**Creating a 3S2P Lithium-Ion Battery Pack**

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I recently got myself two spools with five meters of white LED strip that I want to utilize in a future portable lighting project, so once again it was time to choose a suitable battery type.

Due to the superior gravimetric and volumetric energy density, I wanted to either use Lithium Polymer or Lithium Ion. The advantage of Lithium Polymer batteries though is that you can easily get them in pre-made packs that feature multiple cells and thus possess a high enough voltage to power the LED strip directly without boosting the voltage.

Only problem is that the LiPo batteries can be a bit dangerous if you're not careful. So wouldn't it be useful if we could combine common 18650 Lithium-ion cells in a similar pack? Well, of course it is possible, and in this video I will show you how to create such a battery pack, how to attach a BMS (a.k.a Battery Management System), and how to create a decent housing for it all. Let's get started.

**The Six Lithium-Ion Cells**

The six Lithium-Ion cells that I will convert into a battery packs are INR 18650-25R with a capacity of 2500 milliAmp hours each. To get close to the required 12 Volts of the LED strip, I need to place three of them in series to create a voltage range of 12.6 volts when fully charged and 7.5 volts when completely discharged.

In addition to that, I will add a second battery to each cell in parallel in order to double the overall capacity of the battery pack. So in the end, we will have a 3S2P battery pack with an energy of 55.5 Watt hours. Enough to power 5 meters of the LED strip for 1.6 hours.

**Connecting the Cells**

Now to connect these cells properly we need a bit of Nickel Ribbon. Mine has a width of 5 millimeters and a thickness of 0.15 millimeters, which will easily carry the required 3 Amps for the LED strip.

Note there are two ways to attach the ribbon to the batteries: The first and recommended way is to use a spot welder, which utilizes a burst of energy in a very short amount of time to weld the ribbon to the battery. A spot welder itself can be bought for around two hundred dollars from China.

However, since I still had two modified microwave transformers laying around from a previous hacked episode, I simply removed the worn-out cable heads, added new cable shoes, and attached a bolt with three nuts, two washers, and two rings to the cable shoe. And finally clamped the nail as electrode in between the two toothed rings.

**The First Modified Transformer**

The first modified transformer though, with an output voltage of 1.7 Volts, was not powerful enough to create a proper weld. And the second one, with an output voltage of 7.5 Volts, was a bit overpowered for the job even after decreasing its amount of secondary coil turns and thus lowering the voltage down to 4.7 Volts.

I simply was not capable of creating a proper weld. So we went ahead and used the recommended spot welder method.

**Attaching the BMS**

The BMS will cut a charging current once one cell exceeds a voltage of 4.24V to prevent an overcharge. Only problem is that the circuit does not balance charge the rest of the cells, which makes a balance connector still mandatory.

However, on the other hand, the BMS also cuts the discharge current when one cell reaches the voltage of 2.3V to prevent an over-discharge. Also, there is an overcurrent protection of 26 Amps and thus obviously a short-circuit current protection.

**The Final Product**

With those added protection features, the battery pack is finally complete but it still looks a bit fragile and unprotected even with a couple layers of Kapton tape. So I went ahead and designed a decent housing for it with 123D Design that I then 3D printed with my Delta printer.

After 6 hours the print was complete, and I slid the battery pack inside it, secured it with a job of hot glue, mounted the XT60 Connector and balance connector with two component adhesive to the lid of the pack. And once that was dry, pushed it in place and secured it with two M3 bolts and two nuts which I placed inside the lids beforehand.

And just like that you can make your own Lithium Ion battery pack. I hope you liked this project; if so don't forget to like, share, and subscribe. Stay creative and I will see you next time.

