Tello without BMS
- Thread starter carsco
- Start date
You want to desolder BQ24259 from the main board? Hard to tell what will happen, but I'd treat lack of response on I2C requests as hardware failure.
Noone forces you to anything.
Again, this is speculation - I doubt anyone desoldered any chip from the main board and expected this to run.
But normal practice in designing such a system is - the chip next to ours doesn't respond -> announce HW fail.
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Why don't you simply try it with another cell or other external power supply providing about 4V?
I would expect that Tello works. We have already other threads here in the "mods" section about similar modifications.
I would expect that Tello works. We have already other threads here in the "mods" section about similar modifications.
What manages the battery on Tello is the BQ24259. The battery itself does have transistors for cutting power, but they seem to be a part of a simple undervoltage protection circuit, without any memory.
If you remove the circuit only, then yes, it should fly. There is no feedback from that block to BQ24259.
You should probably read BQ24259 datasheet and draw conclusions from there.
Ok, let's look at the circuit:
WM004 Battery Board
Tools for handling firmwares of DJI products, with focus on quadcopters. - o-gs/dji-firmware-tools
github.com
First you'll notice 4 identical chips. They have 6 legs, but chips often merge legs together - so hard to draw conclusions from that alone. But there are 4 of them, which suggests they might be connected in parallel to allow higher amperage through the circuit - these are probably MOS transistors for cutting off power.
Now there's a diode on the left. Why would you need a diode in such circuit? It could be for reverse current protection, but then it would have to allow the large current as well, and there's only one, small diode. So what else it could do? There are Zener diodes, used as voltage reference sometimes - is that it? Do we need a voltage reference?
If we have cell undervoltage detection - then yes, we need a way of detecting if cells are below 3V, and Zener diode would help with that.
So if we have power switch + zener diode, one thing which is missing for a complete CUV circuit is a voltage comparator - and I'm pretty sure one of the remaining chips is just that.
So this leaves us with one unknown chip, plus few discrere components. Caps are most likely for stabilization of power supply to the chips, so can be ignored. One resistor is signed RT, which suggests it's a temperature sensor? This is a bit wierd, as BQ24259 datasheet suggests a different type of sensor. But I haven't read the datasheet really, only watches pictures. so not sure. The chip might be a buck converter for the comparator, or part of the temperature measuring circuit.
Not that hard, right?
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