Hi there!
Just got a pretty powerful (20A) charger, now trying to figure out what needs to be changed in charger/bms/circuit to charge multiple esk8s at the same time.
Soldered separate cables to charger output, but this only charges one battery and drains the other (showing negative amperage in the app).
Here is a wiring schema:
Any tips appreciated!
3 separate charger outputs for starters, in your schematic you’re effectivly parallelling 3 packs. They will start pushing current on one another, but maybe thats your intention?
Yeah that makes sense. Maybe if you put a barrier diode in series with each cable you’ll be able to avoid draining between packs. But packs wont charge simultaniously until they reach about the same voltage.
Well bms controls the ground while charging so the packs are not directly connected to each other.
Why is that? Why it is so different from powering bulbs in parallel for instance?
Uhhh no. Think of a bms not as a smart charger with a dc input but something that draws a small current from the highest voltage cell groups and it can set charge/discharge limits.
roughly the current going into the battery when charging is the:
charge voltage - battery voltage * internal resistance
when you hook up the batteries all together in parallel in prep to hook to the charger. the higher voltage one will start charging the lower voltage ones… with no current control. (battery is not a charger) so it can be very very high if the voltage difference is high.
Most BMS won’t stop discharge through the charge port. So it won’t protect from this.
with the diode idea, the batteries with the lower voltage will get an increased share of the current, It might get all of the current from the charger, and be charging faster until they are all even.
I suspect the diode idea also isn’t practical tho? too special of a diode required for currents/voltages involved.
To charge multiple skates, you need multiple chargers. So, a few small chargers and not one giant charger. Sorry for the bad news.
Thanks for the input, but the question was how to modify my current setup. In other words, I’d like to have a solution similar to multiple device charging over usb.
with usb charging, each device has it’s own built in charge controller.
so similar to what @b264 mentioned a charger per battery pack.
The charger is the bit that does CC/CV ie maintains a max charge current and max voltage to match the battery packs need, as well as an eventual charge cycle cutoff. (usually charge current below some cutoff )
you could do something where you get a large power supply. (your charger could maybe act as that psu ) and a bunch of chargers without power supplies. for example the 12s icharger x12 to manage each battery.
or you could risk off into parallel charging as long as you are ok making sure the voltage differences aren’t to great and you realize that you’re doing some extra cycles on the cells when one board is charging them to even out. but this isn’t really advisable unless you’re confident in what you’re doing.