WEBVTTKind: captionsLanguage: enI recently got myself two spools with five meters of whiteLED strip that I want to utilize in a future portable lighting project, so once againIt was time to choose a suitable battery type.Due to the superior gravimetric and volumetric energy densityI wanted to either use Lithium Polymer or Lithium Ion.The advantage of Lithium Polymer batteries thoughis that you can easily get them in pre-made packs that feature multiple cells andthus possess a high enough voltage to power the led strip directly without boosting the voltageonly problem is that the LiPo batteries can be a bit dangerous if you're not careful.So wouldn't it be useful if we could combine common 18650 Lithium-ion cells in a similar Pack?Well, of course it is possible, and in this videoI will show you how to create such a battery pack,how to attach a BMS a.k.aa Battery Management System, and how to create a decent housing for it all.Let's get startedThe six Lithium-Ion cells that I will convert into a battery packs are INR 18650-25Rwith a capacity of 2500 milliAmp hours eachTo get close to the required 12 Volts of the LED stripI need to place three of them in series to create a voltage range of 12.6 volts when fully charged and7.5 volts when completely discharged.In addition to thatI will add a second battery to each cell in parallel in order to double the overall capacity of the battery pack.So in the end, we will have a 3S2P battery pack with an energy of55.5 Watt hours.Enough to power 5 metres of the LED strip for 1.6 hours.Now to connect these cells properly we need a bit of Nickel RibbonMine has a width of 5 millimeters and a thickness of 0.15 millimetersWhich will easily carry the required 3 Amps for the LED strip.Note there are two ways to attach the ribbon to the batteriesThe first and recommended way is to use a spot welderwhich utilizes a burst of energy in a very short amount of timeto weld the ribbon to the battery.A spot welder itself can be bought for around two hundred dollars from China.But since I still had two modified microwave transformers laying around from a previous hacked episodeI simply remove the worn-out cable heads, added new cable shoesAttach a bolt with three nuts, two washers and two two rings to the cable shoe,And finally clamp the nail as electrode in between the two toothed rings.The first modified transformer though, with an output voltage of 1.7 Voltswas not powerful enough to create a proper weldAnd the second one, with an output voltage of 7.5 voltswas a bit overpowered for the jobeven after decreasing its amount of secondary coil turns, and thus lowering the voltage down to 4.7 VoltsI simply, was not capable of creating a proper weld.So we must go with the second, not recommended option; soldering.Before doing that though we firstly must measure whether the voltage of the parallel cells is close to one anotherOtherwise one of them could charge up the other one with an unhealthy amount of currentThen I create a shorter length of the nickel ribbonpre-tinned those on both sides and use small pieces of P240 sandpaperto abrade the positive and negative terminals of the batteriesAfterwards I added a bit of solder to each contactwhich already shows you why this method is not recommendedbecause it heats up the battery which can lead to capacity losses and other problemsbut nevertheless, I then inserted each battery pair into the designated spacersand use the previously created ribbon pieces to connect them in parallelAfterwards I organized the three battery pairs in this arrangementto add the missing two nickel ribbons which are mandatory for the series connectionAll that was left to do was to add an additional pieceof the ribbon to the positive and negative terminalas well as the 7.4V point and the 3.7V point according to the scheme.After double checking that all the voltages at the tabs make sensethe positive and negative tab received an unnecessary thick 10AWG cablethat connects to xT60 connectorto later supply the main current to the load.The 7.4V and 3.7V tab however are important as wellsince they need to be hooked up to a 3S balance connectorjust like the positive and negative terminals shown in this arrangement.And just like that we have the lithium-ion equivalentto the 3S lipo battery, that we can now balance charge through the help of an appropriate chargerBut we are not finished yet, because we can still add a BMS circuit to the battery packBy simply gluing it on top of the pack and soldering the battery terminal wires to the circuitaccording to its labels, we just added a lot of useful protection featuresFor example,by supplying a charging voltage of 12.6 volts to the output wires the pack begins to chargeAnd the BMS will cut a charging current once one cell exceeds a voltage of 4.24Vto prevent an overchargeOnly problem is that the circuit does not balance charge the rest of the cellswhich makes a balance connector still mandatory.But on the other hand the BMS also cuts the discharge currentwhen one cell reaches the voltage of 2.3V to prevent an over discharge.Also, there is an overcurrent protection of 26 Ampsand thus obviously a short-circuit current protection.And with those added protection features the battery pack is finally complete,but it still looks a bit fragile and unprotectedeven with a couple layers of Kapton tape.So I went ahead and designed a decent housing for it with 123D Designthat I then 3D printed with my Delta printer.After 6 hours the print was complete and I slid the battery pack inside itsecured it with a job of hot gluemounted the XT60 Connector and balance connector with two component adhesive to the lid of the packAnd once that was dry pushed it in place and secured it with two M3 bolts and two nutswhich I placed inside the lids beforehandAnd just like that you can make your own Lithium Ion battery pack.I hope you liked this project, if so don't forget to like share and subscribeStay creative and I will see you next time