. Leaving it set to bulk/absorb daily isn't necessary, and if flooded batteries, they could run low on water and expose plates.
    I've been happy with my Morningstar CC (and they have great customer support) but the more features I hear about Midnite CC's makes me envious. 
    Current test system: 4-100w Renogy panels mono/poly, 1 string of 4 panels in series - 24v 100Ah AGM Battleborn LiFePO4 batteries - Morningstar MPPT40 CC - 1500W Samlex PSW inverter
  • EstragonEstragon Registered Users Posts: 4,303 ✭✭✭✭✭
    Oddly enough, while I've been happy with my classics, I recently bought a couple of Morningstar PWM controllers. The MN features are nice, but result in a fairly high tare consumption.

    The new controllers will be used to float banks over the winter because main arrays have tended to get and stay snow covered in the last couple of years and the classics run batteries down just being on.
    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
  • rp3703rp3703 Registered Users Posts: 123 ✭✭
    Well, I went with the MN Classic 150 SL(Solar Only) over the Morningstar because it could handle all the panels I plan to use(Not to mention, It's cheaper) but after looking over my MN calculator results a second time, I probably should have bought a 250 since it would have allowed me to wire 5 of the panels as one string, which was all I need. Now I'm forced to use 3 strings of 2. That would have eliminated 4-50' PV cables and two breakers, easily making up for the increased cost of the 250.

    I plan on disconnecting my batteries and taking them home at the end of each season. I'm too scared to leave them relying on panels to and not drying out for the 11 months out of the year I'm not up there. 
    1860 W (6) Rensola JC310M, Classic 150, [email protected] (8) Deka DSGC15 FLA's, Victron Phoenix Multi 24/2500 Inverter
    Powering-20.5 CuFt. Fridge, 1 HP Submersible water pump, UV, Washing Machine, Gas Dryer, Gas Stove, Lights and Receptacles
    Off Grid Cottage on lake in Northern Ontario 46˚N 
  • littleharbor2littleharbor2 Solar Expert Posts: 1,451 ✭✭✭✭
    One thing to consider with the classic 250 is it's max output of 63 amps, compared to the 150's 96 amps. You did mention you went with the 150 because it could handle all the panels you intend to use.

    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, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

  • rp3703rp3703 Registered Users Posts: 123 ✭✭
    Yeah, just did the calc's. The 250 will do it but not well, Hyper VOC. The 150 is the safer way to go.
    1860 W (6) Rensola JC310M, Classic 150, [email protected] (8) Deka DSGC15 FLA's, Victron Phoenix Multi 24/2500 Inverter
    Powering-20.5 CuFt. Fridge, 1 HP Submersible water pump, UV, Washing Machine, Gas Dryer, Gas Stove, Lights and Receptacles
    Off Grid Cottage on lake in Northern Ontario 46˚N 
  • EstragonEstragon Registered Users Posts: 4,303 ✭✭✭✭✭
    Generally speaking, the 200 and 250 only make sense if you need to go longer distances. There's a rule of thumb somewhere on the MN site - something like >150' for the 200 or thereabouts.
    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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