backchannel - low specific gravity on large bank

from this post on the DIY Solar Forum (the excellent forum owned by Will Prowse)

stated problem

Specific gravity on FLA bank is low (~1.060) as measured by both refractrometer and hydrometer.

intital thoughts

  • partial stage of charge - likely
  • errant reading due to electrolyte stratification - less likely but possible
  • errant reading due to lack of temperature compensation

working to figure out what OP has

No temp given for electrolyte SG, so who knows. Also, I had to read all the posts in two unrelated threads to glean anything about what the OP was working with:

  • 2x Interstate 420Ah 903-S (L-16HCL?) 6v in series for 12v. These are tall batts which may make stratification more likely
  • 700w of unnamed panel in unnamed configuration. I’m guessing 2x 350w in series, based on the MT-50 showing Vpanel == 66.0v.
  • unnamed Kisae Abso inverter/charger run off a genny. Guessing a IC122055 since that matches his pic and the 2000w inverter output.
  • undetermined 30A EpEver MPPT replaced by undetermined 40A EpEver MPPT

If you want help, don’t make it harder for people to help you.


The battery manufacturer specifies C/10 charging (42A in this case) and Absorp at 14.7v.

  • The inverter/charger can reliably provide the current current up to 14.4v according to the manual. It also says the Flooded (14.4v) config is the default, so hopefully he has that going for him.

EpEvers default to SLD (“sealed”) profile, with Vabs == 14.4v. It can be set to FLD (“flooded”) where Vabs==14.6v or the custom USER profile where exact setpoints can be configured. Absorption duration limited to 180mins no matter what (EpEver’s achille’s heel IMO). It is unlikely that solar alone would max out the 40A charger reliably.

Overpaneling relative to the controller is a neat approach to dealing with variable solar harvest. It’s a way to deal with excess power. This system is seriously lacking in charging power so overpaneling the controller is unproductive. OP needs to overpanel the battery.


Stop the bleeding, then charge better in the future

stop the bleeding!

This may take several days, depending on how bad the batteries are hurt by partial state of charge.

  1. check electrolyte covers the plates
  2. check/charge batteries separately to make sure one doesn’t have a dead cell or some other unrecoverable problem
  3. configure the existing controller for “maximum smoke” Vabs == 14.7v, Vfloat == 14.7v, Veq ~15.5v
  4. ensure the Abso is set to Flooded (the default, Vabs == 14.4v)
  5. run the genny in the morning to run the Abso until solar charging voltage overtakes genny voltage, then stop genny
  6. after acceptance falls to ~4A check water levels, disconnect loads and EQ until SG stops rising.

going forward

  1. configure the existing controller in line with mfg recommendations: Vabs == 14.7v, Vfloat == 13.5v, Veq 15.3-15.7v
  2. run the genny in the morning until solar charging voltage overtakes genny voltage
  3. if that doesn’t do the trick or no one is present to run the genny then add a third identical panel for 1,050w and increase controller to 60A. Or add two panels for 1,400w and another 40A for them.
  4. observe to assess whether or not the bank is already damaged or even killed by undercharging. Even if it needs to be replaced at least we have charging under control now.


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