Need help with equalizing AGM

Basicplus
Basicplus Solar Expert Posts: 25 ✭
in Off Grid Solar & Battery Systems #1
I have a pair of 6v 220amp/h Discover agm batteries that are not staying at equal voltages during discharging. If I draw around 40 amp/h out of the bank, battery one will be at 6.4 and the other at 5.9v, this it with a 10 amp load. I am trying to equalize the low voltage battery at 2.58v per cell at 2.2amps. I am charging at constant current. My charger was able to generate a graph of voltage vs time, the graph was going as expected until the voltage started to fall off.

Is the voltage falling off because the plates are accepting more charge and should I continue with the charging until the voltage rises to the eq level again.

Thanks..
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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #2
    Re: Need help with equalizing AGM

    I'd say your seeing outgassing and the destruction of the cell.

    Typically AGM's are not designed to go to such a high voltage.

    Here is Discover Energies description of 'Balance Charging' They don't list a terminal voltage.

    Includes the words "...after the Absorption Stage" and "...for no longer than 4 hours." and "Warning: Do not equalize charge GEL or AGM batteries! "
    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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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #3
    Re: Need help with equalizing AGM

    Unless the manufacturer has a specific equalization procedure AGM's are not to be equalized.
    AGM's do not accept high Voltage charging, and your 2.58 per cell is well over the normal maximum.
    In all likelihood that battery's vent has opened, it has gassed, and it is now ruined.

    A Voltage difference between two batteries in a string of 10% like this (5.9 vs. 6.4) is not a big concern. Switching their position in the string would have been better to see if they "equalize". This had also better be discharged Voltages as they are near 50% SOC level for a resting Voltage.

    Another example of why flooded cells are better.
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  • feedhorn
    feedhorn Solar Expert Posts: 103 ✭✭
    #4
    Re: Need help with equalizing AGM
    Basicplus wrote: »
    Is the voltage falling off because the plates are accepting more charge and should I continue with the charging until the voltage rises to the eq level again.

    Voltage falloff probably due to one cell overheating and drying out as it becomes shorted. Not sure if it could recover from that damage.
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  • PNjunction
    PNjunction Solar Expert Posts: 762 ✭✭✭
    #5
    Re: Need help with equalizing AGM

    This appears to be one manufacturer that allows for AGM equalization.

    Equally fascinating is that they actually provide charts for the typical IUI equalization routine. That's very rare, as most manufacturers don't think the average consumer is going to graph their charge. Bravo on the powerlab 6 chart.

    http://www.discover-energy.com/d-series-deep-cycle/dgc6a-220d

    I'm not exactly sure if that is your battery or not.

    In your case, as soon as the voltage started to drop at the end, I would terminate the EQ charge, and certainly no longer than 4 hours if it didn't drop.

    Equally interesting is that they seem to be able to handle 2.6v per cell, which makes me wonder if that is the "normal" cell charging voltage, which is certainly much higher than the usual agm! The IUU, or CC/CV routine chart shows that.

    This makes me wonder if under most normal circumstances where one charges at the typical 2.4v per cell, one might be consistently UNDER-charging these at that voltage! Holy cow - I'd dig into the specs more to find out if you need to pump up the voltage of your charge controller for standard CC/CV charging with no eq.

    I'm a little freaked out since these are lead-calcium grids, and not pure-lead types. In either case, just be sure you have temp-monitoring going on during the EQ process.

    *** Something doesn't feel right here. Are you SURE that the powerlab6 is doing a TRUE constant-current charge, allowing the voltage to rise regardless of the current, or is it just maxing out the power supply during bulk (simulating a CC), and merely using the absorb voltage as the transition to CV when it goes into absorb mode? You would have to purposely put the powerlab 6 into a CC mode.)

    On page 76 of the powerlab manual, I see no way to put it into a true CC mode, other than just maxing out your power supply during bulk. Something is weird here, and I hope it isn't battery degradation. ***
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  • Basicplus
    Basicplus Solar Expert Posts: 25 ✭
    #6
    Re: Need help with equalizing AGM

    Thanks for the replys...

    I am no expert, and was under the impression that gel cell and agm should never be equalized. The discover info on there web site states they can be equalized at 2.58v per cell at 1amp per 100amp\h of capacity for up to 4 hours. Life line batteries also states they can be equalized. I find it hard to believe that being at 2.58v for for 2 hours at 2amp charge on a 220amp cell could destroy it. The battery stayed cool and there was no bulging. I have put a 2.5amp load on each 6v and will draw them down 25amps and check the compare the voltages.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #7
    Re: Need help with equalizing AGM

    Before you go drawing them down, what did you manage to charge them up to? If you haven't achieved a good resting Voltage in each battery then nothing has been accomplished.
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #8
    Re: Need help with equalizing AGM
    Basicplus wrote: »
    I find it hard to believe that being at 2.58v for for 2 hours at 2amp charge on a 220amp cell could destroy it. .

