Lead acid capacity in freezing temps

mountainmanmountainman Posts: 109Registered Users ✭✭
My batteries specs are 208 amp hr but only 50% at 0 degrees. Question since at 50% on capacity do I charge on 10% of 208 or 104 amp hrs. One more thing which is worst on a battery bank discharging to 50 soc and charging at c10 or discharging to 75% soc and charging at c 5. On cloudy days charging with generator at c8.
Blue ridge mts. Renogy 400 watts manual tracking . Epever mppt 30. 2 GC 208 ahr. 300 watt psw inverter. 2 kw genny. Iota 55.

Comments

  • mike95490mike95490 Posts: 7,709Solar Expert ✭✭✭✭
    Cold temps slow down the chemical reactions in the battery ( Li batteries go downhill fast below +40F)

    But I know of nobody who changes charge rates with temps.  The BTS (battery temp sensor) with many high end charge controllers, adjusts the charging setpoints + & - according to temps, but not the amps.   So I dont think I'd worry about it.
    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
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  • mountainmanmountainman Posts: 109Registered Users ✭✭
    So keep it at as is. Any thoughts on which is worse on battery bank daily 75% soc at 5% charge rate. Or 50% soc at 10% c rate?
    Blue ridge mts. Renogy 400 watts manual tracking . Epever mppt 30. 2 GC 208 ahr. 300 watt psw inverter. 2 kw genny. Iota 55.
  • BB.BB. Posts: 27,568Super Moderators admin
    Probably not a huge difference.

    Some have argued that both of those are 1x charging cycle. So, from a pure $/ah cycle cost, a 50% discharge is supposed to be more cost effective.

    Personally, use the system the way you need it. Don't drive yourself nuts trying to be perfect.

    Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • softdownsoftdown Posts: 1,825Solar Expert ✭✭✭✭
    0 Freedom or 0 Canadian?
    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
  • EstragonEstragon Posts: 2,451Registered Users ✭✭✭✭
    > @mountainman said:
    > So keep it at as is. Any thoughts on which is worse on battery bank daily 75% soc at 5% charge rate. Or 50% soc at 10% c rate?

    A 75% SOC is probably marginally better, BUT there are other factors to consider. Assuming a cold bank (0°f?), sulfation will take much longer than it would with a hot bank, so going to 50% may not be so bad as long as it doesn't stay there for long (like many days/weeks). Also, charging with a generator from 50-80% or so can be more fuel efficient that charging from 75-100%.

    IMHO, you should give a cold (FLA) bank all the current it will take, assuming voltage is compensated for temp by a RTS. The only reason I limit current is to prevent overloading the generator in use. I don't change the limit based on reduced winter capacity.
    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
  • mountainmanmountainman Posts: 109Registered Users ✭✭
    Thanks everyone. In reviewing my battery specs at 75 soc they should last around 7 years but at 50 soc roughly 3 years so from a money stand point 75 soc would be better. So im gonna add 2 more batterys. On cloudy days in early morn I run a 2000 watt generator on a bulk of c6 35 amps with what I have now or c12 with 4 batteries from a dumb car charger for 2 hrs or so. Until the volts reach 14.8 then let solar take over Even on cloudy days I'll get about 2.2 amps.
    Blue ridge mts. Renogy 400 watts manual tracking . Epever mppt 30. 2 GC 208 ahr. 300 watt psw inverter. 2 kw genny. Iota 55.
  • mcgivormcgivor Posts: 1,894Solar Expert ✭✭✭✭
    Yes the batteries will last longer but will require a larger bank to supply the same Ah as a smaller bank discharged to 50%, that's where the $/Ah comes in, when calculated the actual energy cycled is close, but replacement means they will be new more often, you pays your  money and makes your choices, basically a matter of opinion, I'll keep mine to myself.
      1500W, 6× Schutten 250W Poly panels , Schneider 150 60 CC, Schneider SW 2524 inverter, 8×T105 GC 24V nominal 

  • 706jim706jim Posts: 205Solar Expert ✭✭✭
    My experience with cold batteries is that it doesn't take much to knock them down.

    And not much to bring them back up.

    FLA at about 0F.
    Island cottage solar system with 1400 watts of panels, Trace DR1524 MSW inverter, Trace C40 PWM controller 8 Trojan L16's. My 25th year.
  • mountainmanmountainman Posts: 109Registered Users ✭✭
    With the larger bank I'd be able to go a cloudy day without using the gen. I think the gas savings tips the scale for me.
    Blue ridge mts. Renogy 400 watts manual tracking . Epever mppt 30. 2 GC 208 ahr. 300 watt psw inverter. 2 kw genny. Iota 55.
  • mcgivormcgivor Posts: 1,894Solar Expert ✭✭✭✭
    With a larger bank the PV needs to be able to recharge after a cloudy day, if currently you have the need to run a generator, the need will be still there, only for longer periods, albeit less often.
      1500W, 6× Schutten 250W Poly panels , Schneider 150 60 CC, Schneider SW 2524 inverter, 8×T105 GC 24V nominal 

  • mountainmanmountainman Posts: 109Registered Users ✭✭
    I understand what your saying larger bank. Needs more pv and longer gen charger time even more gas!!! I'm maxed out on a 30 amp controller so more panels more racking more wire another controller.200 amp hrs in winter isn't enough for me
    Blue ridge mts. Renogy 400 watts manual tracking . Epever mppt 30. 2 GC 208 ahr. 300 watt psw inverter. 2 kw genny. Iota 55.
  • mcgivormcgivor Posts: 1,894Solar Expert ✭✭✭✭
    Having a 12V system restricts expansion going 24V would allow double the PV on the same conductors, same controller, if compatible, but would require an inverter change, inverter chargers are better than using a car charger, in terms of efficiency. Battery wise, less parallel connections smaller conductors and fuses/breakers. All comes down to needs and of course budget.
      1500W, 6× Schutten 250W Poly panels , Schneider 150 60 CC, Schneider SW 2524 inverter, 8×T105 GC 24V nominal 

  • mountainmanmountainman Posts: 109Registered Users ✭✭
    I'm in a rv so guess I'm stuck with 12 volts. I use 75 amp hours per day. My panels bring in 100 or so on a good day. But my batteries in these temps are giving 50.My thoughts were with 400 amp hrs I'd be able to get my 75 and still have enough solar to recharge in a day?
    Blue ridge mts. Renogy 400 watts manual tracking . Epever mppt 30. 2 GC 208 ahr. 300 watt psw inverter. 2 kw genny. Iota 55.
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