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  5. Looking for feedback on my QBMS configuration and settings.

Looking for feedback on my QBMS configuration and settings.

  • Bill C.

    Hello, I have been using my REC-BMS setup with the following settings for the past month. Some of the settings that my electrical engineer designer has specified are different than what I've seen in this forum and would appreciate any feedback as I am still learning how the REC alogrthms and logic work. (The manual is not written for beginners and perhaps not well written for experienced people either.) I am posting a series of screen shots so that anyone that is interested can compare and constrast their feedback.

    All helpful comments are appreciated! ;-) 😬

    Questions:

    1. How does the REC BMS algorithm work when the Balance End Voltage is set higher then the End of Charge Voltage?

    2. Is there any way to tell when the REC is balancing by using the web page through the Wifi module?

    The 24v system consists of two batteries built using CALB 230 cells, arranged as a 4P8S X 2 for 64 cells. I am  using the REC master with two slaves. One differnce is that in order to fit into the battery box of my sailboat, I've had to go with two batteries with each battery "bending" cell 6 to fit. We are using 4/0 Ancor tinned wires with high quality Selterm lugs as leads and as the replacement bus bars. As you can imagine, the impedance on cell is higher when bulk charging, but settles down after charging and while discharging. See the pics.

    My engineer has prgrammed to REC with the following settings. He is very experienced and has created dozens of these systems. He feels that these are the correct settings for my battery set up. 

    Thoughts?

    These differ from the ones I found on this forum:

    Thanks in advance for any insights or help you can provide. 

    Cheers, Bill C.

     

    __________
    Cheers, Bill

    0 likes
  • B


    Your question:
    1. I cant explain you, I don't know this in detail.  But the 3part manual page you post don't sound correct to me. I never have seen this document, no time at the moment to study the details.
    In REC factory manaul, see REC default settings, these values are set the same, that why I keep them always the same.

    2. check manual for this command, and enter in "manual communication" in the WIFI app. WCIB?   show which cell is balancing

    About your settings.
    I see for me strange thinks, but all settings are up to the tech that installed them.

    3. Why CLOW and CMIN are that low?
    dangerous low in my view, better to keep to REC defaults.
    4. Your restart voltage for charging again is set at, if voltage is below 13.16V Is this what you really want.
    5. Max cell voltage I prefer 3.6 or 3.65

     


    I would suggest the following settings.
    Which will result in float 13.4.
    Restart to bulk if SOC is below 95% (If SOCH, is still at factory setting)

    Balance end voltage  3,52
    Balancing start voltage  3,45
    Cells max difference  0,25
    END of Charging V 3,52
    END off charging V Hys 0,17
    Cell over-voltage switch-off  3,65
    Cell over-voltage switch-off  Hys 0,15
    Cell-under voltage  switch-off 2,8
    Cell-under voltage  switch-off Hys 0,05
    MIN cell V discharge (inverter  CAN) 2,9
    Charge float voltage Coefficient  1

     

     

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  • Bill C.

    @Ben I've looked across all of the documentation and tried to use WCIB? but the command is not recognized in the manual command line. 

    __________
    Cheers, Bill

    0 likes
  • R

    Bill, I looked over your parameters and in my opinion, they are pushing the limits on both the high and low voltage side. Between 3.5 and 3.7V there is only 1-2% capacity so I would tend to be a bit more conservative.  You also have a large hysteris but that will only allow it to work under large imbalance condtions.

    Setting your end of charge to only 3.5 means that although it can balance to 3.65 volts it will likely never get there.  If it were my system, I would set both of these parameters closer to 3.55 to 3.6

    For the WCIB command, you dont mention what rev firmware your BMS is using but it may be you just need an upgrade.  You can get them here.

    https://rec-bms-na.com/product-manuals/

    Finally, I understand that the in an upcoming release the wifi module will include a viewable "balancing" status.

    Hope this helps,

    Rick

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  • Bill C.

