Time for Upgrade, Comments needed

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  • dishxpertdishxpert Registered Users Posts: 22
    Re: Time for Upgrade, Comments needed

    Also, how long should i set my Charge controller to absorb at 28.8V? Its currently on the default value of 1 hr.
  • inetdoginetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Time for Upgrade, Comments needed
    dishxpert wrote: »
    Also, how long should i set my Charge controller to absorb at 28.8V? Its currently on the default value of 1 hr.

    The right answer to that is that you should see what the battery SOC (as determined using the hydrometer) is at the end of the hour of Absorb. If it goes down steadily day by day, your Absorb is too short.

    A very crude rule of thumb is that your Absorb should be about the same length of time that you spend in Bulk. But longer will not hurt as long as the charger is set to switch to Float at the right voltage and current.

    But if your panels only produce for 5 hours and Bulk lasts for three, you may have a problem. :-)
    SMA SB 3000, old BP panels.
  • BB.BB. Super Moderators, Administrators Posts: 32,008 admin
    Re: Time for Upgrade, Comments needed

    Probably, ~2 hours during summer and ~4 hours during winter (yea--absorb if there is daylight) as a start.

    Monitor the specific gravity and water usage... If you need to refill a cell roughly every 2 months--Probably doing OK.

    If you are using very little water, you need to up the absorb time (and possibly voltage a bit too). If you are refilling the batteries once a month or more often, back down on the charging parameters.

    Of course, this also depends on you getting over 90% state of charge a couple times a week. If you don't have enough panels/sun to replace the power used--then you need to do something (boost with generator, cut back on power usage, add panels, etc.).

    The deeper you discharge the battery bank, the more absorb time (and possibly higher voltage) you will need.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • dishxpertdishxpert Registered Users Posts: 22
    Re: Time for Upgrade, Comments needed

    Thanks alot, i will increase my absorb time to 2 hours and see...
  • dishxpertdishxpert Registered Users Posts: 22
    Re: Time for Upgrade, Comments needed
    inetdog wrote: »
    The right answer to that is that you should see what the battery SOC (as determined using the hydrometer) is at the end of the hour of Absorb. If it goes down steadily day by day, your Absorb is too short.

    I invested in a cheap Deca hydrometer today. At the end of 1 hour of Absorb stage, my trimetric was reading 98% full and SC was in the white region, 1.250-1.260.

    Whats my next move? Should i equalize to get it in the green (>1.260)?
  • BB.BB. Super Moderators, Administrators Posts: 32,008 admin
    Re: Time for Upgrade, Comments needed

    Equalize means to recharge the "low cells" even though the high SG cells read 100% charged. I.e., you are trying to reduce the spread of SG from ~0.015 to 0.030 or worse, to near zero spread.

    What you need to do is recharge the battery bank to "full charge". But, you really do not know what "full charge" is for your battery bank yet.

    So... You can set to absorb voltage (~29 volts typically) and recharge until all cells are bubbling equally, and that none of the cell SG is rising (read SG every ~30 minutes). Once the SG has stopped rising, then log the temperature compensated SG for all cells--And that is your "new" 100% full charge. Normally, you would be just reading one cell (your pilot cell for day to day or week to week verification of state of charge--You only need to check all cells when equalizing or finding your 100% state of charge).

    For equalization, you typically set the charging voltage to ~30-31 volts (you want the charging current to be about 5% of the battery bank 20 Hour AH capacity--I.e., a 200 AH battery bank would be ~10 amps equalizing current) and you check the cells as you charge (every 30 minutes) until they stop rising--then stop charging.

    "Equalizing" is hard on a battery bank--You only want to do it when needed (if spread of SG is > ~0.015 to 0.030 or greater. Some Vendors recommend equalizing every couple months for their flooded cell batteries (find the manual for your batteries and see what they recommend). In some cases, their numbers are quite different (Exide tends to have much higher voltages recommended--If I recall correctly). Monitoring water usage (top off a flooded cell every couple months is usually "about right") and battery temperature/bubbling activity (not too hot, not too much bubbling) usually gives you a good indication that everything is happy with your battery bank. Lone cells that bubble excessively or not at all may be signs of impending trouble.

    And when charging to 100% or equalizing, you want to monitor the battery bank temperature and ensure that it does not exceed factory maximum specifications (if it does, stop charging, let cool, then resume equalization/100% charging later).

    And for normal operation, you want to ensure your battery bank is >90% SOC several times per week. Don't try to get 100% every time (or every day of week)--That is hard on the battery bank and may use a lot of distilled water.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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