So, I'm looking at a charger which charges 4 LiFePO4 batteries in series, it basically works by constant current charging until they are charged to a certain limit, and then the rest is charged by constant voltage charging.
Furthermore, some of the circuitry implemented is for protection of overcharging the cells, in this circuit each cell charger module has a tl431 which when reaches a certain limit allows current to pass through it, switching the transistor on and opening a short circuit path for the current thus stopping the charging of the corresponding cells.
The circuit diagram is attached and is explained by its maker here if you would like to give it a read
https://keithwelliott.com/2016/07/14/openadr-battery-charger-circuit/

My question is:
so by the working mechanism of the tl431, the top battery for example will stop charging when the voltage from cathode to anode is higher than the voltage across R6 right? thing is, wouldn't the voltage from cathode to anode always be higher than the voltage across R6 since they are all connected in parallel... and whereas the voltage from cathode to anode is equal to the voltage of the battery, the voltage of R6 is less than that since it's part of a voltage divider.....
but this clearly makes the protection circuit malfunction indefinitely.... is there something wrong with the circuit or did I make a mistake somewhere?
Furthermore, once it has stopped charging and the current has been shorted... what makes us so sure current won't flow from the top battery to the other batteries.

 

by the working mechanism of the tl431, the top battery for example will stop charging when the voltage from cathode to anode is higher than the voltage across R6 right?

Wrong.
The TL431 starts to conduct when the voltage across R6 is nominally 2.5V.
For R6=1kΩ, the current through R6 is 2.5mA at that point (negligible current flows into the TL431 control pin).
This current also flows through R5=400Ω giving a voltage drop of 1V.
The nominal voltage where Q1 starts to conduct is thus 2.5V + 1V = 3.5V.

And it doesn't "short" across the battery at that point, the transistor just starts to conduct to bypass the battery current while maintaining the battery voltage.

once it has stopped charging and the current has been shorted... what makes us so sure current won't flow from the top battery to the other batteries.

The batteries are in series, not parallel, so current can't independently flow from one battery to the other.
If you look at the required complete circuit path, you will see this.

Have you tried simulating the circuit?

 

Wrong.
The TL431 starts to conduct when the voltage across R6 is nominally 2.5V.
For R6=1kΩ, the current through R6 is 2.5mA at that point (negligible current flows into the TL431 control pin).
This current also flows through R5=400Ω giving a voltage drop of 1V.
The nominal voltage where Q1 starts to conduct is thus 2.5V + 1V = 3.5V.

And it doesn't "short" across the battery at that point, the transistor just starts to conduct to bypass the battery current while maintaining the battery voltage.
The batteries are in series, not parallel, so current can't independently flow from one battery to the other.
If you look at the required complete circuit path, you will see this.

Have you tried simulating the circuit?

Where did you get the 2.5V from though?
and no I haven't simulated it as of yet, because I wasn't really sure what to expect..
Thank you

 

Where did you get the 2.5V from though?

It is the specification for the TL431 chip.

 

It is the specification for the TL431 chip.

but isn't it supposed to be a programmable (changeable) voltage though?

 

but isn't it supposed to be a programmable (changeable) voltage though?

If you read the Datasheet for it, you wouldn't be asking stupid questions.

 

If you read the Datasheet for it, you wouldn't be asking stupid questions.

The people who actually helped and had a reason to speak didn't complain.... You didn't even help..... and are compaining props to you!!!
If you wanted to tell me to check the datasheet, then you could have said that and I'd be fine with it..... but you didn't..... so keep it shut!!

 

It is the specification for the TL431 chip.

Actually I got it eventually, thanks a lot

 

Thanks guys, you were all very helpful!!!

 

Wrong.
The TL431 starts to conduct when the voltage across R6 is nominally 2.5V.
For R6=1kΩ, the current through R6 is 2.5mA at that point (negligible current flows into the TL431 control pin).
This current also flows through R5=400Ω giving a voltage drop of 1V.
The nominal voltage where Q1 starts to conduct is thus 2.5V + 1V = 3.5V.

And it doesn't "short" across the battery at that point, the transistor just starts to conduct to bypass the battery current while maintaining the battery voltage.
The batteries are in series, not parallel, so current can't independently flow from one battery to the other.
If you look at the required complete circuit path, you will see this.

Have you tried simulating the circuit?

It sort of looks like a lithium cell balancer - more or less the right general direction, but not quite how I'd go about it.

 

It sort of looks like a lithium cell balancer - more or less the right general direction, but not quite how I'd go about it.

Sir, your recommendations are more than welcome

 

Sir, your recommendations are more than welcome

Buy an off the shelf balancer module unless you *REALLY* know what you're doing.

Overcharging a lithium cell can make you wish you hadn't!