sharky5656

After I have cycled both batteries - discharging as much as I can and charging them to 100% with a day or more of rest afterwards, everything seems to be back to normal. The Vd is within the range of 5-10mV on each bank. What I have done also is to let them discharge as far as they will go (before force charge request) and charging them back up to 100% simultaneously while they are in communication with each other and the inverter and leaving them for a few hours to rest. Now, there is still some current difference between the batteries (something like 2A while charging or discharging, but the SOC develop equally more or less, as well as the total voltages) but this has been the case from day 1 and I guess is due to the difference in cable length, different terminals used, etc. This is something I will be dealing with next in order to minimize differences. I will continue monitoring the state of things in the following weeks and report if something new comes up so that other people may find some helpful information. I wanted to ask you for a final piece of advice. Given that the batteries force request a charge when they reach something like 15% SOC and I cannot drop them further under normal circumstances (without cutting off grid power) and forcefully discharing them that way, what would you say is the best and most practical/convenient practice when it comes to giving them a chance to calibrate the Voltage-SOC relationship without having to disconnect grid power. On the Deye if I set in the Time of Use a discharge up to 8-10%, it never reaches that, as the force charge request kicks in. In other word, what do you do to keep your batteries happy? Thank you all for the helpful information and advice!

Will do, thanks! Currently I am cycling the slave battery for good measure, afterwards I will get back to the sneaky master one! The slave battery was also way off in the SOC calculation, because it was at around 18-19% SOC when I heard the "click", everything went dark and the inverter reported low DC voltage, the battery was at 46 volts, which is the stated discharge cut-off value, printed on the side of the case.

Thank you! I will talk to the installers as I am not supposed to be dealing with this, being just a hobbyist and not a professional! I cannot see any washers and all of the cables that I have access to, at least, are indeed very tight. The bad thing about our situation is that space is rather limited and is complicated further by a wooden column that sits between the two batteries, increasing their spacing perhaps needlessly. The inverter is on only one side of the wooden column. I am saying this with respect to the cable lengths. Or maybe there is some way in which the installers could make them equal lengths, we will see. Thank you very much for the in-depth suggestions, as previously noted, I will talk to our installers and try to figure this out. This morning, when I looked at the state of the battery after last night's restart, the cells were still out of balance by about 260mV. Hi there! The BMS should be either a Pace BMS or a Gobel BMS (from what I understand, it is something of a rebrand of Pace by Gobel, but I am not sure). The firmware, reported by PBMS tools is P16S150A-21545-1.05, which leads me to believe that the BMS is Pace P16S150A, because I was able to find such a model on Pace's website. As of now, I feel like the issues are with the BMS itself (or maybe with some of the cells as well), because last night's restart did not make any sense - I find it impossible for the battery to go from 53.2 to 56 volts in a matter of a minute or two without something catching on fire or maybe I am missing something fundamental in my understanding.

Hi! Thanks for joining in! The cable sizes between the master and the inverter, as well as between the master and slave batteries are 35mm2 (AWG 2). The max discharge amps on the inverter are set at 185A because this gives me something like 0.46C which the manufacturer of the batteries says it's ok. The max charge current is 150A but this is more of a theoretical limit only, as I have a water heater that turns on at noon, so the batteries charge more often at something like 40-50 (for the last month the maximum charge current achieved was 110 amps for a little while (hopefully split rather evenly at around 55 amps for each pack), which is again well within manufacturer specs and recommendations. The batteries themselves report to the inverter some way higher currents allowable such as 420 amps discharge and 210 amps charge (when both are connected and turned on; if only one, then it reports half ot these values), but that is a bit too extreme for me. The battery model is listed on Deye's website as "approved", whatever that means, and is set up according to Deye's instructuons (RS485, instead of CAN, protocol option 12 on the Deye (no explanation given what 12 is.) I say this in terms of the charge and float settings, as I (nor the installers) have configured them specifically, instead we are relying on the BMSes reporting what they need. The slave + is connected ot a secondary + terminal on the master. The same is done for the -. Each of the two batteries has two + and two - terminals/poles. The master battery then connects to the inverter, i.e. a single pair of cables carries the current to the inverter. I am attaching photos of two bats and inverter. Cheers!

