I let a friend ride around a little bit, but when he was done he didn’t turn off the controller. (About 6 days ago) Not a big deal, right? I know I had low voltage cutoff set on the Vesc, so I wasn’t too worried at first. (And it should turn off after inactivity too, right?)
So I plugged in the charger, but nothing happened. The bms was shut off, so there was no Bluetooth connection to it.
Then, I tested the voltage of the main leads off the pack, and then…
The voltage has since risen to about 7 volts since I unplugged everything. Way too risky to do anything besides recycle it now, right?
But more importantly, how did this happen and how do we make sure this never happens to anyone again? Of course I has bypassed the bms for discharge, which is kinda a requirement for what we do. Why would my low voltage cutoff be set to 54v, but it somehow ended up at 5v over the last couple days? The discharge on the bms was also set to off before this happened.
I would really appreciate anyone’s thoughts/ideas.
The low voltage cutoffs are for running the motor, your battery was drained by the ESC idling on. Since the esc doesn’t have an auto shutoff (see latching switch) it’ll just kill your pack. It’s like leaving your engine on and running out of gas.
The pack is cooked. Recycle it and move on. If someone (one specific forum member) tells you otherwise, ignore him. He’s a massive liability.
BMS discharge would’ve stopped this from happening, but it comes with risks on a vehicle without mechanical brakes. If you have mechanical brakes, I would actually suggest it.
That doesn’t exist in vesc land. There are escs that utilize software hibernation (vesc auto shutoff) that’ll turn off after a defined time of inactivity. Those arent really susceptible to this kind of failure.
6 days seems crazy fast.
there’s no other drain on the pack?
I suppose it’s not fast if it was already very low when you parked it. getting from 2.8/cell the rest of the way down is fast.
and as others mentioend vesc low voltage cutoff is about preventing the motor from drawing current. it doesn’t stop the idling electronics. which shouldn’t be that much of a draw, but some vescs have been called into question in the past as having a higher draw.
Yeah that’s what I thought too. Could be because of the way I have regen set up. When there’s no user input, regen is at 100%. When it was on the power supply it was showing it was drawing a bit over 5w idle. And I assume the battery was around 40% or 3.55v/pc. So yeah, I guess the math works out…
You’re not alone. This is exactly what killed my eFoil project. I finished building the battery pack, and it was huge, but the pack had some other electronics in it for communicating with the remote, and I left those on all winter long.
So in the spring I went to get back to it and the pack was completely dead. I hadn’t even started fiberglassing the board yet.
I agree with the idea of a low voltage alarm, or some sort of physical disconnect device that triggers when the lowest battery threshold is met. It could be as simple as a a voltage supervisor chip that trips an electromagnet that kicks open some sort of physical connection like a knife switch.
Probably a pain in the ass to design test and build give how rarely this happens.
I 100% agree that other electronics such as lights and other accessories should be on a non-bypassed bms (unless there’s some unique reason I’m not thinking of), but sometimes buying a massive BMS isn’t a good option. Whether it limits the current your motors can output or is just a space/cost issue, it just doesn’t make sense sometimes. Still feel like we need a third option, or at least some sort of backup that could prevent very unfortunate scenarios like these ones. Feel free to correct me, but that’s my position on the issue right now.
Ugh that’s not fun. I’m also interested in building some sort of efoil day (soon hopefully). That’s really painful. It’s not just the cost that hurts, but all the hours put in making sure everything is designed as cleanly and functionally as possible. Hope you will find the opportunity to give your efoil project a new attempt some day!
