AGM battery charging

stmar
stmar Solar Expert Posts: 373 ✭✭✭
in Old Battery Tech Discussions #1
Conext SW4024, solar array, 4 X 6volt 400ah Lifeline AGMs, Morningstar PS30 PWM solar controller.
With the SW4024 it goes to pass through at 26.5 volts, uses no battery power. During the day the array keeps the batteries at high 27's to low 28's and battery power is utilized for loads along with the grid. When the sun goes down the voltage drops of course and with my Sunfrost RF16 it draws the voltage down to the mid to high 25's. My question: Is this kind of daily exercise and fluctuation good? I have had the new inverter for a few months now and I have only seen it go into charge mode one time, that is triggered when the voltage is below 25 or when the grid comes back up after an outage.
This is a different philosophy than my old Trace, it kept the batteries at Float, 26.8, all the time, constantly charging when grid and/or solar were available. Seems like the new unit should utilize the produced power more efficiently.
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #2
    IMO, battery charge/float regime should start with battery manyfacturers recomended values, and adjusted if need be based on your specific application. It shouldn't be based on what a charge controller thinks it should be.

    I don't know about your Lifelines in particular, but 28+v seems to me to be fairly high to hold an AGM all day unless it's cool/cold. Some makers recommend higher voltages than others though, so you may want to check your specific batteries.
    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
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  • stmar
    stmar Solar Expert Posts: 373 ✭✭✭
    #3
    I misspoke, the 28 volts is the max, it does not constantly stay at that depending on power usage during the day. Lifeline AGMs do handle higher voltages than other AGMs, you can even equalize/condition them like regular flooded batteries. My main concern was overnight with the voltage dips.
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #4
    Fully charged "resting" voltage is ~25.5, so it sounds like they're staying +/- fully charged overnight.

    In this application, I'm not sure it's really necessary or desirable to go much higher than float voltage every day though.
    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
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  • Marc Kurth
    Marc Kurth Solar Expert Posts: 1,186 ✭✭✭✭
    edited September 2018 #5
    stmar said:
    I misspoke, the 28 volts is the max, it does not constantly stay at that depending on power usage during the day. Lifeline AGMs do handle higher voltages than other AGMs, you can even equalize/condition them like regular flooded batteries. My main concern was overnight with the voltage dips.
    Couple of quick comments, based on standard temp 77F (25C):

    Lifeline's like lower voltages than some other AGM's. (It's higher current that they like)
    Float 26.4v to 26.6v
    Bulk/Absorb: 28.4v to 28.8v
    Your 400 ah battery bank is only considered fully charged when the current draw drops to 2 amps when charging at the Absorb voltage.
    If the battery bank is fully charged, you don't want to hold it at 28v. This will gradually dry them out. I have seen expensive battery banks destroyed because they were floating at 27.6v to 27.8v continuously for 12 months.
    Static voltage (at rest) is 26.0v for Concorde Lifeline/Sun Xtender batteries up to about 5-7 years old,
    Expect to see 25.8v in years 6-9, then 25.6v for the duration.
    If you see 25.4v or lower after fully charging, it is likely time to equalize. In my experience, equalizing at 30v for 2-4 hours is a starting point if your battery bank will not accept a full charge. In some cases where the sulfation was allowed to get out of control from gross undercharging, an 8 hour equalizing run is required. Sometimes twice at 8 hours.

    Marc



    I always have more questions than answers. That's the nature of life.
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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #6
    @Marc Kurth said 
    Your 400 ah battery bank is only considered fully charged when the current draw drops to 2 amps when charging at the Absorb voltage. 


    Not questioning your knowledge but that seems very low, 0.5% capacity 
    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.  
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  • Marc Kurth
    Marc Kurth Solar Expert Posts: 1,186 ✭✭✭✭
    edited September 2018 #7
    Yes, Sir - I know that it seems crazy. It falls in the same category as their extremely high maximum charge rate.
    In fact, most people don't believe it when I say it, but that is straight from both the Sun Xtender and Lifeline manuals. When I first learned that about 12 years ago, it sounded questionable, so I confirmed it with their chief engineer. It has proven to be true in the hundreds of projects that we have been involved in.
    Typical time in Absorb is 2-4 hours to reach this low current.
    See page 19 in the Tech Manual: http://centexbatteries.com/lifelinetech.pdf
    As I tend to repeat, all AGM's are not the same.

    I always have more questions than answers. That's the nature of life.
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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,970 ✭✭✭✭✭✭
    edited September 2018 #8
    When in doubt read the manual.  ;)  Sometimes you have to have them pay you to read it...  
    I rescued a few AGM banks during the recent fires because the installers could not get into the area.
    Lucky I had my Marc Kurth cheat sheet because the internet was out. 

    Lot's of flooded batteries in the Carolina's. Crossing my fingers for a few friends back there. YUK. Nice u-tube below on the storm.
    https://www.youtube.com/watch?v=V3U6D1C-sjM

    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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