Can't calibrate AH's/SOC on JK BMS

[PrivatePIlot]

Hey all. I've done some searching and reading here on the topic before posting, FWIW.

Fresh 4s 280ah build. 200A JK BMS. The pack is performing well and with conservative settings is showing around 271AH in and out.

I cannot for the life of me get the amp-hours/SOC to calibrate properly. It seems that the BMS only thinks the battery is about 1/4 it's actual size - when fully charged and running a load test the SOC drops like a stone and bottoms out at zero with at least 60-75% of the AH's still there. When charging it pegs out to 100% SOC and shows "280ah capacity remaining" after maybe 60-100ah of input.

I've fully cycled the battery at least twice now and it doesn't seem to be "learning" anything.

I considered doing a factory reset, but it seems (based on further reading here) that only the Android version of the JKBMS app has the factory reset option, and we are an iPhone household. I'm presuming this will fix the issue and I'm sure I can find a friend to do the reset for me with their phone, although the exact calibration procedure from that point is also a little foggy.

Can anyone offer any insight?

 

[RCinFLA]

I assume you are getting a 100% full reset when doing a full charge. This is required to clear Columb counter.

Have you used a clamp on DC amp meter or other shunt to verify the JK BMS amperage readout?

If one or more of the ten shunt resistors have a bad connection it will show greater current than actual.

 

[Aly_Oops]

Yes, the app has factory reset option. I only have Mac & IOS.

Judging by some of the pictures of SOK-BMS posted, most have very bad balancing cell differences. Seem many think that 3.4 cell voltage is fully charged. (nope: it can be anywhere between 20 to 80 percent, depenbding if you saturated the cell to max voltage first) Also, new batteries should have their cell saturated at least once. 3.6 to 3.65 vdc.

Depending on the version of SOK BMS, set absorption to 14.6 and be prepared to run in absorption mode for a week. Yikes, I had to do that with one client. There 2.0.3 version work better, but still has difficultiy in balancing (Needing 3 hrs absorption to have cell 3.6 but V Differ varies from 10 to 20 mv.

It seem SOK is still in the learning curve. Price of early adopter, I guess.

 

[Vi s]

- Deleted - Sorry wrong thread

 

[Hans Kroeger]

Yes, the app has factory reset option. I only have Mac & IOS.

Judging by some of the pictures of SOK-BMS posted, most have very bad balancing cell differences. Seem many think that 3.4 cell voltage is fully charged. (nope: it can be anywhere between 20 to 80 percent, depenbding if you saturated the cell to max voltage first)

OK, but may I add a little comment? If you charge an LFP cell with a moderate current to 3.4 Volts and stop charging close to 0 Amps the cell will be 100% full. See

Charging Marine Lithium Battery Banks | Nordkyn Design

nordkyndesign.com

Also, new batteries should have their cell saturated at least once. 3.6 to 3.65 vdc.

Can you explain why?...... or point me to your source of this info? Is this just hearsay?

Depending on the version of SOK BMS, set absorption to 14.6 and be prepared to run in absorption mode for a week.

I am certain that this is not a good idea. A week at 14.6 V (3.65 V if all cells are in sync, more than 3.65 V for cells out of sync) means heavy stress on those cells (except the cells are from Winston) . I try to avoid cell voltages above 3.55 V at end of charge. I start and stop active balancing at 3.37 V even though voltage drift of cells is not pronounced until cell voltages go above 3.45 V. There is no absorption time required for LFP cells. You may want to stay for some time (1 hour max) at the "end of charge voltage" (between 14.0 and 14.2 V for an S4 configuration) to allow your balancers to do their job, and then fall back to a float voltage at or below 13.4 V. If cells drift apart so that a balancer cannot get them in sync, one must charge/discharge those out of sync cells individually to 3.5 V. Passive balancers requiring 3.6 V to turn on are no good. Active balancers are preferred over passive ones, but it is important that they go to sleep mode at low voltages to avoid bottom level balancing.

Yikes, I had to do that with one client. There 2.0.3 version work better, but still has difficultiy in balancing (Needing 3 hrs absorption to have cell 3.6 but V Differ varies from 10 to 20 mv.

It seem SOK is still in the learning curve. Price of early adopter, I guess.