Creating Your Own Lithium Ion E-Bike Battery Pack: A DIY vs BUY Comparison
In the last episode of this video series, we showed you how to create your own sensored ESC (Electronic Speed Controller) to power an electric bike wheel with low voltages. However, since the achieved rotation speed was too slow and not many people want to create their own ESC for an E-bike conversion, let's rather switch back to the controller which was included in the kit.
To test it, I got myself a new lab bench power supply that can output up to 60 volts. I connected its outputs to the input of the controller and slowly started raising the voltage. Approximately at around 40.6 volts, the controller started working as it was supposed to. By cranking up the voltage even further, we were able to reach a voltage of over 54 volts.
Now that our controller is working properly, let's move on to creating our own battery pack for our E-bike conversion project. We'll be using lithium-ion cells, which are known for their high energy density and long lifespan. The data sheet of the utilized lithium ion cells states a constant-current constant-voltage method with 1.25 amps and 4.2 volts.
To create our battery pack, we first need to prepare the necessary components. We'll be using 13 lithium-ion cells, which will be connected in series to achieve a higher voltage. We'll also need a BMS (Battery Management System) to keep all cells at an equilibrium voltage of 4.18 volts and add overcharge, over-discharge, and short circuit protection.
To solder the balance connector wires to the battery, we simply need to follow the label on the BMS. This means that we'll be connecting B1- to the ground potential, B1+ to the 3.71V potential, B2+ to the 7.4V potential, and so on until B13+ connects to the 48.1V potential.
Once all the red LEDs lit up during charging, the process was complete. We can now connect our load through the P-terminal and the usual positive voltage wire of the battery pack.
Now that we've created our own lithium ion E-bike battery pack, let's compare it to buying one from a store. According to eBay prices, the DIY option was in fact cheaper! However, if you add labor costs and the cost of a battery spot welder, then it would only be cheaper if you plan to create more than just one battery pack and care for customization.
In this episode of our E-bike conversion project, we declared that both DIY and BUY are the winners. We hope that you're looking forward to the final chapter of the project and don't forget to like, share, and subscribe to stay creative!
WEBVTTKind: captionsLanguage: enin the last episode of this video seriesI showed you how to create your own sensored ESCin order to power an electric bike wheel with low voltagesbut since the achieved rotation speed was too slowand not many people want to create their own ESC for an E-bike conversionlet's rather switch back to the controller which was included in the kitto test it I got myself a new lab bench power supplywhich can output up to 60 voltsso I connected its outputs to the input of the controllerand slowly started raising the voltageand approximately at around 40.6 voltsthe controller started working how it was supposed tonow by cranking up the voltage even morethe wheel started rotating continuously fasteruntil I reach the limit of my power supplythat means we will need a battery pack which can covera voltage range of at least 40.6 volts to a maximum of 61.5 voltsa suitable choice of batteries would be 18650 lithium ion cellssince they offer a great volumetric and gravimetric energy densitycan deliver enough currentand let's face it everyone uses them for E-bike battery packsbut while searching for a compatible battery pack on eBayI noticed the rather high prices which got me wonderingwhether DIY-ing your own E-bike battery pack would be cheaperso in this episode of DIY or BUYlet's find out what goes into creatingyour own lithium ion E-bike battery packand whether it is truly cheaper in the endLET'S GET STARTEDthis video is sponsored by JLCPCBone fact about themJLCPCB was the first PCB company that cut the price from $70 to $7on 2-layer PCBs 10 years agoupload your Gerber files to order 10 professional PCBs for only 2 dollarswhen inspecting the data sheet of most lithium ion cellsthen we can find out that they got a nominal voltage of 3.6 to 3.7 voltsand maximum charging voltage of 4.2 voltsand have almost no capacity left when they got discharged to 3 voltsthat means we got a voltage range of 3 volts to 4.2 volts per cellthus for our controller voltage range it would make sense to put 13 cells in seriesto create a battery voltage range of 39 volts to 54.6 voltswith a nominal voltage of around 48.1 voltswhich not surprisingly is the advised voltage of the controllernext we need to know the maximum required current of the controllersadly though my dry test with the lab bench power supplydid not present an exact answerand the product page does not mention the current as wellbut luckily it states 1000 watts at 48 voltswhich would equal a current of around 20.83 ampsthe next best common lithium ion cell which can output 20 amps continuouslywas the Samsung INR 18650-25Rwith a capacity of 2500 milliamp-hoursbut just to be on the safe side and to double the capacity of the battery packI decided to use two of those cells in parallelwhich thus ultimately equaled