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Battery Spot Welder (CD Welder) || DIY or Buy

Battery Spot Welder (CD Welder) || DIY or Buy

In a previous project video I showed you how to create a battery pack out of 18650 lithium ion batteries. Back, then I utilized a rather riskier and not recommended methods of connecting the battery cells together. By soldering the nickel strips directly to them. This can be dangerous because you heat up the battery quite a bit which according to its data sheets can lead to problems. So even back then I tried an immediately failed at doing some DIY spot welding. With the two salvaged microwave transformers which I had lying around from another failed wedding video. But since I want to create a bigger battery pack in the near future I’m in dire need of a battery spot welder and truth be told I almost bought a cheap one for around 200 euros. Which seems to be capable of doing the job without a problem. But before buying I wanted to try the DIY route and see whether I could create my own battery spot welder. Which is the subject of this DIY or by episode. And spoilers I will fail terribly. Let’s get started! [music] When it comes to spot welders Then we can either use a big transformer in combination with some power electronics To create small energy pulses with the length of a couple of milliseconds Or we can create a CD welder aka a capacitive discharge welder This method still uses power electronics to create millisecond pulses of energy But the main power source are this time capacitors. As you might know if capacitors get connected to a voltage source then they get charged up and can also hold this charge for a while and if you short the capacitor leads with a nickel strip then we get an energy burst which in this case is not enough for welding though Since the 220 microfarad capacitor only held an energy of zero point zero two four seven five joules. But if we instead utilized super capacitors with a capacity of whopping 100 farads connect six of them in series Utilize Kapton tape to create a poor man’s capacitor bank and charge the pack up to 15 volts Then we successfully stored around 1875 joules of energy Which should be plenty for spot-welding. That means it was time to create the control circuitry around the capacitor bank As electrical switches I went with IRL 2505 N channel MOSFETs, which can handle up to 104 amps Thus I used one for the charging process of the capacitors and three in parallel to discharge the capacitors during welding. Additionally I utilized four TCO four 4420 MOSFET driver ICs Which already ends the power electronics part for this project. For he control electronics I went with an Arduino Nano as the brains of the organization, a 128 by 64 OLED display so that we can see what pulse time is currently used and whether the capacitors get charged up a rotary encoder to adjust the port’s time and initialize the charging of the capacitors and finally a pedal for sewing, to which I soldered one channel and the ground cable of an audio cable So that I can connect it to the circuits through an audio jack in order to activate the discharge pulse. To those main components I then added some complimentary ones and started turning this theoretical composition of components into a proper schematic through the free on-line circuit design software called Easy EDA Not only did I make sure to connect all the components to the correct Arduino pin and counterpart But also make sure to utilize the correct package with included PCB footprint Because once the schematic was complete. I did not feel like connecting this big number of components to one another on a piece of perfboard Instead I click the convert to PCB button and started arranging all the PCB footprints of the components Once I was happy with the layouts I then started tracking the copper traces on the top and bottom layer at the end I placed thicker copper traces for the power electronics and created a solid copper region for the ground potential and with that being done, I exported the Gerber files and ordered five of the PCBs through JLC PCB. Which was not only affordable, but also only took one week for them to arrive. Now even though the PCBs look like they would work without a problem, there still was a problem. Which was that I did not use to correct footprint for the DC jack. So I had to enlarge the holes, which did work out eventually. That means it was time to first [solder] all the SMD capacitors to the PCB and afterwards all the through-hole components which all and all took roughly around 30 minutes. And if you’re wondering for what the big 10 ohm power resistors is used Then let me tell you that it is used to slowly charge the capacitors while providing feedback voltage to the Arduino. So that the microcontroller knows when to stop charging. Only problem was that the feedback voltage can easily exceed 5 volts, which the 5 volt Arduino certainly does not like. So as an afterthought I interrupted the feedback copper trace and added a 2 kilo ohm/1 kilo ohm voltage divider to lower the voltage. And with that being done the hardware was complete, and it was time to program the microcontroller Now I will not go into too much detail on how I created the [code]. Since I already talked about interfacing each one of the utilized components in previous videos. Let me just say that I used an external interrupt for the rotary encoder, pin change interrupts for the push button and the paddle button and a super simple delay function to create the welding pulse. So after uploading the code, connecting the capacitor bank and a DC voltage of 15 volts to the circuits It was time for testing and as you can see the rotary encoder control works. Charging the capacitors is possible and even the pedal switch created a precise pulse according to what we have set with the rotary encoder Beautiful, right? Well here begins the depressing part, since the capacitor bank was always connected to the welding terminals no matter whether there was an impulse or not The problem was, which I found out after too many hours of troubleshooting the missing reference potential from the discharge MOSFETs Which I could not add as an afterthought because that would have shortened out the main power supply. So all in all this project was a big bummer for me. But it shows beautifully that buying a product can often saves you a lot of nerves. Now for me going back to the schematic and fixing this problem is not worth it. Since welding projects seemed to be my kryptonite. But if you want my project information to fix it or see a functioning CD welder then simply have a look in the video description. As always, thanks for watching. If you enjoyed watching my failed attempt, then don’t forget to like, share and subscribe Stay creative, and I will see you next time! With a functioning project…hopefully.

