Friday, April 29, 2011


I've been working on a new version 2.5 firmware for the Capacitor Discharge Welder and also a package that will contain the newest firmware, gerber files, Bill of materials, manuals and an extra 6 pages to explain how the circuit works and trouble shooting procedures etc. I've included Version 2.1 and version 2.5 in case a bug shows up. Version 2.5 has a change to the charging system, taking the stress off mosfet Q4, slowing the charge intervals and two points on the control board can be jumped with a wire to change the maximum voltage of this welder from 20 to 23.2V. This will increase the energy of the welder from 600Ws to  807Ws. You will need 25V capacitors to use this feature and Diode D10 has to be changed. UPDATE: I'm busy doing some final tests on the firmware. I did not get a very big response about making everything available so I'm going to start by making the updated chips available

If you don't know how to program a processor, you can buy one of these programmers.
 This one is $34.95  : K8076 serial programmer   

 This one is $69.95 : Cana USB programmer

It is as easy as starting the software supplied with the programmer, plug your microprocessor into the programmer, connect the programmer to your computer, load the Hex file and click on "write". It will only take a couple of seconds.


  1. are you not going to keep your code secret and sell chips saves people copying your project?

    there is people out there that will try to profit from it after you doing all the leg work in design.

  2. I know, It makes me think Johnny!!! Maybe I shouldn't.

  3. Those who have since migrated from MPLab would just as soon purchase a pre-programmed processor. I hope this option will be made available!

  4. ...and then there are those of us who would like
    the source code so that we can add our own custom
    options without having to re-invent the welder.

  5. If I make it available you will get a HEX file not the source code

  6. Fritz,

    I'm a student at the University of Wisconsin-Madison.
    I'm working a rebuilding a 8kWhr traction pack for
    one of the vehicle teams on campus which involves welding 1050 A123 cells together. We cannot afford
    a commercial CD welder and your design is the most
    robust one that I've come across. I would be interested
    in the package mentioned above. calederer'at'

  7. Here is a guy that used this welder to weld 1976 A123 cells together. He first used copper and had to redo it because the copper was too thick and cracked when they bent it. He had to redo the battery pack with nickel and did about 40 000+ welds.,%202011

  8. Hi Fritz
    I've been following your blog on and off for some time.
    I was hoping to get the time to put a welder together, but at the moment it lays in a distant future.
    The announcement to make a package containing the info to fabricate a welder was sweet music in my ears.
    I hope you choose to make the package despite the lack of response to the idea.

    best regards

  9. Hi Fritz,

    I think some of us have just been sitting in the background patiently waiting as we appreciate the great work you have done on this project. You have given us all a great project and I will have my welder completed soon. I will send you some pics soon.


    1. WOW... how time flies. Not quite 5 years have passed and I still haven't finished this project. I swear I will get you some pictures shortly. I fired up the welder for the first time on the weekend and promptly blew Q4 and D5 :-( I have ordered replacements and will fault find when they arrive. Maybe I got some counterfeit IRFP2907's , I know there was a problem with this at the time. I have ordered replacements at a substantially higher price this time (RS Components) just to be sure. Running V2.1 firmware as 2.5 wasnt released when I started this project, I may have to look at purchasing the new firmware, more power is always a good thing...

    2. Let me know if you need help Jayson

    3. Well got my new IRFP2907's today and compared them to the originals I have, I'm really not sure why I bothered installing the original ones. They definitely were not genuine parts. I have just spent the last 4 hours pulling the welder apart, removing the IRFP2907's and installing the new ones. What a job. During the removal process I found at least 4 with exploded cases :-/
      Got it all back together and what do you know, it works.
      Thanks for the great project Fritz.
      I will email you a quick photo to show where I'm up to.
      Still more to do but I'm currently a very happy camper.

    4. You can find a few pics here
      I will publish more when I tidy it up a bit.
      Fritz, could I please purchase the latest hex file from you?

    5. Great looking welder Jayson!! If its ok with you, can i put some of your photos on here?
      You can purchase a ver 2.5 processor here

  10. Hello Frit congratulations for your project.
    If it 's possible I would like to list to buy the processor has already
    been programmed.
    I have already built a simple soldering iron that works well, but I can only
    weld a nickel strip.
    I saw that your welder weld many materials.
    I await your positive response.
    Sincerely Beto
    Sorry for my English

  11. Hello Fritz
    I hope you publish version 2.5 of your soldering iron, I and my friends are waiting to be able to build your protegetto oh is the most comprehensive found on the net.
    I would like to buy a microprocessor already 'programmed.
    Excuse my English.

  12. Hello Fritz,

    Like Sebastian I have been watching your blog for some time. I'm kinda of a green horn so I have not posted on your sight. Been watching and learning. The only thing I have been reserved about is the chip-set. Are you still planing on doing the Kit? Like many others on here I want to thank you for the work your have done on this project. I have been looking forward to completing my own unit and posting pictures.


  13. Dan, I am going to make the ver 2.5 microprocessors available, hopefully this weekend, to the guys that already bought boards from me, I have processors on order. I'm not sure what kit you are talking about but I sold the bare boards with processors including the manuals, BOMS, schematics and all documents needed to build one of these welders. I don't have any boards left. I will make another run if I can get enough people interested.

  14. Hello Fritz,
    I really appeciate your job.
    What I want ask you is the possibility to get the PCB files of old version, the one NOT smd. Can you give it?
    With regard to old version of firmware is it free or do I have to pay for it? If yes in what way?

