Yes, but this is not the cause for the differencies in my case. There were no current peaks, and the independend measurement tool was an amperemeter and not a smart shunt. And the differencies started to occur after installation of the new firmware of the BMS, which indeed solved problems with far too high SOC calculations.
So my assumption is, that JK introduced a factor which is multiplied to the real current measurement only in discharge mode. Their intention was to calculate a more precise SOC value, and they achieved that with this “dirty” trick. SOC values are indeed much more precise now, but at the cost of displaying wrong discharge currents.
I don’t know about best. Only the different mechanisms used by different manufacturers.
You don’t want a breaker tripping as the bms cannot reset it.
What you can have is a relay that is opened and closed by the BMS when it wants.
Some have two - one for charge and one for discharge. Some just have one global one.
The fets can do something similar, it depends on what bms you use.
No i haven’t.
I have a system specifically set up to abuse system components and haven’t as yet had an issue there.
You can DC SPDs if you really want to. But those too have a lifespan. With good measuring and monitoring though you should see a problem long before there is one.
i have some systems with emergency stops set up that are both physically driven and software controlled. But for most installations i have not needed to go beyond a design and good set up. (9 years is the oldest system i have under my belt with lithiums anyway)
Recovered cells the oldest bank i have is 4 years.
For a short circuit situation with high currents, I designed the 100A breaker to disconnect before the BMS opens its MOSFETs. Therefore it also protects the BMS.
There are JBD (Jiabaida) Smart BMS that have a Relay instead of MOSFETs.
But I still think that MOSFET switching is superior since you can controll Charge and Discharge with seperate MOSFETs. Also Relais have a high standby consumption. Sure, there are bistaibel relais available…but those stay engaged, even if the BMS fails…so no real option in this application.
You could also look into the very expensive REC-BMS.
Maybe you should just calibrate both charge and discharge measurements? Or replace BMS if it cannot be calibrated. Mine is dead on when discharging as well.
Yes. There will always be pro’s and con’s. I happen to have a bistable battery protect relay, but that is being used for a whole different application.
I calibrated the charge current, and this resulted to a really good measurement of charge currents. They are accurate (meaning showing the same value as an independend amperemeter) within 1% at very low and very high currents. And at the same time this resulted to very inaccurate discharge currents - 18 amps from the BMS are measured at 12 amps by the amperemeter. Of course I can now calibrate the discharge current, but this will only result in very inaccurate charge current measurement.
But you don’t understand that this was not so with the older BMS firmware. They changed that, and at the same time they claimed to have solved the wrong SOC problem. IMO this was their dirty trick to achieve exactly that.
By the way, regarding your picture: my system reads the current from the BMS.
Maybe we have different firmwares. Mine definitely allows separate calibrations for charge and discharge with no “dirty tricks”. My system also uses JK BMS for primary current&power reading, but I exposed Multiplus data just to show you that with a proper calibration, they both match quite well. JK BMS and Multiplus are within about 1A regardless of how the current is flowing.
My FW is relatively new. I flashed it about a month ago. No issues with SOC either.
JK Inverter BMS PB2A16S20P? Hardware version V15A? I am using firmware V15.35 and installed it about 2 months ago when it was the most current version. There is no and never before was no separate calibration for charge and discharge.
SOC issues with JK BMS (old versions and newer “inverter” versions) are widely known. Andy (offgridgarage on YouTube) discusses these problems in all details.
Thanks for the correction. When I bought the REC BMS a couple of years ago, there was only a solinoid relay available. Seems like they developed a failproof circuit of the bistaible relais in the meantime.
I’ll check the in depth BMS details when I get home and have a chance. It is a 200A v15 JK inverter BMS. I know SOC issues are widely known, but I also bet that most people don’t calibrate their JK BMS, or don’t run latest FW. And even those who calibrate, may not do it for both charge and discharge.
I previously showed that mine is accurate when discharging. Here is charging as well (diagram shows JK BMS power, Multiplus is not far off). SOC also behaves perfect.
Hello, I heard of that SOC Problems with earlier versions, but I have this problem with actual and last version 15.38 of the JK Inverter BMS PB2A16S20P:
The RCV/RFV Timings are 1h/8h, 100% SOC Voltage ist set to 3.50V, so after 1h it should be automaticaly set to 100% SOC and switch over to RFV, but it does not the first nor the second…
DVCC ist Enabled and the BMS is the master.
Any suggestions?