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100 thoughts on “Battery Spot Welder (CD Welder) || DIY or Buy

  1. You are one very clever lad, even though it didn't work as you expected, you've made something, millions of people couldn't. Thank you for posting.

  2. For use on a few batteries, any thoughts on just using conductive (copper?) tape, instead of spot-welding those nickel-plated steel tabs?

  3. Stumbled back onto this project — I found this and thought you might find it interesting… — (he's literally using a car battery and copper nails, and it works…) 😅

  4. DUUUDE you did so well! this is normal with invention. you must fail before you can succeed. finish it off or you will get cancer 🙂

  5. Errrr, or maybe it shows you that you chose the wrong approach? This doesn't need any circuits at all, just a fitting car battery with a solenoid and a switch attached to it in the right way. Scott here has a tedency to overcomplicate and draw obviously wrong conclusion.

  6. Large caps, high voltage (30v+), 12v lamp as soft-start cap charger, thick wire and copper terminals. Done. Rapid discharge of current from the Cap(s). Energy in a Cap E=CV^2 which is why higher voltages are good.

  7. Have you seen this project? That is a way to stay into the DIY spirit and weld…

  8. Once I'm in on something I'm really in — as some said its a matter of pride.
    …And amazingly it always works out in the end…
    But then its also why sometimes I choose NOT to go the DIY route – because it could
    be a large rabbit trail and who knows when you'll come back out of Wonderland. LOL

  9. Nice try. I connected 6 supercaps to this Kweld nicely done DIY spot welder. It works much better than the one you were looking to buy.

  10. Rather disappointing… a spot welder is stupid expencive, id MUCH rather build one for cheaper, which is something many people have done.

  11. can someone please tell me if the way he makes pcb is still a well paying job and how do I go about getting a job like that? Thank you

  12. I know this is an old video nowand think you might have something else now but ali express has one that works with a transformer for like $15 you need your own transformer but still

  13. I have 1500+ cells, and that's only the start of my project, I need to spot weld them, I built smaller banks by soldering, I don't like to. And it does NOT look that great, there is spotwelder timing boards available on Amazon, I thought about maybe trying a SSR or a group of MOSFETs, for the pulse switch, from caps, and either use a 12v or so battery, of a mot transformer, rewound for high current 10-18vdc, to charge the caps at about 30-50 amps, I don't have super capa , I do have about 3 farad of caps, surely with the transformer and a couple farad of capacitance will spotweld!!! I do not want a failed project, I can't afford the loss at the moment, . I need it to work that's why I'm here! Great video even if it's a fail, still a great learning process, it makes you think more than a " how – to " video….. Thank-you,, ,,, ,, , .

  14. Just use a 12vdc battery with at least 200 CCA up to 600 CCA and a momentary switch. Its got enough power and is super easy to do.

  15. Hi! Stilllooking for a spot welder for welding Li-Ion cells? I just came across this video, no electronics required, just a proper 12V car battery. It seems to be working very consistently and delivers a perfect job. Super simple.

