Difference in Battery level vs voltage

[Michael Raz]

Edit: This morning (early AM) the CC is now showing battery capacity at 93% (better match to system voltage). Not sure if it has “figured out” things or the issue will continue but I’m just going to keep an eye on it. It may have been related to the fact that late yesterday I changed the setting for capacity from the default 200ah to 435.

Original:
I finished updating my cabin system with new batteries, 2x345 panels (along with old 315 panels) and an EPever 40amp CC for the new panels. Everything seems to be working well but I’m seeing a discrepancy on the CC display. Earlier today the status showed 100% charged. This evening the battery voltage on the controller is 12.7 and a separate meter shows 12.65 (no load) but the CC is showing the battery percentage at 55%. The CC set for flooded with a 435 ah capacity (2 Trojan L16h-ac).

I’m not sure if I should be concerned about the difference or I’m misunderstanding what the CC is indicating.

[Rob Beckers]

Michael, the 'state of charge' indication on the EP-Solar charge controllers is a rough indication at best. Divining SOC from battery Voltage is a black art to begin with, and the moment you start charging a lead-acid battery the Voltage goes up a great deal (which would indicate "100%" when obviously a battery doesn't go from, say, 50% SOC to 100% in two seconds flat).

I wouldn't read too much into what the charge controller says. Instead, keep an eye on specific gravity readings after a full charge (when you know the batteries should be "full"). As long as they are hitting 1.265 for each cell all is well.

To have an idea of how much is left 'in the tank' I like the MidNite MNBCM SOC meters. They have an LED that lights up on a scale from 10 - 100%. It's still not very accurate, but gives a decent idea of what's going on, as long as you ignore the 100% LED. When it shows 100% it just means the battery is charging (and they should have labelled it that way).

-RoB-

[Michael Raz]

Thanks for the response Rob. My initial concern was trying to figure out what “Battery Capacity” field in the EP was showing. I was confused by it showing 100% while still charging (or sun being available) then dropping to 50 or so in the evening when both battery voltage and specific gravity (with batteries off load) showed a full charge. I’ve only just noticed the small line in the manual “Battery capacity, In Charging” which would explain what I was seeing - doesn’t mean anything when not charging. This had more to do with trying to make sure I had everything up and running properly and I’m comfortable now that I do.

Thanks for all the help with the new components. I’m really satisfied with the upgrade!