Re: [electricboats] One cell out of whack. Replace it or stay with it.

Again, that JK BMS itself can only bypass 2amps around a cell.  So if more than 2amps of current is coming into the pack trying to charge the cells, bypassing alone will not keep one or more cells from going nuclear…   Rather, you need each and every charging source to be informed to throttle back its charging current to ensure the BMS can do its job.

I imagine that most of our BMS setups merely balance cells and do not directly control shore charger, let alone solar and wind.  In many or most cases, that's okay for shore power charging since the charging is over many hours, the cells are expected to be quite balanced, charging target voltage is appropriately safe and the charger's output current throttles back as the target is reached.  But can the same be said for these solar and wind charge controller outputs?  If either's target voltage is inappropriately high, you can easily imagine exceeding the BMS bypass capability.

 

From: electricboats@groups.io [mailto:electricboats@groups.io] On Behalf Of Dan Pfeiffer
Sent: Sunday, June 29, 2025 6:33 PM
To: electricboats@groups.io
Subject: Re: [electricboats] One cell out of whack. Replace it or stay with it.

Assume BMS processor is reading cell voltage and passing it along to other software inside it. Otherwise check wiring to that cell anyway. Agree very bad running cell to 4.? volts. Might consider swapping it out after fault is fixef

Best regards

Lee Eldridge

0427874796

On 30 Jun 2025, at 02:54, Peter Knowlton via groups.io <pqknowlton=gmail.com@groups.io> wrote:

Question for those who have familiarity with the JK BMS's. I have 16 Eve lifepo4 cells for a 48v 280a battery bank. I have 6 - 24v, 220w Newpowa solar panels and a Silentwind 400 for wind generation. The Silentwind has a dedicated Silentwind PWM charger and the panels have a Victron Smart solar charger 150/30. I am using a JK 300a BMS. A couple weeks ago I was testing all the components to make sure they were acting as they should. So, I turned on the solar and wind chargers, went back to land for a few hours, and when I came back there was one cell that was  4.29v and the rest were around 3.35v. (See the first screen shot below.) Fearing a runaway cell, which will expand horribly if the charging condition is not stopped, I turned off the solar and the wind. After a couple hours all the cells were back down to around 3.35v, including the 4.29v cell. Ran the engine at half throttle for about half an hour the next day and the cells stayed in synch with each other the whole time as they were collectively discharged by running the motor. Then, day before yesterday I tested the charging, again, using solar and wind and, again, after a few hours, this same cell went up to 4.20v and every other cell was around 3.35v. When I turn off the charging the cell, again, goes back down to 3.30v and, gets in balance with other cells as they all settle to .004v of each other after a couple hours. Shouldn't the BMS shut down any cell that goes above 3.65v if that's what the over protection voltage shut-off is set at? I am concerned that the BMS isn't shutting off the charging for the "runaway" cell when it reaches 3.65v, which is the charging high voltage protection shut-off I have set on these cells. I just don't know if its the BMS or the cell itself that is the problem, since I believe any cell can get overcharged if the BMS is not working properly for that cell. Although the BMS is brand new. I am thinking of switching the BMS wire for the runaway cell to another cell and see if the same overcharging condition happens to that cell and see if the original cell, with a different BMS wire now, stays at the same voltage of the other cells or overcharges again. Attached are some screen shots of the cells and the setup through the JK BMS app. Any ideas or suggestions appreciated. You all have provided me over the years with the most thoughtful advice and I thank you for that. If you can't open the zip file of screen shots I can send them individually. 

 

Peter Knowlton

Dartmouth MA