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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.


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4 years ago

Lithium calls are very sensitive to over charging and to some degree to over discharging.

The 18650 you have MAY have a protection cct attached to them in which case they just need a suitable power supply with a few volts over the nominal supply and a suitable current to charge them in a reasonable time. Generally 4 x C where C=discharge rating.

HOWEVER if they are not protected your best bet is to buy a lion charger intended for Radio control use, Hobby king is as good as anyplace to start,


Answer 4 years ago

Thank you very much for your answer.

I figured out now the exact specifications of my cells. These are panasonic CGR18650D's Got that datasheet over here: http://www.rosebatteries.com/pdfs/Panasonic%20CGR1...

It seems like they are not protected right?

What if I buy one of these BMS boards for 4S packs. http://www.aliexpress.com/item/2PCS-LOT-Free-shipp...

Can I then charge them with a normal wall wart with a voltage of at max 4x4.2V=16.8V and with 4A? Or is it the easier way to take one of these chargers instead? with the same wall wart? http://www.hobbyking.com/hobbyking/store/uh_viewit...

What would be the best choice to make?

Or do I need both for best safety?

Thank you


Answer 4 years ago

As always any answer I give is going to be complicated and not guaranteed because I am not there and I don't know what electronic skills you have.

1. the data sheet does not say the batteries are protected.

2. As far as I can see used correctly the charge discharge protector should be Ok. However you may find it hard to locate a suitable wall wart that can supply 16.8 volts at up to 30 Amps (the MAX charge rating for the board) - mind your not likely to use that but even 2.4 amps x 4 is potentially 10 amps if you only charge at their discharge rate (recommended).

3. The RC charge option will give you the opportunity to balance each cell automatically. Different cells often charge at different voltages and rates resulting in some under charging and some over. A good charger monitors each cell voltage and alters the charge accordingly (usually by discharging the higher cells until they match the pothers.)

Thus the cells in a battery pack each need an individual connection brought ot to a balancing plug this is usually white and if you look at a number of RC battery packs you should be able to see it as a second connector.

there are multiple 18650 battery chargers out there for all number of cells


Not all that expensive,

Charging Lipos is fraught with dangers, they are very sensitive to over charging and may gas, bloat and split resulting in a fire sometimes.

You should NEVER leave them charging unsupervised this includes your phone, lap top etc. (we all do it).

Over discharging them may result in their not taking a full charge in future hence the proliferation of cells with protection ccts built in.

About the best I can say I think.

Be careful your house/car/person may be worth more then the audio system.