# How do I charge this odd 4S Li-ion circuit?

I am trying to make a battery pack that will power my electronics. I need to make +7V and -7V. The +7V needs to have a decent amount of capacity. I have proposed a 2S6P circuit for the +7V supply with a 1-Ohm STAR resistor network to balance the midpoints. To make the -7V I just tacked a 2S circuit below ground.

To make things complicated each cell has a Battery protection IC BQ2970 to prevent reverse polarity insertion, short circuit protection any many other things. So each cell in the schematic is actually representing Pack+ and Pack- in the second picture

I am designing my PCB to include a charger option. How do I go about charging this? Is there an IC or circuit anyone can recommend?

Well most big companies have battery charging chips, like

https://www.analog.com/en/parametricsearch/11471#/

Linear Tech also used to have equalizer chips. My RC-Battery charger has one.

In general... a µC, and a powerfull buck(boost) Stage can charge Lipo's that's how my RC-Battery charger works. You just need also to measure voltage and current as lipos need tight control. If you do it wrong, prepare to call the fire department.

• So a charging chip for each individual cell? Sep 18, 2020 at 16:47
• no. if the charge level of the cells is almost equal you can charge em together. If you build in a equalizer (you really want), it will manage the charge level of single cells. I am still not sure if you better not drop that two cells for the negative voltage but place a dc converter after the pack and generate the +V 0V -V there. It will be much easier to charge a uniform battery Sep 18, 2020 at 16:54
• So you are saying I can just hook up a 4S charging circuit to the entire circuit, even with the BQ2970? The positive side has 6 cells in parallel and uses those resistors to balance the charge as an equalizer. Is charging those batteries in parallel a problem? Also a DC converter is very noisy and will be detrimental to any precision circuit to create a -V. A Battery is the least noisy option to make a negative voltage.. Sep 18, 2020 at 16:59
• The BQ2970 should not matter, they will only act if something is wrong... use a equalizer IC not resistors - resistors can't really equalize (some cell just hold charge while others get a bit discharged). And Of Course you need to do some filtering after the DC/DC. Sep 18, 2020 at 18:43
• I cannot use a DC/DC converter here. Is it safe to charge the 4S circuit with the 6P only on the high side, say using a charge IC like that of the LT3652HV set at a constant current of 2A? Sep 18, 2020 at 20:01