An E-Bike Battery Pack Without Spot Welding

In somewhat of a departure from their normal fare of heavy metal mods, [Make It Extreme] is working on a battery pack for an e-bike that has some interesting design features.

The guts of the pack are pretty much what you’d expect – recovered 18650 lithium-ion cells. They don’t go into details, but we assume the 52 cells were tested and any duds rejected. The arrangement is 13S4P, and the cells are held in place with laser-cut acrylic frames. Rather than spot weld the terminals, [Make It Extreme] used a series of strategically positioned slots to make contacts from folded bits of nickel strip. Solid contact is maintained by cap screws passing between the upper and lower contact frames. A forest of wires connects each cell to one of four BMS boards, and the whole thing is wrapped in a snappy acrylic frame. The build and a simple test are in the video below.

While we like the simplicity of a weld-less design, we wonder how the pack will stand up to vibration with just friction holding the cells in contact. Given their previous electric transportation builds, like this off-road hoverbike, we expect the pack will be put to the test soon, and in extreme fashion.

36 thoughts on “An E-Bike Battery Pack Without Spot Welding

  1. Large high current, high voltage battery banks are soldered or spot welded for a reason
    you really don’t want dicky connections on such a thing … at several dozen amps threw a few milliohms of contact resistance can create several watts of heat that can easily snowball as the heat speeds up oxidation
    not saying its wholly unsafe, but i am saying i wont be powering my house off temporary contact li-ions any time soon :P

      1. no it wont, the hotter the contact gets the more it will corrode making the connection even hotter, the resistance will go up as it heats and can easily get red hot, pumping all that heat in to the battery causing even more problems with resistance
        im going to agree with lou and say in any high power constant load application like motor driving … its probably totally unsafe
        high power pulse applications like an ECig or low power applications like a sensor, flashlight, your 5W diy projects are probably okay with press fit contacts like a socket
        but i mean your soldering so much already … just solder your batteries in your DIY projects
        takes no time at all with a little bit of flux and a chisel tip and while your at it get protected batteries
        a good rule of thumb is when dealing with li-ion batteries, dont cut corners

        1. “a good rule of thumb is when dealing with li-ion batteries, dont cut corners”
          So never solder directly to batteries! Buy batteries with solder tabs or build/get a spot welder.

          1. no, 18650 cells are soldered in industry all the time, there are literally jigs for it sold professionally and defined by samsung and LG
            as long as you dont hold the iron on it for an hour its more than alright

          2. Never solder anything if you can’t solder properly with the right equipment. I solder reclaimed 18650s all the time and have never had one get hot. But then I have 40yrs practice and the right equipment.

    1. Can you please explain why would such kind method of battery connection loosing power? If comparing the same method of glass fuse holder, which has on one side spring connector, and on another site flat-solid? And, we know the fuses have big role in electricity world, which need to do job very accurate, and reliable.

      1. a good rule of thumb for li-ion batteries is to never cut corners … if you dont know why someone does something and you dont want to look it up … just do it too
        plus a DIY spot welder is a very fun project and a good way to upcycle your old microwave and frayed jumper cables

      2. In fact, I do have a clue. This fire-trap relies on the spring-action of the metal maintaining a very-low ohm connection. Just a few hundredths of an Ohm, from oxide, dirt, frog-snot or whatever, and now you have a few (to many) Watt heater. In a confined space. Pushed together by Plexiglas /plastic . Which gets soft when hot. Which “pushes” the connections together less. Creating more resistance. Creating more heat. In a confined space. Making the plastic soft.. Getting the joint hotter…. Anyone want to make a prediction here? Any fortune-tellers about? I will take a shot. IT ends in fire. a metal fire. A lithium metal fire. Word of caution, don’t try to put it out with water.

        1. Fortunately it’s no Li-metal fire. There is no metallic lithium in a lithium ion battery. But there is still enough flammable stuff around: Organic electrolytes: flammable; carbon electrodes: flammable; Acrylic holder: flammable. And abunch of stored energy when the pack is charged.
          But it’s still worse then “relies on the spring-action of the metal maintaining a very-low ohm connection”: there are no metal springs, the “elasticity” of the PMMA is supposed to press on the contact. But when it gets warm it gets more plastic. Polymers are often called “plastics” or “thermoplastic” for a good reason.

          1. It’s actually even better…a charged litihum ion call has the (very) porous carbon negative electrode loaded with metallic lithium, giving waaaay more surface then if it was just a chunk of metal…
            If you use enough water you will definitely put it out, but personally I’d recommend trying dry sand ;-)

  2. Colin Furze installed a pulsejet engine into a street bicycle, making “the most dangerous unsafe bike ever”. But I think the e-bike with the unwielded battery pack from this entry, is even worse.

  3. Like the design and think it’s great but is there not a big problem there with it?.
    It being all plastic won’t it get hot and start causing problems? Plus it’s not very sealed up well but then I know you made it open for air to get around it. But all that plastic stacked together to hold the batteries won’t it get hot when you run something that takes a load of power will it not warm things up inside that plastic sandwich you made? All am I getting this all wrong?. It look nice what you done just not sure on the safety side of it?.

  4. Back to point. Decades ago I figured out thst 7-11 met tbe criteria for “several.” The median is 9. Several dozen is 9×12=108. I^2R=Power(Loss.) 108×108= 11,664. 11,664 x 0.001 Ohms is 11.664 watts. Forget a few milliohms. 1 causes 11W loss per junction. Recall how warm a 7W Christmas tree bulb got? Several milliohms must be an exaggeration. Hopefully in ALL junction-cases. It would otherwise be untenable.

  5. This is very unsafe. Contacts degrade. There is no elastic element pushing them. Temperature changes. And acrylic and vibration? No thanks.

    There are so many ways to easily spot weld: 12V acid battery, super caps, microwave oven transformer…

  6. Bully…
    Jolly good chaps ( except the hater wishing leathal outcome )
    Good show I say.
    Post test results when the battery pack is put through its paces— extreme lloads and is a thermal graph or FLIR camera too much?

  7. Nice pack but i wouldn’t draw more than a few amps through a spring connection. I have a couple 3 and 4s spring pack holders, vibration and heat tend to disconnect the cells, in 1p config it just shuts down but may overload a pararelle pack if it were 2p.

  8. umm did they just completly weld shut that enclousure? i saw him applying the glue to the top and the bottom. Interesting design process, make a component and asume its perfect before integrating it into the larger project. Although it could be the ultimate troll because i find my self curious about the next part of the larger project.

  9. Recovered cells is kind of a recipe for disaster in a pack this big – they have been suspect in several electric longboard fires. The serious battery builders are starting to follow Tesla and have cell-level fuses (24 ga wire I think) to a buss bar in their packs.

    Also acrylic seems a little cracky for something that’s going to be in a vehicle. Maybe HDPE? It’s soft, strong and forgiving.

    Otherwise good build!

  10. It looks ehh and ended up heavy and unsafe with its mismatched cells and unreliable connections. But hey at least he engraved the side!

    Seriously this content doesn’t belong here as anything but a warning or example of what not to do.

  11. If that’s make it extreme, what to call my 14S8P pack from recycled cells? My pack will also have the ability to parallel several DeWalt 60V lithium packs to extend range.

  12. Why not use large RC packs from a source like HobbyKing? It feels like a much better option than these heavy battery builds. They’re cheaper per kWh, higher discharge rate, lighter, less labor, smaller volume, last longer due to less internal resistance, etc. I had an 18650 pack, but the weakest links would always need to be replaced and would prematurely wear out the good ones. I started to buy better batteries, but the cost was significantly more.

    I’ve been using two 7S 12Ah packs on my ebike for two years now and it works great. Protection circuitry even monitors battery temps.

    P.S. maybe add article tag ‘ebike’ along with e-bike’.

  13. Junctions between dissimilar metals or alloys are prone to galvanic corrosion. The welding process mixes the metals to a degree forming a zone of alloy between the two which helps buffer the galvanic effect. Contacts essentially do ‘spot weld’ but do so at the asperities only.
    Blah blah blah, it’s complicated! :D

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