@user554252 Also check out Béla Bollobás's Modern graph theory. In chapter 2, the author discusses electrical networks...This book has been on my todo list for many years :(

anyone knows about common faults in cordless vacuum cleaners? I got one here with full battery but upon trying to switch it on it blinks as if the batteries are emtpy

@PlasmaHH Did you use it to vacuum up a demon?

@Asmyldof its not mine, so I dont know, I might ask if they did ;)

@PlasmaHH Tell them it's the only possible answer

That, or maybe bad contact somewhere in the measurement circuit

If you verify that the batteries stay at good voltage when switched on

Else, demons

Or bad batteries

But, demons

battery voltage drops by 150mV for 200us when switching on

ntc with 14.4kOhm sounds reasonable too

I dont like trying to measure stuf on pcbs with conformal coating :/

Try loading the battery with half an amp or such and see what the voltage does

Unless you looked with a scope

Well, even if you did look with a scope

Sharp drop may not register on MM

yes, I looked with the scope. It doesnt seem to try to draw anything much, doesnt even try to switch on the motor.

Demons

Or try with artificial load

the motor should probably draw ~1.8 amps, guess I have to find my box with big fat resistors..

5 lipo in series, drops ~500mV when loaded with 11 ohm, pretty fine I would say

PEBBAM

obviously

Try B-->M directly?

if only I could read what st micro that thing is I could search better for a possible serial output that when I am lucky gives a reason, or I can identify pins, though that thing has another qfn ic that I dont know exactly what it is for, likely todo with balancing, also totally unreadable

Must be a very fancy vacuum if you expect they implemented UART

its an AEG so not too unreasonable

motor turns

Did you try licking all the ground wires?

Demons hate soaked earth

I have stuff to do in the garden tomorrow, I could bury it there

Sounds reasonable

there must be some condition that makes it think its a bad idea to turn on and blink that "battery empty" led ... either because it thinks that the battery is empty or some other error condition...

given that when it charges it blinks in "more than 75% full" mode I would guess it doesnt think its actually empty

well, I think I will go to bed now

@PlasmaHH Single set of wires from bat to PCB, or multiple?

@Asmyldof multiple. One series for power, one set for balancing

Maybe an issue with a balance point or balance wire

I will have to trace them to the IC tomorrow, but there is the correct voltage at the corresponding resistors. If something would be wrong there, wouldn't charging Gail to?

Not if the voltage is always underreported