An Arduino Nano based Spot Welder for battery welding

This Spot Welder can be used to weld 18650 batteries. It needs a 7-12V power source (12V recommended) and uses a 12V car battery as welding current supply. Typically one 45Ah battery delivers enough current to get good welds with 0.15mm nickel strips. For thicker nickel strips maybe you will need bigger battery or two in paralell.

The Welder generates a double pulse, where the first one is 1/8 of the time of the second one. Pulse time of second pulse is adjustable by the potentiometer and displayed on the screen in mS so you can exactly adjust the time. Its adjustable from 1 ... 20 mS.

Watch the Video to get detailed instructions on how to build it.


Project Files:


Due to many requests for the PCBs

If you guys want to buy a set of pcbs to build your own spot welder please take a look in the comments below this instructable. Some people who ordered boards at PCB manufactures are willing to sell some of them. I don't have any more pcbs left for sale.

Step 1: Making the PCB

You can find the Eagle files for the PCBs on my Github.

Easyest way is to order the boards at an PCB manufacturer. For example at pcbway.com .There you get 10 boards for about 20 €. The necessary gerber files for ordering at pcbway.com can be found in my Github.

You can support me by registering through this link http://www.pcbway.com/setinvite.aspx?inviteid=128...

This way you get a 5$ coupon for your order and i get some credits at the shop which i can use for upcoming projects.

But if you like diy you can also build it on a prototype pcb board with hand wiring. This is how i did the first prototype of the spot welder. In the pictures you see a manufactured board looks much cleaner.


