Recommended cable length between L-16 batteries?

Susido
Susido Registered Users Posts: 32 ✭✭
in General Solar Power Topics #1
Could someone please let me know what would be an appropriate length of battery cable for connecting between a pair of L-16 sized batteries (in series side to side with an inch of space between them)?

I'll soon be replacing my existing bank of 16 6 volt golf cart batteries (48 volt system) with (probably) Rolls Surrette S550 and I'd like to make some new cables up in advance but as I don't yet have one of these batteries or know how the connectors are located I don't know how long a cable I should be making. The S550 is 12-1/2"x7-1/8"x16-3/4".

Also I'm considering a new way of connecting my current 2 strings of 16 golf cart batteries using Method 4 at http://www.smartgauge.co.uk/batt_con.html. Anyone think it's a good idea to connect to the inverter from the middle of each string as shown in the illustration there? That would allow me to use quite a bit shorter cables for the inverter connection rather than connecting it from the string ends as I do now (inverter is physically positioned right in the middle of the strings).

Seasonally off-grid ... 468 Ahrs @ 48V (8 Rolls S-605 6v FLA batteries),  24 x 130watt panels, 6 x 260watt panels, 2 x Midnite Classic 150, Whizbang Jr., Magnum MS4448PAE inverter/charger, 2 x Honda eu2000i generators paralleled.


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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #2
    You can probably get a very good idea from the dimensions listed in this link, and combine that with how you plan to position your batteries. .
    https://www.google.ca/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CB0QFjAAahUKEwiN86fbqtHHAhUGGz4KHfBkBs0&url=http%3A%2F%2Fwww.trojanbattery.com%2Fpdf%2Fdatasheets%2FL16REB_TrojanRE_Data_Sheets.pdf&ei=pT3jVc2MLIa2-AHwyZnoDA&usg=AFQjCNG6uAvsg4QsmsqNqI0BoBw49Kr-Eg&cad=rja
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  • Susido
    Susido Registered Users Posts: 32 ✭✭
    #3
    Thank you Wayne. As the battery is only abut 7" wide plus 1" of spacing and not much need to worry about routing the cable around or under watering caps ... I'm thinking a 10" length of cable would be about right. Adding the lug ends would make the overall length 11". Hope that's in the ball park.
    Seasonally off-grid ... 468 Ahrs @ 48V (8 Rolls S-605 6v FLA batteries),  24 x 130watt panels, 6 x 260watt panels, 2 x Midnite Classic 150, Whizbang Jr., Magnum MS4448PAE inverter/charger, 2 x Honda eu2000i generators paralleled.


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  • Iceni John
    Iceni John Solar Expert Posts: 103 ✭✭
    #4
    Susido wrote: »
    Also I'm considering a new way of connecting my current 2 strings of 16 golf cart batteries using Method 4 at http://www.smartgauge.co.uk/batt_con.html. Anyone think it's a good idea to connect to the inverter from the middle of each string as shown in the illustration there? That would allow me to use quite a bit shorter cables for the inverter connection rather than connecting it from the string ends as I do now (inverter is physically positioned right in the middle of the strings).
    I asked this question here recently for my two banks of series and parallel batteries, and the general wisdom is that it will work just fine. For my setup the effective cable lengths are the same whether the power is drawn off the ends or off the two center batteries. Because my batteries are on pull-out trays I need their cables to run to/from the middle, not the ends. My connections will be similar to Method 4, albeit for two series pairs in parallel.

    John

    40' Crown bus with 2kW of tiltable panels on the roof:

    Eight Sharp 255W, two Morningstar TS-MPPT-60, Magnum MS2000, Champion C46540 generator converted to propane, eight golfcart batteries, and maybe a small Exeltech inverter for the fridger.

