Ok folks, so i have a little project that involves having units connected by wire, each unit has Li-ion cells, 3 in series to create 11.1/12.6v. I want to connect the units together so that they are able to balance between each other, if the voltage is within a reasonable difference.

So, PIC16f1825 to measure voltage of cells either side, and if the cells are slightly out voltage wise use a resistor-limited path to allow equalistation... Then a direct switched route for balanced... Of course cells will be protected with 3-cell BMS...

The sort of circuit I was thinking could be like this...



IC6 is a quad switch that can take 200mA each switch. I would only allow connection of the batteries if the voltage difference was about 1V, which shouldn't happen really. I would love to find a more capable IC but even amongst solid state switches they are hard to find for what I want!

Ignore the resistor values on the voltage divider for now as I have not decided on the PIC voltage yet, so both just 1k temp..

What are people's thoughts?

 

Just to add, I'd probably add a couple of PTC fuses in and out to be safe as well.

 

This is a nicely done, well drawn circuit. Well labeled and well organized.
Evidently I am not grasping just what the circuit is supposed to do.

 

If no other I/O etc needed, appears you could use a 8pin PIC?
BTW, good idea to tie the MCLR high with a 10k R. !

 

This is a nicely done, well drawn circuit. Well labeled and well organized.
Evidently I am not grasping just what the circuit is supposed to do.

Thanks, it might be some signals for a small narrow gauge railway we have underground. Hence my need to have seperate battery packs but also the remote possibility to slow charge from an external source all connected devices....

 

If no other I/O etc needed, appears you could use a 8pin PIC?
BTW, good idea to tie the MCLR high with a 10k R. !

Hi thanks, this is far from complete atm!

 

To use an 8 pin PIC device, first you need to understand how to program it, Then you need to know how to write the code that makes it do what you want it to do, and get that correct. Then you need to have the equipment to load that program into that PIC. And then hope that you got every bit of it exactly correct.

If you do it with an analog circuit you need to understand what the analog function will need to be, then you need to design the circuit and build it. And if it is not exactly perfect, then you need to adjust the variable resistors until it is right.

 

Hi MB2, I know how to program micros, was just asking if anyone can see a flaw in my circuit, and if a better, more capable IC can be found to switch. Idea is the batteries packs are 20m apart, I want them all to "normalise" and remote trickle charge (very low, like leave a 12v battery with Li-ion charge manager for a week), so that units don't have to be dealt with individually when it comes to maintainance. The two fets are a power switch IC used to switch potential divider to PIC to monitor voltage of either battery, so inbalance can be assessed. If < approx 1v then resistor will be switched in to limit current. When equal voltage then they will be connected together... As said PTC fuses will be added to ensure no heavy current can surge.

 

Good, then you have the resources to use the PIC. Not everybody has those resources. No obvious flaws in the circuit, but be sure the heat-sinks on the FETs are separated and can't touch.

 

but be sure the heat-sinks on the FETs are separated and can't touch.

BTW, the FDC6330L is a pair of connected FET's in a 6pin SMT/SOIC device.
To wit: an Integrated Load Switch