I'm looking to build a battery pack from lithium-ion 18650 cells, 13s16p (parallel first) to achieve around a 50V (nominal) battery pack. I realize there are probably charge solutions out there with the proper voltage and BMS which can be used to charge the entire pack with balancing and protection; however, my idea is to use a single adjustable buck CC power supply on each parallel cell pack to keep it charged to 4.2V while in series, and then power all of these supplies with a single larger amperage AC-DC 12V supply which can be powered with 120V AC.

I'm wondering if having all of the individual battery chargers powered by the same supply will be a conflict while the packs are wired in series (the inputs would all share a common ground). Does each circuit need to be segregated with a transformer? Is there another way to separate them? Other pitfalls I'm not thinking of?

  • \$\begingroup\$ Buck won't do it, you'll need isolated supplies. Or start with a 50V supply, a single CC charger, and a BMS that handles cell monitoring and balancing like all the others. \$\endgroup\$
    – user16324
    Commented May 11, 2020 at 20:55
  • \$\begingroup\$ 16 in parallel is dangerous unless they're indivually fused. \$\endgroup\$
    – Neil_UK
    Commented May 11, 2020 at 21:12
  • \$\begingroup\$ @Neil_UK the plan was to fuse each cell in some fashion to heavy copper buses. \$\endgroup\$
    – slambeth
    Commented May 11, 2020 at 21:22

1 Answer 1

  1. Does each circuit need to be segregated with a transformer?

Yes, unless it will short circuit.

  1. Is there another way to separate them?

You can use isolated DC converter.

  1. Other pitfalls I'm not thinking of?

Giving each cell a charger is ideal way to charge series cell

By the way (1) need a lot of isolated convertor and charger which quite expensive.

Usually we use 1 CC/CV charger to charge them all and use BMS to balance each cell by discharging and prevent over charging. so as many comment it handy to use BMS.

  • \$\begingroup\$ Appreciate for editing, I'm new guys here this help a lot \$\endgroup\$
    – M lab
    Commented May 12, 2020 at 6:34
  • \$\begingroup\$ I appreciate you answering the my actual questions, and I do get what you're saying about a BMS and a single CC charger for the whole pack. I should have put more info in my original question about why I'm curious in such a solution. Scalability is the main one. I"d like to be able to add more cells packs as needed, as this could grow to be a 100V pack. When getting into larger voltage/current charging solutions, it doesn't get cheaper it seems. I like the idea of each cell having it's own dedicated charger to bring it always to the proper voltage level. \$\endgroup\$
    – slambeth
    Commented May 12, 2020 at 14:39
  • \$\begingroup\$ I totally get your concern, actually I was think that way before. It not right or wrong or design as long as it's meet the requirements. Here the things, when battery have same size it need same current to charge this why we charge all of them once in series. When it's near fully charge it need some current to balance each sell in order to compensate imperfects equals of cells's capacity. So use individual charger for each cell seem a bit overkill. But still your choice. \$\endgroup\$
    – M lab
    Commented May 13, 2020 at 6:39
  • \$\begingroup\$ Thanks for your feedback. One more question. If the battery cells are isolated (are no longer in series), can a single AC-DC power supply be used to power multiple DC-DC CC regulators/chargers? \$\endgroup\$
    – slambeth
    Commented May 14, 2020 at 14:19
  • \$\begingroup\$ Yes it can. But it seem hard to isolate cells every time when charging. \$\endgroup\$
    – M lab
    Commented May 14, 2020 at 17:14

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