Running Sunsynk 12kW Three Phase inverter with a Freedom Won 15/12 (15kWh) battery.
Every now and then I notice the SOC jumping sharply. Mostly from high 80% to close to 100% fairly rapidly. But today I saw this. What is the cause of this?
Even though the inverter measured charging the battery only about 5.8 kWh yesterday, the battery discharged 12kWh overnight. I.e. the full capacity of the battery minus 20%. So it really was full.
There is a Stop button, when you press it it trips the breaker. To turn it back on, first push the breaker down, then back up.
There is a reset button on the side of the box which resets only the BMS. At least, there is on mine.
I have to list a number of things here so bear with me.
There is an issue that crops up on some batteries where the zero-calibration is out. So the battery sees a higher discharge current than actual. This causes the SOC estimate to be lower than actual (especially if it hasn’t been fully charged for a while), so it will have seen more drift. There is a way to fix this, essentially you have to trip the breaker so you know there is absolutely zero current running, and then do a zero-calibration with the relevant software. I don’t know how to do this though.
Diagnosis is fairly easy. With the breaker tripped… does the BMS report a negative current flow? If it does, it needs recalibration.
This may be normal. All batteries suffer SOC drift over time (see page 15 in the manual, linked in the next sentence). The OrionBMS in that thing also has voltage waypoints that can be programmed, voltages known to correspond with a specific state of charge, so it may jump to intermediate SOC levels as well, as it reaches those cell voltages. If the battery has been sitting at 20% for a long time, it may have been much higher than that and just didn’t know. Although, I must say this seems unlikely with this battery. For LFP the voltage waypoints don’t really work between 30% and 80% (the flat part of the curve), so if the battery was higher than 20%, it is strange that it would get stuck that low down.
You could of course just have a bad cell. I hope not… but it is possible. For that you need to see cell voltages.
The newer FW batteries have an ethernet port and you can register on their portal to see the data. But since it’s OrionBMS, you could also just get the software and check it out yourself. If under warranty, you may want to ask the guy you bought it from to check it out. I also imagine the settings could be password locked, but that is a wild guess.
Edit: It seems you need a USB->CAN adapter to talk to the BMS. Since I see you can also use the Torque application (which is really for cars) to talk to the BMS via a Bluetooth can dongle… it could be that this is simply an ELM327 serial to CAN translator… but now I am totally speculating.
I don’t know if this works for other inverters, or if a special Victron profile needs to be loaded, but if the battery supports it and you have a canbus interface connected to a Linux machine, you can do this:
The first 16 bits is the lowest cell voltage (2D0D in this example), and the next 16 bits is the highest cell voltage (300D). It’s little-endian, so you have to byte-swap it, 0D2D and 0D30, which is 3373 and 3376 in this example, that is in mV.
Yeah I have something on the side and a switch in the front. I may try that if it doesn’t go away.
So when it got to 100% this was right as it was able to pull 12kWh (80%) overnight. It must have been at about 60% when it reported 20% yesterday. Because when it reached ~40% it jumped to 100%. So this appears to be what happened.
This seems to have worsened so could be drift I guess?
System is less than a year old so hope not!
I’m going to be away from home for some time, so will leave it and see if things improve and when I get back I can try some of the more complex things, but probably just get the installer to check it out.
Oh one more thing: I am connected to the Sunsynk via RS845 and pushing stuff to Home Assistant (via KellerZA Add On). Is there any chance the detailed cell data is readable via that connection, perhaps just not read via his scripts? Anybody know? Or would that be the inverter reported data only. I see nothing on the Sunsynk web portal that’s not in the KellerZA add on though. I suspect the inverter will only push what it “knows” down the RS845 connection.
This is yesterday and today. You can see today it charged more smoothly but there were two jumps at the end there. One from 87% to 90% and another from 92% to 98%.
Is this not part of the problem? The BMS knows when it gets to 100% by voltage, but if it doesn’t get to 100% for some time, it has to make best guesses about SOC, until the correct voltage is reached.
If you’ve been that low for two days, the BMS will only have a vague idea of what SOC actually is.
All batteries like to be charged to 100% on a fairly regular basis, even if they only stay there for a few minutes.
I hope so. Didn’t think it would be that far out, but I have no idea. Will be away for a week and there will be some sun so battery should be pretty full for next week or two and if it keeps doing this I will start asking questions of installer.
I asked the same to my installer but ended up doing the work myself.
FreedomWon attempted a lot of things, this was before they adapted their manuals to state that you have to charge the battery to 100% at least once a week.
What also happens (as plonkster noted) is the BMS drift and that throws the SOC values out. To prevent that or fix that you need to charge the battery to 100%, but not using SOC values but actual Voltage settings. I have found that if I do the 100% charge per week on SOC then I still need to do an extended voltage charge setting once every 2 months or so to just ensure the BMS keeps the right data.
One of the ways to see this is to check the charge current/power into the battery when it is at 98% or above. If there is still maximum power going INTO the battery then you know the cell balancing and reporting is out.
(Mine did nice SOC drops from 40 to 0 and jumps from 80 to 100).
For what, 2 months(?) now with Cpt weather, at first I kept the bank charged, gave up and left it, most of the time, at 80%. Charges a bit, seldom hitting 100%, then discharges back to 80%.
Balancer starts at 3.45v, so it is far from a “balancing act”, if any.
How do I know the SOC is accurate? Comparing the BMS with the BMV SOC, the two stayed spot on in sync.
Last two days I whacked the batts down to 20% overnight, perfection if I may say so.
And it is not an expensive BMS either.
Makes me wonder about it all. Having spent big bucks, 10 year warranties, and then these irritations people are asking about, and we are not even “halfway”.
… maybe I must just go and sit in the corner and shut up …
