Series/parallel wiring idea?

Most diagrams that show four side-by-side batteries connected in series and parallel are like this: http://www.electricfence-online.co.uk/ishop/images/1047/Serial_ParallelBatteries.jpg If these four batteries are numbered 1 to 4 from top to bottom, this example shows the positive feed coming from battery 4 and the negative feed coming from battery 1. Is there any reason to not have the positive feed instead coming from battery 2 and the negative from battery 3? (This assumes all other interconnections remain as shown.) Aren't the current paths the same either way?

The reason I'm asking is that if I can take the feeds from batteries 2 and 3 instead of from batteries 1 and 4, it will greatly help the cable routing for the slide-out battery trays in my bus.

Thanks, 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

Comments

  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Do the batteries have to be in-line or can they be arranged 2 x 2? ie one 24v arrangement per tray
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • Iceni JohnIceni John Solar Expert Posts: 103 ✭✭
    They have to be inline, just like in the diagram.

    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

  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    Have you tried drawing them with #1 and #3 turned 180*, it shortens up the interconnects to make 24V...
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • Iceni JohnIceni John Solar Expert Posts: 103 ✭✭
    My bus is entirely 12V for both house and chassis. Yes, I know all about the reasons to have 24V instead of 12V, but the extra complexity of mixing two voltages in a bus is not worth it for me, so 12V it is! I would like to keep all four positive terminals in line and all four negatives in line. There are actually two separate slide-out battery trays next to each other, each tray holding four batteries side-by-side as in the diagram, and I want to have both trays' positives all next to each other, i.e. in the center, to minimize any chance of them getting too close to the outer edges of the trays and touching something. This means that one set of four batteries would be a mirror-image of the other set, with all eight positive terminals grouped together in the middle. Does that make sense?

    If I can take each tray's feeds off batteries 2 and 3 it will reduce the length of cables needed when the trays are fully extended out.

    Space is always at a premium in a bus or RV, so I want to make everything as compact as possible while still keeping full accessibility. When the trays are fully extended I can easily reach the innermost batteries to check their SG or tighten connections.

    All the series/parallel wiring diagrams I've found show their feeds coming off the ends, but maybe that's because nobody else has any need to do otherwise!

    Thanks, 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

  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Iceni John wrote: »
    Is there any reason to not have the positive feed instead coming from battery 2 and the negative from battery 3? (This assumes all other interconnections remain as shown.) Aren't the current paths the same either way?
    Yes, that will work. That doesn't solve your main battery issue which is that you have 4 parallel batteries. That is a recipe for a short lived and troublesome battery bank.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • Iceni JohnIceni John Solar Expert Posts: 103 ✭✭
    vtmaps wrote: »
    Yes, that will work. That doesn't solve your main battery issue which is that you have 4 parallel batteries. That is a recipe for a short lived and troublesome battery bank.

    --vtMaps

    No, I have only two paralleled pairs of batteries per tray. Remember that each tray of four batteries is fed by its own separate charge controller (which is in turn fed by its own separate array of four solar panels) - in effect I have two independent house battery systems. Because the two arrays of solar panels will be producing slightly different power levels for three quarters of the year, each array needs its own charge controller - MPPT controllers get confused if their panels are producing different amounts of power (where would the Maximum Power Point be?).

    All my panels are hinged to a central walkway on the roof. They can either lay down against the roof at 21 degrees down, or they can be raised to horizontal (not that I would do that very often), or they can be raised to 21 degrees up, 33 degrees up or 45 degrees up. In summer one side of panels would be down against the roof and the opposite side would be raised up 21 degrees, in spring or fall I could raise the opposite side to 33 degrees, and in winter that side would be fully raised to 45 degrees. This way half the panels will be facing the sun as best as possible, and the other half will be at the 21 degrees summer angle all year long. Got it?! That's why each array of four panels needs its own CC. If I need separate CCs, I might as well have separate battery banks. This way I have complete redundancy - if one CC or one bank of batteries fails, I'll still have at least 50% of my power capacity. I could also change out each bank of batteries at different times, or even use different types of batteries altogether if I had no choice. And in case you're wondering, I can have each battery bank isolated from the other by means of 250A Schottky diodes that will electrically separate them, or if needed I can bypass the diodes and combine the two banks into effectively one large single bank

    It sounds more complicated than it really is!

    I got all eight panels man-handled up onto the roof and have secured them inside each support frame, so now I've got power flowing down to the CCs' circuit breakers. Tonight I'll make the 4/0 feed cables, then I'll have solar-powered AC power for the first time in the bus. Yeah! I'm excited.

    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

  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    here is some good info that may help, as VT said, you will have a charging issue with 4 in series...http://smartgauge.co.uk/batt_con.html
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Iceni John wrote: »
    No, I have only two paralleled pairs of batteries per tray. Remember that each tray of four batteries is fed by its own separate charge controller (which is in turn fed by its own separate array of four solar panels) - in effect I have two independent house battery systems.

