MAX charge rate for Flooded batteries during winter - low sun...

ligwyd
ligwyd Registered Users Posts: 204 ✭✭
My battery specs state that max charge rate can be 10$ to 20% of C20. I have a 630 amp hour bank. So MAX DC charge amps can be anywhere from 63 to 126 DC amps.

During the winter there is considerably less sunshine and so I am wondering if it wouldn't hurt to increase the max charge rate from 10% to 15% or even 20% when charging the batteries.

Summer time 10% seems to keep the batteries up fine but now that we are nearing the shortest day of the year and when its cloudy would it make sense to bump up the charge rate especially when charging from the Gen? At 10% max charge rate I am only using about 4000 watts AC from the 13kW gen.

Thanks for any feedback. Always appreciate it.

Comments

  • Riley
    Riley Registered Users Posts: 63 ✭✭
    I would say for sure. Anytime of year and charging from generator, you might as well charge close to the max charging rate to minimize the generator run time to reduce fuel consumption. Charging at least the mid-point (ie: 15%) is likely going to be better for the batteries in order to prevent sulfation. The mixing and agitation is good for FLA batteries from what I have read. Even in the summer-time, when I need to run the genny, I charge as close as I can get to 20%. 

    Others might disagree but that's what I have read. 
    Off-grid: XW+6048 / 48V FLA battery bank (428 A/H (Rolls S-550 batteries)) / Conext MPPT 60 150 charge controller / SCP / Insight gateway / 12 - 260W solar panels / Kohler 12KW 12-RES propane genset
  • ligwyd
    ligwyd Registered Users Posts: 204 ✭✭
    Keep in mind too that the MAX charge rate only affects the BULK charge period. After that mt XW throttles back charging amps as the battery increases in state of charge.

    But I agree, that might has as well get the BULK charge done as fast is sensible when charging from the Gen and also even when charging from the sun, provided you have enough solar, which is often not the case in the winter during the shortest cloudy or snowy days.....
  • checkthisout
    checkthisout Registered Users Posts: 31 ✭✭
    A healthy charge rate means you're doing a little bit of equalization each day instead of having to cook the battery once a month. 

    I think you will find that as long as you don't exceed 14.4-14.6 volts during the absorption phase, the amperage flowing into the battery will never exceed what the manufacturer lists as the max recomended rate. 
  • Photowhit
    Photowhit Solar Expert Posts: 6,001 ✭✭✭✭✭
    It sounds like you don't have a good uderstanding of how battery charging works.

    Flooded batteries, will generally limit themselves! and they will take less current as they approach a full charge.

    Charge controllers are basically voltage regulators. They actually do little other than monitor the voltage when the voltage is less than the absorb cut off you select. Once it reaches that cut off, the charge controller just limits the upper limit of the charging current to the voltage. This keeps the battery from over heating. Some higher end charge controllers can also limit the current flowing into the battery bank. It is also good to have a charge controller which will limit charging and vary the cutoff voltage with a battery temperature sensor.

    Once the battery reaches the absorb cutoff, the charge controller limiits the voltage and the current which the battery will absorb will slowly taper off to 1-2% as it reaches fully charged. This is the reason it's usually best to run your generator early in the day and let the solar array(?) top off the battery bank. My older forklift battery takes near 4 hours to top off once it hits abosrb voltage.

    Here are basics on battery charging.

    The voltage you are seeing is the system voltage and not the battery voltage. If you are connected to charging or a load it will effect the system voltage.

    During charging, there are basically 3 stages of charging, Bulk, Absorb, and Float.

    BULK;
    First thing when charging starts you will be in bulk, the voltage rises from what ever the system voltage was to a set point, around 14.5 volts. At that point the Charge controller stops the voltage from rising. Higher voltage can damage sealed batteries.

    ABSORB;
    Once the battery hits the preset point the charge controller keeps it at that point. Your batteries are roughly 80% full. Flooded batteries will start accepting less current at 80-85% full AGM/Sealed may go a little longer before accepting less current.

    On many controllers you can set this point, Some will have different presets for Flooded, and sealed batteries, or flooded, AGM, and sealed batteries. 

    The charge controller has a couple ways to know when to switch to float, Most inexpensive Charge controller are just timed for 1.5-2 hours. Some will also see less current flowing through the charge controller and shut it down when minimal current is flowing through the controller. On more expensive charge controller. You can set battery capacity to give the Controller a better idea of when to stop. you can also set a longer Absorb time. Or set 'end amps' a amount of amps flowing through the charge controller to stop Absorb and switch to the final stage.

    FLOAT;
    Once the Controller has determined the battery is fully charged it reduces the voltage to a point where very little current is flowing to the battery. This will prevent the battery from over charging and heating up.

    While in 'Float' the charge controller watch for voltage drop, which would indicate a load. If the voltage begins to drop the charge controller will allow as much current to flow from the panels/array to compensate and maintain the voltage. If the voltage can be maintained, the load will in essence be running directly off the array/solar. If the voltage drops below the preset float voltage, the controller may start a whole new cycle if it stays there for a period of time.

    The system voltage drop you see at night when the sun goes down is the charge controller moving into a resting mode with no energy to contribute to the system.

    The morning voltage may reflect a load present that is effecting the voltage level.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • ligwyd
    ligwyd Registered Users Posts: 204 ✭✭
    Photowit,
    Thanks for the feedback. What is your take on bumping up max charge rate from where I have it set now 10%, to say 15 or 20. My batteries specs say 10 to 20 is ok.....

    Aim is to push the 13kW Gen a little harder to primarily BULK charge the bank faster and second might increase diesel efficiency being that even at 20% MAX charge rate my bank would draw around 8000 watts of the Gen.....
  • Photowhit
    Photowhit Solar Expert Posts: 6,001 ✭✭✭✭✭
    edited December 2021 #7
    What are you setting?
    Your inverter charger? I haven't used one, but didn't know you could set a chare rate. If it has Battery Temperature Sensor, I'd let it go at least to the general capacity of your battery bank. 

    You say you have a 630 ah battery bank, is this 3 strings of 210 ah golf cart batteries? 
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • ligwyd
    ligwyd Registered Users Posts: 204 ✭✭
    I'm referring to setting max charge rate of the XW+ when charging from the Gen. Max charge rate will only affect the max dc amps used during the bulk charge and then the XW tapers down as batteries charge.

    3 strings of four. Discover 12VRE-3000TF batteries. 12 batteries in total.



  • checkthisout
    checkthisout Registered Users Posts: 31 ✭✭
    ligwyd said:
    I'm referring to setting max charge rate of the XW+ when charging from the Gen. Max charge rate will only affect the max dc amps used during the bulk charge and then the XW tapers down as batteries charge.

    3 strings of four. Discover 12VRE-3000TF batteries. 12 batteries in total.




    Unless you are bringing the batteries from zero voltage (such as when new) or the batteries are extremely hot (like arizona ambient temps) then I wouldn't worry about charging current. You will never exceed the max recommended by the manufacturer because the difference between the voltage commanded by the charger and your battery voltage will never be enough. 

    You can also experiment. Pull the caps and see if you see bubbling. You can feel the batteries to see if they are getting warm/hot. 

    What issues are you worried about causing?
  • ligwyd
    ligwyd Registered Users Posts: 204 ✭✭
    I've just read many places that 10% of C20 for MAX charge rate is the most widely recommended, and as such do not like stepping out side that advice unless I have a reasonable justification to do so.

    Might just bump up the MAX charge rate a bit and see how it goes.......


  • BB.
    BB. Super Moderators, Administrators Posts: 33,404 admin
    Watch the battery temperatures and, if you can, use a remote temperature sensor to feedback to the charger (higher battery temperature, lower charging voltage set point).

    More or less, for batteries, every 10C/18F increase in temperature over room temperature (25C/77F) causes the battery to "age" 2x faster (while hot)... Don't exceed the mfg. recommended max temperature.

    And just make sure that they are not bubbling/gassing excessively (light fizzing OK, rolling bubbling, too much current/too high of charging set point).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ligwyd
    ligwyd Registered Users Posts: 204 ✭✭
    You bet. Am utilizing temp compensating charging. Just going to try moving up the Bulk charge amps from 10% of C20 (63 DC Amps) to 15% (98 DC Amps) and see how much faster it Bulk charges.
    Will post anything interesting.
    Thank you all for the feedback. Always appreciated.
  • checkthisout
    checkthisout Registered Users Posts: 31 ✭✭
    I can relate.

    My 2430 Watt array system collected .05Kwh today. 

    Snow and ice on the panels. The little Yamaha is gonna be going full-tilt for the next month or so.






  • wellbuilt
    wellbuilt Solar Expert Posts: 763 ✭✭✭✭
     My system is set to charge @ 13% 430 ah so about 50 amps or so 
      I raise my voltage from 58 v to 59.5 for December Jan feb March 
     I don’t get a lot of solar and it helps the charging . 
     My generator charges at 59. 5 volts for winter and temp compensation bumps the voltage up to 63v 
      My charger Max’s out  
       Even my charge controller dosent put out close to max out put unless I turn the system on mid day .
       I’m into absorb at 1000 am so the charge started limiting out put . 
    Out back  flex power one  with out back 3648 inverter fm80 charge controler  flex net  mate 16 gc215 battery’s 4425 Watts solar .