    Southern California

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  • 706jim
    706jim Solar Expert Posts: 519 ✭✭✭✭
    #5
    After searching local stores for interconnect cables, I ended up at a trucker's supply store and bought 4 gauge cable and solder lugs so that I could fabricate my own interconnects.
    I think about 6" was fine for batteries in series.
    I figured that 4 gauge was plenty adequate for two 24 volt strings in parallel feeding a 1500 watt inverter.
    BTW, the lugs can be crimped onto the cable, or soldered using a small propane torch.
    Island cottage solar system with appriximately 2500 watts of panels, 1kw facing southeast 1.3kw facing southwest 170watt ancient Arco's facing due south. All panels in parallel for a 24 volt system. Trace DR1524 MSW inverter which has performed flawlessly since 1994. Outback Flexmax 80 MPPT charge controller four 467A-h AGM batteries. Insignia 11.5 cubic foot electric fridge 1/4hp GSW piston pump. My 31st year.
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  • softdown
    softdown Solar Expert Posts: 3,897 ✭✭✭✭
    #6
    If it was me, I would wait until the batteries are in place. Then you can make sure the lengths are just right. Shorter is better as long as you can access what you need. I have made cables an 1" too short due to lack of accounting for...everything. Have some worthless cable.
    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
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  • SkiDoo55
    SkiDoo55 Solar Expert Posts: 414 ✭✭✭
    #7
    706jim wrote: »
    After searching local stores for interconnect cables, I ended up at a trucker's supply store and bought 4 gauge cable and solder lugs so that I could fabricate my own interconnects.
    I think about 6" was fine for batteries in series.
    I figured that 4 gauge was plenty adequate for two 24 volt strings in parallel feeding a 1500 watt inverter.
    BTW, the lugs can be crimped onto the cable, or soldered using a small propane torch.
    crimp first then soldier if you want. Don't soldier ONLY as the soldier can melt out under high loads. Wire has attendance to fracture at the solder point if subject to vibration or movement.
    GT3.8 w/4600W Trina 230W, TX5000 w/5000W ET-250W, XW4024 w/1500W ET-250W, 4 L16, 5500W Gen. (never had to use) Yet!!
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  • MichaelK
    MichaelK Registered Users Posts: 236 ✭✭✭
    #8
    For my new L-16s I'm in the process of now making my cables with 4/0 wire, and 12" is just long enough, with connectors with a total length of 2.5".
    System 1) 15 Renogy 300w + 4 250W Astronergy panels,  Midnight 200 CC, 8 Trojan L16 bat., Schneider XW6848 NA inverter, AC-Delco 6000w gen.
    System 2) 8 YingLi 250W panels, Midnight 200CC, three 8V Rolls batteries, Schneider Conext 4024 inverter (workshop)
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  • softdown
    softdown Solar Expert Posts: 3,897 ✭✭✭✭
    edited August 2016 #9
    One using 4AWG, the other using 4/0. Quite a leap. I know an electrician who was using 12AWG for his tiny solar set up. I gave him some 10AWG.

    I've heard that local code is 2/0. I would think that 1/0 would work quite well on systems smaller than ~2000 watts of panels.

    If Susido is still active....how would you compare the L16s to the golf cart batteries that you used previously?
    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
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  • Susido
    Susido Registered Users Posts: 32 ✭✭
    #10
    softdown said:
    One using 4AWG, the other using 4/0. Quite a leap. I know an electrician who was using 12AWG for his tiny solar set up. I gave him some 10AWG.

    I've heard that local code is 2/0. I would think that 1/0 would work quite well on systems smaller than ~2000 watts of panels.

    If Susido is still active....how would you compare the L16s to the golf cart batteries that you used previously?
    Howdy. To be honest I can't say there's been much of a change with the L-16 battery bank instead of the golf carts. They both met my requirements thus far though winter is coming and that is when I need all the amp-hours I can get. One of the bigger differences is that I don't have to worry about adding water; every other month I add some to the L-16s but there's a lot of water reserve in those. Seems to me they are getting to absorb a lot so I don't think it's a case of not working the batteries enough, they just don't use much water.

