Gel Batteries Gurgling

requiredwhen Registered Users Posts: 7 ✭✭

Hi Everyone,

Long time reader, first time poster.

We put together a solar system last year for a cabin that we use as a summer house. Last week we started to have a problem where the solar controller (A cheap PWM model) would stop charging the batteries. There was no error, the LCD just didn’t show any current going from the panels to battery. To fix the problem we would reset the controller (disconnect solar and battery, let stand 20min then reconnect). That would fix it for 2-3 days. We thought maybe the PVMax was to low for our panels output (the problem would happen at peak sunshine). During this time we wouldn’t notice the problem and the batteries drained to 44.5-45V at least 5 times.

Anyway, we bought a new controller:

SRNE MPPT 60A with a 150V PVMax

2 days in and we have a new problem. The gel batteries started gurgling or maybe a squishing noise when at 100% SOC. We had a clear day today and the batteries got up to what the charge controller says SOC was 100%, The battery voltage was 56.7 and was charging at 25A in "boost" mode. 

We used the default settings on the controller for Gel batteries:

Overcharge Disconnect 16.0V

Charge Limit 15.5V

Boost Charge 14.2V

Floating charge 13.8

If the batteries are bubbling my assumption is that they are overcharged or charging to quickly. Is a charge limit of 15.5V to high? 

The other think I could think of is that maybe the batteries are damaged from discharging to 45V. I'm not sure how to troubleshoot this or what to do next.

Thanks in advance!

System specs:

8 Panels:
Pmax: 340W

Current at Pmax: 8.83A

4 series of 2 panels each

Controller (original)

Cheap PWM

Charging Current 60A

Solar Max Voltage 88V 

Controller (new)

150V PVMax

8 Batteries
48V system

12V batteries
 (2 series of 4 batteries each)

Cycle 14.4-14.9

Float 13.6-13.8

Max Charge 37.5A



120V output


Pure sine wave


  • BB.
    BB. Super Moderators, Administrators Posts: 33,501 admin
    Looking at those specifications for the YangTze GEL batteries--They are pretty agressive in their charging specifications (in my humble opinion).

    I am not a battery engineer... The general specifications for GEL batteries is 5% rate of charge and 14.2 volts maximum charging voltage (for US built/supplied--There are some European versions that spec higher charging currents).

    GEL batteries have (historically) been used for UPS systems. Low self discharge, good float/low self discharge, and a mild recharge current (5%).

    The downside for solar has been is that high charging voltage causes gassing. And that causes voids in the GEL which are (?) permanent and reduce the overall capacity of the battery (poor contact between plates and gelled electrolyte).

    If attempting a 20%+ rate of charge and high charging voltage--I would suggest that would only be valid/recommended for batteries that are in the 50%-80% or less state of charge range... When the current goes into quickly recharging, vs gassing (making hydrogen and oxygen gasses).

    In general, you only want to charge above the "gassing voltage" for flooded cell lead acid batteries (where they can be refilled with distilled water):

    Voltage table for cyclic use charging. The higher voltages (above the gassing voltage) should only be used on flooded batteries that can have the water replaced:
    Battery TemperatureCharge Voltage per cellCharge Voltage for a 12 Volt batteryGassing Voltage per cellGassing Voltage for a 12V battery
    -20 °C *2.67 to 2.7616.02 to 16.562.9717.82
    -10 °C *2.61 to 2.7015.66 to 16.22.6515.9
    0 ° C *2.55 to 2.6515.3 to 15.92.5415.24
    10 °C2.49 to 2.5914.94 to 15.542.4714.82
    20 °C2.43 to 2.5314.58 to 15.182.41514.49
    25 °C2.40 to 2.5014.40 to 15.002.3914.34
    30 °C2.37 to 2.4714.22 to 14.822.36514.19
    40 °C2.31 to 2.4113.86 to 14.462.3313.98
    50 °C2.25 to 2.3513.5 to 14.102.3013.8

    Lead Acid batteries can take deep cycling (below 20% State of Charge) as long as they are quickly recharged (not great for the battery, but will not "kill" the battery unless it is old and weak anyway). Letting a lead acid battery sit below ~75% State of Charge--Then they start to sulfate--Days/Weeks/months below 75% SoC (and not cycling discharging/charging daily), is going to sulfate the battery and eventually kill it (in month/year).

    I don't know much about battery chemistry--And these GEL batteries could have different requirements... But the fact you are hearing gassing inside the battery/gel--I would try to avoid that.

