Recommended battery charge voltage - Hot Climate

bigbrovar
bigbrovar Registered Users Posts: 31 ✭✭
Hello guys I have been living offgrid in Nigeria West Africa for close to a year now. My setup has 2 "tubular batteries" which are essentially flooded deep cycle batteries. Product seem white labelled so it's hard to know original manufacturer but it seem to be an Indian brand of so called tubular battery. (Picture attached)

Each 12v battery as a capacity of 220ah at C20 under. Battery are connected in series. Main source of charge used to be from an MPPT EPsolar 3215 bn series charge controller before I installed a victron bluesolar 150/45 MPPT cc ( mainly due to the slow tracking algorithms of the former) I have 3 solar panels (240w x 2 and 220w x 1) connected in series

My previous charge controller had a remote temperature sensor for checking voltage of the battery and temperature adjusted charging. I had the following charge profile

Absorption 29.2v
Float 27.6v
Equalisation (28th of every month) 31v

I have a watt meter connected to the battery which gives me an over view of the battery voltage so I can see the voltage of the battery has it is being charged. With the previous controller the absorption voltage on the watt meter is usually close to that being shown on the meter for the epsolar Controller and I barely have issues with boiling although I have only topped water once in about 8 month of use.

I got the victron controller yesterday and set the charge parameters to about 29v for absorption - note the victron does not have external temperature sensor for the battery but uses the built in sensor for adjusted charging voltage. It's very hot now in Nigeria and average room temperature is about 32C. I noticed that when I connected the victron. My watt meter showed battery voltage of 30v and battery was bubbling in absorption (the way it does only when am equalising with the old epsolar controller ) I was not comfortable with the situation so I set the absorption voltage to about 28.8 when then battery watt meter showed the battery voltage was at 29.9v. I have not used victron product before nor have I used a controller other than epsolar for my setup.

I would like to know what is the best safest charge voltage I can set for my battery bank especially for my climate since I don't have a remote temperature sensor for the battery. A voltage that does not leave my battery under charged nor over charged. Is 28.8v good enough? My daily DOD is about 40%

Comments

  • Marc Kurth
    Marc Kurth Solar Expert Posts: 1,142 ✭✭✭✭
    edited January 2017 #2
    Honestly, "the best charging voltage" is a temperature curve that can only be determined by the manufacturer. You can certainly use a default value, but it may or may not pretty far from where it needs to be.

    I deal with one manufacturer who flatly says: "Do not use our batteries if your charging source does not include appropriate temperature compensation. There is no safe value to use."

    I'm sure that this not what you wanted to hear, but it is important if you want to maximize battery lifespan. If you have exhausted all sources of battery specific information, use a temperature that matches a battery that seems close to yours.

    Marc
    I always have more questions than answers. That's the nature of life.
  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    edited January 2017 #3
    This table can be used as a guide to subtract the respective amount of voltage  by temperature, so for example at 40C you would subtract 0.90v for a 24V battery. The basic setting I use in a similar tropical climate for flooded is:
    Absorbtion  28.8v
    Float             26.8v
    Equalize       30.2

    Which seems to work well, when it gets hot 40C plus, I program the absorption reduction, depending on battery temperature  to prevent over gassing, my battery temperature is very stable and predictable, being in a concrete building, so I only adjust when the ambient temperature outside goes above 40C and battery is 35C. My basic settings are lower than most suggest, those not living in the tropics,  but given the temperatures experienced in general, my thinking it is better to be on the low side than the high, it is a balancing act, dependant upon local climate and system location. 


    If a remote temperature sensor is not used and the temperatures near the 
    battery are stable and predictable, the PWM absorption setting can be 
    adjusted using the PC software per the following table:
    Temperature 12 Volt 24 Volt 48 Volt
    40ºC / 104ºF – 0.45 V – 0.90 V – 1.80 V
    35ºC / 95ºF – 0.30 V – 0.60 V – 1.20 V
    30ºC / 86ºF – 0.15 V – 0.30 V – 0.60 V
    25ºC / 77ºF 0 V 0 V 0 V
    20ºC / 68ºF + 0.15 V + 0.30 V + 0.60 V
    15ºC / 59ºF + 0.30 V + 0.60 V + 1.20 V
    10ºC / 50ºF + 0.45 V + 0.90 V + 1.80 V
    5ºC / 41ºF + 0.60 V + 1.20 V + 2.40 V
    0ºC / 32ºF + 0.75 V + 1.50 V + 3.00 V
    – 5ºC / 23ºF + 0.90 V + 1.80 V + 3.60 V
    – 10ºC / 14ºF + 1.05 V + 2.10 V + 4.20 V
    – 15ºC / 5ºF + 1.20 V + 2.40 V + 4.80 V
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.