AGM Batteries and End Amps

dirtbikrdirtbikr Registered Users Posts: 7 ✭✭

I posted a couple months ago about my off grid solar office at my house about arranging panels to achieve a good voltage level for my input. I have a fairly "complex" setup in terms of parallel strings, but have been monitoring it closely with an ammeter/rotating batteries and have been satisfied with the performance of the system.

My setup:
(5) 100AH 12v Universal Battery UB121000 ( 1s5p
(4) Renogy 12v 150W panels in 2s2p (about 40Voc)
Midnite Classic 150 Charge Controller (Absorb =14.4v for with a four hour time limit (also using EA), Float = 13.4v, both modes are temperature compensated)
AIMS 2000W low frequency inverter

With Tcomp on the Midnite, the voltages have been ~0.3V higher than specified which seems alright to me.

I have been decreasing end amps slowly to get a feel for where fully charged is since I cannot do SG readings. I started with EA=10A and worked my way down to 5A after observing from work how it charged and I knew that it would be able to complete (My neighbors have a tree that cuts my production at 2:30PM, so my window is from ~8AM-2PM of solid Phoenix sun). I was out there Saturday while my bank was trying to get into float and I heard them all making a slight fizzing sound (which on a FLA battery I wouldn't be concerned about). I set the EA=10A on the Midnite, a minute later the bank fell into float and the gurgling/sizzling settled down and eventually stopped. I was under the impression that I could take the bank down to ~1% of its capacity in amps and it should be fine. I also know that the hydrogen and oxygen are supposed to recombine within the battery itself, but I have never heard an AGM make noises before. I left the EA at 10A and charged it that way yesterday. Am I damaging these batteries if I can hear them? To compare the db level to something, I would say it sounded about as loud as someone whispering from about ten feet away.

Here is my thingspeak channel with the temperature, humidity, and voltage in the office. I have verified this chip against 3 multimeters and it is within .01 volts of all three, so I trust it. Please be aware there are a lot of data points on this page and it may slow your computer down displaying it.

Thank you everyone :smile:


  • BB.BB. Super Moderators, Administrators Posts: 30,520 admin
    AGM/Sealed batteries venting is not a good thing.

    AGM should be "OK" with EA set to well under 1% just fine.

    Perhaps your charging voltage is set too high (over ~14.4 volts for AGM, try 14.2?) or your absorb time is too long?

    Hot battery bank (-5 mvolts per degree C per battery Cell)? 35C battery bank (95F).
    • (35C-25C)*(-0.005 volts)*(6 cell battery) = -0.3 volt Absorb/float offset
    • 14.4 volts - 0.3 volt offset = 14.1 volts @ 25C
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • dirtbikrdirtbikr Registered Users Posts: 7 ✭✭

    • The absorb time can't actually be "too long" when end amps are in the equation, unless end amps is set too low, correct?
    • The bank has never gone above 21C in its life, usually the Classic is reporting a battery temperature of 13C - 18C throughout the day.
    • If I set the voltage to 14.2V, my temperature compensated charging voltage will be in the 14.5V neighborhood, does that sound correct?
    • Do we know the batteries are actually venting vs recombining? Is there a concrete way to tell or is that just tribal knowledge (noises == venting)?

    Thank you!
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    edited January 2017 #4
    You might want to read up on VRLA batteries.... here is a link to some good literature.  VRLA starts in the second section
    lots of night time reading there...
    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
  • dirtbikrdirtbikr Registered Users Posts: 7 ✭✭
    You might want to read up on VRLA baptisteries.... here is a link to some good literature.  VRLA starts in the second section
    lots of night time reading there...

    That is a an amazing resource, thank you so much! I have lowered the charging voltage and float voltage and will see how the bank performs over the next few weeks. I'll definitely be reading through all of those as well, I appreciate it.
  • mike95490mike95490 Solar Expert Posts: 8,764 ✭✭✭✭✭
    You cannot hear gas combining into water, you can hear gas venting from the pressure valve
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    gen: ,

  • PNjunctionPNjunction Solar Expert Posts: 762 ✭✭✭
    edited January 2017 #7
    You are killing your bank, despite what your voltmeter says.  That 1S/5P configuration is the problem.

    SAFETY:  If just ONE cell shorts in that bank, is your wiring prepared to accept a 500ah short?  Ie, when using more than 2 strings, (in this case 5 single batteries in parallel), do you have a Class-T fuse between each of them?  I doubt it.  

    BALANCE:  Using more than 2 strings (or just two batteries in this case), leads to balance problems, despite the measuring you are doing - and this is caused by using an AGM in the first place where you can't check the gravity of each cell.

    Hint:  Fully charge your bank to what you normally think of as full charge.  Disconnect the batteries from the bus / cabling AND each other, let them rest for 12 hours, and THEN take your individual terminal readings.  If any are more than 0.1V difference, you have balance or aging issues, especially if the batteries are not the same age / batch, or worse yet, previously used.

