Questioning myself

bajarickbajarick Registered Users Posts: 2
Hello,
I've been off grid for 12 years. Started out with 4 costco 6v batteries for 4 years then went to 8 Surrete 530 400 ah when we got an electric fridge. 1600 watts of panels. Batteries never went below 80%. Surretes lasted til last summer when one bank wouldn't come up. The other bank started going down and I started researching replacement options. We use about 50 amp hours a night during the winter and about 100 in the summer running fans. I almost got 4 CS Surrettes, 680 ah, but decided to try just 4 surrette 550's  428 ah. They've been in for a month now and I'm at 24.5 using 60 ah overnight. I had expected to be higher than that only using 60ah. Any hints or am I just expecting too much? 24 volt system, Outback CC and Inverter. Batteries usually floating by noon. 
Rick

Comments

  • BB.BB. Super Moderators, Administrators Posts: 29,634 admin
    Battery voltage is an in-exact method of measuring battery state of charge. Do you have a hydrometer (remember to rinse with distilled water several times before putting away to dry--Otherwise the floats can become sticky)?

    https://www.solar-electric.com/midnite-solar-battery-hydrometer.html

    To give you an idea of what the variations in Lead Acid voltages can look like:

    http://www.scubaengineer.com/documents/lead_acid_battery_charging_graphs.pdf

    Also--Many (some/all?) Rolls/Surrett batteries are known to need relatively high absorb (charging) voltage--And can require very high equalization voltage (upwards of 32 volts for a 24 volt battery bank--You want to see somewhere around 2.5% to 5% charging current during equalization--And that is enough to get the batteries very hot--Monitor temperature, shut down EQ charging until the next day to cool down the bank, if needed) and many hours (sometimes spread over a few days) to get battery cells balanced, SG back to "full charge", and such.

    Have you measured the voltage across each cell (or battery) to see how much variation you are seeing?

    -Bill


    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • EstragonEstragon Registered Users Posts: 4,092 ✭✭✭✭✭
    New batteries apparently may need a few dozen cycles to come up to full capacity. US battery used to (still does?) make a bit of a thing about their batteries getting up to full capacity in fewer cycles. Maybe some take more than others? Could just be marketing but maybe you'll see it improve with some cycling.

    I would definitely still check SG as Bill suggested.
    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. Super Moderators, Administrators Posts: 29,634 admin
    As Estragon says, "deep" cycling lead acid deep cycle batteries is good for them (and helps "form" the plates in new batteries)... Discharge them to somewhere around 75% to 50% State of Charge -- Even it if means turning off the solar panels for a day or so. Cycling to 85% SoC or less is "shallow cycling" and not great for the batteries either.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • bajarickbajarick Registered Users Posts: 2
    Thanks for the replies. Hydrometer reading were very close to what the Trimetric, Mate, and MX were telling me. A bit higher. Working the batteries more is what I was wondering about my last set. I am running a fan at night to see how low it will go....so far about 24.5. And, the last set I had took a while to really get working. 
  • mike95490mike95490 Solar Expert Posts: 8,417 ✭✭✭✭✭
    bajarick said:
    ...... Batteries usually floating by noon. Rick
    How much time do they spend in Absorb ?   i suspect Absorb is not long enough, or the bulk voltage is too low
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

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