    Hi Rick, thanks for the response. Here is a screenshot of the 9m SW/HW. I've checked the website and unless I am missing something, do not see any newer firmware. It will great to be able to see when balancing is happening. Any idea on the release date?

     

    __________
    Cheers, Bill

    0 likes
  • R

    Hey Bill, I am not sure if the Master supports this new function but will check with engineering and report back.

    0 likes
  • R

    This is what we got back, which is encouraging and keep in mind that the Master uses firmware that is keyed to the serial #, and has to be requested from engineering.

    WCIB does not work on Master - there is no such instruction in the Master Manual. 
    We are preparing the  WiFi update that will show the cells being balanced in the Voltage tab for all BMS. Master does not have this feature now. New firmware will send the Packages with all BMS Slaves cells that are being balanced.
     
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  • Bill C.

    @Rick this is indeed good news. Any idea on the timing?

    __________
    Cheers, Bill

    0 likes
  • Bill C.

    @Rick " You also have a large hysteris but that will only allow it to work under large imbalance condtions."

    Because of the need to use 4/0 wires on cell #6 to allow me to "fold" the batteries to fit into the available space. (See the pictures above in my earlier post) The 4/0 wires have a higer resistance than the other CALB bus bars. This causes a slight and temporary cell imbalance when charging at high rates. This goes away when slow charging or in discharge. 

    The electrical engineer that designed the system has been trying values that will work across all of my charging conditions. 

    __________
    Cheers, Bill

    0 likes
  • R

    @Bill I am hoping it will be first quarter 2025.

    0 likes
  • Bill C.

    Guys, thanks for all of the help. I have been moving my settings to match the recommended values from this thread. I have one question regarding float voltages. 

    While away from my boat, I have been using the Multiplus-IIs to keep the batteries in float at 26.80v which matches my calcs. See screen shot where I have parsed the REC manual. See red box at the bottom. My questions has to do with when does the REC send a message to the Cerbo GX and MP-II's to start another full charge cycle and charge the batteries back up to 28.16v? I'm sure the answer is staring right at me in the REC manual, but I am not understanding the variables that are considered to shart a new charge cycle in Bulk.

    __________
    Cheers, Bill

    0 likes
  • Bill C.

    @Ben  

    I've done some additonal reading and in your experience should the BMIN BVOL values be the same for active vs. passive balancing? 

    Perhpas I am thinking about this the wrong way, but doesn't the active balancer in ABMS move charge from the cell with the highest voltage to the cell with the lowest, while the Q BMS bleeds off energy using the resistor?  

    I have both an ABMS and Q BMS systems in my boat.

    Looking through the REC Q BMS manual, and using Ben's numbers (see below) for reference, balancing will start at 3.45v and end at 3.52v.

    According to the REC Q BMS manual, balancing is accomplished using a 3.9 Ω power resistor which by my calculation @ 3.45V equals 0.88 amps and @3.52 equals 0.90 amps of passive power dissipation.

    Does cell balancing ONLY happens between 3.45v - 3.52v during the charge cycle?

    OR, will balacing continue until the battery is either balanced or the voltage drops back to 3.45v/cell? What if you can't fully balance during the charging run up to during that voltage range?

     

     

    CALB 230B specs

     

    Balance end voltage  3,52
    Balancing start voltage  3,45 --> according to the chart above, my BMIN should be 3.39v but I like your value better
    Cells max difference  0,25
    END of Charging V 3,52
    END off charging V Hys 0,17
    Cell over-voltage switch-off  3,65
    Cell over-voltage switch-off  Hys 0,15
    Cell-under voltage  switch-off 2,8
    Cell-under voltage  switch-off Hys 0,05
    MIN cell V discharge (inverter  CAN) 2,9
    Charge float voltage Coefficient  1

    __________
    Cheers, Bill

    0 likes
  • Bill C.

    Can someone explain how the passive balancing alogrithm works on the the REC Q BMS. When you reach the balancing start voltage, in this example 3.45v, does the REC balance one cell at a time by draining charge from the cell with highest voltage? Or does it try to drain charge from several at once?

    __________
    Cheers, Bill

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