Battery charging regime

SpikeandKari
SpikeandKari Registered Users Posts: 7 ✭✭
in Off Grid Solar & Battery Systems #1
Hi, new user (so ignorant!) so please excuse simple question. I'm setting up a Sunny Island 3 KW with four Rolls 290AH batteries in series connected to a Sunny Boy PV inverter with 3kw of panels. Most of the AC generated will be used for water pumping during the day. My question is that the Rolls charging regime is to finish the constant voltage phase of charging determined by the current dropping to a small fraction of the initial constant current phase. The Sunny Island however does everything by timers so how do I work out what the timers should be set to?

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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,102 ✭✭✭✭✭
    #2
    Is your Sunny Island inverter 24 volts nominal?  All I have found is 48 volt versions of the "Island" line. I am asking because you seem to be setting up a 24 volt battery bank.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

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  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    #3

    Hi SpikeandKari,

    Many battery manufacturers DO specify Finishing current,  or Ending Amps as a method of terminating the Absorption charge stage.  For Flooded batteries,  this is often  1 - 3% of 20 hour Capacity.

    A number of Solar Charge Controllers have the ability of ending Abosrb based on the output current being delivered by the CC,  which will also include any load current on the inverter,  etc.  Several CCs can use the actual battery charge current to terminate Absorb.

    For AGM batteries,  many manufacturers specify the a rate-of-change in battery charge current as the terminator.   Have not seen any Solar CCs that can do this.

    As you know,  the amount of time to fully charge a battery during Absorb will depend on the Depth Of Discharge that the battery experienced in the previous discharge,   so using time as the only Absorb terminator  can cause some error in the length of Absorb.

    Are you looking at AGM batteries for this system?

    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
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  • SpikeandKari
    SpikeandKari Registered Users Posts: 7 ✭✭
    #4
    Hi and thanks for your comments. For information the four AGM Rolls batteries are connected in series as a 48 volt bank. I already have all the components of the system so have to work with what I have. My previous off grid experience is on boats where every battery charger and for that matter solar regulator I have used has terminated the constant voltage phase by reference to the charging current falling to a fraction of the initial charging current in the constant current phase so therefore very surprised to find the sophisticated SMA Sunny Island (and what a daft model name!) only using timers! Thanks for Looking, Spike 
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