Don't shoot, I'm working with what I have and trying to approach this from task first principles standpoint.
I'm making a 280Ah 12V battery from EVE cells for a camper"van". In my use case, the battery will see 20A load at MOST. It will be running a car fridge that draws ~5A and occasionally charging an electric scooter with ~10A, plus few usb outlets. I chose such big cells only to provide enough juice, as I plan to be in the middle of nowhere for days.
I will also NOT charge it with solar panels.
So I'm thinking to balance charge it with my ISDT Q8 Max (that I already have) powered by an old desktop PSU that puts out 40A @12V (that I also already have). Charging this way would top balance every time I charge (or at least charge high enough, I didn't find Q8 specs regarding balance voltage threshold).
For the low voltage cutoff I'd be using those lipo beepers, set at 3.0 or 3.1 volts (depending on how out of calibration that particular beeper is). I'll be testing that, but the idea is to warn at least 10Ah in advance about lowest cell getting empty. That would give me ~5h of fridge runtime in case I'm away (but me being away from the battery this long will most likely be extremely rare) and notify me otherwise.
I also have an old watt/ammeter that I'd use to monitor Ah-s and Wh-s given out from the battery after each full charge, to roughly monitor SOC (for example, if I know it's getting empty, I wouldn't leave fridge running unsupervised for hours).
That only leaves us with no temperature monitor/cutoff that BMS-s usually have. I do have some cheapo thermistors with a display laying around to stick between the cells and visually monitor the temperature, but no real option to cut off power automatically. I'm wondering though, charging with 0.1C (~30A, maximum for Q8 Max) and discharging with 0.05C at most, what benefit would temperature sensor of a "real" BMS give? This battery will never see temperatures below 5-10 nor above 30-35 degrees celsius. If a thermal runaway happens (that doesn't really happen with LFP), how much more likely would it be during charging with 0.1C vs just sitting there (considering that it's supposedly a sufficiently smart charger and all)? Or during 0.05C-ish discharge?
All of this humble build would use just a few standard automotive fuses. No fancy inverters, no fancy BMS-s with bluetooth, no 4/0 gauge wires, nada. Just a box with a lid for terminal isolation and a few usb/xt60 outputs on top and a handle to carry. Probably 10AWG wires for flexible bus"bars". A short 10AWG wired plug for charging.
I'm making a 280Ah 12V battery from EVE cells for a camper"van". In my use case, the battery will see 20A load at MOST. It will be running a car fridge that draws ~5A and occasionally charging an electric scooter with ~10A, plus few usb outlets. I chose such big cells only to provide enough juice, as I plan to be in the middle of nowhere for days.
I will also NOT charge it with solar panels.
So I'm thinking to balance charge it with my ISDT Q8 Max (that I already have) powered by an old desktop PSU that puts out 40A @12V (that I also already have). Charging this way would top balance every time I charge (or at least charge high enough, I didn't find Q8 specs regarding balance voltage threshold).
For the low voltage cutoff I'd be using those lipo beepers, set at 3.0 or 3.1 volts (depending on how out of calibration that particular beeper is). I'll be testing that, but the idea is to warn at least 10Ah in advance about lowest cell getting empty. That would give me ~5h of fridge runtime in case I'm away (but me being away from the battery this long will most likely be extremely rare) and notify me otherwise.
I also have an old watt/ammeter that I'd use to monitor Ah-s and Wh-s given out from the battery after each full charge, to roughly monitor SOC (for example, if I know it's getting empty, I wouldn't leave fridge running unsupervised for hours).
That only leaves us with no temperature monitor/cutoff that BMS-s usually have. I do have some cheapo thermistors with a display laying around to stick between the cells and visually monitor the temperature, but no real option to cut off power automatically. I'm wondering though, charging with 0.1C (~30A, maximum for Q8 Max) and discharging with 0.05C at most, what benefit would temperature sensor of a "real" BMS give? This battery will never see temperatures below 5-10 nor above 30-35 degrees celsius. If a thermal runaway happens (that doesn't really happen with LFP), how much more likely would it be during charging with 0.1C vs just sitting there (considering that it's supposedly a sufficiently smart charger and all)? Or during 0.05C-ish discharge?
All of this humble build would use just a few standard automotive fuses. No fancy inverters, no fancy BMS-s with bluetooth, no 4/0 gauge wires, nada. Just a box with a lid for terminal isolation and a few usb/xt60 outputs on top and a handle to carry. Probably 10AWG wires for flexible bus"bars". A short 10AWG wired plug for charging.
