Diy 18650 4s battery pack [How to charge, how to build?]

[CyPF]

I'm building a bluetooth portable speaker.
However, I have some questions about building my first 18650 battery pack.
I have 4 pcs of Panasonic unprotected NCR18650B 18650 3.7V 3400mAh.
My goal is to build a 4s 18650 pack with these batteries, and the battery pack must:
- be inside the portable speaker
- Fully protected
- Safe

My question is, how do I design this battery pack?
I have a idea, but want to know if it is a good way to build it?(see the second picture)
I also have some others questions:
During my searches on internet some people use balanced charge, is it necessary to it use in my case?
If yes how? Do I need to use a power adapttor or lithium li-ion battery charger adaptor?

Thanks for your future help Cordially,

 

[spinningmagnets]

There has been much discussion over the years about how to run a pack (regardless of size) without a BMS. There have been many cases where a faulty BMS killed an expensive pack.

I am not going to say that this is a good idea, but many do it.

I suspect you want to avoid buying an expensive balancing RC charger. They are made to run off of a 12V car socket, but....since many charge at home too...they can take a higher input voltage in order to raise the max charging amps, and to also access a greater efficiency (higher volts allow lower amps, etc). Due to these reasons, they are often built to accept any input voltage from 10V to 30V DC. The well-regarded iCharger 106B is one option to compare others too (106 = 10A of max charge, up to 6-cells capable). If you want to charge with this unit at home, you will need to add a 120V-to-12V power supply (10-18V DC output at 10A max, for the 106B).

There is another route. You can create a gang-socket. Each end of the four cells has a wire going to the Gang-socket, for eight individual sockets (actually ten sockets, see below). A plug is configured so that it cannot be accidentally plugged-in backwards. When the "run" plug is inserted, the pack is configured as a 1P / 4S pack, and will provide an average of 3.6V X 4S = 14.4V. You must add two additional large sockets for the eight sockets to be connected to the "power out" cables.

When you want to charge, pull the run-plug, and insert the charge plug. This plug looks similar, but the butt-end of the pins are connected so that the pack is now a 1S / 4P unit, and can be charged with any 4.1V charger. Most chargers provide 4.2V when the pack is fully charged. Do NOT do that. Look for a "Li-Ion" charger that has a 4.1V setting. Put a resistor between each of the four cells on the charge plug. If not...a cell that is a little high will try to rapidly charge a cell that is a little low. (due to individual cell resistances, a pack that is at 3.7V will have some cells at 3.6V and others at 3.8V, this is the whole reason why "balancing" is needed).

The gang-socket is what Tench did on his Supercharged Specialized Big Hit mid-drive. The two large pins on the right are power-out to the controller. The six large pins on the left are the series pins for the three 6S LiPo packs, to equal 18S. The many small sockets on the blue thing are for charging. Of course there are 25 holes, Three for the negative leads of the three 6S sub-packs, 18 for the positive leads on each cell, and (*scratches head, stares into space, sips beer...drools a little), and four? are unused....He used three RC chargers to tame this beast.

 

[CyPF]

Hello thanks for your reply,
You give me an idea,
What do you think if i put a balanced charger in the speaker,
does it possible the wires stay always connected to the charger and the speaker circuits?
Does it is necessary to have a bms for protect my batteries because they are unprotected?
Link of the balanced charger: https://goo.gl/8JRHTZ

Cordially,

 

[tostino]

A BMS should provide you with balancing, which would allow you to use a bulk charger, and the BMS would simply balance it if it saw any cell voltages differ from the others. You shouldn't need to use a specific balancing charger for this.

 

[999zip999]

A little late but why couldn't a tool pack battery work. Like a 4ah ? Or a small bms off a tool pack. There should be many people on E.S. that have ten or more in a drawer. Look for somebody building packs out of tool packs. Aka Drbass or ?

 

[spinningmagnets]

The best replacement for a 12V lead-acid battery is often a 4S LiFePO4 pack, with added circuit-board protection when it comes to charge/dis-charge. You may have better luck looking into LiFePO4 components.

 

[CyPF]

Hello,
Which Bms can you advise me for charge my batteries pack?
link batterries: Panasonic unprotected NCR18650B 18650
https://www.fasttech.com/p/1345500
Cordially,