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JK BMS 4S combined with Victron BMV-712

Bari Rosch

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Joined
Sep 6, 2022
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14
Hey all,
Im testing my 12V, 280Ah LiFePO4 battery in combination with the 4S JK BMS (B2A8S20P-H) in my anticipated RV setup.

I found out that if you place the BMS between the battery and the BMV (see drawing attached) that the BMV does not record the proper charge currents. E.g. I charge with 25A (which is shown both on the Multiplus and the BMS), and the current on the BMV is somewhat between -8A and 18A (depending if the led screen is lit on the BMV). Also other charge current (5,10A) the readings are way off. Discharge currents it does not seem to have a problem.

If I remove the BMS the BMV does depict the correct charge currents. Also shipped the BMV to Victron and they tested the unit and said it was working properly. When connecting the BMV directly to the battery and/or hooking up the BMS after the BMV (basically swopping the position of the BMV and BMS) the BMV does report correct charge currents. I did a factory reset, current calibration all does not seem to work, so I guess the problem is with the JK BMS.

As I see the BMS as part of my battery I would like to place it directly on the main negative of the battery, and this is also how its regularly done on this forum. Anyone else experiencing this same problem? Where/how did you install the JK BMS in your systems? Is it a faulty unit, or is simply not possible to put this BMS in between the battery and BMV. What would you recommend me to do?

JK BMS details:
Vendor ID: JK_B2A8S20P
Hardware version: V11.XW
Software version: V11.12
Version: V4.8.5
 

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I've got this exact same issue (see: https://diysolarforum.com/threads/jk-4s-200a-bms-electrical-noise.45500/).

Appears to be a problem with the new 4-8S JK BMS as I don't have this issue with my 16S JK BMS. I also had issues charging with some power supplies.

I haven't found a solution and will most likely raise a support case with JK via their aliexpress store. I now have 4 of these BMS all with the same issue. It does work with a SmartShunt (without display), however even this shunt makes a buzzing sound when charging which has never happened with any other BMS.
 
I've got this exact same issue (see: https://diysolarforum.com/threads/jk-4s-200a-bms-electrical-noise.45500/).

Appears to be a problem with the new 4-8S JK BMS as I don't have this issue with my 16S JK BMS. I also had issues charging with some power supplies.

I haven't found a solution and will most likely raise a support case with JK via their aliexpress store. I now have 4 of these BMS all with the same issue. It does work with a SmartShunt (without display), however even this shunt makes a buzzing sound when charging which has never happened with any other BMS.
Thanks for the reply. I didn't see those other threads before. I got proper readings (charge/discharge) from the BMV, when placing it between the battery and BMS, however this introduces a new problem. I now got arcing sounds coming from my multiplus while charging the batteries. Without the BMS installed, no sounds, Stopped testing for now and removed the BMS and waiting for a response from Hankzor. I'll try to add sounds tomorrow. Also saw this thread with same issues: https://diysolarforum.com/threads/jk-bms-inducing-noise-to-rail.40706/ , therefore stopped testing with my multiplus :)

Im really wondering if its a "early release" problem or a problem with all their 4S/8S B2A8S20P ones.
 
Are there any news on this ?
I use a 4-8S JK BMS together with a BMV712 and a SmartSolar MPPT 100/30.
 
Only thing I can think of is the way the 712 is doing 120 Hz ripple current filtering and ground reference asynchronous shifting.

Do you have discharge disabled on BMS when you see the charge current shifts?

Charge or discharge disabled on BMS adds a diode voltage drop across BMS due to the disabled MOSFET body diode but when current gets greater than a few amps it overrides the disable setting during the periods of higher current to avoid overheating on MOSFET's body diode. This would cause an asynchronous voltage reference shift in 712 negative input line.
 
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I left my lead battery to a lithium with a JK BMS B2A8S20P this summer. I had 3 issues :

1 Some noise with high current charge (more than 20A). I didn't really pay attention until I saw yesterday on the forum some reports about this.

2 I had fake readings from the BMV 712 with high current charge. I verified with an amperemeter and under 13A current the BMV 712 was accurate and above was not ( the current was underestimated). I didn't think it could be because of the BMS, I tough the RJ11 cable was faulting. So I shortened it and now readings are accurate.

3 Three days ago, the BMS entered in a boot loop emitting crazy beeping. Charge and discharge were disconnected and there was no way to connect the app. I installed/uninstalled/reinstalled an older version of the app and now it's working again. But how long time ?

Well, this BMS B2A8S20P is quite worrying
 
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Only thing I can think of is the way the 712 is doing 120 Hz ripple current filtering and ground reference asynchronous shifting.

Do you have discharge disabled on BMS when you see the charge current shifts?

Charge or discharge disabled on BMS adds a diode voltage drop across BMS due to the disabled MOSFET body diode but when current gets greater than a few amps it overrides the disable setting during the periods of higher current to avoid overheating on MOSFET's body diode. This would cause an asynchronous voltage reference shift in 712 negative input line.

