Using Midnite Brat to charge 12v batt from 24v Battery?

aglicknmexaglicknmex Posts: 40Solar Expert ✭✭✭
Got oddball need to keep a 12v battery hot from my 24 volt solar/ battery bank.
PWM  Brat would be  fine as I have a steady 24 v source.
 Manuals on MidNite site do not make it clear if I can charge 12 from this higher voltage source?

Other suggestions appreciated.  Need at least 20 amp charging for 12 v Battery.
The brat does 30, so it is attractive!

Comments

  • EstragonEstragon Posts: 2,936Registered Users ✭✭✭✭✭
    I'm not so sure about using a brat. You can get huge current from a battery, and I can imagine some nasty sparkiness as the pwm circuit opens and closes.

    Maybe something like this?

    https://www.solar-electric.com/12to24or24to.html
    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • animattanimatt Posts: 294Solar Expert ✭✭✭
    i have in the past successfully used morningstar 45a mppt controller.  Pv +- terminals connected to 24v battery bank. and  Battery +- terminals connected to 12 volt bank. worked well.

    I had a dedicated 24v to 12v device which died. Swapped out with the backup mppt controller and was back in business.

    You may want to try midnite forum to get an answer directly from them about their product.
  • aglicknmexaglicknmex Posts: 40Solar Expert ✭✭✭
    I have a large occasional load so 24-12 converter won't do.
    Will check with MidNite.
  • mike95490mike95490 Posts: 7,957Solar Expert ✭✭✭✭
    I belive the better MPPT controllers can do that, but with a PWM, you need to use a ballast resistor to limit current so you don't blow the internal fuse or MOSFET
    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 ,

  • aglicknmexaglicknmex Posts: 40Solar Expert ✭✭✭
    MidNite confirms what you say Mike.
    Ballast resistor wastes energy...
    Nice thing about a solar charger is 3 stage .

    Ideas for basic mppt charger ?
    It can charge 24/7 with Battery as power source, so maybe I could get by with 10amp or so. 
  • aglicknmexaglicknmex Posts: 40Solar Expert ✭✭✭
    I'm looking at Victron mppt 75/15 at 88 bucks. 
    I sent a note to Peter Kennedy at PKYS  asking if it will work or burn up??
    Any ideas or experience anyone??

  • mike95490mike95490 Posts: 7,957Solar Expert ✭✭✭✭
    Morningstar solar used to have a white paper somewhere, stating that their MPPT controllers could do that, and would not void the warranty.
    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 ,

  • aglicknmexaglicknmex Posts: 40Solar Expert ✭✭✭
    Great info, thanks!?
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