  16. Could i use 20 330v caps and a board from a disposable camera flash to charge them up and then short them to weld? I have thos stuff here because of a coilgun i made. I would only need to short the capacitorbank instead of discharging it into a coil…

  17. Actually there is a CD welder that is easy to build, but Hocky Puck SCR's are not cheap, and the same for low inductance capacitors that can handle up to 180v and have screw terminals.

  18. Well, you can't say you didn't TRY! At least you were able to figure out where your mistake was! and show us.

  19. Sir, you dose not explain clearly like "electro boom" sir……you are not clear and so selfish..I DONT LIKE THAT

  20. I always like your videos. But this time unlike. Was expecting mature circuit and schematic design. Anyway nice try.

  21. If you succeded on the first try how would the prices compare? Would the DIY working one be worth it over the bought one? How efficient would they be comparatively?

  22. Am I the only crazy individual who sees a simple relay as a solution? Just connect the normally closed contact to the capacitor bank charging, so when it's not in use, it's charging up to the desired voltage (interrupt current flow via Arduino, can be even done via traditional electronics), and use the pedal switch to energize the coil, and connect the normally open to the welding terminals, so you short the capacitor bank while you keep the pedal pressed AND disconnect it from the charging circuit at the same time.

    Add a second always energized relay, with its normally closed contact connected to a discharging resistor, so that when the welder is powered, it works normally, and when it's unpowered, leftover charge is simply discharged as heat, to avoid unpleasant surprises.

  23. Why would you hook up the 100F capacitors in series? Wouldn't you want them in parallel so they add to a total capacitance of 600F?

    Edit: Oh wait energy formula is (1/2)(C)(V^2), so you would want to increase voltage as much as possible, nevermind.

  24. How many light bulb prototypes were made before one actually worked? Try, try, try try… Try try again!

  25. Hi. great work. I was wondering if this timer could be used with a battery?

  26. Hey Scott
    I am having a great time watching all your DIY videos and I really appreciate all your hardwork in explaining them to us.
    I thought to ask a question like "why can't a flash circuit from old roll cameras used to make a spot welding machine to connect lithium-ion batteries".
    I really appreciate your time to reply me.

    Thanks and keep scotting 😊

  27. I like your honesty, even when you fail due to errors we all do with projects, you still present valuable informtive and clean instruction as to why. Thank you keep it up

  28. Thanks for sharing… Alot of DIY'ers post video that are successful and don't or rarely show the disadvantages. You my friend are a trust worthy guy and your videos seem more authentic. Good job. After all failing is how we succeed ! 👍

  29. Great video! My deep respect for you, to admin mistakes and willing to publish them! This way even we can learn from your mistakes. How great is that!
    Love your channel!

  30. Thank you so much for sharing. It's very informative and interesting to watch how you went about the challenge. Despite the project not being exactly what you wanted, hopefully, after the frustration dies down, you'll find invaluable lessons learned. This stuff was way over my head but it's inspiring.

  31. I'm really struggling to see how adding a reference potential to the mosfets as an afterthought will short out the main power supply. Isn't the voltage at the gate not connected to the drain and source? Wouldn't the data signals going to the gate be a completely separate circuit? Isn't the fact that the gate is missing a reference potential proof that the gate and source aren't continuous?

    It's so incredibly difficult to learn all of this. I was scrolling through comments looking to see if anyone had already asked my question and I found a comment from myself 4 months ago trying to figure out capacitors haha.

    Edit: Okay so after a week of deciphering this alien language I've come to the realization that he doesn't care about the gate potential. For some reason he doesn't need a pull-down resistor for the gate. My best guess on how to fix this as of right now is to connect Cap- to ground. How that shorts the power electronics I have no idea.

  32. You don't use any flux!!!? That is why your soldering seems shitty… get some good MG Chemicals flux in a syringe and apply it where you will solder and it will be like magic…. Also I tend to wet the tip of my iron with solder and apply it that way, as long as you contact the component long enough to prevent cold joints this is fine. Also… I wuold have just desoldered the FETs and made an air wire for your reference… ignoring the PCB ground.

  33. So he intentionally or accidentally used two different reference voltage symbols and ended up with two nets? When I was new to EAGLE I managed to somehow turn my GND into two nets without noticing too.

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