<p>Hi,</p><p>i need PCB or 2 (Germany)......</p><p>Thank you</p><p>Michael</p>
<p>I can send you. I have 20 piecess</p>
<p>Merhaba!! Elinizde var mı hala PCB?</p>
Evet var
<p>Still have the following kit in EU (can also ship to RU or USA):</p><p>- PCB</p><p>- Arduino</p><p>- Foot switch</p><p>Drop me a message is you are interested!</p><p>Regards, Janos</p>
<p>How many will be costs in RU PCB?</p>
<p>Has anybody in EU finished product for sale?</p>
<p>I finished my spot welder today. Uses copper bus bars and avalanche protection mod. Lots more info in my build log which starts on page three of this thread: https://endless-sphere.com/forums/viewtopic.php?f=31&amp;t=80315&amp;p=1215403#p1215403</p>
<p>I cannot thread opened, can you tell me which nummer TVS dioda ?, thanks.</p>
I saw diode series with(?) between plus and min accu, what dioda is that ?
That's the TVS diode. See the thread for more details.
<p>9 PCB's available in France (Paris) ;-)</p>
<p>That is what I was looking for... Very well done. Can you use main charger for it of just a car battery?</p><p>Ripleyxlr8: </p><p>I would be interested in two sets - Ireland. send me some info on freederix [at] gmail [dot] com thank you</p>
<p>Hello, I have a few boards for sale in EU.</p>
<p>hello sorry for bothering you, can you supply with 2 of these boards? Thank you</p>
<p>Does anybody have extra PCBs to sell to EU ?</p>
<p>Hello, I have a few boards for sale in EU.</p>
<p>I have 5 spare sets of boards for sale in Australia, I accidentally ordered two different colour boards (red control board and green mosfet board) colour does not affect functionality! Please let me know if interested.</p><p>More details about build to come later. Thanks</p>
<p>Nice build, but do the electrons move faster through the red board? Did you have to change the code to compensate? The electrons are already upside down so may fall out of the PCB.</p>
Close, but to be honest it has nothing to do with the electrons, it is all temperature related, the green keeps the mosfets a lot cooler, I was worried that they might get a bit hot on a red board.
<p>Ahh, that makes perfect sense, the red one would also be so much easier to solder. I just feel bit stupid now :-)</p>
<p>Hi KaeptnBalu, I really like your design, though I was wondering if I could re design the PCB to not use the MOSFET gate drivers and instead just use ~10K resistors to drive the gates of the MOSFET's. The switching time would only be a few milliseconds so I would think it would work fine. If theres a reason that your using gate drivers instead of just resistors please let me know!</p>
<p>The switching time of a few milliseconds will be too long - the total time it's on for may be less than that! You could try using the cheaper TC4424/MIC4424YN (available from AliExpress) or a single driver such as MCP1407 driving all of the fets.</p>
<p>I need to order more mosfet as blew them and need to change.</p><p>Can I use this one? IRF1324</p><p>Thank you.</p>
<p>Yes, they are the best available for 12V and lower. If you are using a lot of current you could try this mod to stop the fets failing. https://endless-sphere.com/forums/viewtopic.php?f=14&amp;t=81400&amp;start=550#p1218325</p>
<p>well, as. matter of fact l am using more current. Thought it would be a good idea to order a big (100A) battery. And on top of that I put it over 2meters from where I weld (hopping to save space on my table). I used very big AWG cable (35mm2).</p><p>I did like 60 li-ion head welds. Then it started to over shoot. That is no matter the value that I set. It seems to keep pushing 20ms.</p><p>I though that it just had to be the fets. I went ahead and ordered these more expensive ones that you say are better. I checked the old fets and the seemed fine too.</p><p>I had a spare board. So I decided to rebuild the to part with the arduino on it. Not I cannot see any visible damage on any of the components (resistor diode etc). Once I was done Installation it the old lover (mosfet) part. what ado you know. It started to work again. Then jus the smile was getting back on my face, exact same thing happens.</p><p>Does anyone have am</p><p>any ideas?</p><p>Note the most weird thing is that the first time that it happened, I restarted the system including arduino. This help for another 10 welds, then started all over again.</p>
<p>First, putting the battery that far away is not a good idea. When mosfets fail in this application it is because of inductive spikes. Wire inductance is proportional to it's length so it will cause bigger spikes.</p><p>Your issue sounds a bit like a heat problem (possibly caused by inductive spikes) But if it was really doing exactly 20ms when you selected a different number it is most likely a software problem. That is because the max duration of 20ms is only defined in software, it has no relation to the hardware.</p><p>I made quite a few changes to the software recently which is now merged into the main repository. You may want to test that out but I didn't notice any obvious bugs like you've described and I don't think I changed anything that would affect it.</p>
Yes it is very weird. The first time, I too tought it was heat. <br>But it is not mosfer.<br>As is started working, once I rebuilt the top part.<br>I always use the latest version. <br>The interesting thing is that the led ans pot work correctly according to the digital readout. Also the led duration I can is longer or shorter. The reason I say that it is shooting 20ms is that it just burns trough the plate 0.15mm, but then stops (now I think of it, could it be it stops from me releaseing the pedal?). Also mosfets are not blown and are working. Which again is very curious. <br>Why I think it was heat. Is that the first time I let it rest for 10mins (cool) and it started to work again. However after that it did very few good ones and then failed permanently. Meaning that even a whole days rest did not help.<br>That first time it failed, it was definitely warm and I did a lot of heads none stop. But the new board was just 7 or so. So total of about 20 welds. <br><br>
<p>So are you saying the upper boards work for some time and then fail and don't ever work properly again?</p><p>It doesn't sound like a software problem if that's correct, but still worth investigating as that is probably the easiest to debug/fix (for me anyway).</p><p>Have you got any way of measuring the pulses from the top board? Storage oscilloscope, logic analyzer or another arduino would work.</p><p>If the LED duration visibly changes then you're not using the latest software version as it stays on for the pulse time + 50ms. It was updated yesterday.</p>
<p> I don't have any of those equipment. So I cannot run any test. is it possible that the single schottky failing would case such issue?</p><p>I mean what a would be I experience if it fails?</p><p>I don't have a spare right now orderwise I would chech if replacing just that would sort the issue?</p><p>what do you thing. it is definitly not the software.</p>
<p>I don't know where my last comment went, I replied to this a couple of days ago. I doubt the schottky would have failed. As far as I'm aware it is only there for reverse polarity protection. If it failed the spot welder probably wouldn't turn on.</p><p>It sounds like the Arduino may be resetting.</p><p>What power supply are you using? If your power is tripping or if you are directly using the 12V battery to power the spot welder it may cause these symptoms.</p>
I see/saw your comment and, I did reply. I use a separate 4s lipo battery with switching BEC set to exactly 12v. So we can rule that out. Is there anything else on the top board that could be causing this? The main symptom is that a hole is created in the strip. As a sign that is is getting way more than the 5-6ms that I use to wels the 0.15mm stips. <br>To correct my first comment again. Mosfets are not blown. Replacing them all did not help. Behavior conti6. Only thing that helped is rebuild the top part with everything replaced. But unfortunately only temporary solution. <br>Mosfets are ok. Gates are locked till I press the pedal. And they stay locked after pulse. Problem is pulse is zero or too long. Not in between.
I think I will give it one more go. Inhave so many cells to weld. <br>I will buy a smaller battery 50A.<br>Also rebuild the entire thing (for a third time with new pcd and parts) <br>I will noy add extra cable, just do like everyone else and have the battery right in front of me. <br>I would like to add this schottky and tvs diode that you recommend. <br>Would you be kind enough to point the right ones out to me with a direct link. For example from here Reichelt.de<br>Thank you very much
<p>I doubt the schottky would have failed. As far as I'm aware it's only there for reverse polarity protection. If it failed it would probably be open circuit and the spot welder wouldn't turn on.</p><p>There's a chance that the arduino could be reseting on every weld. Do you use a separate 12V supply for the spot welder? Any chance this could be tripping or resetting when driving the mosfets?</p><p>It was me who replied about the avalanche protection diodes on endless-sphere. For some reason instructables takes a long time to email me notifications of comments on here.</p>
<p>thank you. it is so kind of you to try to help.</p><p>I use a separate source for 12 for the arduino. 4s lipo with switching bec set to 12 volts constant.</p>
<p>Also if you wanted to use an even more efficient MOSFET to create less heat you could use the IRF1324S-7PPBF. It has a RDSon of only 800uOhms/0.8mOhms which is crazy! Link to datasheet, http://www.mouser.com/ds/2/196/irf1324s-7ppbf-935685.pdf</p>
Hi everyone<br>I can't find RK09K113-LIN50K poti in my country. www.reichelt.de company does not cargo to Turkey.<br>Can you find an alternative site could take this? (Aliexpress or Ebay)<br>Thank you<br>
<p>Any 50K linear pot will do, I used one of these :-</p><p><a href="http://www.ebay.com/itm/381374716268" rel="nofollow">http://www.ebay.com/itm/381374716268</a><br><a href="http://www.ebay.com/itm/182176305958" rel="nofollow">http://www.ebay.com/itm/182176305958</a></p><p>However the PCB footprint is different so I just connected it up using some flying wires, it actually turns out to be better if you're mounting in a box, you can attach the pot directly to the side of the box with a nut.</p><p>The small blue trim-pots are another alternative, however adjustment would be a pain.</p>
<p>Thank you very much</p>
<p>You don't have to use a 50k&Omega;pot. Almost any linear pot that fits will work. For example even going down to 1k&Omega;will dissipate 0.025W which will probably be within specs. You could probably go up to at least 1M&Omega; without problems.</p>
<p>Thank you so much. I have 50k poti. I can use this. Maybe use enclosure. </p>
<p>I spent a while improving the Arduino sketch. I have submitted a pull request but for now you can get it from here:<a href="https://github.com/MichaelLawton/Arduino_Spot_Welder/blob/9edd5b7b8992a4d4819fba79d9dd5e6e051724c8/arduino_spot_welder/arduino_spot_welder.ino" rel="nofollow">https://github.com/MichaelLawton/Arduino_Spot_Weld...</a></p><p>I have made lots of changes, but none to the features or operation of the spot welder. Mainly I have improved the display subroutine and the potentiometer reading.<br><br>Most important changes:</p><ul><li> - Display code is now non-blocking. So pulse will happen as soon as switch is pressed, not a few hundred milliseconds later<li> - Display updates immediately and shows ones place digit when adjusting pot<li>&quot;1&quot; digit in tens place shows on left which is more readable<li> - Hysteresis added to the potentiometer reading<li> - Potentiometer midpoint shifted so 20 milliseconds gets 0.5/21 of a turn, the same as 1 millisecond<li> - Display only flashes when showing two digit number<li> - LED stays on for 50ms after pulse<li> - Cleaned up display blanking code</ul>
<p>Thanks for your work on this and sharing it with us.</p>
<p>Note that the changes have been merged now, so just use the file from KaeptnBalu's GitHub</p>
<p>I'm not sure if I have skipped it somewhere but what size are the Nylon standoffs?</p><p>Also could metal standoffs be used?</p><p>Thanks</p>
<p>They are 11.6mm http://www.ebay.com/itm/172248383171?var=471069475076</p>
<p>And no, metal standoffs would create shorts.</p>
Can we use 12v 60a switching power supply instead of car battery?
<p>Nope. It needs 500-2000A.</p>
<p>Jeg har noen kort, sender i Norge kr. 100.- for kort display og frakt :-)</p>

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