Hi there,
I want to design and make a battery charging system for NiMh and NiCd with quick charge ( 2A ) and automatic cell number determination.
I chose a LTC4060 for this, since it does pretty much everything already.

I am currently thinking about the "number of cell selection" which uses binary encoding to determine the number of inserted cells. I thought about automatically detecting this.
Current status and approach:

• So my idea was to put the cells in series and for each cell measure the voltage across the + and - pole to determine if a battery is inserted
• With a(4x) difference amplifiers(single cell voltage) and a(4x) comperators(compare vs threshold) i want to throw a HIGH-state for each line that is having a battery.
• Since they need to be in series i want to prioritize only the highest number of cells
• For now i did this by connecting these with AND gates, so a higher line is only HIGH when the previous is HIGH (and cascaded these)
• ( it would be nice to have a error detection for wrong battery alignment as well, like Inserted-inserted-missing-inserted which would cause 1-1-0-1, but thats beyond my scope for now)
• I then use a descrete priority encoder circuit (4-to-2) to generate the binary code
• with this binary code i would also like to switch transistors for the BAT pin of the LTC4060 so i need the 2-to-4 decoder circuit.
• i want to avoid cutting edges since i dont know yet how to handle missing cells in between

I am currently thinking about buying CD4051 mux/demux ICs for doing the de/encoding stuff ( since i dont have any more of those ancient descrete logic gates )

Now i have some questions regarding this:

• To me my approach looks overly complicated, but it seems to work in principle (diffamp->comperator->encoder->decoder for switching correct number of cells to the BAT PIN), has anyone a better idea how to accomplish this?
• What happens if i have multiple channels "HIGH" like in the case of eg. 1-1-0-1? What is the output state?
• How could a error detection for cells not in series ( 1-1-0-1) look like?

Thanks for reading

 

I made some progress and solved some issues. Its not efficient but it should work. A microcontroller would have been easier for sure, but i liked the discrete logic and OpAmp design

So, i did end up using Quad-OpAmps as voltage substractors, then i needed a negative power supply so i chose a schmittinverter oscilator circuit. The negative voltage is then inverted ( another quad op amp) and compared against a minimum cell voltage ( voltage divider).

This gives me digital logic that I wanted for the LTC4060. I used a modified 4-to-2 priority encoder circuit and added error/validation logic for that detects missing cells and checks if the cells are in a serial alignment.

This logic then goes into the LTC4060 programming pin, and into a 4051 demuxer in order to open the correct transistor for the charging circuit.

Its not fully tested, maybe someone can have a look at the schematics. I also need to appease the KiCad electrical rules check which throws some warnings and errors.

When this thing is finished i ll make the same charger with a microcontroller in order to remind me how much more effort the discrete logic is :-x

 

I have 8 cells and eight 50c charging modules. I buy a single cell holder for $1.20 and the most complex part is to fit the cell into the holder and watch it charge.
When the green light comes on, I use all my skill and electronics knowledge to remove the cell and put it back into the battery pack.
Next year I am going to finish my Masters of Electronics course.

 

I have 8 cells and eight 50c charging modules. I buy a single cell holder for $1.20 and the most complex part is to fit the cell into the holder and watch it charge.
When the green light comes on, I use all my skill and electronics knowledge to remove the cell and put it back into the battery pack.
Next year I am going to finish my Masters of Electronics course.

Haha
Its just a "learning electronics" project that I do with no need for it aka a hobby. I registered here to be able to ask specific questions that are obviously so stupid and newb that no one cares. I am glad that at least you are nice and not even slightly toxic