Charging 18650s while amp in use?

Hey guys,

I have an idea about a portable boombox which should be capable of running on batteries, as well as off mains supply. 18650 cells seem to be the lightest for a given capacity, so perhaps I'll stick with them. The point is that I want my device to get charged seamlessly without any manual switches or so - just like a laptop (for example: battery is at 30% .. plug in charger .. battery is now at 80 %.. disconnect charger.. and the laptop works uninterruptedly the whole time).

I thought about this: 4A 5A PCB bms Protection Board for 4 Packs 18650 Li ion Lithium Battery Cell 4S | eBay but I don't know if I can just connect the load (amp) parallel to the batteries to achieve the desired function or I have to make some adjustments?

Any suggestions?


2016-05-29 9:35 pm
The simple answer is: No, that's a bad idea.

There are various ways to do what you want. One of them is to pick a lithium ion charging IC that includes the required functionality. I think Microchip calls it load sharing, and TI calls it PowerPath. It looks like the BQ24702 from TI would do the trick. This is in addition to the battery protection circuitry.

If you aren't planning to spin your own board, you'll have to see what boards you can find with multi-cell charging chips and then work with that.

Someone else might be able to suggest an circuit to use to do the automatic switching. Or, use a power jack with a physical switch that can disconnect the amp from the battery when the power is attached.

On the subject of battery protection circuitry, look for a board that also does charge balancing.