Need expert help on new large battery bank for off grid..

bryhan67bryhan67 Registered Users Posts: 17 ✭✭
Hey guys, I have a vacation home off grid and I am building a new battery bank.  The system will be 48v. My inverter will be 48v 3000 watts.  I got a good hook up on 12 volt AGM batteries they are 140ah at 20hr rate. I bought 24 of them.  I will make 6 strings of 4 batteries each. I know its overkill but I could not pass up the deal. We only go a few weekends a month so most of the time the bank will be at idle.
Here are my questions:

1. I have a buss bar on each end. Cable length from each string in 18". I will need to buy 12 cables for 6 strings. What guage cable do I need for this?

2. I would like to run breakers. Should I run a breaker on each string? Thats 6 breakers. 

3. What size breakers do I need for each string?

4. Coming off the bus bars combing all the batteries what guage wire should I run to the inverter? These two cables will be 32" each.

5. I have a midnight solar 200. How critical is it for the output cables to be the same length?  Would 18" pos and 50" neg be a bad set up?

6 In the middle of each string I will run a 1" x 1/4" copper flat bar about 4" long. so the battery have a 1" space between them. It gets up to 100deg here. Is this copper bar sufficient?



Thanks
Bryan


48v.jpg 148.8K

Comments

  • jonrjonr Solar Expert Posts: 1,281 ✭✭✭✭
    Be sure to use a clamp DC ammeter to check balance between each series string.  I have a Mastech MS2108 (cheap but adequate).

    I am available for custom hardware/firmware development

  • mike95490mike95490 Solar Expert Posts: 8,340 ✭✭✭✭✭
    Well, if you must parallel batteries, you are doing it right .    The battery wire from the Charge Controller, keep it short,  but they don't need matched lengths.  And go a size larger if you can, the Classic does not have a voltage sense line, and because of the high charge amps, it's sensed voltage will not be well calibrated,

    3,000w inverter @ 46V would be 65 amps.  I'd put 50-70A DC breakers (from Midnight Solar) on each battery string. Mounting breakers might be an issue, because the arc chute wants to be oriented with the breaker upright, as if it were in a panel.  The leads in and out of the breakers count as part of the matched lengths.

    Battery cable wires, assume only one string is working , 65A at full load in the inverter would be #4 wire, I'd use #2 - good for 95A, and you need margin so your 70A breaker blows before the wire does.

    I'm sure there's some spec that says 60A circuit to be wired with 120% rated wire (72A)

    Bus bar to inverter, at least 1/O cable.  There will be starting surges from motors, and you want the inverter to be well fed.

    Battery - Battery interconnects, you want something that will flex, and not bend/crack a terminal or case,   Either tinned flat braid, or MT cable.
    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 ,

  • WaterWheelWaterWheel Registered Users Posts: 325 ✭✭✭
    I'd make sure you have enough panels to easily charge that bank.     Here is a suggested fuse that is easy to mount for each string. https://www.amazon.com/gp/product/B0019ZBTV4/ref=oh_aui_detailpage_o05_s00?ie=UTF8&psc=1

    Not as handy as a breaker but a lot easier to mount.

    Conext XW6848 with PDP, SCP, 80/600 controller, 60/150 controller and Conext battery monitor

    21 SW280 panels on Schletter ground mount

    48v Rolls 6CS 27P

  • bryhan67bryhan67 Registered Users Posts: 17 ✭✭
    What are the odds all the current will passing through 1 string?  I can see thats our your setting it up..  If I was pulling max 65 amps that would only be about 11 amps per string?  Instead of fuses I would like to do individual breakers. Any tips on a good clean set up for 6 breakers?  Confused on Midnite Solar's breakers. They seem to be more for panels. 

    What about somthing like this?
    https://www.bluesea.com/products/category/14/32/Circuit_Breakers/285-Series



  • mike95490mike95490 Solar Expert Posts: 8,340 ✭✭✭✭✭
    If something happens, one or 2 or more strings may fail (likely in a massive parallel setup)
    OR
    in 4 years when you replace batteries, you may only purchase 2 strings, and work the snot out of the battery bank, saving money on excess bank capacity.
    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 ,

  • Raj174Raj174 Solar Expert Posts: 690 ✭✭✭✭
    Reread Mike's post, it's good information. You will not find a better breaker than those made by Midnite Solar.

    Two of these enclosures can mount the six breakers, 3 in each.
    https://www.solar-electric.com/mnedc-quad.html

    This is the breaker used in the enclosure, I believe Mike suggested 70 amp.
    https://www.solar-electric.com/pamodccibr.html

    Remember, the breakers protect the cable and must be able to carry the full amperage draw of the inverter.

