Can you use 2 - 24v chargers on a 48v bank?

rgk1
rgk1 Solar Expert Posts: 135 ✭✭✭
in Off Grid Solar & Battery Systems #1
Recently made the swap from 24 to 48 volt system.  As yet I do not have a 48v charger, but do have 2 - 24v chargers.  Numerous cloudy days and the impending/now up us ice storm has forced me to charge the battery bank with other than solar.  After shutting everything down, I disconnected the wire between batteries 4 and 5 making 2 banks of 24v and hooked up a charger to each bank.

The question is, could I have left all 8 in series with the system up and running as normal and just connected a charger at each 24v part of the 48v series string (Charger #1 with positive at battery 1 and negative at battery 4 and Charger #2 with positive at battery 6 and negative at battery 8)? Battery 1 positive and battery 8 negative are the 48v leads to system.
4-Risen 320 watt in series/parallel, 8-215ah 6 volt GC2 batteries in series, Exeltech 1100 watt/48 volt inverter, Tristar 45 MPPT controller.
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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #2
    Either way would work because each charger is an independent circuit, as long as the chargers are identical in design, using different chargers could result in half the bank being charged at a different rate. Either way, monitor the voltages of each string of 4 to ensure they are close to one another and when the sun eventually returns do an equalization without loads, assuming flooded lead acid, to bring things back into alignment, if AGM I would suggest an extremely long absorption without loads, for the same reason.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #3
    I would say "maybe".  

    Your chargers have to provide "isolation" they can't have either output connection tied to ground internally, or tied to the powerline neutral.  So as long as they don't provide any sneak paths to the other end of the battery, it should work.
    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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  • rgk1
    rgk1 Solar Expert Posts: 135 ✭✭✭
    #4
    Thanks mcgivor and Mike95490.  The chargers are both Iota 24V.  One is newer than the other, but seem to have same voltages.  The wire on the right, between the top row and the bottom row is what I was wondering if I MUST remove to charge this way, or if it can be done in the 48v configuration. Just  so we are on the same page. 


    4-Risen 320 watt in series/parallel, 8-215ah 6 volt GC2 batteries in series, Exeltech 1100 watt/48 volt inverter, Tristar 45 MPPT controller.
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #5
    If you know how to use an ohm meter, measure each Iota with the low ohms scale:
    narrow AC blade to both outputs -, +
    wide AC blade to both outputs -, +
    ground wire to chassis
    ground wire to both outputs  -, +
    Then flip reverse the meter leads and do it all  over again.
    Then do both again at the high ohms scale ( uses a higher voltage)
     Even after all that, it may blow smoke, but it cuts your chances down
    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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  • BB.
    BB. Super Moderators, Administrators Posts: 33,634 admin
    #6
    Just to be clear, do the resistance (Ohms) tests with no AC or DC voltage on the power supplies (any voltage present could smoke the Meter when measuring resistance).
    Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • rgk1
    rgk1 Solar Expert Posts: 135 ✭✭✭
    #7
    Sounds like it is going to be much safer to remove the one wire and make 2 - 24v banks and charge independently.  First time I have had to figure out an external charging method.  Hopefully the last till get appropriate 48v charger. Thank you all for the replies!
    4-Risen 320 watt in series/parallel, 8-215ah 6 volt GC2 batteries in series, Exeltech 1100 watt/48 volt inverter, Tristar 45 MPPT controller.
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