Dear Community,
I have run into the problem of the terminal voltages differing from the bus bar voltage.
To give you some background on my setup:
I have a 16s Lishen 272Ah (280Ah) system with batteries from Shenzhen Basen. As a sidenote: They tested between 282 and 287Ah.
My system is supervised by a Batrium WatchMon 4 with Longmons (I had that one leftover from my 18650 battery built) and the Batrium controls cooling fans and a relay (Kilovac EV200). I have also designed a little pre-charge circuit to prevent high inrush current. The battery is connected to a Sunny Island 6.0.
After about a month of the system running, I also compressed the cells due to the aforementioned difference in voltage between bus bar and cell terminal voltage. I first thought this was due to the cells slightly expanding and contracting, changing the contact area between bus bar and service. However, this turned out to potentially not be the case.
Removing the washers holding down the bus bar and moving it a little bit on the cell terminal and re-fastening it fixes the problem for a couple of days/ weeks, but the problem also always occurs with different cells and I can’t clearly define a pattern, if it mostly happens on the positive or negative cells.
The cell voltages measured at the bolt screwed into the cells always measure a correct and reasonable cell voltage but the BMS (measuring on the bus bar) measures a sometimes 100mV higher or lower voltage (charge – discharge at 70A ) than what the actual cell voltage is, causing it to stop the charge / discharge or limit the current.
I would obviously like to have a fix that doesn’t involve unscrewing and re-fastening the bus bars every couple of days and I am not sure if the slight changes in size of the cells (even if the cells are somewhat compressed) or some form of galvanic corrosion causes the problem.
I have run into the problem of the terminal voltages differing from the bus bar voltage.
To give you some background on my setup:
I have a 16s Lishen 272Ah (280Ah) system with batteries from Shenzhen Basen. As a sidenote: They tested between 282 and 287Ah.
My system is supervised by a Batrium WatchMon 4 with Longmons (I had that one leftover from my 18650 battery built) and the Batrium controls cooling fans and a relay (Kilovac EV200). I have also designed a little pre-charge circuit to prevent high inrush current. The battery is connected to a Sunny Island 6.0.
After about a month of the system running, I also compressed the cells due to the aforementioned difference in voltage between bus bar and cell terminal voltage. I first thought this was due to the cells slightly expanding and contracting, changing the contact area between bus bar and service. However, this turned out to potentially not be the case.
Removing the washers holding down the bus bar and moving it a little bit on the cell terminal and re-fastening it fixes the problem for a couple of days/ weeks, but the problem also always occurs with different cells and I can’t clearly define a pattern, if it mostly happens on the positive or negative cells.
The cell voltages measured at the bolt screwed into the cells always measure a correct and reasonable cell voltage but the BMS (measuring on the bus bar) measures a sometimes 100mV higher or lower voltage (charge – discharge at 70A ) than what the actual cell voltage is, causing it to stop the charge / discharge or limit the current.
I would obviously like to have a fix that doesn’t involve unscrewing and re-fastening the bus bars every couple of days and I am not sure if the slight changes in size of the cells (even if the cells are somewhat compressed) or some form of galvanic corrosion causes the problem.