DC Breakers and Wire size for 48V Battery Bank w/ 3 Charge Controllers...300A

Tmp4000Tmp4000 Registered Users Posts: 31 ✭✭
Hi All,

Was wondering if I can get some insight into the following:

  • I am planning on a 48V battery bank:  24x --  2V Rolls 20S33P - 1883AH, which will be charged with 3x MidNite Classic 150 controllers (parallel into the positive bus bar and into the negative bus bar). 
  • Conext SW+ 8548E inverter will be used.
  • The inverter will draw max 180A...but the surge capability of the inverter is up to 12000W...which is 250A.
  • The maximum current output from the Classic (assuming perfect weather) will be ~100A...so for three Classics that is almost 300A that will go into the battery bank max...right ?
Questions:

1). What is the best way to protect the battery bank via breakers for 300A and what size wiring should I use ? I am having troubles finding breakers rated for 300+A that will work with 2/0 or 4/0 wiring. The ones I did find are more for commercial that cost almost $1000.

2). Instead of using one thick wire (like 4/0) for the battery positive cable, can multiple lower gauge wire be used instead (paralleled with their own breakers) ?

Any advice much appreciated!




Comments

  • littleharbor2littleharbor2 Solar Expert Posts: 704 ✭✭✭✭
    A little info on Midnite Classic controllers,

    MidNite Solar Classic MPPT Charge Controllers
    Model Maximum output current at battery voltage *
    12 VDC 24 VDC 48 VDC
    Classic 150 96 A** 94 A**  86** A
    Classic 200 79 A 78 A 76 A
    Classic 250 61 A 62 A 55 A
    Classic 250KS 40 A (120 VDC battery)

    * Maximum output current is reduced at higher array voltages. See manual for more details.

    ** Output currents over 80 A require 110A or 125A breaker. Verify that there is sufficient space in the DC Power Center or breaker panel.

    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.

  • mcgivormcgivor Registered Users Posts: 1,304 ✭✭✭✭
    Each controller could have its own separate breaker going to the battery, the battery to inverter could use parallel conductors each with its own protection in parallel, it is important to understand that overcurrent devices, fuses or breakers, are not installed to protect the battery or the inverter, but rather to protect the conductors between the two. As long as the anticipated loads are not the maximum value, 12000W in the case of the inverter, the overcurrent protection can be undersized, as long as the are able to provide protection to the conductors. The size of the conductors are dependent on loads and distance, obviously larger is better to reduce voltage drop but large gauge can be difficult to work with. So as an example 4 parrallel 1/0  copper conductors can, depending on type, handle around 150A each, include a 100A breaker in each parallel leg, will provide 400A maximum capacity whilst still providing protection, conservatively. In the event of a short circuit, which is the purpose of overcurrent protection, all the breakers will trip to protect their individual circuit conductors. The only downside of a parrallel layout is multiple breakers,  more connections, including the need to turn multiple breakers off to provide disconnect, unless linked with a bar.
    Although not answering your questions directly, I hope this provides some insight.

      1500W, 6× Schutten 250W Poly panels , Schneider 150 60 CC, Schneider SW 2524 inverter, 8×T105 GC 24V nominal 

  • KeithWHareKeithWHare Solar Expert Posts: 138 ✭✭✭
    According to the chart littleharbor2 posted, the maximum output from a Classic 150 at 48VDC is 86 amps. For three, that would be a theoretical maximum of 258 amps. You didn't say what panels you are configuring so we can't verify how close to the Classic 150 maximum you are likely to get.

    Each charge controller output positive should have it's own breaker, probably 110 amp but it depends on the wire size you use.

    According to a wire ampacity chart I found (http://www.cerrowire.com/ampacity-charts), the ampacity of 4/0 wire is 230 amps at 75 degrees Celsius, 260 amps at 90 degrees C.

    The largest breaker I see on the Arizona Wind and Solar site is 250 Amps (https://www.solar-electric.com/mnedc250.html).

    This is a lot of potential power in the system you describe. Plan very, very carefully. If the physics of the plans are not working out, adjust your expectations, not the physics.

    Keith

  • EstragonEstragon Registered Users Posts: 1,616 ✭✭✭✭
    IIRC, the biggest wire that will fit in a classic is 4ga (not finely stranded, which doesn't fit well). You could splice a short length of 4ga to something bigger if going a long distance to minimize voltage drop, but the breaker would still need to protect 4ga.
    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
  • Tmp4000Tmp4000 Registered Users Posts: 31 ✭✭
    edited November 18 #6
    Here is my system diagram. I added what I think are the right size breakers and wiring. What do you think ? View the full size picture for all the details (the forum post re-sizes the image).

  • EstragonEstragon Registered Users Posts: 1,616 ✭✭✭✭
    I don't know that the fuse at the battery positive is needed, but doesn't hurt I guess. Negative is typically tied to ground somewhere. Other than that, it looks reasonable to me.

    If there are long distances from array to combiners, or combiners to controllers, you might want to check voltage drop for the distances and currents involved.
    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
  • Tmp4000Tmp4000 Registered Users Posts: 31 ✭✭
    Estragon said:
    I don't know that the fuse at the battery positive is needed, but doesn't hurt I guess. Negative is typically tied to ground somewhere. Other than that, it looks reasonable to me.

    If there are long distances from array to combiners, or combiners to controllers, you might want to check voltage drop for the distances and currents involved.
    The Midnite 150 manual says that it comes with GFP protection...which internally connects the ground to DC:

    The System's DC Negative conductor must not be bonded to earth ground. The Classic does this with its internal Ground Fault Protection circuitry. The battery negative and ground are not bonded together directly but are connected together by the Classic‘s internal GFP device. All negative conductor connections must be kept separate from the grounding conductor connections. The equipment ground terminal inside the Classic must be connected to Earth Ground for the internal DC-GFP to work.

    Do I still need to ground out the DC Negative side ?
  • mike95490mike95490 Solar Expert Posts: 7,307 ✭✭✭✭
    Have you looked into using the Midnight E panel ?  Simplifies many things, nice box for the breakers &  wires.

    My concern - your Combiner Boxes and Array ground.  To me, that's a Lightning Magnet, bringing any strikes, into your power shed and all your gear, before it sees any ground.  Not sure what Code in your area calls for, or how your array is installed (pole, ground, roof) and the feasibility to ground the mounting structure seperatly from the electrics.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • Tmp4000Tmp4000 Registered Users Posts: 31 ✭✭
    edited November 18 #10
    mike95490 said:
    Have you looked into using the Midnight E panel ?  Simplifies many things, nice box for the breakers &  wires.

    My concern - your Combiner Boxes and Array ground.  To me, that's a Lightning Magnet, bringing any strikes, into your power shed and all your gear, before it sees any ground.  Not sure what Code in your area calls for, or how your array is installed (pole, ground, roof) and the feasibility to ground the mounting structure seperatly from the electrics.
    I will look into the Midnight E panel...haven't seen it. 

    This system will be in a 'mobile' container....in the middle of an array of towers, each tower about 60' tall. The towers will have their own lightning protection. I am assuming that if lightning strikes the area...the towers will take the brunt of it...and not the solar system. But yes...it might be a good idea to ground out the panels with rods outside the container.
  • Tmp4000Tmp4000 Registered Users Posts: 31 ✭✭
    Here is my updated system wiring. The MidNite E-Panel I don't think will work:  there is no room for the 3 breakers for the Inverter wiring and Battery Bank wiring. At least I don't think. They have a model with 2x  250A breakers sticking out on either side...but there is not enough depth to put another 250A breaker for the Inverter positive lead. Can anyone confirm ?

    Do you think it will be okay if I use single 4/0 for both the Inverter and Battery Bank DC Negative sides ? On the DC Positive side, I will use 4/0 w/250A breaker for the Inverter and for the Battery Bank I will parallel two 2/0 w/250A breakers each. At the Positive Terminal on the Battery, I have a last-chance-catastrophe-save 350A in-line fuse.


  • EstragonEstragon Registered Users Posts: 1,616 ✭✭✭✭
    Tmp4000 said:
    Estragon said:
    I don't know that the fuse at the battery positive is needed, but doesn't hurt I guess. Negative is typically tied to ground somewhere. Other than that, it looks reasonable to me.

