Greenish/turquoise corrosion at negative terminals of Concorde SunXtender AGM bank

jnh
jnh Registered Users Posts: 8 ✭
in Off Grid Solar & Battery Systems #1
While moving my small 24V Outback system to another room, I discovered some sort of turquoise-colored corrosion on the negative terminal of each battery, as well as a lesser amount on the positive terminal of the one attached to my inverter.

These are Concorde SunXtender PVX-3050T's-- 6V 305Ah AGM's, about 3-4 years old. I had thought that AGMs, since they don't vent or leak acid fumes were mostly immune to this sort of thing, which I've seen on car batteries often enough (except then it's usually the positive terminal that corrodes, leaving more of a blue colored deposit rather than green. Concorde in particular advertises corrosion-resistance copper allow terminals, etc.

Batteries had been set up in a place where I couldn't easily inspect the terminals, so the problem went unnoticed until I started to disassemble the system and all this stuff started flaking off. The system doesn't seem to have noticeably degraded in terms of performance-- no more voltage drop under heavy load than usual-- possibly because the inner parts of the connection, nearest each terminal post were still clean copper-on-tin, and still tightly fastened.

Any idea what might be causing this, and what I could do to prevent a recurrence? I have spare 4/0 interconnects on hand, in case the old ones can't be adequately cleaned and/or repaired.

Oh, PowerCheq equalizers were attached to the bank, if that makes any difference, with cheap hardware-store ring terminals crimped onto those (the equalizers will never pull or push more than 1-2A).

I have tried to attach a photo to this post. In case it doesn't come through, a copy is also at vt11.net/corrosion.jpg
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  • westbranch
    westbranch Solar Expert Posts: 5,183 ✭✭✭✭
    #2
    Re: Greenish/turquoise corrosion at negative terminals of Concorde SunXtender AGM bank

    No expert but the green should be copper oxidation. cure is to clean it off the lugs and coat with anything from Vaseline to No-OX paste (cheapest to most expensive) available at you NAPA or similar store...
    YMMV
     
    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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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #3
    Re: Greenish/turquoise corrosion at negative terminals of Concorde SunXtender AGM bank

    The posts generally have O-rings on the posts that will keep them from leaking, but will all things there is no guarantee they won't leak. Keeping the charging Voltage and Current within the manufacturers limits is important. Using the correct torque on the Bolts / Nuts will keep the stress down. Another thing you can do is to use a copper washer on the Post / Bolt to raise the lug if it's against the plastic on the case and pulling the post up on the battery. Put some Vaseline or dielectric grease on the lugs.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #4
    Re: Greenish/turquoise corrosion at negative terminals of Concorde SunXtender AGM bank
    westbranch wrote: »
    No expert but the green should be copper oxidation. cure is to clean it off the lugs and coat with anything from Vaseline to No-OX paste (cheapest to most expensive) available at you NAPA or similar store...
    YMMV

    Actually green would be copper sulfate, a sure sign of the presence of some amount of battery acid (or else acid rain if left outdoors).
    An AGM will still vent if over charged, and depending on where the vent exits on those batteries, there may be nothing else which would react to the presence of acid fog, droplets, or a surface film before it got to the terminals, so the source is not necessarily right at the posts.
    But there will be some pressure inside the AGM before the valve lets go, and damaged seals at the posts could cause some slow venting there.
    If the problem goes on long enough, your AGMs will lose capacity because of loss of electrolyte. But that may be longer than their useful life for other reasons.

    Not sure why it is primarily (entirely??) at the + terminals unless the leak is actually there though. Well, maybe so: If there is a small current from one battery terminal to the other through a surface film, it will cause the most corrosion of the copper at the + terminal. You can have a potentially conductive contamination of the top of the battery which will show high resistance when perfectly dry, but then absorb some moisture from the air in times of high humidity and become conductive. Drying the film out will be a temporary fix, but carefully washing it off and/or neutralizing it is the long term fix.
    SMA SB 3000, old BP panels.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #5
    Re: Greenish/turquoise corrosion at negative terminals of Concorde SunXtender AGM bank

    Also--Look closely at the positive terminals and the side of the case... Over time, the positive grid will corrode (from oxygen gas generated during charging). It can "extrude" some battery posts (look for posts pushing out of the case) and/or make the sides of the case expand.

    Obviously, positive grid corrosion is unrecoverable and one of the paths to death for a lead acid battery (one web comment I read thought that because AGM are electrolyte "starved" (at 95% of mat capacity), that this made them more likely to suffer an early death from positive grid corrosion because it is not submersed in liquid).