    Whew! I am relieved that you don't have 4 batteries in parallel.
    Iceni John wrote: »
    This way half the panels will be facing the sun as best as possible, and the other half will be at the 21 degrees summer angle all year long. Got it?! That's why each array of four panels needs its own CC.

    There is nothing wrong with having two independent systems (and sometimes it is advantageous), but you are wrong about needing two controllers just because your panels have different orientations. As long as each array has the same Vmp and all panels in any one string have the same orientation, you do not need to have two controllers. Under virtually all conditions both arrays will have the same voltage and a single MPPT controller will find a very acceptable maximum power point.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • Iceni JohnIceni John Solar Expert Posts: 103 ✭✭
    And another reason I have two controllers is that 2040W of panels at 12V is too much for one Morningstar CC. If I had a 24V house system then one Morningstar would handle that much panels, but for better or for worse I have a 12V system. I know there are some other makes of CC that can handle more power, but I really like the Morningstars - I do NOT want fan-cooled CCs because of potential dust problems where I may be parked much of the year.

    So, this is a very wordy long-winded way of asking if my crazy idea to connect the batteries' feeds the way I want is possible. If you think it's OK, that's good enough for me. My brain hurts when I try to think through seemingly-simple questions like that!

    Many thanks for your help and for putting up with my semi-lunatic ideas!
    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

  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Iceni John wrote: »
    And another reason I have two controllers is that 2040W of panels at 12V is too much for one Morningstar CC.

    Now that is a good reason to have two controllers... but differing orientations of the arrays is not in and of itself a good reason.
    Iceni John wrote: »
    So, this is a very wordy long-winded way of asking if my crazy idea to connect the batteries' feeds the way I want is possible. If you think it's OK, that's good enough for me.
    As I previously mentioned, your battery wiring scheme is OK. Have fun in the bus!

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • Iceni JohnIceni John Solar Expert Posts: 103 ✭✭
    westbranch wrote: »
    here is some good info that may help, as VT said, you will have a charging issue with 4 in series...http://smartgauge.co.uk/batt_con.html

    Yes, those folk have some good ideas, and I'll trust what they say. However, their wiring suggestions are for four batteries in parallel, not four in series and parallel (that is effectively only two in parallel). And they're English, which means they must be right . . . (Just kidding.)

    Thanks, 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

  • BB.BB. Super Moderators, Administrators Posts: 30,488 admin
    2x 6 volt batteries is the same as 1x 12 volt batteries.

    Remember that a battery is a set of 2 volt cells in series.
    I personally like 2x 6 volt batteries in series vs 2x 12 volt batteries in parallel.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    John, I am confused , is your bank to be 2 trays with 4 batteries each in 12 volt or 24 volt config... reason I ask is the diagram you posted is for 24 volt.. and you keep on talking about needing JUST 12V.?

    http://www.electricfence-online.co.uk/ishop/images/1047/Serial_ParallelBatteries.jpg
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • Iceni JohnIceni John Solar Expert Posts: 103 ✭✭
    westbranch wrote: »
    John, I am confused , is your bank to be 2 trays with 4 batteries each in 12 volt or 24 volt config... reason I ask is the diagram you posted is for 24 volt.. and you keep on talking about needing JUST 12V.?

    http://www.electricfence-online.co.uk/ishop/images/1047/Serial_ParallelBatteries.jpg

    Each tray of four 6V batteries will produce about 450Ah at 12V. The two trays will be effectively paralleled together to provide 12V at about 900Ah to the inverter and DC load center. Because each tray of batteries is separately charged by its own CC, I don't regard the eight batteries as being 2-series 4-parallel, but instead they are two separate banks that are each 2-series 2-parallel. I hope that's more than a semantic distinction!

    Sorry if that drawing was misleading - it was the only depiction of four series and parallel batteries in a side-by-side configuration that I could find on the internet. See, nothing's simple!

    So, tonight I'll be making lots of 4/0 feeder and interconnection cables, not only for the house feeds to the two Blue Sea 6006 switches, but I also have separate feeds to a separate pair of Blue Sea 9001 and 9002 switches for taking the house batteries' power to the bus's starter motor. This way I can start the engine off the house batteries in an emergency, or at least boost the two Group 31 start batteries if I need more Reserve Capacity - it takes a lot of power to turn over a big diesel engine in cold weather. I replaced my two 8D starting batteries with Group 31s because the 8Ds are too damn heavy, but there may be times I need some help from the house batteries. This is why it's important to keep the house battery cables as short as possible - there's going to be a lot of cables in a relatively small space, and I don't want then tangling and getting caught on things when I pull the trays out.

    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

  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Iceni John wrote: »
    Each tray of four 6V batteries will produce about 450Ah at 12V. The two trays will be effectively paralleled together to provide 12V at about 900Ah to the inverter and DC load center.

    What do you mean "effectively paralleled together"?
    Iceni John wrote: »
    Because each tray of batteries is separately charged by its own CC, I don't regard the eight batteries as being 2-series 4-parallel, but instead they are two separate banks that are each 2-series 2-parallel. I hope that's more than a semantic distinction!

    Just because you have two charge controllers doesn't mean they are not four batteries in parallel.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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