Weekend spot welder - Page 1
Forum section: electronics / projects

author: hacklordsniper
author_rank: Frequent Contributor
timestamp: October 15, 2011, 08:20:23 pm
content: Thinking what could be done this weekend i knew immediately when i seen some caps derived from junk yard diving some time ago. A small spot welder.I was thinking before about building one and consider two strategies. First one was to build a line powered H-bridge power supply powering a few KW switching transformer and generating alot of amps on the other side (something similar like a small induction heater i designed) in short bursts. Since i wanted something more safe and transportable i decided for capacitor discharge system.Checking what other fellows have done in this area i understood second method is better and widely used. The only change is that other people use PIC-s, ATmega and what not to drive the power bridge. Since im old school analog and any kind of programmable device is banned from my lab i will design an analog version of itI did the power side today, tested and working powered by a FG and mosfet drive IC. Tomorrow i will build the control electronics. Basically what im aiming is 2 X 555 for simple PWM and second will be used as "one shot" switch and as an time adjustable interlock between "welds"

author: jackbob
author_rank: Regular Contributor
timestamp: October 15, 2011, 09:01:38 pm
content: So are you building an induction coil for induction heating? Or a capacitor spot welder? Your board looks fantastic you did a goo job as far as I can see on my iPod screen. But you may want a good fan or some way of keeping that heatsink cool because those fets can get hot. 555 is probably the simplest way of making pwm but I have had it fail me several times. Don't be scared to try microcontrollers they do require programming and what not but with a little research on the Internet you can get it fast. There are also ic's designed just for pwm and those are a step up from the 555 and easy to work with and don't require prigramming. But if it's just a hobby thing and you just want a simple easy way to make it work a 555 is the best solution.Jacob.

author: hacklordsniper
author_rank: Frequent Contributor
timestamp: October 16, 2011, 12:41:11 am
content: Quote from: jackbob on October 15, 2011, 09:01:38 pmIm building a capacitor spot welder. Boards look nicely thankfully to pcb router i acquired allowing me to make any board in 5 minuttesI have about 10 kg of various SMPS controler ic-s but i love designing things with 555, its lika a challenge because this was my favorite IC when i was young.I allready managed to make a circuit for it, will test it tomorrow but now zzzzzzzzzz...

author: jackbob
author_rank: Regular Contributor
timestamp: October 16, 2011, 12:51:40 am
content: I wish I had a pcb router I would be making boards like crazy. I understand why you want to use a 555. It was my first ic ever learned too and it is great, there are countless projects you can make with it and it's simplicity makes it so desireable. Are you like me staying up really late till I get my project right? even if I have school the next day I can be up till 2 am working on something till it works right.

author: RCMR
author_rank: Frequent Contributor
timestamp: October 16, 2011, 08:30:29 am
content: I built my own spot-welder using a microwave oven transformer and didn't worry about discharging capacitors.it happily welds up to 0.5mm stainless steel and simply involved removing the secondary from the MWO transformer the winding a couple of terms of heavy-gauge insulated wire (I used some stranded copper but others have used welding earth-leads or even copper tubing).The result is an output of 200-300A continuous at 1.2-2.5V (in most cases). This will fuse think sheets of most metals very easily and eliminates all the hassles of charging up (expensive) capacitors etc.I have a foot-pedal in the primary circult so I just energize the transformer for long enough to fuse the two pieces of metal together.KISS rules!You can get a glimpse of my home-made spot-welder in this video

author: hacklordsniper
author_rank: Frequent Contributor
timestamp: October 16, 2011, 09:07:51 am
content: Quote from: jackbob on October 16, 2011, 12:51:40 amIf the project is interesting i don't come out from the lab from Friday 16:00 till Monday 6:00 h. Unfortunately i need to go to work and spend some time with family ocassionaly.The driver is complete, PCB is made and is just being milling as we speak. Its a 2 layer so it will take some time and then i need to wait for 2 hours for tin plating to finish.Quote from: RCMR on October 16, 2011, 08:30:29 amI definitely agree with your KISS principle but i wanted to avoid line powered device and wanted to make it as compact as possible since i don't need it very often and don't have much space for storage. Also the caps are from dumpsterBut great work, definately!

author: jackbob
author_rank: Regular Contributor
timestamp: October 16, 2011, 09:57:23 am
content: Sounds just like me all weekend working on projects. Where did you get your pcb router it's amazing I don't know how I'm living without one. Oh and just wanted to give you a quick reminder I can't te if those caps are flash rated but if not they WILL explode eventually from arcing. They may last up to 500 times maybe more if your lucky but they will not last forever and don't let them catch you off guard because those things are crazy. @RCMR, looks like you got a whole manufacturing plant nice tools and I like your spot welder too. Nicely crafted not some cheap fast job, it looks very professional nice work.Jacob.

author: XynxNet
author_rank: Regular Contributor
timestamp: October 16, 2011, 10:06:33 am
content: After spectaculary blowing a faulty cap in a simple demo capacitor spot welder, i now use a simple transformer like RCMR. It is way simpler and to me it seems to be way safer.

author: hacklordsniper
author_rank: Frequent Contributor
timestamp: October 16, 2011, 03:18:54 pm
content: Quote from: jackbob on October 16, 2011, 09:57:23 amThe router is a Collinbus PCB BOX, however its not a product you want to buy unless you are ready sitting few hundred hours with it to make it perfect. Its definitively something that i wonder how did i live without it until nowThe board has been populated and tested, and it works. However im not too much happy about the capacitor performance. It seems that they gave their life to silicon heaven long time ago (although they were not suitable from the start i thought they will work for some time). Oh well it was fun while it lasted and few things learned