Battery Genius Question: What is the tradeoff for higher 20h capacity L16 batteries?

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benthere
benthere Solar Expert Posts: 113 ✭✭✭
Hi all,

I'm thinking about how much more life my 5-year-old Rolls S600 battery bank has in it and what the failure mode is likely to be. Hopefully nothing dramatic!

Anyway, I'm wondering - a little late maybe - what I traded away when I got a 450AH L16 instead of a 325AH L16. Judging by the spec-sheets, the higher capacity batteries weigh more and so may have less room for sediment at the bottom before they short? Does anyone know the answer?

My thinking, when I selected the higher capacity batteries, was that by going to the 450AH batteries I kept it to one string and avoided the problems inherent to parallel strings.

PS. There are no signs of problems with the battery bank, I'm just trying to think ahead.

Comments

  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
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    Re: Battery Genius Question: What is the tradeoff for higher 20h capacity L16 batteries?

    there are many threads here about Rolls batteries and their need of higher than 'normal' charge voltages and time per charge phase in order to achieve the 'expected' lifespan for those batteries..

    I suggest a forum search for Rolls and a lot of reading.

    hth
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
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    Re: Battery Genius Question: What is the tradeoff for higher 20h capacity L16 batteries?

    Hi benthere,

    Generally, L-16 are good for at least 5 years. 8 years is great. You appear to have a single string at 48 V. Good decision on not having multiple strings! In my opinion, more than 5 years is all gravy. And since you have 5 years service from them, you appear to be doing things correctly in caring for them.

    Generally batteries in cyclic use have one failure mode that is a shorted cell, and another that is a high impedance cell. In my limited experience with L-16s, high Z is more common than a shorted cell, or one that has high self discharge.

    IN my personal experience with Surrette Flooded batteries, they do NOT require high charge voltages. The ONLY exceptions that I have read about was one chap that said that he had Lead Calcium Flooded Surrettesc that required 64 V Absorbs. This is 5.5 volts higher than ANY of the Surrette Flooded batteries in use here require. AND, some folks who are Grid Tied/Grid Interactive may have screwy Absorb or Float voltage settings. This high Absorb voltage requirement appear to be some sort of myth, based on what I have seen here.

    Am just speaking of the Surrette S-530s and 4KS25sFLAs that have been in service for nine years here.

    Bottom line, it appears that all that you are doing is working well. Would just recommend that you continue to monitor SGs and continue what you are doing.

    Simply my observations from actually USING Surrette Flooded batteries in off-grid cyclic applications. YMMV Good Luck, Vic
    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.
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
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    Re: Battery Genius Question: What is the tradeoff for higher 20h capacity L16 batteries?
    westbranch wrote: »
    there are many threads here about Rolls batteries and their need of higher than 'normal' charge voltages and time per charge phase in order to achieve the 'expected' lifespan for those batteries..

    There are threads about other industrial batteries needing higher than 'normal' charge voltages. With RE charging, you only have two parameters: absorb time and absorb voltage. When you don't have enough time (because the sun sets), you can compensate a bit by raising the voltage.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
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    Re: Battery Genius Question: What is the tradeoff for higher 20h capacity L16 batteries?

    I'm also a Surrette user and agree with both Vic and vtmaps.
    One difference I found in the failure mode however (in my last bank which were not surrette) was that they simply lost capacity. SG and no load voltage remained good to the end, but they could no longer sustain any useful load. Another thing of interest is that I had 3 parallel strings, and I later realized that when one string failed, the other two did a good job of covering for the bad string, until finally the last string said good bye. They were by the way, 11 years old when they earned their retirement. They had an easy life, probably never drained more than 10% below full charge. And yes, I'm aware that some say they should at least once in a while be taken down to the 50% state to extend their lives, I never once did that, nor, right or wrong, am I doing it now with the Surrettes.
    I made sure the new bank was one single string and chose Surrette because being made here, I could pick them up at the factory door, but also they are among the very few, or only two volt L16 batteries that are manufactured as a single cell, instead of a 3 cell, six volt battery (L16) rewired internally for 2 volts. Thus each Surrette 2 volt L16 has only one single fill cap for checking electrolyte level and SG, instead of three.
  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
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    Re: Battery Genius Question: What is the tradeoff for higher 20h capacity L16 batteries?

    Here is the expected life of a Battery based on capacity and re-charge. It's hard to know if it actually is true or not. I do think it represents how the life of a battery as far as capacity goes, you start with it's first cycles lower than it's 100% capacity, you then have the sweet years and then it begins a down hill slide until it no longer keep's up with system demands. From this explanation ( if you buy it ) don't over charge to meet some unrealistic expectation of 100% recharges everyday because someone says it the only way.

    For those of you that want to know how a Battery filled with 1.265 Electrolyte can climb to a 1.280 reading during a over charging Equalization, the answer is below. It comes from the lead sulfate trapped in the lead when the plates are formed and then released during shedding.


    Attachment not found.

    .
    Short Story : I once bought a New Cadillac that had a Amber and Green light on the dash that told you when you were getting the best gas mileage based on engine vacuum pressure, I thought how cool is that. After watching it for a while it began to drive me crazy as they switched back and forth. It took all of the pleasure out of driving the car and became obsessive. I finally covered them with electrical tape and started to enjoy life. I know if your being too obsessive about batteries it's not worth the effort, do your best and remember, their expendable.
    .
  • SolInvictus
    SolInvictus Solar Expert Posts: 138
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    Re: Battery Genius Question: What is the tradeoff for higher 20h capacity L16 batteries?
    Vic wrote: »
    Generally batteries in cyclic use have one failure mode that is a shorted cell, and another that is a high impedance cell. In my limited experience with L-16s, high Z is more common than a shorted cell, or one that has high self discharge.
    Based on my experience over 23 years with a total of 16 L-16 batteries, the only failure I have observed is the specific gravity of the electrolyte decreasing and charging being unable to restore it. Cell 2 is dying because my rely switched charge controller malfunctioned, and I did not catch it before the battery was over-charged.

    ... date .... | time|temp|volt| density (g/cm^3)
    ... (MST) ...|(24hr)|(F) | (V)|cell 0 |cell 1 |cell 2
    2013-10-03| 13:00| 71|6.79| 1.260| 1.265| 1.265
    2013-12-22| 15:30| 42|6.90| 1.240| 1.245| 1.200
    2014-01-05| 15:25| 43|7.05| 1.245| 1.265| 1.200
    2014-03-12| 12:15| 53|6.82| 1.275| 1.280| 1.160
  • BB.
    BB. Super Moderators, Administrators Posts: 33,442 admin
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    Re: Battery Genius Question: What is the tradeoff for higher 20h capacity L16 batteries?

    More or less, decreasing specific gravity in one cell sounds like a "partially" shorted cell.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset