How to Build an eBike Battery

0:00 in the shop all it up for Halloween my son recently got an ebike he got a rad power rad Runner 2 and it comes stock with a 48volt 14 amp battery and he loves it just the way it is but me being a dad and being me I know he could use something a little more powerful so I'm going to build him a 52 volt 25 amp battery and that should give him about twice the range and maybe even a little bit higher top speed depending on how it goes uh and it's going to be about twice the size of the stock battery but I think I can still make it fit in the and I'm going to build it out of these this is an 18650 lithium ion cell kind of looks like a doublea battery but a little bit bigger and need a little over 100 of these in various combinations to get to that capacity and voltage and I figured I'd start with some Theory show you how you select these batteries what

0:46 sort of combination you get them in and then show you how it's built I built ebik batteries before but I never really documented the process and I want to try out my new camera rig here I got a iPhone 15 Pro Max looks pretty good right yeah so as we build it we'll get to see some Cool Tools tools like this this is a battery welder pretty neat and if you don't really care about the theory and just want to skip to the good stuff you can check out the chapter markers below all right I think that's it oh but as always Safety First all right let's do a little bit of battery Theory here so one of these cells these 18650 lithium ion cells you'll generally see them referred to by their nominal voltage which is usually going to see 3.6 or 3.7 volts that's sort of the amount of charge they have when they're 50% full and the full range

1:33 goes from about 2.8 or 2.9 3.0 volts you'll see different numbers for the low end up to 4.2 volts on the high end so if you go any lower than that or any higher than that you damage the cell but we'll look at a device later called the BMS the battery management system and that's going to manage charging and discharging to make sure that we do not damage the cells and again generally when you see these calculations you'll see them referred to against the nominal voltage which will'll consider 3.7 so if you were to take a multimeter test one of these batteries 3.7 volts the capacity is 3200 milliamp hours that's not quite as easy to test with one of these you can hook something up a load and you can measure how much current is going through them and you'll see a total which will hopefully be around 3200 milliamps as advertised so I got to get from 30.7 volts up to 52 volts and 3200 milliamp

2:21 hours up to 25,000 milliamp hours so how we going to do that so turns out if you wire batteries in series like this end to end you you start multiplying the voltages so got double the batteries you got double the voltage 7.4 volts same capacity though 3200 Mah hours if I had a third one now we're up to 11.1 volts same capacity so I want I not only Want More Voltage I want more capacity as well and how do I get that so then I do what's called wiring them in parallel so now if you were to test these two wires here that joined up the positives and negatives you'd see the original voltage 3.7 volts but now the capacity is doubled 6,400 Mah hours and same thing if we added a third same voltage up to 9600 Mah hours for the capacity though and then you can combine series and parallel and you end up with something like this so in this case we've got four

3:07 in series which gives us 14.8 volts and we've got three in parallel which gives us that 9600 milliamp hours and you'll notice they're connected not only on the ends but in between here so all the nodes are connected now this layout you'll see we have quite a while to go to get up to my desired voltage and capacity so this layout is going to start getting pretty unwieldy right you're going to end up with a bunch of batteries like this which is not ideal to mount on a bicycle so what if we sort of Bend these in on each other and we end up with a shape like this so you'll see positive and negative sort of alternate and the current is going to flow through like that and but you'll see we still have one big overriding negative and one big overriding positive and if you measure those two that's going to be your final voltage so you can combine that with the parallel layout and now they're going

3:52 Series this way and parallel this way this is the most efficient shape to mount a B on up with like a nice little rectangle so how many of these do I need to get to my desired voltage and capacity turns out I need 14 in series 3.7 Vols * 14 gets me to 51.8 which is just about 52 you see these numbers are a little nebulous it's never quite the exact voltage you're looking for but it's close and then to get to the capacity we need we're going to need eight of these so 3200 milliamp hours time 8 gets us 25,600 milliamp hours and you'll see this referred to this sort of series versus parallel counts referred to like this in this case I'm building a 14s 8p battery 14 in series eight in parallel and if you multiply those two numbers together you get 112 So we need 112 of

4:38 these cells to build this battery we're almost ready to start building but first let's take a look at why I chose these cells these are available with all kinds of different specs so let's see why I went with these particular ones so here's where I got my batteries this is the 18650 battery store.com I'm went with these Eve 33 vs and you can see the capacity there 3200 milliamp hours but then there's also this 10 amp number what is that so if we scroll down here we can see that's the continuous discharge rating so that's you can continuously draw 10 amps from one of these batteries and generally you don't want to go anywhere near this limit it is possible but there's a thing called voltage drop where instead of having the maximum 4.2 volts when you're pulling 10 amps the voltage might drop to 3.2 so you're not getting anywhere near the voltage you think you're going to get so you can stick like half of

5:24 that or below you're good and you figure okay well how do I know what does this need to be for my use case and in the case of the ebike you're looking at what kind of amperage the controller draws so on the red Runner 2 the stock controller will draw maximum of 25 amps and there's upgraded controllers that'll draw up to 35 amps and you're looking at this number and saying oh man this is nowhere near 35 amps but you have to remember these batteries are wired in parallel and the parallel then stacks these amp ratings so you can actually pull from an eight P pack you can pull 80 amps continuous discharge again you don't want to go near that you want to stick to half so figure four 40 amps that's well above our 35 amp rating right each battery is only pulling 4 and 38 of an amp or so so that should be well within that

6:09 range and let's compare this to some other batteries on here why did I go with this one well if you look at the Sam the famous Samsung 30q this is the capacity here is only 3,000 milliamp but it has a 15 amp continuous rating so you might have some kind of a use case we need to be able to draw a lot more current and you have to go with a battery like this even though the capacity isn't as high if you compare that to the 35e now this has another 500 milliamp hour of capacity 3500 but it only can draw 8 amps continuous so something to keep in mind and then I'm looking at the price these are six bucks per sell this is six bucks per sell these were normally six bucks but they're on sale right now for three so I went with these ones and when you're looking at these you want to make sure you get the flat top which is what we're looking at not

6:54 the button top button top kind of looks more like a classical ablea battery with a little nubbin we do not want those you'll see the brackets and these nickel strips that we use to weld on do not work with this style you need a flat top style and this side has some interesting categories here so you can go in here and look at you want a pack build and you want high capacity is what you worried about so you're going to look into here and these are going to be all their high high capacity ones 3200 3500 3450 there's even a 3500 that does have a 10 amp draw but see that's 8 bucks per sell or you go in here and say you know what I don't need a I don't need a ton of high capacity I just want the cheapest ones I got and you can look in here so right now because these are on sale this is in this category but you have one these guys here where this is only 2,000 milliamp but look at this charge you could do 30 pull 30 amps from that battery wouldn't last very long

7:40 2,000 but and they're cheap 225 yeah so this is the most popular size is 18650 and that number refers to the actual size of the cell it's 18 mm in diameter and 65 mm tall and there's another uh popular size that's 21700 I don't know that some of the equipment some of these brackets that we're going to use use to hold the battery together I'm not sure that they're all available in this size they probably are but I haven't really dug into them I stick with the 18650 but these are because they're bigger they generally have a higher capacity so you see there's 30 4500 milliamp hour some of these are the same there's 3,000 milliamp there's 35 amps draw there's 4,000 I think I've even seen a 5,000 yeah there's a 5,000 milliamp hour one so if you really need a lot of capacity that's the way to go all right here's

8:26 everything we need to build the Pack surprisingly not that much stuff we got our batteries they generally come in a box like this of 100 and then I had a few more than that right the 112 So a couple extra around the side there we've got this pack bracket 18650 pack bracket so what this is is these hold the batteries like so and then you put the top on holds in there really well and presents these little Nubs here for welding and ends up with a really nice structurally strong unit really holds it together well and this bracket is available in all these different little sizes 1X one 1X two 1X three these are actually 4X FS together and there's a couple little extra spots so I think I had some threes that I had to fill in and it has these little bracket systems that kind of like locked together so you can see just slide them together really

9:13 nice and then here's that BMS I mentioned the battery management system and this is a 14s this handles 35 amps so it'll definitely cover the stock controller and should cover an upgraded controller as well I think it might let a little little bit more than 35 pass now and then if it needs to but if it stops the battery output because of the new if a new controller is drawing too much current I'll just have to upgrade that put a new one in this is nickel strip nickel ladder I call this 2p because it'll put two of them in parallel and what happens is when you put this bracket on this is how you weld this ladder will fit right in these little spots like this and you'll weld weld weld along the batteries there like that we'll see that in a moment this is some Captain tape capton Capone just non-conductive tape kind of

9:59 tap down some of these loose wires we'll have flopping around and then I got my voltmeter and I have the voltmeter here because generally when you get these cells you want to test them to make sure the voltages are all very similar when you put a bunch of these in parallel we've got our parallel strips going this way as soon as you weld the conductor on here going to weld the strip on these batteries will all try to rush and charge each other if they're if one of them is low so if you had one of these is at 3.2 one of these at 4.2 a ton of current is going to run in there and try to charge that one battery and that can be very dangerous so generally you want to make sure all the ones in these parallel strips are very similar voltages and these probably will be CU they're right from the factory but a lot of these guys build these packs they Salvage batteries from like laptop packs and there's no telling what the voltages will be so you'll want to test them all and then kind of group them in similar

10:45 voltage units and if you have some you have a couple outliers that are super high super low you have to charge them up or discharge them to kind of get them in the same as the other group so I'm going to work on testing these out I'm not expecting them to be anything crazy this one right now is [Music] at 3.46 and I bet they're all be pretty similar yep 3.46 so I'll go through and test these and then we'll pick back up after they're all tested as expected all the voltages on these are very similar so we can go ahead and start populating our bracket and we're going to put these in the

11:30 parallel rows and each parallel row is going to face the same direction so these are all going to be up and then this next row is all going to be down and remember our illustration the voltage is going to go through like this current so we just going to go through here and keep alternating rows there we go and then it's just a matter putting the top on let's make sure we got minus plusus plusus plusus plusus plusus plusus plus okay roll

12:16 trting good get our top on this is always interesting to get these to line up oh that went on pretty easily you can see now when it's done it's a pretty good solid brick has a little bit of a Twist to it actually once we weld on the nickel strip it'll get real stable so it's looking good all right on to the next step next up we're going to cut our nickel strips to fit so we're going to lay one across here and I want to leave a little tab sticking out on one end and this stuff is so thin you can cut this with scissors and I believe this is 05 millim thick and there's ampure ratings for this as to how much amps

13:01 these can carry and I think I'm going to double these up just in case so I'll weld one on and then I'll weld another strip on top of it so I'm going go down here and I need to cut one 2 3 four five six 7 double that 14 and then the other side we're not going to do it like this we're going to offset by one so this will get a single line down here and then it'll be nickel strips in between so 1 2 3 4 five six so 14 on the other side 12 on this side and then we'll make two single strips for

13:53 here you want to be careful when shopping for nickel strip cuz a lot of them are steel with just a nickel coating which doesn't conduct nearly as well you want pure nickel strip you'll usually see it listed that way and you can test it you can put it into a solution of salt water and if it rusts it is steel All Right nle Strips cut ready for the next step ready to start welding here got our battery welder and each pulse here is set to 30 jewles that's one pulse of the weld to be that much power and got our battery in our bracket and normally I would start over here but it's kind of in the way of everything here for the camera so I'm going to start over one and you want to make sure when you got your ladder here it's not like Offset you see it's laying on the plastic and not really flush you want to make sure it's really good in between

14:39 there and I have the welder set that all I need to do is hold it on and right now set to 2 seconds before it'll actually do a pulse I'll turn that down here in a minute make it a little bit faster but just for demonstration there's also a it comes with a foot pedal so if you don't want to have this automatic mode you can manually trigger with your foot and you might hear some fan noise come on as the power comes on for the welder I'll try to minimize that all right so we're going to start here uh we'll start here on the minus on this side and the way this ladder is it has a little gap between so I'm just going to straddle that Gap and you'll see as I hold electrodes on as soon as they both touch you'll hear a rising tone and then it fires and there we go I'll just give it

15:25 a little tug make sure so that's the whole battery itself moving in there but the weld is on there really good and then I like to do two on each so I'll do another one here and now let me turn this trigger delay down just to speed this up a little bit move it down to like 410 of a second here and I'll kind of go down the whole row here of the minuses and just give it some nice firm pressure make sure it like it's a good good W on there and I can see the charger is off

16:11 off screen here but you know every time I do a pulse it draws a little bit of juice to to charge these capacitors back up and I'm ready to go again and as I go and do a bunch of these these these cables will start getting warm so they're fine right now but we'll see how far I can get before it gets too warm and also when you if you press and hold afterwards you'll see this display I'll give you some statistics so I'll do a hold here and see so we let it know was okay that was the ninth pulse was 30 Jews went for 18 milliseconds and it was what that said there 1100 amps in one shot pretty good and then it'll also give us the final temperature I think of the unit so if I need to let it cool off let's see 18 1200 amps uh resistance 31 C so we're good

16:56 I'm going keep going okay that whole Row's done goes pretty fast once you go and it's so oh there's the fan kicking in and people we like this method instead of soldering cuz soldering adds so much heat and it's a lot of heat soaking into the battery which isn't really good for it but this is like so quick and instantaneous there's no heat at all when I touch these it's completely cool all right so now we'll go down the positive row

17:47 here oh so I might not have had very good contact there on that one try that again I can feel these are starting to get warm oh had bad one there it actually like looks like it burned right through the nickel on that one ah let me continue on my electrodes are getting a little burned looking here make sure I got my good pressure yes I think that was the problem here is I was I wasn't really the pressure was a little bit off on that one side there we

18:32 go that's better so there we go that row is all done and then my little tab sticking out if you can see that on the camera that'll be where the BMS is hooked up cables are a little warm but not too bad start in the next row here and I want to make sure my tab is in the back not the front I'm going to give myself some extra down pressure makes I have really good contact

19:23 there these are starting to get pretty warm let's see what the actual temperature of the unit is here hold it this time and see the temperature read out 18 1200 juw 1200 amps resistance 1.2 35 so the unit itself isn't getting that much warmer but these cables are getting starting to get warm it's just getting a little uncomfortable to touch right here is getting kind of toasty if you can see that the wires actually move there's so much current coming through here it moves the

20:15 wires pretty warm okay so I might let this sit for a minute and just cool these off but then we'll continue on here all right so that's that side completely done so we're going to flip it over and now this is where we want to start getting careful so previously we were only connecting two rows at a time so remember 3.7 3. 7

21:01 74 total so we're making like little 7.4 groups now as we start stacking on here it's going to start multiplying so every time we put another one on that's like doubling that voltage so we want to be a little more careful not anything crazy just we want to make sure make sure we don't have any random pieces of metal laying around it's going to fall and Bridge a couple of these things they say the human skin response is your skin is dry enough up to like 50 volts or so before you start getting worried about getting shocked and this is going to be 52 volts so we're getting close to where you could in theory get shocked by your own battery pack so we just want to take our time and make sure we're doing what we think we're doing and again make sure no random stuff is going to randomly Bridge anything so again we're not going to go if we did

21:46 this that'd be very bad because we' be creating two short circuits so we can make sure we're going to offset by one so just to make sure that doesn't happen I'm going to do my single first I'll do my single across here and then we'll go and then it's going going to end with a single all right so let's do a test now so now we've got four in series we're going down and then up and then down and

22:33 then up so if we test between here we should be around 14 volts or so probably a little less cuz remember instead of the nominal 3.7 these were about 3.4 from the factory so there we go we're at 13.8 13.9 almost so we're getting there all right so now if we test between our positive and our negative we should be at around 52 volts what is that 48.4 yeah and the charge a littleit lower but once we charge up that'll be do good all right so I have to do a second layer of nickel strip and then we're ready to hook up the BMS here's our battery pack all

23:18 complete we got our double layer of nickel strips and here's all those little tabs so what are those tabs for so if we look at the BMS remember all these wires coming off each of these wires connects to one of these tabs in sequence down the pack and it allows the BMS to monitor the voltage of each of these parallel rows so if we start here at the packs minus right this will be Z volts and then 3.7 7.4 11.1 14.6 and it climbs as you go down and that lets the BMS do something called balancing where we can balance the charge between each of these rows so after a lot of charge discharge Cycles one of these rows could be at 4.2 at maximum charge and another one here is at 4.1 ideally want everything at 4 4.2 so this allows it to sort of monitor each row and bleed off some voltage here and there to make sure everything get charged up to

24:05 4.2 and then there's two big wires here there's a p minus and a B minus the B minus connects to the batter's minus so this is going to wrap around and connect on there and then the P minus is where you pull your charge from so this is probably going to run down the way this is going to mount on the bike the motor connector is here at the bottom so I'll run the minus down and then I'll run the positive over to a connector here to discharge the pack and then to charge it I'm probably going to 3D print a little bracket here and have the little charging port so another p+ or I guess it's a B+ will come up and connect up to the connector along with another Branch off of this and that'll be where you charge it from so the next step is to sand up these so I can get solder to stick to them so I'll s rough these up just a little bit and then we'll solder wire on each one going down the pack and then once we connect these

24:52 big guys then we're just about done and we'll just heat shrink the whole pack and it'll be ready for install okay we just about ready to start soldering up these wires here so I've got my BMS I just put a piece of Captain tape just to kind of hold it there temporarily as I'm wiring things up I'll leave the wires a little bit long probably just in case I want to move that I've got some flux paste help my solder flow a little better got my solder got my soldering gun warming up got my wire strippers and I got a little piece of sandpaper so what we'll do here is for each tab we'll kind of scratch it up a little bit give the s or something to stick to and this is the the ground starting with so that's going to start with this

25:38 wire and I'll figure out if it's going to be absolutely the final position to be something like that but I'll leave just a little bit extra up and we'll trim this and we'll strip it and I'll put just a little bit of solder on it and we'll give ourselves a nice little pool of solder for this to stick to and doesn't need much and then we'll Bend this over a little bit and we'll just solder this wire on that's it so the first one's done and then I'll

26:24 just go down the road here and I got to make sure I alterate I'll probably do all these top on first just this is the position the battery's in so I'll do every other wire here and then we'll flip over and do the other ones so like this next one the next one in line would go down to this one but we're going to skip that one and do this one this one's going to come up here there we go and then we'll know we did the wires right because the very last wire here was the very last one there so that counting I think turned out okay so now flip it over wire up the other side and then I'll just do a double check to

27:10 make sure I got all these correct okay all the balance wires are connected I double checked that they're going to their proper ones so now we got to wire up the minus the B minus stick that up here scuff that up a little bit I notched out a piece of the plastic there so that way that wre can like nest in there and that's going to sit just like that so I tined this up so this guy's ready to go so let's add some solder here okay it looks pretty good let's see about the positive end all right we're at the positive end of the battery and I think what I'm