Thank you for the suggestions! 1. Each battery has a tiny screen with some info, including the cell voltages. Now that the master battery has been left on a full charge for the past 36-48 hours to let it balance, the figures I saw were voltage difference 0mV. However, while reporting SOC 100%, the battery voltage displayed was 53.2V, which seems too low for me. Regardless, I switched off the battery in preparation for making the slave battery the master in order to let it discharge and charge fully, same as with the original master battery. Just out of curiosity I decided to switch the original master battery again, however, which immediately made it start charging with 35-40 amps or so. The battery voltage rather rapidly increased to 55.99V and has remained there with the cell voltage difference climbing to 126mV. Last I checked, the battery was drawing 1.5-2Amps intermittently. I have decided to give it 8-10 hours more to see what happens with the voltage difference between the cells and with the overall voltage displayed. Unfortunately, I did not think of checking the actual voltage with a multimeter. 2. The cable connections seem very solid and I would say they are barely warm to the touch, never hot. As for DC fuses, we do not have such fitted between the battery and the inverter. When the experts were putting in the system, I asked why they are not installing DC breakers as well, and the reply was that the Deye has a DC breaker inside it, as well as the battery has one as well inside it. Cannot check that, as both are under warranty and I cannot open them. Regardless, seems strange to me, as I find it just a bit more convenient to have such a switch, if not for something else. Will ask them again about it and will request that they install them. 3. I have not tried charging them without comms, I will try it after I have given both batteries the chance to charge fully and balance, as it has been around two weeks since they have been fully charger (November in the northern hemisphere , not much free energy). I am attaching photos of the master battery screen. Tomorrow I will see what has happened and will eventually discharge the slave battery (making it master and transfering comms) and charge it 100% with a 1-2 days of balancing. Cheers! P.S. I still have not contacted installers/manufacturers with a warranty claim because I like sorting something out myself, if possible and if something trivial, learning something along the way, and then going for these measures.

Hi guys, I've tried searching pretty hard for my issue but to no avail... I have two identical batteries (made by Optonica, 200Ah each, a local company) in parallel that have the same Pace BMS each (I believe it is the P16S200A-0001-20A; both have the same firmware version). As of yesterday, one of the batteries has started discharging way lower than the other one and with way higher currents. E.g. one (the master battery) of the batteries discharges below the set threshold of 19% SOC in my Deye inverter, while the other battery is still at around 25-35%. This results in the master battery requesting force charge from the inverter and both batteries start charging from the grid, again retaining the difference in SOC between them (even though the other battery is still above the 19% threshold). What is worse, sometimes the master battery (regardless if it has higher or lower SOC that the other battery) discharges into the second battery when there is no load on the system and hte PV is sufficient for powering it, without discharging the batteries, so the difference in SOC gets even larger. What is even worseER, the two batteries do not split the load even remotely evenly - the master battery, even though it is at a lower SOC, would sometimes supply 80A, while the other, at a higher SOC, would give off only 10-15-20A. I have even seen a situation in which only the master battery was powering the whole house (no PV available, as it was in the evening), AND it was charging the other battery, i.e. the inverter was reporting something like 50A drawn from the battery, while the master battery's own screen was reporting 70A discharge with the 20A difference being reported as positive (charge) current on the other battery. When the batteries are charging, the master battery (the problematic, in my opinion, and the older of the two by 6 months) takes charge rather slowly; e.g. the master battery, while at 25% SOC may be charging at 15A, while the other battery, while at 30-35% SOC, may take charge of 40A, regardless of whether the charge comes from the grid or excess solar. This started happening out of the blue with nothing in the system having been changed. Do you have any suggestions, please? I have currently turned off the other battery and left only the master battery working and have discharged it fully and left it to charge to 100%. When the master battery is operating on its own, the discharge stops at precisely the set percentage in the inverter. When both batteries are turned on, the inverter recognizes that and adjusts the SOC (averaging it), as well as the charge/discharge current limits, as it has always done. This leads me to believe that it is not a communication issue between the two batteries, as only the master battery communicates with the inverter directly. As far as I am aware, the BMSes should not allow more than 20A of current to flow between the batteries, when they are at a different SOC, but this is also violated at times. Voltage difference between the cells with little or no load can't remember to have exceeded 20mV for any of the two packs. TL;DR Two batteries, same capacity, same nominal voltage, same BMS and firmware, both 16S; one of the batteries discharges with much higher currents, charges with lower currents, sometimes powers the whole house AND charges the other battery. Sorry for the long post, I am still trying to get a grasp of the whole mess. If you have any suggestions, they would be more than welcome. Thank you!