How should I charge 3 lithium ion batteries?

Hello!

I'm new to battery charging and I was wondering. What is the best way to charge and manage 3 18650 cell batteries? The load is about an amp and I have a 4.7 amp power supply to charge them. I'd like to be able to charge the batteries and also power my device.

Thanks for your response!

How are the batteries connected, ie series or parallel?

Lithium batteries can explode or start fires if improperly charged.

The best approach is to use a single cell charger intended for lithium batteries, and charge them one at a time. Otherwise, if the cells are to be used in series, for safety you need a balancing charger.

jremington:
Lithium batteries can explode or start fires if improperly charged.

The best approach is to use a single cell charger intended for lithium batteries, and charge them one at a time. Otherwise, if the cells are to be used in series, for safety you need a balancing charger.

Thanks for the response,

I plan on using the batteries in series, i'm aware that i need to use a 3S balance board, and a constant current converter to charge them, but is it safe to draw power from the batteries while charging? and where do i connect the load to?

Thanks!

You can draw power while charging, it should just mean the charger takes longer. A full BMS is the best
approach if doing this, as it can detect both under-voltage and over-voltage on every cell and cutoff, and
arrange for balancing during end-of-charge period, and perhaps report the pack's state on a display (fancier
ones). The load connects to the battery. The charger connects to the battery, and the balancer also connects to the cell junctions. Most packs use a separate JST style connector for the charger/balancer,
you should adopt this standard for your home-build pack ideally.

You must have over-voltage, under-voltage and over-current cutoff with lithium packs (the former
is only needed for charging of course).

If you never let cells reach full charge the balancing won't really happen, which might be an issue if
charging while drawing power. A full balancing charge isn't needed every discharge cycle though.

Make sure the charger or BMS is a match for the chemistry of your cells. (most are 3.7V nominal 4.2V
full charge, but some vary significantly, like LiFePO4).