    -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 ✭✭✭✭
    #6
    Re: Greenish/turquoise corrosion at negative terminals of Concorde SunXtender AGM bank

    you may also see a corner of the black plastic top lift up a tad. this is pressure related, but i was assured by concorde that this is ok and it is still sealed. you may wish to check with concorde, but most likely you just need to clean things up and put something on it as was suggested to prevent any corrosion. i only advise the contact with them to be sure as i've never seen that on mine. i did see a powdery white on mine.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #7
    Re: Greenish/turquoise corrosion at negative terminals of Concorde SunXtender AGM bank
    niel wrote: »
    i did see a powdery white on mine.

    OK, here is a correction and an addition to my earlier post.

    Copper sulfate is blue, not green, but I would call the color in the photo blue. A much more greenish color would be copper chloride (more commonly seen in copper around swimming pools.)
    And finally, if all of the moisture is removed from the hydrated copper sulphate by heating, the color will go away and you will be left with a grey-white powder.
    If adding a small amount water to your white powder turns it green, Niel, then you also have copper sulphate. If it does not, then you may just have a dried acid residue with no copper in it at all.
    SMA SB 3000, old BP panels.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #8
    Re: Greenish/turquoise corrosion at negative terminals of Concorde SunXtender AGM bank

    too late for me to determine as it was only seen once years ago and this is on the single old 1040t that has lost its capacity already.

    i do have 4 more newer ones for my inverter and no sign of anything on them.
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  • jnh
    jnh Registered Users Posts: 8 ✭
    #9
    Re: Greenish/turquoise corrosion at negative terminals of Concorde SunXtender AGM bank

    Thanks for the feedback. I've removed the suspected copper sulfate with a wire brush and fine-grit sandpaper, and will also clean the top of each battery case with baking soda & water to get rid of any acid residue.

    Is the "NoOx" mentioned above the same thing as "Noalox," used to prevent oxidation of aluminum wire terminations? Or similar enough? I have a bottle of that on hand already, along with some "Permanex battery terminal protector" gel from an auto parts store. Which of these would be better to use?

    My charge controller voltages and Outback "SellRe" voltage (grid-tie battery voltage target) have probably been set a little too high, especially in light of the Flexmax-60's occasional voltage overshoots during dynamic sun conditions (scattered clouds rolling through, etc.)

    There was one day that I came home from work to a faint sulfur smell in the room. I never found exactly what caused that, and suspected that a second, very old battery bank with marginal cells (since removed) was responsible.

    I might have overtightened the terminals too during installation, since I don't have a proper torque wrench and was cinching them down very tightly using a ratchet set. Wll try to back off a little on the force this time. I hope no permanent damage was done to the O-ring seals...
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  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    #10
    Re: Greenish/turquoise corrosion at negative terminals of Concorde SunXtender AGM bank

    Hi jnh,

    IMHO, you do NOT need to use NoAlOx. It is a bit messy, and as you note, is intended primarily to prevent Alunimum corrosion in electrical connections.

    With AGMs, just make certain that all charge sources have a Battery Temp Sensor (although, with the correct OB giblets, BTSes can be shared).

    Vaseline should be just fine, and is very inexpensive. Opinions, 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.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #11
    Re: Greenish/turquoise corrosion at negative terminals of Concorde SunXtender AGM bank

    the voltage is overshooting on the controller? that's not a good thing. this could've popped the vents and you could've been smelling the batteries, not sure though as i lightly popped my vents for a short duration with light current and higher voltage.
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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #12
    Re: Greenish/turquoise corrosion at negative terminals of Concorde SunXtender AGM bank
    Vic wrote: »
    with the correct OB giblets, BTSes can be shared.
    Translation please???
    SMA SB 3000, old BP panels.
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #13
    Re: Greenish/turquoise corrosion at negative terminals of Concorde SunXtender AGM bank
    inetdog wrote: »
    Translation please???

    With an outback hub one battery temp sensor can be shared by all outback inverters and chargers connected to the hub. --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Shadowcatcher
    Shadowcatcher Solar Expert Posts: 228 ✭✭✭
    #14
    Re: Greenish/turquoise corrosion at negative terminals of Concorde SunXtender AGM bank

    I had this problem with a deep cycle battery that is attached to a back up sump pump. I used a copper wire brush and coated the terminal with dialectric grease and have had no recurrence.
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