Circuit for Matrix of fully isolated 18650 cells

Thread Starter


Joined Aug 25, 2019
How might you approach the circuit design for the following scenario...

1. Given 1000 x 18650 lithium ion cells (it could be any number of cells).

2. Ability to charge any single cell, independent of the others.

3. Ability to discharge any single cell, independent of the others.

4. Ability to run tests and gather data on any single cell, independent of the others.

5. Assuming one or more TP4057s for charging/discharging components is fine.

6. No more than 1 cell (4.2V) will ever be accessed at once.

7. No more than 0.5 amps will ever be delivered or drawn from one cell at a time.

This requirement brings to mind old-fashioned switchboard (without the human operator) with 100 rows and 100 columns, but with lithium ion cells at each row/column intersection rather than phone line. It also brings to mind a string of individually addressable LED lights, but with cells, which are not just a load, but also a source.

Since this requirement ONLY requires accessing a one cell at a time, using as few components as possible is a key design objective. Could this "Cell Switchboard/Relay Board " be built with a single TP4057? Could it be build with fewer than one relay per cell (maybe a Row Relay and a Column Relay???) Are relays even mandatory to achieve the full isolation...maybe a TIP41 or comparable BJT? Might multi-channel or multi-pole relays or transistor arrays be leveraged to reduce the number of components, while maintaining full isolation of each cell?

At any rate,my questions are that of a layperson, trying to understand how real electrical engineers might approach the circuit design for this EXACT requirement.
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