    If you notice this kind of disparity, charge each battery *individually* to full, preferably with an ac charger, and then reassemble.  The reason is that it is much easier to get only 6 cells of a 12v battery properly charged, than it is to ensure that a 30-cell highly paralleled one is.

    What you are hearing at what is considered a "normal" absorb voltage of 14.4v, is one or more of the 30 cells gassing, while some others are undercharged.  This disparity gets larger over time if you do not get on top of it.  With an agm as you know, there is no way to check on the health of an individual cell.  You've got 30 to look after, and with 5 batteries in parallel, it is easy for them to hide problems from you.

    Keeping more than 2 agm batteries in parallel more of less weds you to constant maintenance.  Ask any of the 1990's EV guys running huge banks of Optima or Genesis agm's.  They will be instantly familiar with the sound you are hearing at that distance. :)

  • EstragonEstragon Registered Users Posts: 4,478 ✭✭✭✭✭
    It might also help to measure temps of individual battery cells and interconnections with a handheld meter while charging. The classic will only see the temp at a single point where the RTS is installed.
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
  • mvasmvas Registered Users Posts: 382 ✭✭✭
    edited February 2017 #9
    The size, equal length and location of each wire connecting your batteries in parallel is extremely important for equal charge of all batteries:

    Also, do you have 1" air space, for cooling  between each of the 5 batteries?
    If not, then the middle battery will be much warmer than the other four batteries

    Hissing is bad.
    Are all 5 batteries the same age?
    Are all connections clean and tight?
    Equal (symmetrical) length heavy gauge wires?
    Disconnect the battery bank for 24 hours, then measure the resting voltage of each.
    Does one battery have lower voltage than the other four batteries?

    When charging at 14.4 volts ...

    a) Can you measure a Voltage difference between any two (+) terminals ?
    Measure between ...
    Bat 1 (+) & Bat 2 (+)
    Bat 1 (+) & Bat 3 (+)
    Bat 1 (+) & Bat 4 (+)
    Bat 1 (+) & Bat 5 (+)
    Bat 2 (+) & Bat 3 (+)
    Bat 2 (+) & Bat 4 (+)
    Bat 2 (+) & Bat 5 (+)
    Bat 3 (+) & Bat 4 (+)
    Bat 3 (+) & Bat 5 (+)
    Bat 4 (+) & Bat 5 (+)

    b) Can you measure a Voltage difference between any two (-) terminals ?
    Measure between ...
    Bat 1 (-) & Bat 2 (-)
    Bat 1 (-) & Bat 3 (-)
    Bat 1 (-) & Bat 4 (-)
    Bat 1 (-) & Bat 5 (-)
    Bat 2 (-) & Bat 3 (-)
    Bat 2 (-) & Bat 4 (-)
    Bat 2 (-) & Bat 5 (-)
    Bat 3 (-) & Bat 4 (-)
    Bat 3 (-) & Bat 5 (-)
    Bat 4 (-) & Bat 5 (-)

    If you can measure a voltage difference then you do not have symmetrical parallel wiring.

  • mcgivormcgivor Solar Expert Posts: 3,408 ✭✭✭✭✭
    edited February 2017 #10
    To help identify which cells are gassing, spray some gas leak detector solution, or soapy water, over the vent caps and see which ones bubble.
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • mvasmvas Registered Users Posts: 382 ✭✭✭
    dirtbikr said:

     I was out there Saturday while my bank was trying to get into float and I heard them all making a slight fizzing sound 
    Hmmmm ... all 5 batteries were making a hissing sound?
    Water, as H2 and O2, is venting from your batteries and it cannot be replaced.
    That makes me think your Charging Voltage is a little too high,
    and / or your batteries are actually warmer internally than your temperature probe is measuring / reporting.

  • JohannJohann Solar Expert Posts: 244 ✭✭✭
    edited February 2017 #12
    About a year ago I inherit 10 used 75ah sealed AGM batteries. One was bad from the start.
    I hooked them up in parallel as a 12 volt nominal system. About every month, one of the batteries went bad until I had 6 left.
    One of the 6 batteries went bad and that battery started to smoke and spew droplets and was so hot that I could not even touch that bad battery and not to mention the fumes that where released. I keep my batteries outside and I could smell the very strong battery smell inside my house which alerted me that there was something wrong with my system. My good batteries dumped all their power into the bad battery and caused it to boil at night. The good batteries where hot also. Needless to say that the rest of the batteries did not last long after that.
    So, keep your batteries out of your living area even if they are sealed AGM batteries. They could kill you if something is going wrong. I learned that AGM batteries do not like to be wired in parallel. 
    A deal to get a forklift battery fell through, but at least I have other LA batteries that I can open and check the fluid level and SG. No more sealed batteries that I can not check for me, lesson learned.
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