    As you learn more about this type of battery and how they work, you'll learn why they are so easily murdered compared to flooded.
    Flooded will normally stand up to a fair amount of charging / over charging abuse. on the other hand, as has been mentioned by others, gel and AGM batteries are generally not forgiving of such abuse. Instead AGM will vent gasses and dry out. Gels will form gas bubbles that hold the gelled electrolyte away from contact with the plates. Their electrolyte generally cannot be replaced and that's why they are so easily murdered.
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  • Basicplus
    Basicplus Solar Expert Posts: 25 ✭
    #9
    Re: Need help with equalizing AGM

    They were charged to 7.1v at 30amps until C/20, these being the parameter I set. The eq was done at a constant 2.2amps which was also graphed. I have taken the load off and will let them rest and then compare voltages before and after a load test of each. This was a controlled EQ done to the manufacturers specs, I was just curious why the voltage dropped off. I know that if I were to hit the EQ button on xantrex truecharge 20 it would ruin the battery in no time. My best guess is the voltage was dropping off do to resistance rising, not the plates accepting the charge.

    These batteries have been my furnace bank for my rv and have been in service for three years, maybe 40 cycles. I also have a set of 6v lifeline 220amp batteries that have been in service for 8 years. I load tested both banks with a 10amp load for 6 hours and the discover were uneven and the lifeline were the same voltage after the load.





    The pl6 is a great charger, it is capable of 1000w charging and is powered by 2 12v 90amp server power supplies in series. Its main use is for charging lipo batteries, as it can balance charge 6s lipo packs.
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  • PNjunction
    PNjunction Solar Expert Posts: 762 ✭✭✭
    #10
    Re: Need help with equalizing AGM

    Gels are easily murdered by applying higher agm voltages to them by the clueless, and are not appropriate for solar in the first place with their C/20 max charge rate.

    AGM's are usually murdered by an insufficient charge, by applying lower gel voltages to them. You have to REALLY abuse an agm to get it to vent. They are NOT delicate wall-flowers as compared to flooded, and I really dislike seeing marketing FUD creep into our excellent forum. In the hands of children or idiots, you can get ANY battery to go nuts.

    I don't know what the sudden deal is with the flooded cheerleading I see creeping up on us. I thought this forum was about how to take care of what you find fits your application, and how best to take care of it. All that does is drive the signal to noise ratio higher and higher in the threads and pretty soon cheerleading above all else holds sway.

    But back to the original issue of the EQ. I don't think Basicplus has damaged them. I have done limited EQ's like you have on HIGH quality agm's, and suffered no problems - no venting, no drama, no major heat etc. They were made to take it like these apparently are.

    What concerns me about the chart, is that the IUI algorithm usually shows the last "I", at a higher voltage than the absorb. This is not the case with the charts here. I'd really like to speak to their engineering department and ask if holding cells at 2.6v as per their own charts will stay within warantee. It could possibly be the case that the charts themselves are wrong, and other than those, I don't see any other specific voltage references.

    In the end, just do a discharge test and see if you still meet the capacity spec without either battery going low voltage prematurely. I see you know the score owning Lifelines, which I was going to reference, but you beat me to it, and glad they are working well for you.
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  • Basicplus
    Basicplus Solar Expert Posts: 25 ✭
    #11
    Re: Need help with equalizing AGM

    Thanks.. I found the info from the Discover site, they call it Balance mode..

    If a Balance Mode is included in the charging algorithm it would typically happen after the Absorption Stage. This would become the third stage and the “Float Stage” would then become the fourth stage. A balance mode is similar to an Equalize function for flooded batteries but is performed against tightly controlled current, voltage and time. For example the current should be limited to 1 amp per 100 amp hour of battery capacity and the battery should not be maintained at the balance or over voltage limit for less than 1 hour and for no longer than 4 hours
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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #12
    Re: Need help with equalizing AGM

    What voltage are they holding currently 3 hours or more after your balancing attempt?

    Typically in a flooded battery Lead Calcium batteries are designed to live in float and have minimal deep discharging, I don't really have a clue in an AGM battery. I hope they are Okay, how old are they?

