I would like to build an autonomous system that contains:
– An Arduino board (later, it will be just the chip)
– A LED strip
I decided to use 3×3.6V lithium batteries in series. So, the idea is to have the 3 batteries in series that supply the Ardiuno board and the LED strip in parallel.
Now, my problem is the charging the batteries.
After research online, I see that the best solution would be to charge them in parallel. There are many dedicated charging circuits on eBay or aliexpress for charging at 4.2V, is that good ?
To be able to have a good charging time, I need a output current of 2 or 3A, right ?
If this solution is good, when a will plug the 5V input and charge batteries, there is no risk for LED strip and ardiuno board ?
Or I will have to open the circuit when I plug my supply ?
When I will plug my supply, it will apply 4.2V on each battery. So, in series, I will have 3 x 4.2 = 12.6V. So, I need to check if LED strip and arduino if ok with that voltage, right ?
For arudino, it should be ok, for LED strip, I'm not sure, the normal voltage is 12V.
Thanks for your help,
Best Answer
Note that you cannot just put lithium cells in parallel without balancing them first (to make sure they are equally charged).
Also, you cannot just charge Li-cells by applying a voltage, if you do that, don't be surprised if the cells get too hot or even explode ! You need a dedicated charging circuit or module.
But let me propose a much simpeler solution: Just balance your cells, then connect them in parallel. Charge them using a charging module, feed that module form a 5 V power supply. These modules can easily be found on ebay.
To make the 12 V for the LED strips, use a DCDC boost converter. On ebay you can find these and most have a trimmer to set the voltage to the 12V you need for the LEDs.
You can also feed the arduino from this 12 V, make sure you connect the 12 V to the power adapter socket (Vraw) so that the voltage goed through a regulator which will supply 5 V or 3.3 V (depends on your Arduino module) to the microController.
You can make it extra fancy by monitoring the battery voltage through a voltage divider and feed that to the Arduino. When the battery voltage gets too low then the Arduino can detect that and switch off the LEDs so that you know its time to charge the batteries. :-)