Charge/Discharge a Battery Pack Wired as a Segregated Paralleled Series

Question

This is my first post on EE, so I'll try to be as simple but detailed as I can.

I have a 12S10P pack that I want to segregate into a 6S4P + 6S4P, 6S3P + 6S3P, 6S3P + 6S3P for "cautionary" LiIon balance charging. (My charger only goes up to 6S anyway..) I still want to draw power from all 6 at the same time in a 12S10P config. I broke out MS Paint and unleashed my art skills to demonstrate the masterpiece. In this picture, imagine the top right cells are being balanced charged. There are no diodes in place. I don't know if balance charging will interfere with other cells in the pack (the ones in blue.) If there is unwanted adjacent charging, how do I stop that from happening? Ask questions if you need clarification.

Answer 1

You can't balance the cells with this configuration (6SPx). The Problem if one cell is charged more than the others you'll not be able to figure it out. You have 12S10P configuration, for example if you use a balancing circuit with a configuration of 6S4P you'll balance each individual cell of four branches of your battery with different voltage which can leads to over voltage or under voltage of the cell and damage your battery pack. You can use your balancing circuit with 6S to only balance 6 cells in serial in your case. So you need about 20 balancing circuits to balance your individual cells safely.

Answer 2

I have a 12S10P pack ... I still want to draw power from all 6 at the same time in a 12S10P config.

Assume there are no diodes in place.

I don't know if balance charging will interfere with other cells in the pack. If there is unwanted adjacent charging, how do I stop that from happening?

If all cells are hard connected in an 6SNP arrangement and you do not disconnect strings while charging one string then if you are applying voltage across a 6S string to charge it and doing "something" (not specified by you) to achieve balance then you MUST be charging all strings.

It is not clear why you would think this is not the case.
Rather than drawing large arrays of cells in general form without details of what you wish to do or wish to try to achieve, you would probably be better off to draw a simplified diagram with just a few cells.
I have shown a hard connected 3S2P array below. Using something like thatto explain what you plan and using enough detail to make your proposed method clear will help people understand what you are proposing.

Use this to (try to) explain how you think you could possibly "balance charge" one 3S string without affecting the other one.

There is a very good circuit diagram drawing tool incorporated in this system - click on the cct diagram icon at the top of the question window or use Ctrl-M to answer it. It is easy to use and quite intuitive (albeit a little "clunky"). I used wires to 'build' the battery pack as their battery symbol show 2 or 3 cells with no intermediate connections.

A major problem is that if you DO somehow balance charge a string it is then different in charge state from other strings and imbalanced outputs or inter-string current will flow.

What you SHOULD do is explain

• what you wish to achieve overall
• what application
• what cells
• what currents
• what charger
• what balancer

and then ask how to achieve what you wish.
If you do not yet have a balancer etc then asking how rather than telling us what you wish to do when you do not know how to do it makes more sense.

This is a rough 3S2P circuit diagram.
How could you balance the left string without the voltages affecting the right string?

^{simulate this circuit – Schematic created using CircuitLab}

Answer 3

^{simulate this circuit – Schematic created using CircuitLab} New batteries are balanced <0.1% but aging and C/40 usage can quickly age this imbalance to 1% and at 10% the battery is no good in the array. This can be measured by internal ESR and meter or with LED indicators in the array to help balance.

• Smart balancers use a half bridge PWM with series L between each string cell and can get complex unless designed on a PCB or purchased.
• dumb balancers use passive loading like TVS Zener with PTC protection rated power of 10% during CV mode charge current.
• I suggested cheap Red Power LED's as both passive balancer and indicator if carefully chosen.
• at first this may seem like overkill until batteries age and you want to extend life by balancing then removing mismatched failing cells.

• IF you install thin short wires between cells, they can act as Fuses just like the ones in Tesla 2 batteries. Then you can reduce but not eliminate the risk of mismatched cells shorting out. Tesla batteries all have microfuses on each anode and cathode of 4000++ cells

• then with <0.5% matching you can string many hundredsin parallel

** - compute max ESR of string and increase 25% with matched short ESR fuse wire divided by total N cells using AWG tables for ESR/mm **