AGM Battery Temps

stmarstmar Posts: 293Solar Expert ✭✭
This time of year my batteries show mid 60's to 70 temperatures per the SCP Battery Temperature Sensor which is hooked to a negative terminal on the the battery bank. When I do the equalization/conditioning at 31 volts @ 80 amps for several hours what temps should I expect and what temps are too high? Lifeline 4 X L16 6 volt 400ah AGM bank, Conext SW4024 inverter.

Comments

  • EstragonEstragon Posts: 2,962Registered Users ✭✭✭✭✭
    IMHO, you should see very little increase in temp.  AGMs are generally quite efficient, so a properly functioning battery should put available current into charging, not heating.

    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
  • BB.BB. Posts: 28,088Super Moderators, Administrators admin
    For AGM batteries, when you EQ them, you generally just do the normal absorb voltage for an extended time (4-8 hours). If you do get the voltage too high, the amount of gassing goes way up--Which generates heat (from the gassing) and more heat from the catalyst recombining the gasses back to water (typically, the top of  the battery or battery caps get hot where the catalysts are installed).

    EQ is hard on AGMs, you do not want to do that very often (something like once every 6 months). Catalysts do not last forever... Extended "recombination" wears the catalysts down over time.

    At some point, you should see the charging current drop down to 0.1% of capacity for AGMs.

    Lifeline batteries are supposed to be quite different than other AGMs in that they can take very high voltage when you are trying to recover capacity (something like 17 volts..... Check the manual for exact instructions). But that should only be done if you suspect there is a capacity loss for your bank.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Posts: 7,970Solar Expert ✭✭✭✭

    attaching a BTS to a terminal post is sometimes not the best place.  Bury it in the middle battery, tape it to the side with duct tape, and cover with a bit of insulation so you measure battery temperature, not air temp.

    Battery terminal is handy, but if there is any cable connection resistance, you get heating, which gives you a false high temp.  And if the battery is heating , that big copper heatsink wire pulls heat away and you get a false cool reading.
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  • stmarstmar Posts: 293Solar Expert ✭✭
    With my old Trace I had the BTS attached to the side of the battery but the manual for the new SW4024/SCP said to attach it to the terminal if possible for a more accurate reading. It would have been much more convenient to attach it to the side of the battery but I followed the manual. Was that not correct?
    The Lifeline manual did say to EQ/Condition the batteries at .2C (80amps) @ 31 volts for a 24 volt bank for 8 hours.
  • EstragonEstragon Posts: 2,962Registered Users ✭✭✭✭✭
    I believe the conditioning charge would normally only be done when there is an apparent loss of capacity.  Is this the case for your bank?

    If I was doing this, I'd probably want to monitor the process using a multimeter and IR thermometer rather than relying on the charger alone.  If temp compensation is off/inaccurate for whatever reason, bad stuff can happen.  If temp got to 110-115°f, I'd stop.  
    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
  • BB.BB. Posts: 28,088Super Moderators, Administrators admin
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Marc KurthMarc Kurth Posts: 447Solar Expert ✭✭✭✭
    stmar said:
    With my old Trace I had the BTS attached to the side of the battery but the manual for the new SW4024/SCP said to attach it to the terminal if possible for a more accurate reading. It would have been much more convenient to attach it to the side of the battery but I followed the manual. Was that not correct?
    The Lifeline manual did say to EQ/Condition the batteries at .2C (80amps) @ 31 volts for a 24 volt bank for 8 hours.
    I would suggest that you start by re-reading the manual. That is not what it says at all, and that would actually be impossible to do.
    The [email protected] is correct, but why do you feel that you should equalize? As Estragon already said, EQ is help recover lost capacity from improper charging.

    Perhaps you are confusing the specified minimum charge rate for repetitive ultra-deep discharges? That has nothing to do with Conditioning/Equalizing/Deep discharge recovery. 

    Marc

    I always have more questions than answers. That's the nature of life.
  • stmarstmar Posts: 293Solar Expert ✭✭
    edited November 2 #9
    I must not be understanding the manual. Here is what I was referring to from the maual:
    "The conditioning charge should then be applied by charging for 8 hours.At 77°F (25°C), the conditioning voltage should be set at 2.58 PC (15.5 volts for a 12 volt battery)" It does have to do with Repetitive ultra-deep discharges so that is where I am going wrong. Thanks for straightening me out.
     At this point I think I will just not do anything and see if the system holds up during the winter. Still trying to understand the new SW4024 and how it works with the system.


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