Charging 12 volt battery with 24 volt panel putting out ~10 watts.

softdownsoftdown Solar Expert Posts: 3,494 ✭✭✭✭
Think this was maybe discussed a few years ago. Getting ready to charge up my newfangled 5 acre electric fence. The battery weighs about 50 pounds. The panel is a seven year old Harbor Freight panel rated at 15 watts when new. Figuring it was probably good for about 12 when new, maybe 10 watts now.

Think we decided it was probably OK to do such low power charging at 24 volts. Could have used a charge controller but the steel electronics box is already very, very crowded. Plus I like to keep outdoor electronics simple. This environment is frequently extreme.
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

Comments

  • mike95490mike95490 Solar Expert Posts: 9,089 ✭✭✭✭✭
    edited October 2018 #2
    You may need (am I actually saying the D word ? ) a diode to prevent the panel from discharging the battery at night, if you are not using a charge controller.
    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 ,

  • ArcanistArcanist Registered Users Posts: 8 ✭✭
    Yes you will need a diode or else your battery will discharge through the panel at night time. A controller would be wise to prevent overcharging.
  • softdownsoftdown Solar Expert Posts: 3,494 ✭✭✭✭
    Reading 15.15 volts at 8:45am reading at 37F - ideal solar conditions - cool and clear. It doesn't look like the battery self-discharged.

    Arcanist - do you have a background in this? ~10 watts is not a potent charge.
    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
  • ArcanistArcanist Registered Users Posts: 8 ✭✭
    edited October 2018 #5
    @softdown
    I have a diploma in electrical engineering and I've build my own solar setup for a house bus, but I am still new to the game.
    I'd stick a cheap controller onto it.
    Did you measure this with the panel attached or detached? 15 volts seems too high for a 12v battery and much too low for a 24v battery.
  • softdownsoftdown Solar Expert Posts: 3,494 ✭✭✭✭
    ~15 volts is not unusual for a lead acid battery. You may be right but I now remember doing this in years past and doing fine. Got 9 years out of the subjected battery though the panel was only used one winter. This is a cool environment, batteries last longer.
    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
Sign In or Register to comment.