This is a motorhome setup that we live in full-time.
Have 2 Victron Multiplus 12v/3k inverters. 6 SOK 12v/314ah batteries. The batteries are daisy chained together with battery one’s positive going to the inverter and battery sixes negative to the inverter. The Cerbo GX is attached to battery one. The display only reads battery one.
The issue I am having is that battery one rapidly discharges while the others discharge at a much slower rate. For example, yesterday battery one got down to 4% while the average across the other five batteries was 88%. This caused the entire system to shut down because it was reading just the first battery at 4% and 10.4v. The Cerbo GX is connected to battery one, which reads the low SOC and voltage.
Battery one BMS is set to “Parallel” and CAN protocol to “Victron”. The other batteries are set to “Parallel” and no CAN protocol selected. This was what SOK suggested.
The installer said that the setup should allow for even discharging across all batteries and that this might be an SOK BMS issue.
Any help on how to get the batteries to discharge more equally would be greatly appreciated.
The first battery is connected to the GX over Canbus, but the others need to be daisy-chained to the first through the RS485 cables. This will allow the first battery to send aggregated data to the GX.
A parallel bank can discharge unevenly when theres an issue with the interconnect cabling. Since the first battery got discharged down to 10.4V but the rest did not, and the common negative is connected to battery six, then the issue is most likely on the positive side between battery 1 and 2.
Another possibility is that battery 2-6 disconnected due to their BMS having no communication to the first one or some other cause. I guess you are able to read out each battery individually over bluetooth, is there some indication that the BMS had switched off or some fault?
Are you able to monitor the batteries while discharging? You should be able to see the current distribution, ideally it would be the same on all six batteries
I am actually going to try and get under there and conirm the comm cables are installed correctly. Need to go back to the SOK manual and assure that. It would make sense that they may not be accurately connected since it doesn’t seem 2-6 are not communicating with #1. Should 2-6 have CAN set to Victron like battery #1???
The batteries are all charging currently since we are boondocking and that first battery was so low.
Well, I may have figured out the culprit. I am hoping this is the entire issue.
The positive terminal on battery 2 was loose. Arched. Burnt the SOK comm wire and Cerbo wire. The Cerbo wire seems to still work, but obviously the SOK Comm wire was burnt too much.
I am going to replace the burnt wires and hope that solves everything.
ed tracking each of their current amps, once I had tightened the loose positive lug on battery two.
I haven’t had a chance to clean the lug or cables on battery two yet, but will be doing that soon.
I was amazed that the next to last column, 15:45, their SOC was pretty balanced. This while after we were traveling for about 4 hours and not on shore power.
Holding them for longer at higher voltages will bring them into balance.
But your datas shows the difference in current over them, that is the issue i am referring to with ohms law. It will work some batteries harder than others over time. If you are going to keep the set up as is (besides the bit more clean up) then consider periodic rotation in the set up as part of maintenance. This will also give you a chance to regularly check lugs and torque (vibration being what it is in mobile) and prevent further problems.