    56.7 volts (aka 14.75 volts @ 12 volt ref) and 25 amps charging current seems to indicate that your bank is not at 100% SoC...  Using the chart from your specifications, you should see ~13.0 to 13.2 volts "resting" (3+ hours of no-charging/no-discharging) across each 12 volt battery...

    GEL batteries are very charge efficient... If your controller is holding 56.7 (~14.2 volts) @25C/77F, you should see the charging current drop to below 0.1% rate of charge (150 AH battery, ~0.15 amps)... And, at least for now, I would suggest stopping charging at 1% rate of charge (1.5 amps per string or 2x1.5a = 3.0 amps--Drop from ~14.2 volts "absorb" down to float voltage charging of ~13.5 to 13.8 volts @ 25C).

    For first time solar folks--It many times make sense to buy 6 volt @ ~200 AH "golf cart" flooded cell deep cycle lead acid batteries. They are reasonably rugged/forgiving, and "cheap" (vs AGM, GEL, and more expensive FLA batteries). Plus you can check the specific gravity of each cell and figure out the "real" state of charge (SG readings are the "gold standard").

    Right now, your best bet is to use a voltmeter and check the voltage across each battery (and log)... Do this when charging/discharging/resting... You are looking for "differences" between batteries. If everything is "the same", generally the bank is healthy (assuming you are measuring ~12.1 to 13.2 volts "resting" and ~13.5 to 14.2 volts or less when charging, no less than ~11.5 volts when under load and approaching 50% state of charge). If you see one battery at "12 volts" or at "16 volts" when charging, and the rest are around 14.x volts--Then you have an issue to check (cabling, possible bad battery, etc.).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • BB.
    BB. Super Moderators, Administrators Posts: 33,501 admin
    Hello Requiredwhen,

    I am not sure you flagged your own post on purpose or by accident... If you wish to remove your post--Just reply here in the discussion and I will remove.

    -Bill "moderator" B.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • requiredwhen
    requiredwhen Registered Users Posts: 7 ✭✭
    Thanks BB!

    I can manually set the battery charge settings on the controller. I'll try dropping the "Boost" setting to 14.1 or 14.0 to see if I can get under the gassing voltage. 

    When I check the voltage of the batteries, do I need to disconnect them? 

    Thanks again,

    PS. Sorry didn't mean to flag the post. I tried to edit it then deleted it by accident. 
  • BB.
    BB. Super Moderators, Administrators Posts: 33,501 admin
    No problem Steve... We are here to help. The "gear" to the upper right of your post "frame" will let you edit.

    Because you have batteries in series (really series/parallel strings), that is a perfect configuration to check battery voltages without disconnecting.

    The only time you need to disconnect batteries to measure their "true" voltage is when they are connected in parallel--You are then measuring the "group voltage" instead of one battery (or cell) voltage.

    I am assuming you did not "ladder" the batteries (where you connect in series, then cross connect between neighboring batteries to make parallel connections too). "Laddering" is not necessary and (I believe) complicates battery management/inspection. Laddering does nothing if everything is working correctly (no parallel current flow in "ladder" wiring). And if there are problems, the parallel connections "hide" individual battery "issues".

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • requiredwhen
    requiredwhen Registered Users Posts: 7 ✭✭
    I dropped the Boost charge and float charge to 13.2 and gassing has stopped. I'll try slowly raising them to find the sweet spot. 

    I did not ladder the batteries, sounds like a lot of wires! I have the 2 series connected at bus bars. 

    The voltage difference between the batteries is .15 (ranging from 13.15 - 13.3). Is that acceptable? 
  • BB.
    BB. Super Moderators, Administrators Posts: 33,501 admin
    For resting voltage, that appears to be fine (~100% state of charge).

    13.2 volts (12 volt reference) is too low to charge--And really not even high enough to float.

    Use your voltmeter to confirm your charging voltage setpoint... 14.2 volts (at 25C) is a good start for absorb.

    And the battery bank should automatically reduce charging current to below 1% state of charge when the batteries are full. Double check the voltage across each battery and verify that they are all 1/4 the charging voltage.

    Longer term, a nice diagnostic tool is a DC current clamp capable DMM. The ability to check current flow in any wire by just placing the clamp over one wire is really nice--And for things like parallel battery strings, you can verify if they are sharing the current--Or not: (nice medium price AC/DC current clamp DMM) (low cost "good enough" AC/DC current clamp DMM)

    Note--The common clamp meter is an AC ONLY Clamp Meter with AC/DC DMM aka volt reading mode... For our needs, you want an AC/DC Current Clamp DMM. (the common clamp meter can only measure AC current. The clamp meter descriptions are a bit confused at times).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset