Hacker News new | past | comments | ask | show | jobs | submit login

A battery management system handles this.

You still charge the pack in series, but the BMS will discharge cells that have a higher voltage than others. This results in all cells having similar charge levels.

It doesn't change the charge time, though. You're putting the same amount of energy into the pack either way. 14.8V @ 100mA applied to 4 cells in series is the same energy as 3.7V @ 100mA applied to 4 cells individually. Can't escape the laws of physics.

If power efficiency is critical (solar applications, for example), the BMS might have fancy switching circuitry to re-route energy from overcharged cells to undercharged cells. This is expensive, though, so most BMSs just use resistors to burn off extra charge from overcharged cells.




> You still charge the pack in series

I understand that's how it's done, but can we charge faster if we DECIDE NOT to charge in series? I take it the answer is no?

Imagine a series of 14 cells. I could charge them as a whole, but there is normally some limit on how much power I can pump into it. Now suppose that I disassembled the series and now I have 14 cells that I can charge independently before re-assembling them back. If I did that, would I gain anything? If nothing else this should prevent unbalanced charging, reducing overall heat of the pack and allowing higher current overall?

I can see that some packs advertise 5a charge current and other packs of the same capacity offer 10a or even 15a. Wonder why is there such difference.


It would be marginally faster (best case probably a percent or two) for a much more expensive charging circuit. The reason for this is that you can discharge batteries much faster than you can charge them.

Also, it seems like you're imagining that you can charge batteries with more power if you charge them in parallel instead of series. This isn't true since you're just trading a higher voltage/lower current for a lower voltage/higher current.


No free lunch for me then. Thanks for explaining.




Guidelines | FAQ | Lists | API | Security | Legal | Apply to YC | Contact

Search: