On the moment I’m working on the battery part of my esk8 built. I’m kinda sure I want to make a 10s3p batterypack with p42A cells.
So i want to charge my batterypack with a BMS and I was reading about this system.
First of all I realised (after reading) it would be safer (for my body) to use this BMS only to charge the batterypack.
I found this diagram of @b264 and for me it seems to be a good solution to discover any problems with my batterypack. If i’m understanding it right; if the battery discharging fails the light would light up?
I do see a fuse in this diagram. Can someone explain me what the stats of the fuse has to be?
I’m unfurtionaly still a noob, but I hope you guys could learn me some more. I really want to make a safe buildt so I’m sorry I maybe ask stupid questions
I don’t think it works that way. In this diagram the only benefit I can see from having the lights hooked up to the BMS discharge port is that the BMS should automatically turn them off if the voltage gets too low. I suppose that way the lights act as a small diagnostic tool in case your BMS thinks something is wrong / goes wrong itself?
I’m not an expert in what break time you need for the fuse, but in general, a fuse that is rated for 2x your planned charge current is a good idea so that it doesn’t warm up / cause unneeded resistance when charging normally, but it’s still there to blow up in case you short your charge port / use the wrong charger or something.
I don’t think it works that way. In this diagram the only benefit I can see from having the lights hooked up to the BMS discharge port is that the BMS should automatically turn them off if the voltage gets too low. I suppose that way the lights act as a small diagnostic tool in case your BMS thinks something is wrong / goes wrong itself?
Ahh thx for your explaination. Sounds logic!
Thanks again!
Is this diagram OK then? I just based it on the upper one. ( I know i forget the BMS balance leads)
Looks good to me! Just remember the light needs a buck (step-down converter) to convert your battery’s variable voltage down to a constant 12V or 5V for your lights
I don’t see benefit of that light. When you activate your system lamp will turn on and when battery is empty or BMS disconnects discharge if one cell group falls below set threshold, light will turn off. It will disconnect power from ESC and you will loose the power. Lamp will shut off at the same time ESC does.
The “light” label is for any external non-critical load (Like, say, headlights. Or tail lights. Or underglow. Or a fan, or a pizza pocket warmer.) Obviously you would probably want some kind of switch to turn such a device on or off, but we’re purely discussing the wiring of battery-and-BMS-and-ESC, not getting into the details of every different possible build, and all the possible permutations of wiring and powering and controlling various accessories.
No. That’s the whole point of bypassing the BMS for powering the ESC: To make it so that the BMS physically cannot shut off power to the ESC. Depending on your ESC’s battery cutoff setting, you would be able to limp home even after the BMS has turned off the light.
The idea here is to help idiot-proof the system so they even if you accidentally leave your board overnight with the loopkey plugged in and the lights (or whatever) turned on, the BMS can kill the lights to save the battery. The ESC will still draw a little bit of idle power, yes, but it’s a lot less than the lights.
In that case i would just fit relay and connect relay from bms to control the coil and relay to switch off ignition on the esc if there is such. I am mainly orienter to ebikes so controllers might be different
The reason I would put in the light would be to prevent the ESC shuts down, because you can’t use the breaks than eather. The light wil work as an indcator for any problems with the batterypack / BMS.
And that would still defeat the whole purpose of bypassing the BMS.
On an ebike, if the motor cuts out unexpectedly, it’s a lot less of a big deal, because you’ve got a seat and handlebars to hold on to.
On an esk8, if the motor suddenly stops and you’re not expecting/bracing for it, you will go flying and streetface. This is why we try to avoid that - Most of us don’t like the flavor of asphalt that much.
Thanks guys 
