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Seplos BMS v3 with active balancer unit (ABU) - active balancer is manageable!!!

nolan7

New Member
Joined
Oct 14, 2024
Messages
4
Location
Slovakia, EU
I have Seplos BMS with optional balancer board. Reading forums here helped me a lot, I learned that to make it work, I have to change settings in "seplos BMS studio", lines 100 and 101. After changing these two values to something reasonable it works good enough for me. When charging, and when cells are getting into the region of voltage curve, where their voltages starts to get apart, active balancer kicks in and works nice. Before that I had ~250mV difference when fully charged. After making active balance board to kick in automatically the difference is less than 50mV. Some people here think it is not good enough, or that it is bad to balance through all of voltage range. I think it is not a problem, because when the battery starts to discharge, voltages get even closer, maybe 3, 5, max 10mV apart. Unless you discharge very low, they will stay together all the time. In Seplos documentation they explain their idea like this: even if it starts to balance through the range of discharging/charging anywhere on the voltage curve, it is helpful to keep all cells together voltage-wise. Even down there, when some of the cells drop voltage quicker, it pushes energy from stronger cells to weaker. It should help for cell longevity, because weaker cells are not stressed so much, and you can use more energy from your battery pack. This "disbalancing" happens only if you discharge too low. Otherwise, it stays top balanced and it keeps like that all the time. Yes, this process disbalances them when considering top-balance, but that is not a problem, because they got balanced again, when top charged, when they get there. All this process keeps voltages similar all the time, which is good. Not much energy is lost, because it is active, not passive balance. Stress on the cells is negligible compared to normal discharging and charging cycles. There is no downside, I think.

Now to the point of my post: THE ACTIVE BALANCER IS MANAGEABLE. Contrary to seplos statement and general consensus, that active balancer is a stand alone unit and all values are fixed, this is not true. In the seplos BMS studio v2.0.0.1 there is an option on start that lets you choose BMS or ABU. If you choose ABU, you can connect to the balancer board and have a look on the pictures what you get there. I used USB to RS232/RS422/RS485/TTL converter. On the Active balancing unit board, there is one white unused connector, with four pins. On the backside of PCB it is marked GND, MCU_RX, MCU_TX, +3V3. I connected them to my USB to serial converter (also I the pictures) and then I am able to connect to ABU. I can change anything I want. This is for you, who are not happy with default values. Sorry for the poor quality of the pictures.

There is one small problem with this but there is a workaround solution. On the "parameter management" page, when you would normally use "real all" to fill up fields with values from your balancer unit, it does not work. There is a problem with reading the last value, line number 33. Workaround is to read each line manually by clicking the blue arrow. It works on all lines except the last one. Also the writing with green arrow seems to work correctly. Login is the same as for BMS use.


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Those delta numbers you are reporting are not exactly healthy looking and it is natural for the delta to converge on discharge.
You have some unbalanced cells. Maybe over time they will converge if you bought decent cells.
 
I have Seplos BMS with optional balancer board. Reading forums here helped me a lot, I learned that to make it work, I have to change settings in "seplos BMS studio", lines 100 and 101. After changing these two values to something reasonable it works good enough for me. When charging, and when cells are getting into the region of voltage curve, where their voltages starts to get apart, active balancer kicks in and works nice. Before that I had ~250mV difference when fully charged. After making active balance board to kick in automatically the difference is less than 50mV. Some people here think it is not good enough, or that it is bad to balance through all of voltage range. I think it is not a problem, because when the battery starts to discharge, voltages get even closer, maybe 3, 5, max 10mV apart. Unless you discharge very low, they will stay together all the time. In Seplos documentation they explain their idea like this: even if it starts to balance through the range of discharging/charging anywhere on the voltage curve, it is helpful to keep all cells together voltage-wise. Even down there, when some of the cells drop voltage quicker, it pushes energy from stronger cells to weaker. It should help for cell longevity, because weaker cells are not stressed so much, and you can use more energy from your battery pack. This "disbalancing" happens only if you discharge too low. Otherwise, it stays top balanced and it keeps like that all the time. Yes, this process disbalances them when considering top-balance, but that is not a problem, because they got balanced again, when top charged, when they get there. All this process keeps voltages similar all the time, which is good. Not much energy is lost, because it is active, not passive balance. Stress on the cells is negligible compared to normal discharging and charging cycles. There is no downside, I think.

Now to the point of my post: THE ACTIVE BALANCER IS MANAGEABLE. Contrary to seplos statement and general consensus, that active balancer is a stand alone unit and all values are fixed, this is not true. In the seplos BMS studio v2.0.0.1 there is an option on start that lets you choose BMS or ABU. If you choose ABU, you can connect to the balancer board and have a look on the pictures what you get there. I used USB to RS232/RS422/RS485/TTL converter. On the Active balancing unit board, there is one white unused connector, with four pins. On the backside of PCB it is marked GND, MCU_RX, MCU_TX, +3V3. I connected them to my USB to serial converter (also I the pictures) and then I am able to connect to ABU. I can change anything I want. This is for you, who are not happy with default values. Sorry for the poor quality of the pictures.