a 13S2P lithium ion packwith a capacity of 5 amp-hoursand nominal voltage of 48.1 voltsand a possible constant output current of 40 ampsso I went ahead and ordered 30 of those cellsfrom a trustworthy German sellerhow do I know that they are trustworthy?well after receiving the cells and visually inspecting themI measured the voltage of all of themand noticed that they were all very close to one anotherwhich was not only a very good signbut also indispensablesince we want to connect two cells in parallelif they would have a big voltage potential differencea parallel connection could result in a large current flowand the destruction of the cellbut anyway to turn 26 of those cells into a nice looking battery packI will be utilizing those plastic spacerswhich can hold 2 cells eachso I connected 13 of them in series through the help of the interlocking systemplace two batteries with the same orientation in the first rowand alter the orientation of the next two cells continuouslywhile filling up all the spacersonce that was done I added the remaining spacers to the top of the battery pairsand connected them as well through their interlocking systemto connect the cells to one anotherI got this 7mm wide and 0.3mm thick nickel ribbonwhich can handle up to 30 ampsso I started creating 26 smaller pieces of the nickel ribbonwhich were long enough to connect all the parallel cell pairsnow to create the actual connectionsI wanted to avoid soldering this timebut as you might knowI recently failed at creating my own battery spot welderthankfully though a viewer sent me a solution to this problemthe so called kWeldwhich is basically a pretty advanced battery spot welderafter doing a bit of assemblyit can be powered by a LiPo batteryand therefore can create suitable welding spots without a problemaccording to its manual it is recommended to use an energy of 100 joules for 0.3mm nickel stripswhich I use as a standard value for all my battery pack weldsand as you can see creating the welds is really not that complicatedsimply press the electrodes onto the metal with a distance of roughly 3mm to one anotherpush the foot switch andTHERE YOU GO! :Dnow I created two welding spot pairs for each battery terminalwhich resulted in a total of one hundred and four weldsand once that was doneit was time to measure and cut another 24 nickel strips for the series connectionswhich need to get connected to the parallel batteriesin the here shown arrangementso I created another 96 welds for the series connectionsin pretty much the same manner as I did it for the parallel cellsand with that being done our 13S2P battery pack is basically completeand should deliver us a voltage within the previously calculated voltage rangewhich it did :)the only remaining question is: how to charge it up?the data sheet of our utilized lithium ion cellsstates a constant-current constant-voltage methodwith 1.25 amps and 4.2 voltsif we multiply those values for the 13S2P battery packwe would get 54.6 volts and 2.5 ampsthis means I can set my lab bench power supply current limit to 2.5 ampsthe voltage limit to 54.6 voltsand simply hook it up to the battery terminalsto which I soldered thicker 10 AWG color-coded wire beforehandand not surprisingly the charging process worked like a charmbut as soon as I got closed to the target voltageI interrupted the charging process to measure the voltage of each battery pairand as you can see the voltages are still pretty close to one anotherbut let's imagine we repeat such a charging process several hundreds of timessince no two batteries are completely the samethe voltage gap between the cell pairs will grow and growuntil one will eventually give upwhat we need to prevent such an event is thisa BMSaka a Battery Management Systemnot only it keeps all cells at an equilibrium voltage at 4.18 voltsbut it also adds an overchargeover-dischargeand short circuit protectionto use it we simply must solder its balance connector wires to the batteryaccording to its labelthat means B1- to the ground potentialB1+ to the 3.71V potentialB2+ to the 7.4V potentialB3+ to the 11.1V potentialand so on and on...until B13+ connects to the 48.1V potentialfinally we simply connect the ground wire of the battery to the B- terminaland add two more black wires to the P- and C- terminalnow to charge the battery packwe reconnect the positive supply voltagebut connect the ground potential to the C- terminalthis way the battery now charges like beforebut simultaneously the battery charges itself through the BMSand once all the red LEDs lit upthe charging process was completeand thus we can connect our load through the P- terminaland the usual positive voltage wire of the battery packand just like that the creation of my DIY E-bike battery pack was complete :)but one question remains...was it CHEAPER?well according to eBay prices it was in fact cheaper!but only a tiny bit :(but then again if you add labor costs and the cost of a battery spot welderthen it would only be cheaper if you plan to create more than just one battery packand care for customizationso all in all I hereby declare that both DIY and BUY are the winner of this episode!and with that being said I hope you're looking forward to the final chapter of the E-bike conversion project!as always don't forget to like, share, and subscribeSTAY CREATIVEAND I WILL SEE YOU NEXT TIME!
