737G+ 4.3KW Battery Spot Welder, Automatic Pulse Welding Machine for 18650 14500 Lithium Batteries Battery Pack (110V)

Works ok on thin metals, does not work on thicker metals. I suggest looking for a spot welder 14K power or more.

I just received this welder today and am posting my initial impression after putting it through its paces with test strips, not having used it on live cells yet:The manual is printed in Chinese with no English translation, and I cannot find manuals for download on Sunkko's site, so this is disappointing. It was easy enough to discern how the various features work.I tested welding to the test patch, with the included nickel-plated strips and with a coil of 0.2mm nickel and it did a perfectly good job; when I pulled the strip away the weld remained behind. I then used the welder to build up the positive lead with several layers of nickel on three flat-top cells in a flashlight where I had finicky connections (button-tops would have been more appropriate) and it did a perfectly good job.---I'm keeping this updated as I work on my welder. It has snowballed to the point where I am going to be rewinding the transformer, which is wound with a CCA bar -- or really CPA, since they appear to have used copper paint or gilding rather than plating(!!!)---For an easier fix, I looked closer at the front terminals; it's just copper strands shoved into the connector and an under-size screw which is apparently to clamp down on the cable but does not. Instead of removing those terminals, simply solder the wire into the terminal. I just received a 737G+ and found that the termination point of the cables is where these losses are incurred.The finely-stranded OFC wire is not the problem nor is it crappy; fine-stranded OFC wire actually costs a premium over solid or coarse-stranded wire, so you do not need to replace the cable nor do you need to re-coil the transformer. That both the fixed head and pen tap off of the same coil, and are actually using the same cable and the fixed head works perfectly is evidence of that. The difference is the connections in the fixed head are actually crimped with the crimp being clamped upon to make the fixed head connection, while the pen electrodes just have the cable shoved into them and a simple screw plunges into the cable end but really does not improve the connection by a measurable amount.To fix:Remove the screws from the front terminators/jacks, push the jacks off the cables, and out through the front. Put the jacks in a vise, and tin the interior of the electrode. Then, unbolt the transormer to give yourself some slack, push the cables out through the front of the unit, twist the end tight to compact it, and coat the interior of the jack and the table itself with flux, generously, and use propane blowtorch to heat the terminator, and touch the solder (I'm using conventional 60/40 on mine for its melt and flow characteristics) to the cable and jack, and it will be drawn into the connector. Remove heat, let the jack cool, and once the solder has solidified (you'll see the color and lustre change in an instant when the solder freezes) you can then use a spanner/wrench as a heatsink or other means to bring the temp down quickly, and then you can shove the jack back into the unit, then do the same to the other electrode. Also note, there is an additional lead coming off of the welding pen jacks on the 737G+, so you will need to make sure you reconnect this; on mine I am going to simply insert it into the cable and use a soldering iron to solder the connection once it is completed. I'm 99.9995% confident this will solve the problem as I can measure the resistance change when I nudge these cables where they insert into the jacks.----Mod completed, and the behavior is better (when the pen is cool), and resistance from one terminal to the other is now under 1ohm. The resistance of my multimeter leads is 0.5ohm, so the resistance of the coil from terminal to terminal is 0.5ohm.The way the coil is terminated into the jack terminals is the end of the coil are wrapped in a copper foil (yes, it's foil - I did not grab my calipers but I would be very surprised if the copper sheet is even 24ga) which is then shoved into the jack, and then a small screw is inserted through the terminal, to pierce the foil and realistically does very little to improve the connection. It's a very crappy implementation. I took the jack out, etched it with acid then tinned it, and then I soldered the cables into the terminals.However, each lead from contact to electrode tip is around 1ohm apiece, resulting in 3 ohms total resistance in the circuit. Lo and behold, I initially had several successful welds in a row with the pen with the welder set to 50%@2p. Once the pen heated up, I could no longer get successful welds of 0.2mm Nickel to nickel. Nickel to steel is still no problem. I now get more successful welds, before the welding pen heats up. Once the pen is warm, no more nickel-to-nickel welds until I let the pen cool. The pen needs to be redesigned.Mod, pen rebuild:I disassembled the pen, took out the electrodes and put them in a vise, heated them with a prpopane blowtorch, and then I fed the electrode+cable joint with as much solder as it would suck in, and then reassembled the pens, leaving the cooling vents uncovered but wrapping the rest with kapton tape to hold the pen together.. I can now weld at 12P@70% even .20mm nickel to .20mm nickel, but because I had overdone it a little with the solder (some sucked up into the cable so it inteferes with the spring) the retraction feature is lost. I already had a new pen on the way but I was so excited by the progress I made that I would follow through.Now the entire loop electrode to electrode through the transformer is only about 1.5 ohm warm while previous to soldering the joints, each electrode was 1.5ohm apiece when cool, and it increased by about 5x when warm (not even hot). So, I basically reduced the cold resistance from 4.5 ohm to 1.5 ohm, with much of the resistance at the jack-to-cable connection, where the "O" plug is still not soldered (I wanted to try to save the boot intact) and the O plug is still used rather than hardwiring the pen.The pen jacks and pen itself both need to be redesigned. Copper foil is NOT a proper crimp, and a simple metal screw is not a proper clamping method - and the screw appears (by eye and feel; I did not do a spark or corrosion test) to be iron or mild steel, not even stainless or nickel.----Followup a couple weeks later:I've noted some improvement to the point where the handheld probes will blow holes in nickel on 2p@99%, but whenever the welder warms up (only a few spot welds) current drops by a couple hundred amps - this is after only a few welds of 0.2mm nickel. While splicing OFC welding cable to the leads that are crimped and soldered to the transformer taps, I noticed copper is so thin that it burns off and green coloring of the flame disappears (proving the copper clad is ultra-thin) the leads melt easily with a standard propane torch, and when I tried to twist them, it behaved like CCA rather than OFC. I crimped the end of the lead and put the crimp in a vise to file it to verify my suspicion, and sure enough - no sparks, plus filing down the cross-section reveals a silvery aluminium sheen, with no traces of copper (remember, I'd burned off the copper and the flame no longer had a green tint). The stock cabling in the welder is copper clad aluminium!Looking into it further, I unwrapped the secondary coil, and while it does have 3.5 turns, it is a flat bar, and when I scratched it, what appears to be copper _PAINT_ chipped off, revealing aluminium underneath. Also the solder joint in the crimp holding the lead to the tap is globular, indicating a cold solder joint. Given that Aluminum starts out with 55% more resistance and the resistance vs. temperature curve is steeper than that of copper's, it's not difficult to see why these welders struggle.So, let's list the problems, shall we?* the jacks are poorly secured to the internal leads* the secondary winding is aluminum* the leads coming off the secondary taps are CCA - with an _extremely_ stingy copper cladding* The hand probe leads are CCA* The connections in the hand probe are just awful as the loose, high-resistance connections from the lead to the probe jacks* The fixed welding head suffers from the same flaws, but due to the shorter length of aluminium to the connections and the smaller number of loose, high-resistance connections, it works fine until you've had a very long welding sectionAs such I'm going to be cutting out the secondary winding from the transformer, and will be replacing it with 4ga OFC cable. I am debating whether to grind/polish/gold plate the probe jacks, design and 3D print a new front panel and incorporate low-resistance MIG/TIG probe connections designed for high amperage use, or design a breakout box with MIG/TIG terminals. In any case I am poopcanning the aluminum cabling.-----Mod complete, welder is still anemic. Quite honestly, this does not live up to even warranty of merchantability because this welder is so flawed. I bought a BATTERY POWERED welder that outperforms this sunkko heap of junk.

Remote wand wouldn't create welds adequate to weld .2mm strip even at full power.Welded ok from wands on box, but my pack is far too big for that method, returning.Manual seriously lacking.Probe grinding kit is a damn joke.What's little specs are in the manual require a 40-60amp 120v wall socket. This doesn't exist.Make a unit that will work off of the standard 20amp socket available in the U.S. or don't bother.

The head line says it all, just a week flash weld use only the thinnest nickel strips

Not worth anything. It cant weld the thinest gauge nickel when turned up at the highest setting. Very disappointed