Determining battery health

palausystem
palausystem Solar Expert Posts: 122 ✭✭✭
If you get decent SG readings, can the battery still be heavily sulfated? How do these two factors relate?
I' asking because I'm measuring 1.250 on my Surrettes which is not far from the factory Fully Charged (1.255-1.270) but I believe them to be pretty gunked up. I don't know what they are supposed to look like at six years of age but when I look in a cell a lot of crusty stuff visible.
One symptom I have besides fast draining power is the Bulk phase is very short just recently- voltage rises much quicker than it used to. We do have one bad cell in one of the two strings - SG is 1.205, and we are getting a warranty replacement for it soon.
We are getting a new smaller battery as soon as the money comes in.
As covered in other threads, I have too much battery (800Ah) to PV (3kW)
Thanks for your comments
Off-grid 48v, 3 kw PV, Sunny Island 5048U, SunnyBoy, US Battery RE L16XC  6v, 800ah, Genset: Kohler 8.5 RES propane.

Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Determining battery health

    Everything else equal (and it never is) you could not have a normal SG reading on a sulphated cell. The sulphur that coats the plates comes from the electrolyte solution, and removing it from the solution reduces the density of that solution. If the electrolyte level is not correct you can get a false high reading.

    Consider that you have a difference of about 0.100 in SG reading between "good" and "dead". A difference of 0.020 is sort of 20% discharged. If that's all the SG will come up to then you've lost 20% of the capacity. This is not exactly right but is close enough to explain the principle. (I put that in for the nit-pickers.)

    Sulphation is not the only thing that can wreck a battery. Plate oxidation, warping, or shorting can show similar results.

    The only thing you can do is crank up the Voltage and see if some Equalization will improve SG readings. While you're waiting for the new batteries.
  • palausystem
    palausystem Solar Expert Posts: 122 ✭✭✭
    Re: Determining battery health

    "Plate oxidation, warping, or shorting can show similar results".

    I assume by "similar results" you mean low SG or are we talking other symptoms too...?
    And what causes these other conditions?
    Off-grid 48v, 3 kw PV, Sunny Island 5048U, SunnyBoy, US Battery RE L16XC  6v, 800ah, Genset: Kohler 8.5 RES propane.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Determining battery health
    "Plate oxidation, warping, or shorting can show similar results".

    I assume by "similar results" you mean low SG or are we talking other symptoms too...?
    And what causes these other conditions?

    Low battery capacity even if the SG appears normal; those conditions reduce plate surface which reduces actual capacity. The difference between having a small battery with 1.265 SG and a large battery with 1.265 SG; size of the plates in the battery. If you lose effective surface area for any reason you lose actual capacity.

    Warping is usually caused by high temperature such as having too much current put to them. Oxidation is a normal process which can be accelerated by improper charging. Shorts are mostly caused by accident or defect in manufacture.
  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    Re: Determining battery health
    ... I don't know what they are supposed to look like at six years of age but when I look in a cell a lot of crusty stuff visible ...
    As covered in other threads, I have too much battery (800Ah) to PV (3kW) ...

    I believe that the crusty stuff (often grey in color) is eroded plate material that circulates in the electrolyte, and on Surrettes winds up settling on the top of the Moss Guard (plastic gizmo on top of the plate separators). This build-up is normal, as batteries age. Just be careful when using your Hydrometer, to gently squeeze the bulb when returning the electrolyte to the cell, you probably do not want to blast this material down into the separators ... some winds up there anyway, but just try to be gentle.

    Six-ish years is not too bad from L-16 batteries.

    Just my opinion, but if one is careful with DOD, AND you have charge sources that can charge at a minimum of 10% of 20 hour Capacity, you should be fine IMO ... know that this has already been covered elsewhere.

    As an aside, one string here (1280 AH) has 3.15 KW STC of PV ... knock on wood. Opinions, 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.
  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    Re: Determining battery health
    One symptom I have besides fast draining power is the Bulk phase is very short just recently- voltage rises much quicker than it used to.

    Since you have an AC coupled Sunny Island system, what have you set as the Boost voltage? And the "Full" voltage and interval? The SI doesn't do a daily absorb like other chargers, so you could try modifying the voltages to get them working well with your batteries.

    The SI will keep float charging until the batteries dip below 70% SoC or until a set number of days pass (I think it's about 5 days). So the batts can be sitting for a while on float charge without ever doing an absorb.
    Using the SI's charging idea, the "Boost" charge should have a higher than normal absorb voltage, but not quite EQ voltage. The purpose of this charge is to cause gassing and boost the SoC up past 80%. The next important setting is the "Full" charge, here you can use the absorb voltage and set a very long absorb time to make sure it gets the batteries to 100% SoC every 14-20 days. These are all finger-in-the-air values, if you notice that even after a full charge the batts aren't actually fully charged, you can increase "Full" voltage and/or time.
    In addition, you can also set the EQ as recommended by surette.
  • palausystem
    palausystem Solar Expert Posts: 122 ✭✭✭
    Re: Determining battery health

    Stephen DV - I want to get your ideas on making the SI 5048U work better for me but I think I'll start a new thread for that to keep things neat. Please see my post in Offgrid "Sunny Island charging strategy". Should be up within the hour.
    Thanks
    Off-grid 48v, 3 kw PV, Sunny Island 5048U, SunnyBoy, US Battery RE L16XC  6v, 800ah, Genset: Kohler 8.5 RES propane.
  • palausystem
    palausystem Solar Expert Posts: 122 ✭✭✭
    Re: Determining battery health
    Low battery capacity even if the SG appears normal; those conditions reduce plate surface which reduces actual capacity. The difference between having a small battery with 1.265 SG and a large battery with 1.265 SG; size of the plates in the battery. If you lose effective surface area for any reason you lose actual capacity.

    Warping is usually caused by high temperature such as having too much current put to them. Oxidation is a normal process which can be accelerated by improper charging. Shorts are mostly caused by accident or defect in manufacture.

    What's good way to determine the actual battery capacity loss? Special tool?
    Off-grid 48v, 3 kw PV, Sunny Island 5048U, SunnyBoy, US Battery RE L16XC  6v, 800ah, Genset: Kohler 8.5 RES propane.
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    Re: Determining battery health
    What's good way to determine the actual battery capacity loss? Special tool?

    You can do it best with a load box that will pull constant current from the battery as its voltage decreases and measures the time and current till the low voltage cutoff is reached. But you can get a relative idea between two different batteries or the original battery numbers and later battery numbers just by using a constant resistance load and timing.

    If you want to compare your numbers to the published 20 hour capacity (C20) of the battery you need to use a load box to get the same constant current that the manufacturer used for their test.
    SMA SB 3000, old BP panels.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Determining battery health
    What's good way to determine the actual battery capacity loss? Special tool?

    Special tool; no easy way for the average person to determine capacity.