I have a Backfire that had been stored for a long time and when I plugged it into the charger it it blinked red/green several times before it went red and started to charge. I assume this is because the battery was at or slightly below fully discharged.
During the charge process I noticed that one of the banks (this is the flexi-deck kind where each battery bank has its own section of the cover) the center bank was significantly hotter than the rest of the banks - as measured by putting my palm on the plastic.
I stopped the charge and left it outside overnight.
The question is, is this normal for one bank to heat up and the rest not? Or is it a fire waiting to happen?
I’ll likely take it apart and measure all the banks, but I wanted to get a take from the battery pros.
If it sat and the cell was low the bms will try to raise that cell to meet the voltage of all the others, so on paper the cell will get hotter than the rest that aren’t receiving as much power.
That being said im not familiar with the internals of the backfire boards, but they might mount the bms in that center bank which would also be the reason for the heat as its burning off that extra energy to balance that low cell.
If anything sits for an extended period of time I always open it and check it before plugging it in, Maybe it got too hot in the garage, or like me the salty sea air makes it way into everything even in the garage.
Check it with a multi meter get cell readings, that should tell you right away whats going on, and if they are all good, plug it in and monitor it. Hope that helps
Most esk8 bms won’t start balancing until the very top of the charge and they do so by bleeding off the higher voltage cells to match the lowest voltage cells.
The charge ‘should’ get cut off if any one cell reaches overvoltage before the rest of them are full, but this is not always the case.
@DougM if it concerns you enough to ask here, it definitely warrants opening up and inspecting. I’d be measuring voltage of individual cells while standing and then also while under charge. My guess is that the hotter group is charging faster, could be a dead cell(s), broken welds or poor connections.
It is the 2 middle groups, so probably 21.3-24.8, possibly 14.2,17.75 depending on which way it’s oriented. I don’t have any way of monitoring individual voltages during the charge process but I should. I’ll look into hacking something together.
In the meantime it’s been on trickle charge (1.5A) for about 4 hours and nothing’s gotten unusually hot so I’m going to just let it cook for however long it takes.
I wonder how hot it actually got? Any chance of it being a bottle neck on the pcb and not the cells as 4a is pretty low current to have much heat at all from the cells let alone being able to feel it through the enclosure. Might actually be beneficial to charge it faster just to see where the problem is
I don’t think so, there’s nothing particularly interesting about the way the PCB is setup, all the balance is traces on the board and they are pretty big. GND and +V use double-traces so should easily handle 4A.
The above 3.55 on the cells was after maybe an hour or 2 on the big charger (when I noticed the heat), so they could easily have been at or slightly below 3.2 when I started the charge. Maybe there’s something weird about bringing cells up from minimum V.
The trickle charge terminated so I’m going to put it together and take it for a test ride tomorrow. After that I’ll put it back on the big charger and keep an eye on it with the thermal camera, maybe in 15 minute increments.
Ok, I took the board out today for a short ride (because light rain) and it is a very well behaved board.
Not powerful, and the tires are really plasticy but it’s really quiet and definitely designed with beginner riders in mind. I’ve always wanted a simple little lightweight board i can keep in the car that can also serve as a loaner board and this is probably it.
One thing to note is that it has this auto-on feature where when you turn on the remote the board turns on. Really cool except in instances of very long storage. I’ll be interested in seeing what the range is now as compared with new.
So now I have even more boards than I ever intended. I need an intervention.
