questions about conditioning/equalizing charge for AGM sun extender battery.

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grunt
grunt Solar Expert Posts: 37 ✭✭
in Off Grid Solar & Battery Systems #1
I have 8 sun extender 6 volt batteries (pvx-224OT) for my 48volt back up system. It is almost 3 years old iirc and is showing some moderate signs of capacity loss. I run a full charging cycle once a month as maintenance. They run at float voltage from sun down to sun up and only get used in case of a power failure. My question has to do with applying an equalizing charge to the bank. The owners manual that comes with the batteries explains all the recommended voltages to run for a 6 and 12 volt battery for a charging cycle but in the section out lined for applying an equalizing charge just states 15.5 volts for 8 hours after the normal charge cycle. It does not discriminate as to what battery size ( 6volt or 12 volt) that this charge is supposed to be applied to. I am missing some thing here. Any help would be greatly appreciated.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,443 admin
    #2
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    Re: questions about conditioning/equalizing charge for AGM sun extender battery.

    Typically that would be 15.5 volts for a "12 volt battery bank"... 24 volts would be ~31 volt equalize and so on...

    More or less, it is not really the voltage but the current that is feed into an equalizing bank (typically, not to exceed 5% rate of charge). Higher than that is hard on the plates and will heat the battery bank up (need to monitor bank temperature).

    If your batteries mostly sit in float and are deep cycle (not telcom/UPS batteries designed for "float service")--Cycle them to 75% or even possible near 50% state of charge--At this point, you (appear to) have nothing to lose. Cycle then recharge a few times and see if they get better no not.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #3
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    Re: questions about conditioning/equalizing charge for AGM sun extender battery.

    i would ask how you know the bank has lost capacity?

    please tell us the current charging parameters you currently have and what kind of source like as in solar, wind, etc through what controller. for solar be sure to tell us the absorb voltage and the float voltage set points.

    do cycle the batteries down to say 50% -75% soc as bb suggested a few times and make sure they get their full charge before instituting the next drain. (these are not telcom batteries bill) as to the eq this should be done only as a last resort so get that out of your head for now. if you have a dvm or dmm to measure the at rest voltages of the batteries individually with nothing into or out of them for at least 3 hours (basically disconnected from everything). please do so and accurately report this back to us. this will be a running log book. designate each battery for identifying what battery has what voltage. for instance starting from the + output for the full 48v that battery may be #1 and then progressively go back to the 8th battery that is connected to the 48v - connection. the battery position can be designated too if we opt to have you switch batteries from their current positions. this may be a, b, c, etc and start from the same point you do when labeling each battery, but let's see where we stand before you opt to move any batteries around for we may make other suggestions.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,443 admin
    #4
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    Re: questions about conditioning/equalizing charge for AGM sun extender battery.

    From the Working FAQ Thread:

    http://forum.solar-electric.com/showthread.php?5556-Working-Thread-for-Solar-Beginner-Post-FAQ

    We get questions about how to "recover" a sulfated/failed battery--Here is some information about AGM battery "recovery":
    mtdoc wrote: »
    FWIW there are some AGMs that claim to have a shelf life of "up to 2 years at 25* C".

    Perhaps this is just marketing hype?

    Checking the voltage at rest is a good idea.

    BB. wrote: »
    Here is a thread how one company (Concorde) recommends to "recover" their AGMs... Not supposed to apply to any other brands of AGMs:

    Sulfated Lifeline Concorde AGM Batteries

    And here is a great thread from DapDan with information on how one place recommends to restore AGM batteries (new catalyst caps, adding water to cell, etc.):

    Low rest voltage on GNB absolyte IIP cells

    In the end, trying to do "extreme" things to batteries should be done in a safe area and always under some sort of supervision/monitoring (don't want to overheat the cells and blow acid around) and performed while wearing appropriate safety gear/gloves/face shield/water/hose/baking soda nearby/etc.).