27:55 going to do is this is where the bike the battery mounts to the bike and the motor connectors that are down here so I'm going to wire this in have the connector hanging off the bottom like this and then I'll hook the minus up this will run up battery to the P minus wire on the BMS and it's going to be it would be a little unsafe to wire these up and then have two dangling wires at 52 volts floating around so I think what I'm going to do is connect them to the connector first and then wire them to the battery and for that we're using the xt60 connector these are sort of become a standard in in the ebike world and there's also like an xt30 and xt90 and that the number refers to how many amps this can handle 60 amps so well above our 35 amp potential maximum and the way these are generally wired is the male end was will be the end that's

28:40 providing power so the male end is going to come on here and then I'll wire up the female end into the bike and then the charging port will also have a female end and you can actually chain batteries together and multiply Your Capacity uh realized another way I could s solder this up without putting the heat right on these batteries is I can solder this wire to a little piece of strip first and then weld this strip to the battery so I'm I'm going to do that big old pool of sold

29:36 here okay that looks like that's connected on there pretty good so now we ready to wire up the negative from the connector up up to the BMS and I've got the other wire here going to the charge port again 12 gauge and I'm going to use these crimping terminal lugs here so rather than try to solder all three of these together I'm just going to crimp them

30:26 together that's pretty good and then we'll heat shrink it all right that looks pretty good and then we'll see about connecting the charging cable but if we did this right we should be able to check this connector and see what our voltage is at there we go there's our 48 so the Pack's ready to discharge we just have to hook up the charging port and we can charge it up try it after some experimentation I decided to do the same thing with the Positive lead on the charging connector and that's put one of these

31:13 Crim connectors in here so I split this cable put in a crimp connector and then I ran a secondary cord all the way up here to the top and I didn't get a chance to solder them into the connector so it was going to have these bare wires flopping around so I just stuck a piece of electrical tape on the end there make sure they don't spark against something but both the positive and negative are going to get trimmed here and they're going to basically face off the edge there I went to my computer and designed a little housing for the charging connector and then I went and 3D printed [Music] it

32:00 that is looking pretty good let's hook it up to power and see if it charges so I've got a charger this is a 5 amp charger and I put a xt60 on the end got the voltmeter hooked up to the discharge Port monitoring our output voltage so when I plug this in hopefully the charger starts charging one of these LEDs goes out and then we should see the voltage on here slowly start climbing fan turn on LED went out here we're at 49.0 and then we'll see if that starts climbing up there we go 49.1 so I'll let that sit for a little bit and we'll do a little time lapse here and watch that charge up a little to get a sense of the ranges of

32:47 various voltage batteries when they're 0% full versus 100% full you might only have access to the voltage itself you don't really have a real battery meter this chart is amazing shows you every voltage from 0 to 100% for 36 volt 48 volt 52 volt batteries all right that took about 9 minutes to go one volt so you can see when you take power off it kind of drops back down again kind of settles down so all right we going to shrink wrap this and then I got to build a bracket for the bike ready for heat shrink I put a coule couple layers of EVA foam here this bike has no suspension and my sound

33:33 like so like ride off curbs and stuff so rather than have this being like this battery just sitting on a metal support it has a little bit of cushiony foam there so the back of the frame and then the bottom and this EVA foam just comes in these big sheets you cut it with scissors and the heat shrink comes like this I only have this blue right now but I'll probably get some black and then redo this you usually think of heat shink as the little stuff the little pieces for wires but yeah it comes in these huge sheets like this so then we going to try to slide this on here heat it

34:25 up so I'll try to center it in there and the heat shrink really only shrinks this way this way doesn't shrink much these these ends will kind of curl over and depending on how tight it gets I might trim it a little bit but that way this will leave this core at the bottom it's going to wrap around to plug [Applause] in [Applause]

35:25 tada got a nice little brick trim a little bit of that but yeah all right let's trim it up and see how it looks looks pretty good all right let's install that on the bike see how it works

36:27 [Music] [Laughter] got a wire in an xt60 into the bike connector so this is the connector going to the controller

38:03 so there we go how to build me bike battery another project in the books but you know can't help but think that bike could use a little more power hey Jack