Preventing stratification in tall cells

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stephendv
stephendv Solar Expert Posts: 1,571 ✭✭
in Off Grid Solar & Battery Systems #1
When charging my batts I very rarely see them reach their full 1.29 SG reading... only ever seen it after an EQ charge. Even if I absorb for 4 hours, the SG only reaches 1.28 or 1.285. So, I've been thinking of 2 ways to get some more gassing and mixing in the cells:
1. A higher voltage absorb every week, e.g. 2.5V per cell instead of 2.4V for 3 hours, or
2. A short EQ charge every week, e.g. 2.65V per cell for 1 hour

...or just stick to the more standard approach and EQ every 60 days at 2.65V for 3 hours ? My concern with this approach is that the electrolyte has 60 days to stratify.
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #2
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    Re: Preventing stratification in tall cells

    Personally I would try a short EQ every wk. A number of short EQs shouldn't do any more damage to the plates than one long one, and unless the SG in different cells starts drifting in value, these relatively frequent but short EQs could totally replace the standard long one. Keeping track of the SG would show if that were the case.
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  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    #3
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    Re: Preventing stratification in tall cells

    This is one of the big problems using very tall wet cells with solar. There us usually not enough time after the cells reach "full" to give then a good vigerous charge. They really can only get enough equualizing charge if a good mains battery charger is used
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  • Derik
    Derik Solar Expert Posts: 82 ✭✭✭✭
    #4
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    Re: Preventing stratification in tall cells

    My L-16 RE trojans are suppose to be at 1.265 fully charged, and not equalized until sg is less than 1.250.
    My normal sg after a few days of full sun is between 1.250 and 1.255. I almost never equalize my batteries due to them always being in sync and never or almost never below the 1.250.

    Observe your batteries at the end of the Absorb cycle, if they are gassing and bubbling and your adding water once every few months I would think they were mixing?

    I am not sure that more equalizing is the answer, being 90-95% charged daily may be better for your batteries than equalizing them once a week?
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #5
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    Re: Preventing stratification in tall cells

    The thing is that the damage caused by stratification is a very long term thing. If the acid has a density of 1.29 at fully charged, and I'm measuring only 1.28- but it won't rise any more unless I EQ, then surely it means that electrolyte isn't mixed properly(?). I'm sure that keeping them at 90-90% every day is not bad for them, but what I'd like to do is everything possible to extend their life :) But it's a bit of struggle to find out exactly how much stratified electrolyte shortens the life of batts, and whether the difference between 1.28 and 1.29 will actually make a difference. If only there were some long term studies done on battery life and different charging profiles... (I'm looking at you john p ;) )
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #6
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    Re: Preventing stratification in tall cells
    stephendv wrote: »
    The thing is that the damage caused by stratification is a very long term thing. If the acid has a density of 1.29 at fully charged, and I'm measuring only 1.28- but it won't rise any more unless I EQ, then surely it means that electrolyte isn't mixed properly(?). I'm sure that keeping them at 90-90% every day is not bad for them, but what I'd like to do is everything possible to extend their life :) But it's a bit of struggle to find out exactly how much stratified electrolyte shortens the life of batts, and whether the difference between 1.28 and 1.29 will actually make a difference. If only there were some long term studies done on battery life and different charging profiles... (I'm looking at you john p ;) )
    Since you have a Forklift Battery, one would think they would have the answers you seek. They are probably as dumb as the other battery Manufacturers are about their products. Most of the answers you get is not consistent with the information they publish. If you talk to one tech, you'll get one answer and tomorrow you'll get another. Most of the information on the web is just copied from each other and regurgitated. Every once in a while you can find a real study or two, but it might not fit your battery.

    One could assume your's was filled with 1.300 electrolyte. Your close enough that it should not be a issue, but what the heck do I know. There has to be some margin of error in how they mix it and what you measure. Just a degree or two in temperature would do that.

    You could add a Bubbler system, but they add oxygen to the electrolyte and it's known to add to the corrosion of the positive plates. It also take's power to run. You'd probably only need it 5 minutes a week.
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  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    #7
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    Re: Preventing stratification in tall cells