    And--if the cells are otherwise scrap--if you can try some of the above things (if done safely)--you are not loosing much anyway.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • CaptainMitch
    CaptainMitch Registered Users, Users Awaiting Email Confirmation Posts: 2 ✭
    #5
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    I have two 8D, Deep Cycle AGM's which are absolutely sulfated.  In the past I have successfully performed conditioning charges on Gel batts. But no experience with AGM's. With Gel's, following Nigel calder's advice, I drained the battery down to under 1 volt before recharging.  I guess that in addition to cooking off sulfation it "reset's the battery memory (so to speak). These are expensive batteries that were new in November 2014. They were continuously used for a year then the boat has been at the dock ever since and the float voltages have killed it.  Anyone.. please send me your experiences with AGM's.   safeships2@yahoo.com
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  • Marc Kurth
    Marc Kurth Solar Expert Posts: 1,144 ✭✭✭✭
    #6
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    What brand AGM's you have? AGM's are not all the same, anymore than other types of batteries are.
    What makes you say that they are "absolutely sulfated?"
    What makes you say that the float voltage killed them?

    Very importantly, what was your deep discharge recovery procedure after forcing the voltage so low?  

    Marc

    I always have more questions than answers. That's the nature of life.
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #7
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    I'm no expert on AGMs - others here are , but how do you know they're "absolutely sulfated" from sitting at float voltages at the dock? AFAIK, the only way to really know that for sure would be to cut the battery open.

    Sulfation happens when batteries sit in a low state of charge for a period of time. Sulfation itself is a normal part of the battery cycling. The problem is when it's allowed to harden to the point charging can't reverse it. If the batteries were properly floating, sulfation wouldn't be my first guess for damage.

    If you try to "cook it off" with an AGM it will vent gas and permanently lose capacity. My first guess is the batteries were charged too often at too high voltage, and either vented, or developed voids between active material and plates, especially if the boat is in a warm climate and the charger doesn't have a remote temp sensor to adjust charge/float voltage.

    Also, AFAIK, there is no memory effect in a lead acid battery. I know Nigel Caulder is much respected in boat restoration and maintenance, but I would need to be persuaded on this one.
    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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  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    edited August 2017 #8
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    I suspect that there are many chargers that don't do float correctly.    IMO, the best ones charge intermittently and are also adaptive - ie, they gradually learn what float voltage/time is needed to maintain full charge without any over charge.  A simple temperature adjusted fixed voltage is overly simplistic.

    I am available for custom hardware/firmware development

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  • CaptainMitch
    CaptainMitch Registered Users, Users Awaiting Email Confirmation Posts: 2 ✭
    #9
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    Thanks for replies: They are LIFELINE 8 D AGMs.  I say absolutely sulfated because, once taken off charge the voltage drops precipitously with no corresponding amp-hour loss.  My electronics shows amp hours consumed and replaced. With normal loads I can operate for 2-3 days without recharging. In current status I have less than 2 hours until voltage is below 12.0 or less.  What killed them is lack of full discharge before recharging. No cycling through full range.  I think I had the float voltage set at 14.2 which is probably too high.  Appreciate all comments. Anyone have experience on reconstituting as I explained in original post.?
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  • jonr
    jonr Solar Expert Posts: 1,386 ✭✭✭✭
    edited August 2017 #10
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    I'd like to see data supporting this idea that AGM batteries benefit from being cycled.   14.2V float is crazy high and certainly killed your batteries.  13.6V would be more typical.  I doubt yours can be fixed.

    I am available for custom hardware/firmware development

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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #11
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    I would try a charge/discharge cycle on each battery separately. It's at least possible a single cell failed.
    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: 1,144 ✭✭✭✭
    edited August 2017 #12
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    CaptainMitch said:
    Thanks for replies: They are LIFELINE 8 D AGMs.  I say absolutely sulfated because, once taken off charge the voltage drops precipitously with no corresponding amp-hour loss.  My electronics shows amp hours consumed and replaced. With normal loads I can operate for 2-3 days without recharging. In current status I have less than 2 hours until voltage is below 12.0 or less.  What killed them is lack of full discharge before recharging. No cycling through full range.  I think I had the float voltage set at 14.2 which is probably too high.  Appreciate all comments. Anyone have experience on reconstituting as I explained in original post.?

    Yes, many, many times with Lifeline 8D's specifically. I need more info before I can offer the best path to take now.
    What is the standing voltage?
    What is the date code on the batteries?


    I always have more questions than answers. That's the nature of life.
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  • Marc Kurth
    Marc Kurth Solar Expert Posts: 1,144 ✭✭✭✭
    edited August 2017 #13
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    Another approach is: I always suggest contacting your Lifeline distributor for help! 
    I always have more questions than answers. That's the nature of life.
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