    3600W PV, MNE175DR-TR epanel modified, MN Classic 150, Outback Radian GS4048A, Mate3, 54.4V 195AH LiFePO4 no BMS, 4500W genset.
  • bryhan67bryhan67 Registered Users Posts: 17 ✭✭
    I like the enclosures with breakers. Pretty clean and easy to install. Since the enclosure will have 2 empty slots any danger running higher volts from the panels through another breaker and out out controler to the battery bank. That would be 8 breakers in the two enclosures.  What would be a good breaker size before the controler and after?  In the pic is what I am setting up. 
  • softdownsoftdown Solar Expert Posts: 2,285 ✭✭✭✭
    I'm curious about the decision to employ six strings on a part time vacation home. I would have employed more solar and less battery while using 2/0 cables. I'm not an expert of course.

    I can't hardly imagine needing more than 12 of those batteries. In fact, I would be inclined to believe that 8 would work fine. FWIW....I have found that good batteries store OK if kept cool and charged over 12.5 volts.
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
  • Raj174Raj174 Solar Expert Posts: 690 ✭✭✭✭
    edited September 2016 #10
    No technical problem mounting any size of this type DC breaker for any purpose in these boxes. Obviously, they would need to be clearly labeled. 

    Breaker sizes - PV strings- 8 to 12 amps
                             PV to charge controller - 25 to 30 amps, THHN #6 AWG cable
                             Controller to battery bank - 60 to 70 amps, Recommend a THHN #4 AWG cable, although a #6 will do.

    Could I ask why you are using such high voltage PV strings?  Are the solar panels mounted very far from the controller and batteries? Otherwise, three panels in series would have been more efficient.  
    3600W PV, MNE175DR-TR epanel modified, MN Classic 150, Outback Radian GS4048A, Mate3, 54.4V 195AH LiFePO4 no BMS, 4500W genset.
  • mike95490mike95490 Solar Expert Posts: 8,340 ✭✭✭✭✭
    For the simplest, I'd suggest the MRBF fuse blocks and fuses,   A wide selection of fuse ratings.
    https://www.bluesea.com/products/2151/Dual_MRBF_Terminal_Fuse_Block_-_30_to_300A
    With fuses, you loose an easy way to disconnect one string from the system.



    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 ,

  • bryhan67bryhan67 Registered Users Posts: 17 ✭✭
    Sorry for the delayed response. I have been in Rosarito getting ready for a upcoming desert race this weekend. The reason for so many batteries is I bought 150 of them to sell. So if anyone needs batteris in the south west usa or baja mexico let me know. Also I want to run a air conditioner 24/7 when I am there in the summer. I have in confined to one small room.

    As for the panels what am I losing? I have the midnight solar 200v model. The way my roof is perfect wide for 4 panels. I made adjustable frame for summer and winter. Heck my little Honda eu1000 gen is all I need. I don't need any color or batteris. But what's the fun in that. I feeling of running my account for free off the sun.. When I am full time I will need to figure how to a/c all the house... dc mini splits will be the way to go.

    Few times a year I do go for a 2 week stretch.

    Anybody have a good source to buy tined copper cable lugs? I think I will get about 100 of them.
  • bryhan67bryhan67 Registered Users Posts: 17 ✭✭
    Could I eliminate my bus bar and do a enclosure with 6 breakers then one outlet to the inverter? This way would have 6 #2 wires going in and one 1/0 cable going to inverter?

    Something like this? But cant find breakers that will except #2 cable. 

    https://www.solar-electric.com/mndico.html


  • mike95490mike95490 Solar Expert Posts: 8,340 ✭✭✭✭✭
    hydraulic is the way to go.   The host site NAWS, has tinned lugs in the store AND the midnight combiner panels
    https://www.solar-electric.com/36432.html

    please don't use a hammer lug crusher



    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 ,

  • bryhan67bryhan67 Registered Users Posts: 17 ✭✭
    WIth that combiner is there a way to connect #2 wire or lugs from each string? Then a  1/0 cable going to inverter? 
  • jonrjonr Solar Expert Posts: 1,281 ✭✭✭✭
    edited September 2016 #17
     > I have it {AC} confined to one small room.

    In many cases, I think this is a good way to go.  AC for the entire building might take excessive power - but one very well insulated and air sealed room will be much less while providing a place to escape the heat.  If you want to get fancy, consider adding lots of thermal mass and materials that absorb humidity (sort of a thermal and humidity battery).

