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.
Lg Solar Panels Review, 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 a battery management system, and how to create a decent housing for it all. let's get started 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 metres of the led strip for 1.6 hours. 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. but since i still had two modified microwave transformers laying around from a previous hacked episode i simply remove the worn-out cable heads, added new cable shoes attach 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 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 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 another
otherwise one of them could charge up the other one with an unhealthy amount of current then i create a shorter length of the nickel ribbon pre-tinned those on both sides and use small pieces of p240 sandpaper to abrade the positive and negative terminals of the batteries afterwards i added a bit of solder to each contact which already shows you why this method is not recommended because it heats up the battery which can lead to capacity losses and other problems but nevertheless, i then inserted each battery pair into the designated spacers and use the previously created ribbon pieces to connect them in parallel
afterwards i organized the three battery pairs in this arrangement to add the missing two nickel ribbons which are mandatory for the series connection all that was left to do was to add an additional piece of the ribbon to the positive and negative terminal as 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 sense the positive and negative tab received an unnecessary thick 10awg cable that connects to xt60 connector to later supply the main current to the load.
the 7.4v and 3.7v tab however are important as well since they need to be hooked up to a 3s balance connector just like the positive and negative terminals shown in this arrangement. and just like that we have the lithium-ion equivalent to the 3s lipo battery, that we can now balance charge through the help of an appropriate charger but we are not finished yet, because we can still add a bms circuit to the battery pack by simply gluing it on top of the pack and soldering the battery terminal wires to the circuit according to its labels, we just added a lot of useful protection features for example,
by supplying a charging voltage of 12.6 volts to the output wires the pack begins to charge and 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. but 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.
and 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
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