There is one small problem with this but there is a workaround solution. On the "parameter management" page, when you would normally use "real all" to fill up fields with values from your balancer unit, it does not work. There is a problem with reading the last value, line number 33. Workaround is to read each line manually by clicking the blue arrow. It works on all lines except the last one. Also the writing with green arrow seems to work correctly. Login is the same as for BMS use.


View attachment 266592View attachment 266593View attachment 266594View attachment 266595View attachment 266596View attachment 266597View attachment 266598View attachment 266599View attachment 266600
THat's great, I was wondering the same since there was ABU selection in studio. I just didn't rip apart my already build battery to check what interface it is using. It is all make sense now. Could you please export all settings and post here? and Also, would you mind to share a 4-pin connector type you've used ? I guess something like that should be the cheapest option:

1736417487719.png
 
Last edited:
I have Seplos BMS with optional balancer board. Reading forums here helped me a lot, I learned that to make it work, I have to change settings in "seplos BMS studio", lines 100 and 101. After changing these two values to something reasonable it works good enough for me. When charging, and when cells are getting into the region of voltage curve, where their voltages starts to get apart, active balancer kicks in and works nice. Before that I had ~250mV difference when fully charged. After making active balance board to kick in automatically the difference is less than 50mV. Some people here think it is not good enough, or that it is bad to balance through all of voltage range. I think it is not a problem, because when the battery starts to discharge, voltages get even closer, maybe 3, 5, max 10mV apart. Unless you discharge very low, they will stay together all the time. In Seplos documentation they explain their idea like this: even if it starts to balance through the range of discharging/charging anywhere on the voltage curve, it is helpful to keep all cells together voltage-wise. Even down there, when some of the cells drop voltage quicker, it pushes energy from stronger cells to weaker. It should help for cell longevity, because weaker cells are not stressed so much, and you can use more energy from your battery pack. This "disbalancing" happens only if you discharge too low. Otherwise, it stays top balanced and it keeps like that all the time. Yes, this process disbalances them when considering top-balance, but that is not a problem, because they got balanced again, when top charged, when they get there. All this process keeps voltages similar all the time, which is good. Not much energy is lost, because it is active, not passive balance. Stress on the cells is negligible compared to normal discharging and charging cycles. There is no downside, I think.

Now to the point of my post: THE ACTIVE BALANCER IS MANAGEABLE. Contrary to seplos statement and general consensus, that active balancer is a stand alone unit and all values are fixed, this is not true. In the seplos BMS studio v2.0.0.1 there is an option on start that lets you choose BMS or ABU. If you choose ABU, you can connect to the balancer board and have a look on the pictures what you get there. I used USB to RS232/RS422/RS485/TTL converter. On the Active balancing unit board, there is one white unused connector, with four pins. On the backside of PCB it is marked GND, MCU_RX, MCU_TX, +3V3. I connected them to my USB to serial converter (also I the pictures) and then I am able to connect to ABU. I can change anything I want. This is for you, who are not happy with default values. Sorry for the poor quality of the pictures.

There is one small problem with this but there is a workaround solution. On the "parameter management" page, when you would normally use "real all" to fill up fields with values from your balancer unit, it does not work. There is a problem with reading the last value, line number 33. Workaround is to read each line manually by clicking the blue arrow. It works on all lines except the last one. Also the writing with green arrow seems to work correctly. Login is the same as for BMS use.


View attachment 266592View attachment 266593View attachment 266594View attachment 266595View attachment 266596View attachment 266597View attachment 266598View attachment 266599View attachment 266600
One question.
I bought the same cable and connected it like you. I can't connect to the board. What baudrate did you select?
 
One question.
I bought the same cable and connected it like you. I can't connect to the board. What baudrate did you select?
The default BMS Studio setting of 19200,8-N-1 is correct for the board. Make sure you're using the TTL serial pins (not RS485 like the BMS). You probably don't need to connect the 3V3 pin, just GND, TX, RX. If everything is good and it still doesn't connect, you may have reversed the TX and RX pins. Swap 'em around and try again.
 
I just did this balancer connection this weekend. I already had a TTL serial-USB board on hand from Sparkfun: https://www.sparkfun.com/sparkfun-serial-basic-breakout-ch340g.html
I also had some spare JST PH-series connectors from when I built a Victron ve.direct extender. The connector on the Seplos board is not exactly a JST PH-series but it is the correct 2mm pin pitch. I shaved the JST connector ever so slightly with a razor blade and it fits OK for temporary use.
 

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