    In a corrective mode, equalizing on a flooded battery would require checking the Specific Gravity(SG) of the electrolyte, something that can't be done in an AGM battery hence the term Balancing to keep from confusion, regardless it is difficult due to the nature of a sealed battery, at 2.6v the electrolyte would be expected to outgas in a flooded battery, something a sealed battery does on it's death bed, since no distilled water can be added.
    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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  • PNjunction
    PNjunction Solar Expert Posts: 762 ✭✭✭
    #13
    Re: Need help with equalizing AGM

    I should have followed Photowhit's link - that explains what you are all looking at. I was only looking at the charts.

    Right - Bulk/absorb 2.42 - 2.465v per cell. 0.3C max charge current - this all makes sense for lead-calcium agm's. Check.

    Balance - the way I read it is that they are implying just to follow their own specification for EQ. They don't want to call it that, but that is what it is. Is 2.60v the over-voltage limit, and someone in the graphics department didn't read their own "101" manual?

    I think what they are doing is taking the very long road around a way of saying that you want to charge your battery with the normal standards FIRST, before applying the EQ stage. That is, I knew several people that instead of finishing absorb properly, and then doing EQ, went INTO and started the absorb stage at 15v+ immediately - essentially just going from bulk to EQ without a proper absorb in between.

    I have done that, and YES, that will hurt even a quality agm built to take an eq. I don't know why it takes most manufacturers 5 sentences skirting around the issue, when all they had to say was that finishing absorb at the normal rates is mandatory. Perhaps because many consumers just used their farm-charger, cranked it up to 15.5v and walked away. :)

    Is your Powerlab running the latest firmware? Is there some sort of timeout of it's own doing things behind your back.... Makes me wonder if a variable bench supply might be an option to try when doing this eq to see if it follows the same pattern as the powerlab...
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  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    #14
    Re: Need help with equalizing AGM

    Here is a bit more reading for your late nite pleasure, from a maker of telecom batteries generally accustomed to a long float life, but fairly neutral in my view... a good reference... I used the meat and potatoes to come up with my charge settings for my AGM's
    http://www.cdtechno.com/pdf/ref/41_2128_0212.pdf
     
    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
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  • zoneblue
    zoneblue Solar Expert Posts: 1,220 ✭✭✭✭
    #15
    Re: Need help with equalizing AGM

    One explanaation for the OPs curve is the battery is going into thermal runaway. However because the current is being limited (is there a graph of current too OP?, that would clarify what the charger is actually doing), instead of the current climbing, the voltage is dropping.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


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  • Basicplus
    Basicplus Solar Expert Posts: 25 ✭
    #16
    Re: Need help with equalizing AGM

    After a individual 2.5amp load for 8 hours the batteries remained even at 6.3v. I have now put them in series with a 8 amp load to see if they remain even.

    Attachment not found.Attachment not found.Attachment not found.


    It looks like I should have stopped the eq when it voltage reached its peak at the 3.5h mark, not 3-4 hours after 2.58v was reached..
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  • Basicplus
    Basicplus Solar Expert Posts: 25 ✭
    #17
    Re: Need help with equalizing AGM

    So, after drawing the agm,s down in series for 4.5h at 8amps, 59 amp/h total discharge, the batteries have ended up even at 6v under load, the balance charge seemed to have worked.
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  • PNjunction
    PNjunction Solar Expert Posts: 762 ✭✭✭
    #18
    Re: Need help with equalizing AGM

    Outstanding!

    Under a normal charge cycle, what is your normal absorb voltage per cell? I'm still freaked out by their graphs showing 2.6v as the norm, whereas their charging description section shows a typically lower voltage.

    One thing I might add is that in their charging descriptions about the absorb stage, they are on the ball about not specifying a specific "ending amperage" (like .01 or .001C), but rather take into account aging / drying by monitoring for less than .1a change over a 1 hour period. But is your charging gear actually capable of measuring that lack of change and switching to float accordingly?

    If not, I'd fall back to observing an end-amp measurement where it doesn't change over say a 1-3 hour period, and then setting your end-amp detection to just a little bit *higher* so that you don't chase an end-amp that will never be obtained as it ages in between monitoring periods, furthering the drying out process.
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  • Basicplus
    Basicplus Solar Expert Posts: 25 ✭
    #19
    Re: Need help with equalizing AGM

    These batteries will be going back in service in my rv as the furnace bank, they will be charged by a xantrex truecharge 20 with a temp sensor, set to agm. The FMA PL6 charger is used to charge lipo batteries for my rc helicopter batteries, if you overcharge a lipo battery they will puff and explode in flames.

    Thanks again for your replies...
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