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FLA Calendar Life vs Cycle Life

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  • FLA Calendar Life vs Cycle Life

    If a flooded lead-acid battery bank is used in a hybrid setup mostly as an anchor to keep the solar shed from blowing away in high winds, how long would it be expected to last under proper care? I'm assuming what would be involved is an automatic watering system and at least monthly SG checks, and a float charge maintained while the AC power sloshes back and forth between the PV system and the grid.

    The Surrettes are rated at 3300 cycles to 50% depth of discharge and the promo material makes noises about a 15-year lifetime. If the batteries only get cycled down to 50% DOD, say, 5-10 times a year due to the usual power outages we get out here in the backwoods, is that lifespan a realistic one?

    And yes, I do realize that this is a dumb investment, a pad-mounted genset would make much better economic sense, etc. etc. Believe me, I've read enough (and been disappointed enough) about our mostly hundred-year old battery technology to acknowledge Sunking's well-articulated points on that score. Call it a deluded guy's expensive hobby, or the fever dreams of a peak-oil nut job, or both, but I do plan to go ahead with the hybrid system anyhow.

  • #2
    I have 11 years on a set of good quality batteries in full off grid system. I dont know what there capacity is now but they still do what I need them to.

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    • #3
      I've got a battery bank in our weekend cabin made up of "Costco" golf cart batteries. They spend the bulk of their time in float and get used about 20-25 weekends a year. Installed them in March 2010 and they still function as they always have. I don't think you need an automatic watering system. Mine only need water about once a year.

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      • #4
        NorthRick what size are they and how many are you using? Any idea how deeply you discharge them during your weekend usage?

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        • #5
          Originally posted by BackwoodsEE View Post
          NorthRick what size are they and how many are you using? Any idea how deeply you discharge them during your weekend usage?
          A total of six 210amphr 6 volt batteries. Wired 2S3P (yeah, I know not ideal). Degree of discharge varies a lot depending on who's there and the weather. Occasionally they get drawn down to where the battery status light on the PWM charge controller goes yellow. I think that is at 12.1 volts. That would be with a load on so I don't know what SOC that really represents. It's usually my clue to fire up the generator.

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          • #6
            BackwoodsEE

            You will need to bubble the electrolyte periodically, to prevent stratification.
            A Float Charge won't do that.

            Heat will affect the calendar life.
            The number of cycles will affect the calendar life
            Depth of discharge will affect the calendar life
            Low SOC will affect the calendar life.
            Habitual over-charging will affect the calendar
            Low electrolyte level will affect calendar life
            Stratification will affect calendar life

            Do your best to minimize the negative effects from all of the above, to maximize calendar life.

            Each "Formatting" cycle increases the capacity.
            Maybe the "Formatting" process can be manipulated to maximize calendar life?

            Long term an FLA battery used in a standby system with suffer from Grid Corrosion.
            There is always the chance of a manufacturing defect that will cause early battery failure.

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            • #7
              Every battery manufacturer out there spins the numbers and can back it up with test data. But all of it is garbage.

              Great example is cycle life. What you do not know is how that number is determined. It is done in a Lab under ideal conditions. They can do as many as 6 cycles in a day, Say they claim 1500 cycles at 50% DOD would leave you the consumer thinking at least 5 years, But after 3 years you notice they are tired and need replaced. What happened is Calander Life expired. What is Calander Life? All you have to do is look at the warranty. Those batteries you thought you could get 1500 cycles only had a 2 year warranty.
              MSEE, PE

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              • #8
                Originally posted by Sunking View Post
                [...] What is Calander Life? All you have to do is look at the warranty. Those batteries you thought you could get 1500 cycles only had a 2 year warranty.
                Ergo, the batteries bought by Bala must have a 11+ year warranty, and those by NorthRick must have a 8+ year warranty (despite being wired up in a 'self destructive' configuration). Well done I say.

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