Sunkko 737G Transformer Rewiring

I got the 220V version by accident, and I didn't want to wait another month for the right one. I have a 3000VA converter to verify that it worked, now I'm trying to change the wiring for 110V use, mostly for convenience and a proper ground, but I don't think the converter likes the sudden 99% duty cycle demand, as the welder drops out before the second pulse due to the converter switching to a higher demand mode. From what I can tell so far, the transformer is pretty standard. There appears to be two primary windings that were originally wired in series, conventional wisdom says wire the primaries in parallel and it's ready for 110V, however I've never converted a device this way and might be missing something important so feel free to warn me. I got a picture of the primaries with the windings marked, the inner traces were connected originally. The holy grail for me would be a picture of the 110V version wiring.

You want the two windings in parallel for 120v but the phasing has to be right or it will act like a short. Usually there would be markings on the board for where the jumpers go.

That sounds like a very common method to produce a mass-production device for world distribution. If the input is 110/120V AC, and other parts of the world are 220/240V AC, then...you can wire the primary coil in two equally-sized coils.

In parallel, the two input coils would be 120V AC, and in series, the input would be 240V AC.

The conversion was successful, tad bit of a leap of faith on the phasing, but it works just like before. Attached is how I ended up soldering the transformer. The plug, I just chopped the end off and soldered the end of a spare IEC plug.

Hi,
I've received the sunkko 709 110v in a 220v country. It burned when I plugged into the wall. Your modification on the transformer will change the voltage of the spot weld only, the main board will still be a 220v feeded with 110v. In my case it seems that the 110v board didn't handled the 220v.
Now I am about to buy the spare main board and need to make your modification but in reverse.
Do you have more photos of the original connection of the primary winding?

Regards

I'm not sure if the 709 has the same transformer as the 737, but I'll share how to get the 220V setting anyway. Basically, changing the winding config doesn't effect anything else on the machine, it's all about the inductance in the iron core of the transformer. The main board gets it's power from a winding on the secondary side, if the machine was meant for 110V and you fed it 220V, the voltage going to the main board would be double what it's supposed to be, so no surprise that it popped. As stated earlier, these mass produced products intended for global distribution usually have these configurable transformers. The idea is if you want the 220V config, you put the primary windings in series, if you want 110V config, put em in parallel, in both cases you wanna make sure the phasing is correct or it'll act as a short, as fetcher mentioned, though the worst that'll happen is you flip a breaker or pop a fuse in the welder. In the attached picture, I pointed out the spots to solder, it shouldn't matter which wire gets soldered where, but if you want consistency, in my machine the black wire was on the left and the red on the right. MAKE SURE ALL THE SOLDER JOINTS AREN'T BRIDGING THE OTHER TRACES EXCEPT THE MIDDLE. If you're gonna change the plug, you got it easy since with 220V both wires are live whereas with 110V you have to make sure the wire getting the fuse is the live one. Good luck!

Thank you very much!

This model powers the main board directly with 220v or 110v, no secondary winding besides the one used for spot welding.

Thanks again!

I was going to try and rewire mine for 220v because I was not happy with the performance but then I found a video that shows someone who rewired the secondary to get more power. Has anyone else tried it?


https://youtu.be/YpuEL2_Wvz8