I built a mot welder last year. I control it wth a footswitch to a relay. Most of the time it works well but I have a twitchy foot :person_facepalming:
I’ve been trying to think of a way to do a timed double pulse. Wonder if I could use the timing part of the circuit. Hmm?
The version of the board I ordered has an auto pulse feature which would require no use of a foot switch. It sees both probes are in place on the strip, waits 2 seconds, and then pulses the welder.
Do you think the auto pulse could control my relay instead of the mosfets? Not sure if the relay would be responsive enough. I’m assuming not…
i have a question.everybody advice me. please.
if i don’t spot welder. but i Place button on top of cell only.Will it works?
and 2nd choice
if i use little magnet place between button and flat cell .Will it works?
No, you’re right about that. At least the buttons I have are non-magnetic.
For anyone wondering, professional battery spot welders (resistance welders) use the two probes side by side, not top and bottom like a traditional spot welder. So no need to access the underside of the flat top.
I have used some very high end Miyachi welders at work, the two copper electrode tips just sit side by side, how far apart depends on the type of cells, tab material, etc being welded.
Would love a simple setup like this DIY welder for home use on personal projects, and I see no reason a good weld couldn’t be made with something like this.
I’m new here but Peter I get a chuckle out of you telling a guy who does seemingly has done this for a living that he’s wrong.
You are correct, there are many different electrode configurations. My comment was geared towards the stuff we typically deal with here, which are cylindrical cells in a metal can with a metal top, either flat or button. I believe that is the primary purpose of this particular DIY welder. If we get into prismatic cells the process will be different.
I don’t weld batteries for a living, but I am an engineer and have to do it from time to time. There are many variables that go into making a consistent and reliable weld. The professional machines are generally current controlled and pulse very well controlled currents.
The thing is, I am going to accept different things for different use cases. In a mission critical application, get it done by a pro to be sure it will be perfect. For most of us here it isn’t life or death, so we can deal with “good enough”.
There is always a risk of catastrophic failure of a cell when welding, especially with a DIY device. This can be mitigated though by just starting at low power and ramping up.
Because this is not precision pulses, welding the electrode to the workpiece is likely, but not a big deal. Just don’t pulse so hard that the tab gets holes in it. When using never put an electrode directly on the cell. Both electrodes should be on the tab itself. Ideally you want constant pressure, so spring loaded electrodes are best if possible.
Welding a button top directly to the cell is possible, generally though I usually like to weld the button to a tab, then the tab to the battery, and fold the tab over under the button. Then insulating disk and heatshrink.
EDIT: Forgot to mention, the multipath problem for current with series probe configuration can be mitigated by putting slots in the tab material. This is really only necessary with thicker materials though. Might be useful for those FT button tops to put a little slot between the two electrode contact points if going direct to the cell. Many high current devices where super thick tabs are needed use this slot technique, that is why you will see some power tool packs with slots in the tab where the battery is attached.
Back to the regularly scheduled program
I always thought they put the slots it the tabs to annoy the person taking them off. 
Thanks.i wish use with haikelite mt01 or manker mk34/35
Is magnet can works on that.?
Don’t use magnets on the MK34, or the Haikelite MT01. Magnets ok on MK35
What the trouble when i use magnet on mk34 or mt01?
I thought,Because the magnet has twist,is right?
Look at the 4th picture in this thread. ENEDED
If you had loose magnets on top of those cells, they might dislodge when you screw the light back together, and potentially cause a short. That type of light needs button tops or solder blobs, which is what this thread is about with the DIY spot welder.
I think to do this.the flat top inner diameter about 8-9mm. I will use 8mm.magnet put on and lock it by paper insulation gasget(inner diameter 6mm.) and final use shrink tube warp them.
Will it work?
If you’re determined to use a magnet, you should at least “tack” the magnet down with some Super Glue (cyanoacrylate) around the edges. Don’t let glue get between the magnet and the battery, since it is non-conductive. If your paper has 6mm hole, I think a 6mm magnet is best. The paper will then also help to hold the magnet from moving side-ways. Then, use the shrink-wrap to hold the paper.
Posting a quick update. Sorry for the delay guys there were several issues with the BOM the circuit designer who created the instructable did and I had to take time to find their errors and correct them. I also let them know of the issue and they’ve corrected the issue on their end as well.
As far as a BOM http://www.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=54cbf7c8a2
It might be cheaper to get the mosfets from an overseas seller on a place like eBay. They’re $18+ through mouser for 8 but I picked up 10 on ebay for $7 shipped. I’m currently waiting on those to come in to test them
Some of the resistors on the BOM are qty 10 because of the price break for 10+, if you need 3 it’s cheaper to get 10 
RobertB was nice enough to send me some button tops to test and those do appear to weld ok http://i.imgur.com/Q8Jm5iY.jpg
Two of the welds were a little over done so I turned down the pulse time and got the second 2 on the left.
I’m going to be doing additional testing over the next week or so and then I should have about 7 bare PCB sets if anyone wants one to build themselves.
YES! Thanks for the update! :partying_face:
