Extreme soc charge in cold temp?

nyoffgrid
nyoffgrid Registered Users Posts: 19 ✭✭
in Off Grid Solar & Battery Systems #1
Hey all

I've been using my 200ah 24v battery and 3000watt inverter for about 6 months now in my off grid cabin. The warmer months were perfect. Even with all cabin running including ductless ac from 8am until 10pm the soc will be 80% at the end of the day. So I headed into winter thinking I'm good. 

The last couple of times we came to the cabin this winter when night temp drops to 5-10 degrees.. the battery temp, per it's Bluetooth app, was 33f and soc was at 93% upon arrival we then used two 800 watt space heaters to just warm up until woodstove took over.. It dropped to 50% within less than 2 hours. It continued the rapid drop until I had to turn on generator.. 

Obviously temp is what causing this? I'm thinking to maybe try to try put that 800watt space heater right on battery (safely obviously) to try and warm it up quickly.. 

Any ideas/tips? 

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Comments

  • Wheelman55
    Wheelman55 Registered Users Posts: 246 ✭✭✭
    #2
    Give the team here specs on your system. Battery voltage and size will be especially helpful.
    Off-Grid in Terlingua, TX
    5,000 watt array - 14 CS 370 watt modules. HZLA horizontal tracker. Schneider: XW6048NA+, Mini PDP, MPPT 80-600, SCP. 390ah LiFeP04 battery bank - 3 Discover AES 42-48-6650 48 volt 130ah LiFePO4 batteries
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  • Marc Kurth
    Marc Kurth Solar Expert Posts: 1,173 ✭✭✭✭
    edited December 22 #3
    The first thing that comes to mind is that your 1,600 watts of space heater load plus some inverter overhead, represents close to 17 % or 18% of your battery capacity, per hour that you operate both.
    In very round numbers: 200 ah battery x 50v = 10kWh. Two hours of heater operation is around 3.5kWh including some inverter overhead, which is 35% of your battery capacity.
    So, with your battery bank in brand new condition, starting at 93%, it would be at 58% running the heaters for two hours.
    I always have more questions than answers. That's the nature of life.
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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,906 ✭✭✭✭✭✭
    #4
    A very hard thing to do reliably !  Redesign the system is about all there is.

    Winter is where the pedal hits the metal !  The days are getting longer😉
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,111 ✭✭✭✭✭
    #5
    Marc Kurth said:
    The first thing that comes to mind is that your 1,600 watts of space heater load plus some inverter overhead, represents close to 17 % or 18% of your battery capacity, per hour that you operate both.
    In very round numbers: 200 ah battery x 50v = 10kWh. Two hours of heater operation is around 3.5kWh including some inverter overhead, which is 35% of your battery capacity.
    So, with your battery bank in brand new condition, starting at 93%, it would be at 58% running the heaters for two hours.
    Now, factor in that it's a 24 volt battery.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

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  • JRHill
    JRHill Registered Users Posts: 367 ✭✭✭✭
    #6
    One of the things that is not allowed in our off grid setup is resistance heat from a hair blow dryer and up. There has to be a better way to get the cabin warmed up without a major system redo? How about one or two of these (on their own grill bottle?) and a ceiling fan or two?

    https://www.lowes.com/pd/ProCom-25000-BTU-Wall-or-Floor-Indoor-Liquid-Propane-Vent-Free-Infrared-Heater/5015729915?store=

    When done for the season you can just store them away until next season. The ceiling fans, if you don't have them already, are useful all year around.
    Off Grid. Two systems: 1) 2925w panels, OB VFXR3648, FM80, FNDC, Victron BMV-712, Mate3s, 240 xformer, four SimpliPHI 3.8; 2) 780w, Morningstar 30a, Grundfos switch, controller and AC/DC pump, 8 T105. Honda EU7000is w/AGS. Champion 3100. HF 4550, Miller Bobcat.
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  • 706jim
    706jim Solar Expert Posts: 521 ✭✭✭✭
    #7
    Heaters vs batteries = no

    Particularly cold batteries!
    Island cottage solar system with appriximately 2500 watts of panels, 1kw facing southeast 1.3kw facing southwest 170watt ancient Arco's facing due south. All panels in parallel for a 24 volt system. Trace DR1524 MSW inverter which has performed flawlessly since 1994. Outback Flexmax 80 MPPT charge controller four 467A-h AGM batteries. Insignia 11.5 cubic foot electric fridge 1/4hp GSW piston pump. My 31st year.
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  • JRHill
    JRHill Registered Users Posts: 367 ✭✭✭✭
    edited 2:05AM #8
    A block heater for 15-30 minutes is an exception. Getting a machine started may be important than getting another layer of clothes on.
    Off Grid. Two systems: 1) 2925w panels, OB VFXR3648, FM80, FNDC, Victron BMV-712, Mate3s, 240 xformer, four SimpliPHI 3.8; 2) 780w, Morningstar 30a, Grundfos switch, controller and AC/DC pump, 8 T105. Honda EU7000is w/AGS. Champion 3100. HF 4550, Miller Bobcat.
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