    Oh and the cables I eventually had made to fit are 2/0 8" long plus lug length which allow me about 1/2" between batteries if I need to shift them around a bit.
    Seasonally off-grid ... 468 Ahrs @ 48V (8 Rolls S-605 6v FLA batteries),  24 x 130watt panels, 6 x 260watt panels, 2 x Midnite Classic 150, Whizbang Jr., Magnum MS4448PAE inverter/charger, 2 x Honda eu2000i generators paralleled.


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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,894 ✭✭✭✭✭✭
    #11
    You have the right over current protection for 2/0 right? Should be 4/0 if ever need max output!

    Batteries often start using more water when their capacity is aging or dropping.
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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  • softdown
    softdown Solar Expert Posts: 3,897 ✭✭✭✭
    #12
    I may surmise that the L-16s cost at least three times as much as golf cart batteries. I guess you won't have much of an opinion until December strikes....the worst month for solar. The eventual longevity has many variables of course. My take has been that solar batteries last ~ twice as long while costing ~ three times as much.

    ...Waiting for a couple pros to show up howling in protest.

    Did you do 2/0 because of code? Or recommendation? Calling for one size for all applications is just nonsense though par for government logic. Smaller systems could likely use 1/0 while large systems may benefit from 4/0. What I currently think anyway...
    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
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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,894 ✭✭✭✭✭✭
    #13
    Your advice to use non standard battery cable sizes is only good if the right overcurrent protection is used.
    We protect the wire from possibly burning the structure down, right?
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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  • softdown
    softdown Solar Expert Posts: 3,897 ✭✭✭✭
    #14
    It isn't advice.It is saying that "one size fits all" has inherent shortcomings..

    Are you saying that we carry DC breakers for 2/0 but not for 4/0? If someone has a larger system employing 4/0. I should think/hope the inverter and charge controller will have circuit breakers.
    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
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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,894 ✭✭✭✭✭✭
    #15
    We protect the wire from possibly burning the structure down, right?
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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  • softdown
    softdown Solar Expert Posts: 3,897 ✭✭✭✭
    #16
    You seem to be saying that using 2/0 is safer than 1/0 or 4/0. I'm a bit lost on the rational.
    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
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    edited August 2016 #17
    It all depends on the system design and components used... For example, in automotive use--It has been assumed that if you use really heavy gauge wiring vs battery size--You could get away without fusing (the starter circuit for example). The idea being that the battery would be taken dead before the wiring could overheat and start a fire.

    However--When you get to really large battery cells/battery banks--The amount of current that a lead acid battery can supply will usually cause any reasonable size wiring to glow red hot (and/or fuse) before taking battery bank dead.

    And there is sizing the wire for the loads. We need to size based on average current and other requirements (if in conduit, ambient temperatures, type of insulation used, etc.).

    Lastly, we tend to size low voltage DC wiring (48 volts and less especially) to larger copper AWG to avoid excessive voltage drop and energy loss--Especially on longer cable runs.

    If paralleling battery strings--Then you also need to assume that you do not get even current sharing across battery strings. If you have three parallel strings, worst case you may assume that a cable will carry 50% of rated load (not 1/3rd). For example, you can have a high resistance wiring connection, an open cell, or possibly you take one string out of service until a bad battery/cell/cable end can be replaced.

    I don't think Dave is saying that X/0 wire is safer than Y/0 awg. But need to assume that things go wrong and proper wiring plus over current limiter (fuse/breaker) is critical for system safety (My words, not Dave's).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,894 ✭✭✭✭✭✭
    #18
    Yea what he said!
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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  • Marc Kurth
    Marc Kurth Solar Expert Posts: 1,167 ✭✭✭✭
    #19
    Dave Angelini said:
    Yea what he said!