    Trying to do long term studies on charging wet cell batteries is very hard to do. For one thing that obvious it would take years to do the study'. As I already said this type of cell were never designed to be charged by solar energy. In most situations there will be current being drawn from the battery cells at the same time as they are being charged. Secondly the cells are usually not fully charged until some time in the afternoon.This then does not give enough time to give a useful equalizing charge.And what makes it worse you will get some cloud cover for some of the time dropping the available charging power to less than what is needed for the equalize charge.
    The bottom line really is wet cell batteries and solar is not an ideal combination.
    I f you think about it nearly all rechargable batteries were designed to be charged by mains battery chargers. They really are the only source of constant volts and amps. Trying to get 3 hours of constant late afternoon charging voltage is almost impossible with solar.
    I did do at one time experiments with pumping air through the batteries to improve the charging cycle. It did but it has some draw backs. One of its problems if the pump is being powered by the batteries you are charging by solar a lot of the charging advantages is lost by the considerable power needed to power the air pumps 24 hrs a day. When done by a vehicle or industrial engine powered generator this is not a problem but for solar charging it certainly is.
    From discussions with others at work about reliable long term(8yrs)testing of different charging cycles for wet cell (FLA)batteries most agree its an almost impossible task. Far to many batteries required and a huge amount of human time needed to be constantly checking the batteries and adding water etc. And to repeat the main problem the tests would be done with mains battery chargers and most people on here will be charging theirs with solar panels with wildly differing available charging times and different "overcharging" abilities of their systems. ie some will be doing it when no current will be drawn from the batteries others will be drawing power from the system at same time as the equalizing charging is being done. problems,problems,problems.
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #8
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    Re: Preventing stratification in tall cells
    Blackcherry04 wrote: »
    You could add a Bubbler system, but they add oxygen to the electrolyte and it's known to add to the corrosion of the positive plates. It also take's power to run. You'd probably only need it 5 minutes a week.

    Yeah, this is what the manufacturer recommended. But the distributor I bought from said it's not necessary and the regular absorb will cause enough gassing to mix the electrolyte. Different answers from different people, and no one is really invested in making sure I get absolutely the most life out of the batteries. The distributor assured me that with normal 2.4V absorb and EQ once a month that they'll last "a long time". Which is where our goal posts differ, I'm aiming for "the longest possible time" :)

    Bubbling system is tempting, but I'm not sure I have the balls to start drilling holes in my perfectly good batteries.

    John p; understood about the impracticalities of testing this sort of thing. I guess second prize would be to understand the effects of stratification over a shorter time period then extrapolate the results. E.g. Shallow discharge/recharge without EQ for a year- and perhaps using a very high concentration SG to exaggerate the effects. Then compare the plates to a similar system that was EQ'd ?
    So far having enough time and/or power for EQ hasn't been a problem here, the batts usually finish absorb and are at 1.28SG at about noon, so I have at least 2kW spare for the next 4 hours to do an EQ. I'd just like to find a balance between EQ'ing too often or for too long vs. not enough to prevent stratification. And I'm not sure where that point is.
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #9
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    Re: Preventing stratification in tall cells

    It's probably impossible to give one perfect answer to your question. Each answer, like drugs used in humans, has side effects that can be harmful. Like bubbling air through your batteries. You gain by reducing the stratification, but loose by introducing oxygen. The combined overall result in extending life? Questionable. Same for extended EQ sessions. Some questions have no perfect answer and we have to accept that all good things do come to an end.
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #10
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    Re: Preventing stratification in tall cells

    Our batteries are in a stationary position and have issues you never see in a battery that is mobile and shaken and moved around daily. Anytime I move one you can hear the hydrogen bubbles that are trapped between the plates as they break loose. I have a small mallet that I will tap them with to break them loose. I won't use bus bars for that reason so I can shake them from time to time ( I call it Burping ). Does it help them for a longer life ?? I have no clue, but I feel like I did something. To me it makes sense that anywhere the electrolyte cannot reach the plate, you'll have less capacity.

    Of course with a Forklift battery you'd be limited to what you could do. They may have different type separators that don't have that issue.
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  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    #11
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    Re: Preventing stratification in tall cells

    Waynefrom canada. From the tests I did there are no ill effects from bubbling air through the batteries. It really does improve everything. like faster charge time, absorbs greater charge,and definately keeps the sulphation much lower than it would normally be.The bad side for solar is the drain of the pump, because to be really successful it has to be run 24/7.
    The complete test can be found somewhere on this forum if anyone interested.
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  • Derik
    Derik Solar Expert Posts: 82 ✭✭✭✭
    #12
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    Re: Preventing stratification in tall cells

    I think that if you just leave them alone, keep them watered and check the sg frequently they will last a long long time. I think messing with them will shorten their life. I would go by the manufactures recommendation and leave it at that. From what I have read about stratification you will have little or none at your level of SG.

    I also think that solar chaging a wet cell battery is pretty consistant with the right charge controller and load shifting, when my trojan L16 RE's wear out I'll get another group of them unless we have some major tech breakthrough in the next 7 years or so.
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #13
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    Re: Preventing stratification in tall cells
    Derik wrote: »
    I think that if you just leave them alone, keep them watered and check the sg frequently they will last a long long time. I think messing with them will shorten their life. I would go by the manufactures recommendation and leave it at that. From what I have read about stratification you will have little or none at your level of SG.

    I also think that solar chaging a wet cell battery is pretty consistant with the right charge controller and load shifting, when my trojan L16 RE's wear out I'll get another group of them unless we have some major tech breakthrough in the next 7 years or so.

