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Thread: partial charges

  1. #1
    It's easy being green. recumelectric's Avatar
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    partial charges

    Can you partially charge an SLA battery and then ride without doing damage? I'm talking about going to work, charging for a while, and then going off to another site before hitting maximum charge. I've just been all over the internet trying to find an answer to this question, and I can't find one.
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    P7 Fanboy JinbaIttai's Avatar
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    It's bad to partial charge lead acid batteries. I can't remember why exactly, and no longer have access to the book which explained it.

    I'm thinking it also causes sulfation.


    Here's something to back up my memory:
    http://209.85.173.132/search?q=cache...ient=firefox-a

    Look at page 4, first two paragraphs.

    Hope this helps, not too much on the internet on the subject.

  3. #3
    It's easy being green. recumelectric's Avatar
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    I can't get page 4. It ended after page 3.
    When I ride, the troubles just roll off my back.

    Originally Posted by Cody Broken :
    Every ride is a mission, a race, an adventure, a quest.
    Every bike is noble steed, a stalwart machine, a clever device, a stealthy speedster.

  4. #4
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    What kills SLAs are deep discharges. Sulfation starts in the discharge state. You need to charge the battery asap after every use.
    Shallow discharge/charge cycles are ok. Bottom line you should charge them after every use as soon as it is possible.

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    P7 Fanboy JinbaIttai's Avatar
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    Quote Originally Posted by recumelectric View Post
    I can't get page 4. It ended after page 3.


    INTERMEDIATE FULL CHARGE CYCLES
    An observation early in the testing required a change
    in the test procedure. The original intent had been to
    perform several partial charge/discharge cycles in
    sequence. For example, charge to 68Ah input, discharge,
    then charge to 68Ah input and so on until the four
    complete cycles at 68Ah input were complete. Then fully
    charge and discharge the battery before proceeding with
    the next level. It was seen early in the testing that this
    was not going to work, as the capacity resulting from
    68Ah input dropped with each succeeding cycle when no
    full charge cycles were performed between partial charge
    cycles. Therefore a full charge and discharge cycle was
    added between each partial charge/discharge cycle.
    This result has important implications to operational
    PV systems. That is, if a battery is partially charged for
    several consecutive cycles (for example, the array is
    marginally sized and there is a series of less than full sun
    days in the winter) the useable battery capacity decreases
    each cycle, even though the same amount of energy has
    been presented to the battery each day. This is the result
    of battery inefficiencies, electrolyte stratification, and
    sulfate buildup during these partial charges.

    An
    associated full charge, with its attendant gassing, is
    needed to destratify the electrolyte and remove the
    residual sulfate. This sulfate buildup can become a
    problem if this pattern continues for several months. In
    the short term it can be reversed by a full “equalizing”
    type charge, which, in most cases is not possible in small
    PV systems. Battery equalization requires a PV charge
    controller that has been specifically designed to include
    this function. At low charge rates (for example, less than
    C/40) equalization may not be possible because of
    charging time limitations. In any case, this reduction in
    useable capacity will impact system availability and
    should be understood....

  6. #6
    P7 Fanboy JinbaIttai's Avatar
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    Even though you are talking about doing something a little different (a partial charge and then a full charge, instead of consecutive partial charges), I think the advice still applies. Once the battery is sulfated, it is difficult to break the crystals off and would require an equalizer battery charge or a sulfation circuit to get it back to normal again. But then considering that SLA don't live that long, maybe we're only talking about shortening the life from 200 cycles to 175 cycles. It might be worth the convenience to lose 25 cycles. Or maybe it's 10 cycles. Or 50?

  7. #7
    put our Heads Together cerewa's Avatar
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    Here's one way to think about it -

    it appears that sulfation is likely to result, to some degree.

    But how much?

    Looks to me like if you use 10 amp hours and do a full recharge, you get a certain amount of sulfation.

    If you use 5 amp hours, recharge 2 of them, and then use another 5 amp hours, you probably get LESS harm to the battery than if you had just used the 10 amp hours without a recharge in between... but more than if you had just used 5, fully recharged, and used 5 again.
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    Quote Originally Posted by recumelectric View Post
    Can you partially charge an SLA battery and then ride without doing damage? I'm talking about going to work, charging for a while, and then going off to another site before hitting maximum charge. I've just been all over the internet trying to find an answer to this question, and I can't find one.
    With SLA - you should always apply a charge (small or large current, long or short) to this chemistry as soon as possible after drain - within proper temperature limits of course! Doing so will help minimize plate sulfation. So yes, you can partially discharge and apply repeated charge cycles and no excessive damage will occur. In fact, your SLA will last longer if you do apply a charge - even a trickle charge - immediately following use.

    However, if doing this puts the battery into deep discharge condition - you will cause damage but only as a result of draining too much current from the battery during your duty cycle. Having nothing to do with repeated charging.

    I have gone through several sets of SLA with my GoPed ESR750EX and during errands I'm always looking for an outlet to plug-in if even for a moment because of the increased battery life I get from this practice.

  9. #9
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    Quote Originally Posted by gmouchawar View Post
    What kills SLAs are deep discharges. Sulfation starts in the discharge state. You need to charge the battery asap after every use.
    Shallow discharge/charge cycles are ok. Bottom line you should charge them after every use as soon as it is possible.
    Yes, yes, yes - I missed this before posting my long reply but he's saying the same thing I said.

    The article is talking accumulative discharge condition within a PV system. In other words, deep discharge of the battery without enough recharging. Different animal.

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