Using 12volts off a 24volt system

Options
Bobharrow
Bobharrow Registered Users Posts: 1 ✭
in Solar Beginners Corner #1
Could you advise me please? 
I am using 4 identical 6 volt batteries wired in series to give me a 24 / 230 volt system. My question is it ok to use just two of the batteries to power my 12 volt lighting? 

Thanks,
         Bobharrow 

· Share on Twitter

Comments

  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #2
    Options
    The answer is no, center tapping a 24V string will result in the tapped pair of batteries to be discharged deeper than the other pair, the charging source will not fully charge the lower pair despite the series string voltage being satisfied. The result will be failure due to sulfation of the tapped pair, this will occur in a relatively short period of time, especially if the 12V load current is is high.

    The better method to drive 12V loads would be to use a 24V to 12V  DC-DC converter or buck converter, this would ensure the load is placed across the entire string, the same as a 24V load.
    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.
    · Share on Twitter
  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    #3
    Options
    Maybe if you had a device that rapidly (ie unnoticeably) switched between the two of the batteries and the other two.  Would be more efficient and cheaper to build than a DC-DC converter.  If it always drew from the higher voltage pair, it would actually improve balance.

    I am available for custom hardware/firmware development

    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    #4
    Options
    There are converters made for RV/busses/military trucks/etc. that connect to the 24 and 12 volt busses, and will charge/discharge the two sets of batteries to be equal state of charge (24 volt chassis battery, 12 volt house battery from 1x 24 volt bus) both during discharging and charging and floating.

    I don't have time to look up products at this moment--But if you are interested (they are not cheap)--Let me know.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #5
    Options
    If you are just trying to power 12vdc lighting, why not simply change to 24 vdc lighting, or since you have an inverter set up, change to line volatile AC lighting.  Most 12vdc applications off grid these days are for things that are native 12 vdc like RV fridge controls, or radios/TVs that were designed for mobil applications.  I started out with a dual 12 vdc/120vac lighting system, but with the advent of LED bulbs we never use any 12 vdc lights except a couple of night lights.  If not for the fridge and the radio we would change to a 24 or even a 48 vdc system.

    tony
    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    #6
    Options
    Here is an example of 12/24 volt battery balancer (balances both load current and charging current--from 12, from 24 volt bus, etc.).

    https://www.eaton.com/Eaton/ProductsServices/Electrical/ProductsandServices/Transportationsolutions/PowerConversion/Equalizers/24Vto12VBatteryEqualizers/index.htm

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • 706jim
    706jim Solar Expert Posts: 515 ✭✭✭✭
    #7
    Options
    I had the same dilemma. I used very little 12 volt power but had tapped my 24 volt battery as you are suggesting. Eventually, I increased my system size and now just run my inverter 24/7 with the standby circuit defeated. I figure the inverter idling losses are insignificant now and just use a 120 to 12 volt power supply to get 12 volts.
    Island cottage solar system with 2500 watts of panels, 1kw facing southeast 1.3kw facing southwest 170watt ancient Arco's facing south. All panels in parallel for a 24 volt system. Trace DR1524 MSW inverter, Outback Flexmax 80 MPPT charge controller 8 Trojan L16's. Insignia 11.5 cubic foot electric fridge. My 30th year.
    · Share on Twitter
  • just starting
    just starting Registered Users Posts: 235 ✭✭✭
    #8
    Options
    I just happen  to have a 100 amp equalizer copperbussman sitting around...
    200ah LiFePO4 24v Electrodacus Sbms40 quad breaker chest freezer to fridge- Samlex PST 1524 - Samlex pst3024  - 1hp shallow well pump-Marey 4.3 GPM on demand waterheater - mama bear Fisher wood burning stove, 30" fridgarair oven ,fridegaire dishwasher  Unique 290l stainless D.C. Fridge-unique 120l portable fridge/freezer 
    · Share on Twitter
  • Horsefly
    Horsefly Registered Users Posts: 470 ✭✭✭✭
    #9
    Options
    I have a 24V system, and wanted to put in some night lights that run off of DC so I could (if needed) shut down the inverter over night. 12VDC lighting is way easier to find than 24VDC, plus we have a 12VDC car stereo that we installed some time ago for some tunes in the cabin. So, I bought this 24VDC to 12VDC adapter:
    https://www.amazon.com/Pyle-PSWNV720-Power-Converter-Technology/dp/B003P17X8I

    It's been working great. We also use the 12VDC to charge phones and such overnight.
    Off-grid cabin: 6 x Canadian Solar CSK-280M PV panels, Schneider XW-MPPT60-150 Charge Controller, Schneider CSW4024 Inverter/Charger, Schneider SCP, 8S (25.6V), 230Ah Eve LiFePO4 battery in a custom insulated and heated case.
    · Share on Twitter
  • LostOnFiji
    LostOnFiji Registered Users Posts: 3 ✭
    edited December 2019 #10
    Options
    If I have a 24VDC/12VDC (40Amps) converter to provide power to my water pump and several 12V powerpoint, can I also attach a 12VDC/120VAC inverter to the same circuit.  

    The answer is NO, I cannot connect the inverter to the converter and expect it to work.
    · Share on Twitter
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #11
    Options
    LostOnFiji said:
    If I have a 24VDC/12VDC (40Amps) converter to provide power to my water pump and several 12V powerpoint, can I also attach a 12VDC/120VAC inverter to the same circuit.  
    Only if it's a small inverter and does not exceed the 40A allowed.  ( 12v x 40A = 480w )  so  maybe a 200-300w inverter could work.  I say could, because I have no idea what your other loads on the downconverter are.
    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 ,

    · Share on Twitter

Categories