    LOL!
    I always have more questions than answers. That's the nature of life.
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  • WaterWheel
    WaterWheel Registered Users Posts: 385 ✭✭✭
    #20
    Here is a good way to help assure you don't overload those cables.     Just choose the fuse size you need although I'm not sure they offer a 75 amp size which 4 ga cables would need.
    https://www.amazon.com/Blue-Sea-Systems-5191-Terminal/dp/B0019ZBTV4/ref=pd_bxgy_200_2?ie=UTF8&psc=1&refRID=JS0DFSDNQY9E7BCNRNP9

    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

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  • softdown
    softdown Solar Expert Posts: 3,897 ✭✭✭✭
    #21
    Kind of fading away from using 4/0 and thinking 1/0 should be fine unless the system leans toward large. Mush easier to find fuses/circuit breakers for 1/0.

    I have never seen a DC circuit breaker that can handle 4/0.
    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
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,102 ✭✭✭✭✭
    #22
    The 250 amp breakers that came with Trace/Xantrex SW inverter systems could handle 4/0, I believe.

    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,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

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  • softdown
    softdown Solar Expert Posts: 3,897 ✭✭✭✭
    #23
    The breakers on the pro-grade inverters.....sure. I thought we were talking about putting a breaker/fuse on each and every cable.

    I read a couple solar books and do not recall such a recommendation. Nor have I seen anybody employ such an installation.

    In the meantime, I am not going outside until a government Thought Cop tells me that it is likely safe. Shiver.....
    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
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  • 706jim
    706jim Solar Expert Posts: 519 ✭✭✭✭
    #24
    I replaced 12 GC's with 8 L16's in two series parallel strings. I used #4 wire connections due to cost, limited cable length (about 10") and maximum amp draw with my DR1524 (maybe 40 amps per string at most). So far, so good.
    Island cottage solar system with appriximately 2500 watts of panels, 1kw facing southeast 1.3kw facing southwest 170watt ancient Arco's facing due south. All panels in parallel for a 24 volt system. Trace DR1524 MSW inverter which has performed flawlessly since 1994. Outback Flexmax 80 MPPT charge controller four 467A-h AGM batteries. Insignia 11.5 cubic foot electric fridge 1/4hp GSW piston pump. My 31st year.
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  • WaterWheel
    WaterWheel Registered Users Posts: 385 ✭✭✭
    #25
    706,,    sure hope you've got fuses on those battery cables.

    Is 706 your area code?

    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

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  • WaterWheel
    WaterWheel Registered Users Posts: 385 ✭✭✭
    #26
    You can get away with 9" cables between L-16s but I went with 11" to give me some latitude for future replacement batteries.

    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

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  • softdown
    softdown Solar Expert Posts: 3,897 ✭✭✭✭
    #27
    There should be at least an 1" of space between batteries to dissipate heat.
    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
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  • 706jim
    706jim Solar Expert Posts: 519 ✭✭✭✭
    #28
    WaterWheel said:
    706,,    sure hope you've got fuses on those battery cables.

    Is 706 your area code?


    There is a breaker between the batteries and the inverter, but no other fuses.

    706 refers to the model number of an obscure telescope mount.

    Island cottage solar system with appriximately 2500 watts of panels, 1kw facing southeast 1.3kw facing southwest 170watt ancient Arco's facing due south. All panels in parallel for a 24 volt system. Trace DR1524 MSW inverter which has performed flawlessly since 1994. Outback Flexmax 80 MPPT charge controller four 467A-h AGM batteries. Insignia 11.5 cubic foot electric fridge 1/4hp GSW piston pump. My 31st year.
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  • Susido
    Susido Registered Users Posts: 32 ✭✭
    #29
    softdown said:
    There should be at least an 1" of space between batteries to dissipate heat.
    My Surrette batteries are designed so the slightly flared tops can touch each other, at least that's what I read somewhere in their documentation. There's maybe a 1/2" space between the remainder of the battery.
    Seasonally off-grid ... 468 Ahrs @ 48V (8 Rolls S-605 6v FLA batteries),  24 x 130watt panels, 6 x 260watt panels, 2 x Midnite Classic 150, Whizbang Jr., Magnum MS4448PAE inverter/charger, 2 x Honda eu2000i generators paralleled.


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