How to charge a Powerpack of 18650 li-ion cells 4s3p 14.8V? Answered
I plan to make a portable audio system with 4 speakers and a subwoofer which are driven by a 12v TDA2030A 2.1 Amplifier. Everything is already packed in a small enclosure (approx. 30x15x30cm) and works fine so far. At the moment the amp gets it's signal from a 3.5mm audio jack and the power is provided via a 12v 1.5Ah wall wart.
That's what I have for now. But that's not really portable right? So to complete my project I want to add 2 more things - a bluetooth receiver powered with 5v and of course I need to get this thing of the mains. That's where my questions actually starts.
I've read tons of forum posts, instructions and watched a lot of videos about making a 12v battery pack but I'm confused with all that information. From what I've read 18650 Lithium-Ion batteries have an excellent power density and would suit my system best (small enclosure and portable). But of course I'm open for new ideas anytime.
I planed to make the power pack out of 4s3p 18650's from an old laptop battery (don't have the exact data of them yet). So the pack would provide about 8Ah at 14.8V nominal. With a step down converter to 12v it't could power the amp and for the bluetooth I would use a car usb adapter to get the 5v needed. So far so good, but regarding the power pack I have a few questions.
1. Would a 3s4p (11.1V) arrangement be good enough to power the 12v amp since the 11.1V are in average right?
2. The biggest question I have is - How to charge that thing?
As I want to have it as portable as possible, to be able to charge it anywhere from a normal power socket would be ideal. I know there are dedicated chargers for lithium batteries but they are quite expansive and not really handy to carry around. Is there any other solution to handle that?
3. BMS, PCB - I'm confused. From what I've read, to charge multiple cells they have to be in balance right? An over-charging and over-discharging can lead to fire/explosions and to prevent that a BMS is essential right? But first - how do i connect that BMS? Only to each of the parallel strings or to every single cell? Second, is it possible to use that BMS to charge the pack? Maybe also in balance?
4. For the case that the 18650 from the laptop battery are undercharged, where is limit to withdraw them and to charge them to balance with a TP4065 at 1A?
That's it for now.
Sorry for the long text and thank you for reading through it. I read so much on the net but didn't find the right answer for me.