Thanks for this reply. When charging the battery I had both charge and discharge enabled on the BMS.
For now I won't be able to do any tests anymore, I returned the unit to China. When it arrives they'll send me a new one, so it might take a few weeks. Meanwhile I focus on building the van ;)

I took some time to upload the sound recordings of the Multiplus.
(See my previous post for more details). First part is without the BMS installed. Second part is with the BMS installed. This is the reason why I removed the BMS and stopped testing as I don't want to damage the expensive Multiplus.

Hopefully I just have a faulty unit and the new BMS works correctly.
 
I left my lead battery to a lithium with a JK BMS B2A8S20P this summer. I had 3 issues :

1 Some noise with high current charge (more than 20A). I didn't really pay attention until I saw yesterday on the forum some reports about this.

2 I had fake readings from the BMV 712 with high current charge. I verified with an amperemeter and under 13A current the BMV 712 was accurate and above was not ( the current was underestimated). I didn't think it could be because of the BMS, I tough the RJ11 cable was faulting. So I shortened it and now readings are accurate.

3 Three days ago, the BMS entered in a boot loop emitting crazy beeping. Charge and discharge were disconnected and there was no way to connect the app. I installed/uninstalled/reinstalled an older version of the app and now it's working again. But how long time ?

Well, this BMS B2A8S20P is quite worrying

On your 2nd point: I also first thought it was the RJ11 cable (poor connection). I had readings way off both at 5A charging and 20A. Returned the BMV to Victron where it was tested. Worked like a charm. Tested it myself without the BMS installed, BMV worked correctly. Installed the BMS again. Again same problem with faulty/oscillating readings on BMV. This tells me it was not the cable, however happy to read that shortening the cable worked for you.
 
On your 2nd point: I also first thought it was the RJ11 cable (poor connection). I had readings way off both at 5A charging and 20A. Returned the BMV to Victron where it was tested. Worked like a charm. Tested it myself without the BMS installed, BMV worked correctly. Installed the BMS again. Again same problem with faulty/oscillating readings on BMV. This tells me it was not the cable, however happy to read that shortening the cable worked for you.

Was yours any early version JK BMS B2A8S20P? Apparently there were about 20 initial units that had non ideal DC DC converters that drew a large resting current and could overheat and become unstable. An improved DC DC converter (power supply for circuit) is now in current JK BMS B2A8S20P. I wonder if this was setting up some oscillations.
 
Was yours any early version JK BMS B2A8S20P? Apparently there were about 20 initial units that had non ideal DC DC converters that drew a large resting current and could overheat and become unstable. An improved DC DC converter (power supply for circuit) is now in current JK BMS B2A8S20P. I wonder if this was setting up some oscillations.

I was not able to test this (resting current draw) because I shipped/returned the unit 2 weeks ago before this info was known. However I think I ordered it the 1st or 2nd day after release, so might well be the case I had an early version. Not sure though how a larger current draw results/translates to the observed behavior.
 
Hey all, after some time I received a new BMS. I had some time today to install the new BMS and test it. Unfortunately I'm running into the same issues as before. Wrong reading on BMV-712 and arcing sound. Im really wondering if im doing something wrong and/or how this issue can be resolved. I made a video of the setup. Let me know what you guys think.

 
For the BMV misreadings I resolved it shortening the cable going to the BMV screen. I think you can resolve it putting the shunt before the BMS (battery/shunt/BMS).
For the arcing sound, I don't know.
 
For the BMV misreadings I resolved it shortening the cable going to the BMV screen. I think you can resolve it putting the shunt before the BMS (battery/shunt/BMS).
For the arcing sound, I don't know.
Hey Thanks for your reply. I think you mentioned you had only off-readings at higher amperage correct? I might eventually shorten it a bit, but need the length in my RV as well. Also, without the BMS installed cable length is not an issue, so will wait a bit before shortening the cable as a last resort ;). Will try to swap BMS and shunt over the weekend.

Just checked the system/BMS and got an error message CPUAUX Anomaly. Saying: abnormal coprocessor communication. Running the latest app version and rebooted a couple of times but no success. Starting to get annoyed by this BMS, but determined to get it work.
 
Only thing I can think of is the way the 712 is doing 120 Hz ripple current filtering and ground reference asynchronous shifting.

Do you have discharge disabled on BMS when you see the charge current shifts?

Charge or discharge disabled on BMS adds a diode voltage drop across BMS due to the disabled MOSFET body diode but when current gets greater than a few amps it overrides the disable setting during the periods of higher current to avoid overheating on MOSFET's body diode. This would cause an asynchronous voltage reference shift in 712 negative input line.
I did check and tested with charge/discharge and balance on, however still seeing those fluctuating readings on the BMV-712. Actually with all different combinations of charge/discharge/balance toggled on/off it keeps fluctuating. Any clue or suggestion what it could be and how we can resolve this? Thanks :)
 
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