    I am available for custom hardware/firmware development

  • Raj174Raj174 Solar Expert Posts: 690 ✭✭✭✭
    bryhan67 said:
    WIth that combiner is there a way to connect #2 wire or lugs from each string? Then a  1/0 cable going to inverter? 
    The largest cable that this PV breaker will take is a #6 AWG. So if you go with the other DC breakers and enclosures, you may have to find or make a 100 amp buss bar with enough terminal connections for the battery strings and a connection for the 1/0 cable to the inverter. It might a good idea to use one of the Blue Sea MRBF fuse blocks and fuses, that Mike posted previously, at the buss bar for the 1/0 inverter cable.  
    3600W PV, MNE175DR-TR epanel modified, MN Classic 150, Outback Radian GS4048A, Mate3, 54.4V 195AH LiFePO4 no BMS, 4500W genset.
  • bryhan67bryhan67 Registered Users Posts: 17 ✭✭
    I called Midnite solar and always those guys are great. Tough to set up 6 strings. Maybe more simple to run the double fuses. So thats the rout I am going. they said I might have some problems charging some batteries. I will go ahead and make up #2 cables just encase I upgrade to larger inverter in the future.   From controller to buss bar I will run the 6ga with 50amp fuse. I think I will eventually I will buy a deep fridge and keep the batteries at 77deg all the time.  Lots of great help here. I lean more and more everyday. Once I get it set up I will post some pics. 
  • Marc KurthMarc Kurth Solar Expert Posts: 453 ✭✭✭✭
    What is the make and model of the batteries?
    I always have more questions than answers. That's the nature of life.
  • bryhan67bryhan67 Registered Users Posts: 17 ✭✭
    Here is what I built so far. Let me know if you see anything really wrong. All the metal in the rack is so the batteries don't get stolen.  I still need to finish making cables and heat shrink them. Is it ok if all 6 neg cables are about 2 inches longer than the positive? Of is it better to make the positives longer? Also is it critical to have both neg and pos cables same length going from bus bar to inverter?

    Marc the batteries are made by data safe they are 12HX540-fr. Hard to find solar related data on them. If you look up trojans they are identical. http://www.trojanbattery.com/pdf/datasheets/12AGM_Trojan_Data_Sheets.pdf






  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    bryhan67 said:
     Is it ok if all 6 neg cables are about 2 inches longer than the positive? Of is it better to make the positives longer?
    it's ok
    bryhan67 said:
      Also is it critical to have both neg and pos cables same length going from bus bar to inverter?
    Not an issue. each cable should be as short as possible.

    --vtMaps

    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • mike95490mike95490 Solar Expert Posts: 8,340 ✭✭✭✭✭
    If these are indoors in a fairly constant temperature environment, the interconnect cables would be OK.  But if there is a lot of thermal excursions, I'd be concerned that those short interconnects could act like solid rods and stress the battery terminals. Short lengths of heavy wire are pretty stiff, when reinforced with heat shrink
    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 ,

  • bryhan67bryhan67 Registered Users Posts: 17 ✭✭
    edited September 2016 #24
    Whats better keep them shorter or  longer and  put a little  bend it it.  For #2 cable is there a shortest length to go by?  now they are about 4.5" center hole to center hole. Even longer cable when bent gets stiff also and want to twist.  How much thermal excursions are we talking about? We are on the beach in mexico and this will be in my garage. summer temps outside are 100 high and 80 low then in winter 70 high and 50 low. But inside my garage wont change as much.  These batteries never heat up like my old led acid trojans. 
  • Marc KurthMarc Kurth Solar Expert Posts: 453 ✭✭✭✭
    Those are AGM batteries made by Enersys for UPS type duty, rated at 123 ah based at a 20hr rate. They are optimized for high current, short duration output - but they will work fine if you don't deeply cycle them too often.

    I could not readily locate DOD/Cycle rating on these, but Enersys batteries of this general type tend to run around 500 cycles at 50% depth of discharge. If you limit it to 25%-30%, you are likely to get closer to 1000 or more charge/discharge cycles from a new set.

    In general terms, it is important to provide these batteries an extended float time as often as possible.
    I always have more questions than answers. That's the nature of life.
  • mike95490mike95490 Solar Expert Posts: 8,340 ✭✭✭✭✭
    Have you calculated the loss another inch for each interconnect would induce ? Adding an inch or two (the next time you build cables)
    and putting a Z bend/kink in it, will allow stress to be absorbed in the flex of the wire, not the battery terminal.
    But if you are only experiencing a 20 or 30 degree swing, that's not much.  Here I deal with 105F summer and 20F
    See attached pic and link.  (expansion loop)
    http://engineering.stackexchange.com/questions/569/what-is-the-purpose-of-these-diversions-in-a-natural-gas-line



    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 ,

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