    If there are long distances from array to combiners, or combiners to controllers, you might want to check voltage drop for the distances and currents involved.
    The Midnite 150 manual says that it comes with GFP protection...which internally connects the ground to DC:

    The System's DC Negative conductor must not be bonded to earth ground. The Classic does this with its internal Ground Fault Protection circuitry. The battery negative and ground are not bonded together directly but are connected together by the Classic‘s internal GFP device. All negative conductor connections must be kept separate from the grounding conductor connections. The equipment ground terminal inside the Classic must be connected to Earth Ground for the internal DC-GFP to work.

    Do I still need to ground out the DC Negative side ?
    With the jumper installed, that would be your negative/ground bond.
    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
  • KeithWHareKeithWHare Solar Expert Posts: 138 ✭✭✭
    You might want to use 4/0 for the parallel runs between the buss bar and the batteries. From the ampacity chart I looked at, a 250 amp breaker looks to be a bit large for 2/0 wire. The goal of the breaker is to trip  before the wire melts. Consider the case where one of the breakers trips or is accidentally opened.

    Seems like battery negative wiring should match the battery positive wiring.
  • KeithWHareKeithWHare Solar Expert Posts: 138 ✭✭✭
    I looked up the numbers for the JA Solar JAP725S01 panels and ran them through the MidNite Solar sizing tool.

    What is the coldest temperature where this system will be located?
  • Tmp4000Tmp4000 Registered Users Posts: 31 ✭✭
    edited November 19 #15
    I looked up the numbers for the JA Solar JAP725S01 panels and ran them through the MidNite Solar sizing tool.

    What is the coldest temperature where this system will be located?
    System will be located +/- Equator, in the Pacific Ocean. Coldest expected temperature is around 23 deg C. I also used the Midnite Sizing Tool...it's a really great tool. 

    I updated the wiring with 4/0: 

  • Tmp4000Tmp4000 Registered Users Posts: 31 ✭✭
    Added DC Shunt and doubled up on the negative wire from the battery bank:


  • KeithWHareKeithWHare Solar Expert Posts: 138 ✭✭✭
    Consider the worst case short between the positive and negative bus bars.

    You have a 4/0 wire between the battery positive and the 350 amp fuse. Which will melt first, the fuse or the 4/0 wire? With a single battery string, I don't see why you need both a fuse and the breakers. It might be better to connect the 2 4/0

    You then have two 4/0 wires between the battery positive and the positive bus bar, but only one 4/0 between the battery negative and the negative buss bar.

    A couple of additional comments:

    You should have a breaker in the positive wire between each combiner box and charge controller, say a 60 or 65 amp breaker in each line.

    Surge Protection Devices are cheap insurance. It would make sense to have one on each combiner box and one on the AC output from the inverter. If you are going to have a potential generator hookup for the inverter, put an SPD on the generator input.
  • Tmp4000Tmp4000 Registered Users Posts: 31 ✭✭
    KeithWHare, I did indeed add your wiring recommendation and posted an updated diagram several hours ago...post #16. Is it not showing up ? Is the breaker between Combiner Box and CC really necessary ? Okay, I will look at SPD's ... I think MidNite has some good ones.
  • EstragonEstragon Registered Users Posts: 1,616 ✭✭✭✭
    IMHO, a breaker probably isn't really needed between the combiners and controllers, but is quite handy.

    Assuming a short across the controller inputs, is it possible for the panel output to be high enough to open a properly sized controller breaker? I don't think so. That said, there will be times when you'll want to open the breaker to reboot the controller or whatever, and going to the combiner to open all the string breakers would be a PITA. Also, I'm more comfortable working on stuff if I can be certain nobody can make a circuit live without me seeing them do it.
    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
  • KeithWHareKeithWHare Solar Expert Posts: 138 ✭✭✭
    Tmp4000 said:
    KeithWHare, I did indeed add your wiring recommendation and posted an updated diagram several hours ago...post #16. Is it not showing up ? Is the breaker between Combiner Box and CC really necessary ? Okay, I will look at SPD's ... I think MidNite has some good ones.
    Looks like your updated diagram showed up just between the time I started writing and when I hit post.

    The start-up sequence for the charge controllers is:
    1.  Turn on the breaker between the charge controller and the battery
    2. Turn on the breaker between the charge controller and the PV array

    Shutdown is the opposite order.

    Having a single breaker between each breaker and the combiner box will make it easier to start up and shutdown the charge controllers, particularly if the combiner boxes are any distance from the charge controllers.


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