    That Derik, is what I've done with my six L-16's. They're 10 years old now, and still working fine. Who knows what tomorrow will bring, but so far, there's not a hint of any problem with them at all.
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  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #14
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    Re: Preventing stratification in tall cells

    I don't know what type of Traction battery you have but mine was spec'ed at 2.75 to be full charge, I let mine equalize on a regular 30 day cycle off the array, and though a reasonably new battery (9 months old) I'm happy with them reaching full capacity once a month and feel they are with in reason, fully charge if slightly stratified at 2.7-2.8 at the end of the day. It has very little demand on it since I moved, but early fall it will be the sole storage for my new place.

    Since these take a regular hard charge (C-6-8) in their natural enviroment, I really don't worry about the regular, monthly, Equalizing.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • Ralph Day
    Ralph Day Solar Expert Posts: 1,019 ✭✭✭✭
    #15
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    Re: Preventing stratification in tall cells

    "Since these take a regular hard charge ( C-6-8 ) in their natural environment, I really don't worry about the regular, monthly, Equalizing"

    But their natural environment charges and discharges brutally (compared to usual solar/re batteries), and their life expectancy is 5-7 years in a daily use industrial environment. Quite a different scenario than dainty little 10% discharge and charge daily in an off-grid setup. I think I would go with traction batteries if I could get them in my basement. The CS 450 pound brutes from Surrette were hard enough to get down the stairs with the special handcart.

    Ralph
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  • 65DegN
    65DegN Solar Expert Posts: 109 ✭✭
    #16
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    Re: Preventing stratification in tall cells

    Using an absorb time like 4 hours is an arbitrary number. It doesn't take into account the actual battery state of charge, the charge current or the load on the system. I realize that this is likely what the manufacturer has advised but, IMO, it is better to complete the absorb cycle by letting the charge current drop to 1 ~ 2% of total battery capacity. That insures a certain battery impeadance has been reached and that can only be obtained in a fully charged state.
    Also it looks like you have some room to add more solar charge capacity to that battery bank. The faster the bulk charge voltage is arrived at though, the longer the absorb cycle needs to be.
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  • 65DegN
    65DegN Solar Expert Posts: 109 ✭✭
    #17
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    Re: Preventing stratification in tall cells

    John, why do you say,
    john p wrote: »
    Trying to get 3 hours of constant late afternoon charging voltage is almost impossible with solar.
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  • john p
    john p Solar Expert Posts: 814 ✭✭✭
    #18
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    Re: Preventing stratification in tall cells

    65deg N
    For one thing that obvious it would take years to do the study'. As I already said this type of cell were never designed to be charged by solar energy. In most situations there will be current being drawn from the battery cells at the same time as they are being charged. Secondly the cells are usually not fully charged until some time in the afternoon.This then does not give enough time to give a useful equalizing charge.And what makes it worse you will get some cloud cover for some of the time dropping the available charging power to less than what is needed for the equalize charge.
    The bottom line really is wet cell batteries and solar is not an ideal combination.
    I base this on observations of the many solar arrays we have in use at work. Cloud cover is a real killer of panel output, What happens is the voltage drops below the equalize charge voltage then the charger drops out of that phase and reverts to a bulk or maintain charge and will stay like that for some time specially if power is being drawn from the batteries.
    There are many geographical places that have only 4 hrs solar isolation. Therefore if the recovery charge time from the previous night is about 3 hrs how do you get another 3 hrs of equalize charge time. ?? In winter time with even shorter solar isolation time the available equalize time may be zero.
    If you are fortunate to have an "oversized" solar array then you are better off but for most installations, there is little reserve panel power.
    This is the reason many have to resort to using a diesel/LPG/gas generator for the equalize charge
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #19
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    Re: Preventing stratification in tall cells
    65DegN wrote: »
    Using an absorb time like 4 hours is an arbitrary number. It doesn't take into account the actual battery state of charge, the charge current or the load on the system. I realize that this is likely what the manufacturer has advised but, IMO, it is better to complete the absorb cycle by letting the charge current drop to 1 ~ 2% of total battery capacity.

    Unfortunately my charge controller doesn't have an end-amps feature and can only be programmed with a fixed absorb time. When I measured the end amps manually during a long absorb the amps kept dropping every few minutes and eventually stabilised at 3A, i.e. 0.3% of C20 capacity. This took 2 hours with an absorb voltage of 2.45V and is typical of what I see daily. And that's why I chose the 4 hour absorb as an example of a "long" absorb time.
    65DegN wrote: »
    The faster the bulk charge voltage is arrived at though, the longer the absorb cycle needs to be.

    Surely you mean the faster the bulk charge, the shorter absorb needs to be?
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #20
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    Re: Preventing stratification in tall cells

    Thanks for the comments all. Derik I think the "just leave them alone" idea is going to be the toughest to implement 'cause I just love to tinker ;) But yeah, this sounds like sensible advice, normal absorb voltage every day, and a proper thorough EQ once a month that both serves to do a full charge and bubble the electrolyte.
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