Flooded acid battery voltage and temperature.

UpNorthManUpNorthMan Registered Users Posts: 20 ✭✭
Hello everyone,
I've looked for the answer to this question for awhile now and have found conflicting results. I know usable capability changes with battery temperature when using LA batteries.

 But does temperature change voltage?

I have 8 6v golf cart batteries in a series for a system voltage of 48v. If I fully charged the batteries @ 77F and then put them in the freezer for a week. (-20F) Will the batteries still measure the same voltage ?

My weekend cabin has high temperature of 95F and typical low of -50F. The batteries are temporarily stored in a semi insulated box with 15 feet of heat tape for a heat source. Once the batteries are mostly charged, the heat tape turns on. With the cloudy winters and cold here, the batteries seem to get around  0F.

Anyone have a idea?

Thanks
Ed
1000W panels Kid CC 184 ah battery bank @ 48v
Weekend cabin, 250w inverter.
Looking to upgrade inverter!

Comments

  • BB.BB. Super Moderators, Administrators Posts: 32,921 admin
    Interesting question Ed...

    We are all comfortable with the automatic temperature compensation for charging (as battery gets colder, the charging voltage is automatically increased by most "higher function" chargers--It appears typically the "correction range is from 0F to 122F or so).

    Since I live in an area where the average temperatures are from 50F to 75F, I have never had the chance to see what cold and heat do to resting voltages.

    However, this guy is in Maine and used an older FLA battery to check resting voltage from winter through summer (random data collection).

    It appears that his default assumption was that the battery resting voltage does not change over a wide range temperatures vs state of charge... He did find that the "resting voltage" may take 6-12 hours "to settle" on a "warm battery" but take upwards of 10+ days on a cold soaked FLA battery (resting voltage is showing residual surface charge voltage days after charging, even partial charging). The observation from his testing was that surface charge to resting voltage was the result of dissipating the surface charge and not the result of "self discharge" current (which is very low at below freezing temperatures anyway).

    Tests were done on an ~5 year old "WalMart" battery used in a boat--Which was about 80% of new capacity at full charge.

    Anyway--A couple of links:

    https://www.pbase.com/mainecruising/battery_state_of_charge
    https://www.pbase.com/mainecruising/self_discharge

    On another method to ask/answer your question, there is a rough formula for resting voltage vs state of charge from an old thread:

    https://forum.solar-electric.com/discussion/comment/92455#Comment_92455
    ran across this page on why different types of batteries have different starting s.g. fills... Is pretty interesting:
    Specific Gravity vs Applications
    1.285 Heavily cycled batteries such as for forklifts (traction).
    1.260 Automotive (SLI)
    1.250 UPS – Standby with high momentary discharge current requirement.
    1.215 Geral applications such as power utility and telephone.

    As mentioned earlier, the specific gravity (spgr.) of a fully charged industrial battery, or traction battery, is generally 1.285, depending on the manufacturer and type. Some manufacturers use specific gravities as high as 1.320 in an attempt to gain additional Ah capacity, but at the cost of a shorter cycle life.

    ...

    Higher Gravity = vs Lower Gravity =
    More capacity / Less capacity
    Shorter life / Longer life
    Higher momentary discharge rates / Lower momentary discharge rates
    Less adaptable to "floating: operation / More adaptable to "floating" operation
    More standing loss / Less standing loss
    Also on that page is the formula between cell resting voltage and specific gravity:
    Specific gravity = single-cell open-circuit voltage - 0.845 (example: 2.13v – 0.845 = 1.285)
    Or
    Single-cell open circuit voltage = specific gravity + 0.845.

    So, if you are getting 46 volts after resting, if the formula is correct (and your battery is around 77F) your specific gravity should be:
    • 46v/24cells - 0.845 = 1.072 (dead?)
    • 47v/24cells - 0.845 = 1.113 (~20% state of charge)
    Yuasa states that the temperature correction for SG is:
    • specific gravity changes by +.001 for every -3 degrees Fahrenheit.
    J.R. Buchanan did a nice set of charts on battery SG and temperature based on a 100% charge = 1.265 SG.
    So, resting voltage should be (mostly) based on specific gravity of the electrolyte (with a "magic" 0.845 volt offset) for a lead acid battery... However, we do have SG correction based on temperature. It appears that the above results plus this formula would suggesting using the 77F corrected SG readings for the resting voltage calculation.

    -Bill "not a battery engineer" B.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dave AngeliniDave Angelini Solar Expert Posts: 6,296 ✭✭✭✭✭
    I would say if you measure the charged bank at 75F,  then 24 hours later in -20F environment,  the voltage will be very close after a week. It is the months of cold sinking (w/o charge) a lead acid that does long term damage.
    "we go where power lines don't" Sierra Nevada mountain area
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • UpNorthManUpNorthMan Registered Users Posts: 20 ✭✭
    Thank you both for your response. I  see I have some reading for some spare time. I thought  the voltage stayed the same, but have seen some conflicting information in my searches.

    If it's OK,  I  would also like to thank All veterans for their service.

    Ed
    1000W panels Kid CC 184 ah battery bank @ 48v
    Weekend cabin, 250w inverter.
    Looking to upgrade inverter!
  • Marc KurthMarc Kurth Solar Expert Posts: 987 ✭✭✭✭
    edited November 11 #5
    I would say if you measure the charged bank at 75F,  then 24 hours later in -20F environment,  the voltage will be very close after a week. It is the months of cold sinking (w/o charge) a lead acid that does long term damage.

    My experience is the same with AGMs. (still lead-acid.) The voltage that you measure at 75F will be the same at -20F. Voltage decay will be more related to time, not low temperature. Obviously, capacity is a different story!
    We had a customer with a full pallet of new 2v 1200 ah batteries that were forgotten in an outdoor storage area when a snowstorm blew in. (Your tax dollars hard at work) They spent the winter frozen and were at 2.1v when they were discovered during the Spring thaw. That taught me something!
    I always have more questions than answers. That's the nature of life.
  • Dave AngeliniDave Angelini Solar Expert Posts: 6,296 ✭✭✭✭✭


    If it's OK,  I  would also like to thank All veterans for their service.

    Ed
    It is more than OK and I know the boss will agree😎😎😎

    I was reading a list of all of the businesses in North America that were started by Vets. Mind boggling the names.
    "we go where power lines don't" Sierra Nevada mountain area
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

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