A “real” battery spot welder is $1k+, I’m not prepared to spend anywhere near that much.
The cheap Sunkko 788H, 787, 709A models are cheapish ($120, $160, $190 respectively) but are REALLY poorly built. Teardown reviews of these units are a highlight reel of the worst materials and the lowest quality construction you can imagine.
Functional reviews of the Sunkko units are also spotty - a very large (30%?) number of users report that the inrush current just from turning on the unit trips circuit breakers. Many users report even after upgrading to class C and D breakers they continue to have issues even getting the unit to turn on reliably.
Poor performance from the Sunkko units - even if it doesn’t trip your breaker at turn on, it absolutely will trip your breaker if you turn it up above 50% power, which limits you to very thin material. 0.15 x 8mm maximum is borderline and can only be done with the chassis-mounted electrodes. Using the welding pen which makes battery pack assembly much easier, and is a requirement at times on the $190 709A (788 and 787 have no welding pen) is limited to 0.10mm material. I want to build battery packs with 0.20mm or even 0.25mm strips.
I don’t currently have the knowledge to build a DIY arduino welder from scratch, and didn’t want to invest the dozens, potentially hundreds, of hours required to learn/DIY. SOMEDAY I will break into arduino/raspbery PI, but not today.
The Malectrics unit was $114 shipped. (I already own a car battery that can be dedicated to this tool.) I’m considering a dedicated 3S LiPo pack in the future, the unit is fully functional with either.
The Malectrics unit uses a 12V battery as a powersource and welds at (wait for it…) 12V instead of the maybe 3V you will get out of the Sunkko units. With similar current. Much more instantaneous power available from a car battery, than from a 110V 20A wall outlet.
So now that I’ve bought it and am waiting for it to show up, please tell me why I made the wrong choice.
I have already mentioned this somewhere on blf.
I dont see such methode reasonable. Managing with several hundreds Amps current is always difficult.
I have made diy spot welder. Used ac-ac transformer from old microwave (free), 1m of thick (60 sq.mm) wire instead of stock secondary winding, bought controller with mcu localy for near $50 (could make more simple version without mcu much cheaper but Im too lazy when I need custom boards). It is very simple, very robust. MCU just counts time so you can choose number of pulsed and their length. My board have internal switch but there are various of simple solutions when arduino just open and close regular dc-ac relay. Circuit is fully isolated from high current part, I think this is much more safety and broke-free solution. Switch just open current in transformers primary winding, transform ratio is near 100:1 so primary current is low and any proper relay will work long and safe. Also, big current dont go through schematics or any extra parts. Thick wire in secondary winding goes directly to the wire end connectors that are bolted to the thick (~10 sq.mm) solid copper wire rods (that I use as electrods). This makes big sense if power needed for weld is near to the trasformer limit, you have small losses so battery spot welder can (sometimes) weld thick (0.6-0.8mm) pieces of stainless steel.
In spot welding, you have fixed “voltage drop” between two parts which is low (not more that 1.5V) so if you increase voltage it doesnt make any sense. Only big current gives you oppotunity to weld thicker parts. Also, modern car batteries are not so powerfull as you can think. 400-600 Amp - this is what you can get out of them. (I know one guy that tried to measure current of dit spot welder based on big ac-ac transformer. Clamp meter with 1000amp limit have met this limit).
0.2 or 0.25mm battery packs are not reasonable and not real. Have you ever seen them? Nickel strip thickness should be choosen according to the cell case thickness. I used 0.08-0.1mm strips for INR cells and 0.04-0.05mm for regular laptop cells. If youll try 0.15mm strip with regular cell, you wont find suitable welding mod. You will meet situation when you start your test weldings from small ms, increase them until nickel is melted but same time you will easily drill hole in cell top or bottom. Also, tests shows that good solder point can be achived with limited strip thickness. Did you thought why plates for/from brand battery packes have cut in the middle? Otherwise, to much weld current will flow though plate and avoid cell top.
Well you certainly fulfilled my request when I asked to know why I made the wrong choice, lol. :+1:
I read a lot about MOT (microwave oven transformer) spot welders and just didn’t have the desire or energy to build my own, I wanted a pre-built solution, and I didn’t want crap (Sunkko) and I didn’t want to spend $thousands - so I wound up with a DIY unit built by someone else.
I do plan to use split strips so that current path will go more through the cell can, and not bypass the electrodes through the strip. Obviously trials are necessary to determine ideal process parameters (pulse, pressure, mat’l thickness, etc.), but this is part of what I do at work, I feel confident I can set up a good process.
I did a lot of reading (endless-sphere) from people who used their spotwelders to build ebike battery packs and lots of anecdotal evidence supports that it can be done successfully. (that is, it has been done many times successfully)
Oh well, if it is a complete failure I guess I’m only out $114, could be worse.