    Best Regards

  15. RAF, those files are not available, sorry

  16. I would take a set of the boards if you decide to do another run of them.

    thanks Paul

  17. Hey fritz,

    Thanks for the update Fritz. I will keep watching the form to see if you make another run of the PCBs and Chip. I will be getting one. In the mean time I will keep working on my greenhorn skills of surface mount resistors.

    Thanks again.

  18. Greetings,

    I'm interested in purchasing boards and a processor when they become available.

    For some reason the Bill of Materials isn't showing up on Scribd...

    Any estimate of a release date for more boards and the processor so that I can build one of these welders?


  19. Hi Fritz
    How many people do you need to make a new run of the board? I would take two of them and pay in advance, if that helps to keep your cash drain low with this project. Or i build a couple of them and sell them here in Europe ;-) Well to cope with the regulations (CE, EMC etc.) there's some more work involved. I have a new F...ed up 10s10p Li battery here, that needs some work soon... (it was built in PRC with 0.8mm2 straps - for 30A.....)
    In the meantime I found on a german board a project with a double pulse welder, but yours seems to me the better solution, even without knowing the details. Have a look yourself: Maybe i have to build both, at least I can reuse the caps...
    Best regards Rolf, Switzerland

  20. Hi Fritz,
    new to the blog, excellent site and would ready like to build one of these units.
    Also interested to know when the next batch of PCB and processors would be available.
    Thanks very much.

  21. Hello, Fritz!
    I am very amazed with so nice project.
    I am trying to make DIY 1.5Farad Spot welder with SCR and MCU control board, but your project with pulse width looking to be more attractive ))).
    Could you let me know, when project files will be available for download?
    Also I am interested, why not to use as power source a cheap (10-15$) 120W 24 VDC notebook charger from Ebay?

  22. Kreitzz, This welder charges a 3 Farad capacitor in about 180 milliseconds. Your cheap 120W power supply will take about 6 minutes to charge the capacitor to 12V. It will be faster to solder the wires with a soldering iron *smile*

  23. Dear Fritz,
    I have just made several tests - notebook power supply 19V 5A charged my 1.5F cap to 18.5V in less than 8 seconds...*smile*

  24. KREITZZ you are making me have to think here :)I miscalculated the first one, a 120W 24V power supply will take +-70 seconds to charge a 3Farad cap to 24V. At a constant 19V 5Amp it will take 28 seconds to charge a 1.5 farad cap to 19V and about 22 seconds to 18.5V. What you don't understand Kreitzz is that you get different power supplies. You get ones with a constant regulated current and ones that will have a constant voltage at a certain current. This means that at 19V it will supply 5 Amp, if you put a higher load on it the voltage will drop below 19V and if the supply is not protected will give more current. If you got 8 seconds then your capacitor is probably below 1Farad and your supply is an unprotected unregulated supply and supplies more current than 5Amps. However, 8 seconds is way to long for this welder and will not work.

  25. Yes, now seconds are close to reality :). And sorry, but I understand very well about power supply. Indeed, I think my power could drain more than 5A, as well as capacitor could have lower capacity, as usually do manufacturers ). I will check its capacity.
    Morning tests has confirmed the first.
    During charging the current was 1.5->2.5->5.2->6.8->3.5->2.2->1.5A. Thanks for nice discussion :).

  26. hey fritz if the voltage swings around or spends a lot of time adjusting the voltage of the cap via q4 from dammaged caps does it shut the charging circuit down in the new software?

  27. Jono, No, the new and old software only shuts the charging system down when an over voltage occur. There is no protection against damaged caps or an over current.

  28. Fritz, can the processor be reprogramed in the event you release a FW update and would future releases be free?

  29. Yes, you will be able to reprogram the processor in your welder. I have a ver 2.5 available at the moment and will release it later. It is not going to be for free.

  30. Hi Fritz, happy new year! I have been mucking around getting components together for this project for a while now. Had some real fun getting good Caps. I was wondering if and when the 2.5 Firmware would be available?

    regards from Melbourne, Australia (like all the others, I appreciate the efforts you are making)

    Big John

    1. John I have people using car capacitors with a 24VDC surge that thinks they can use the 2.5 Firmware. You need computer grade capacitors to use it because the welder voltage goes to 23V. I have the 2,5 firmware running in a couple of welders, including mine and it is kind of scary to make 23V welds because the wrong pressure on your electrodes will make your heart skip a beat. I am going to wait a while, cant give you a date at this moment.

    2. Hi Fritz, thanks for the response. I have computer grade caps (that was what all the fun of procurement was about). I figured that I would err on the side of what I thought to be the better components.

      Once again vale from Melbourne.

      Big John

  31. Hi Fritz
    I'm still having trouble locating computer grade caps, any suggestions. Maybe Big John form Melbourne could share where he found his. Thanks David

    1. Hi David, Big John here. I lucked out by perusing ebay continually for the caps. It cost me about US$250.00 for three 1 farad 25V computer grade caps. Persistence was my only option.



    2. Hi Big John
      Thanks for the response. Fritz told me to search Ebay for 1,000,000 uf to find the computer grade caps and that worked. You need the commas in the search for it to work though. There is an ebay store called JEA Capacitors that sells these, brand name Tech-Cap. I'd love to visit Australia some day.
      Thanks David

  32. Hi David, oddly enough, this is where I got my Caps from. Regards Big John


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