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Mini Spot Welder from Aliexpress

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hojnikb:
So there seem to be plenty of those kWeld clones on aliexpress including this https://www.aliexpress.com/item/1005001492794726.html?spm=a2g0s.9042311.0.0.53154c4dCZc8CF(link just for reference)

It seems to be pretty common knowledge that these have a high chance of blowing up mosfets due to poor design. Someone seem to found a fix

But it looks like there is already a new revision floating around and this is the one i got
https://imgur.com/gallery/JtHWr2n

Capacitor fix seems less obvious to me. Anyone played around with these newer ones and knows a fix ?

PS: If there's a similar topic already, please merge/delete.

Fraser:
I just received one of these and will be looking at the best position for the additional processor capacitor, if required. Note that a number of components appear to have moved from the processor PCB down to the MOSFET PCB. They are located under the large electrolytic capacitor. The issue of processor voltage drop may have been dealt with in this new version but I will check.

Fraser

Fraser:
Initial inspection of the Mk2 design suggests that the processor supply rail issue has been addressed. The large 10000uF capacitor is connected across the power supply input terminals with a diode in series with the positive rail. I am thinking that this capacitor is now providing the power to the processor and will easily hold up the processor power rail during the welding pulse. The components that have moved from the processor PCB down to the MOSFET PCB are the MOSFET gate drive components that include bias resistors and, what look to be, three transistors.

It would be interesting to see the schematic for the MK1 version of the unit but cannot find much on the internet. From the video you referenced, it appears that the large 10000uf capacitor was on the wrong side of the diode that is in series with the supply to the processor. A simple design error I think and one that looks to have been corrected. A 8 pin IC and what looks to be an option isolator or 4 pin TVS have disappeared from the Mk2 design.

Fraser

Fraser:
Pictures of the unit that I have just received as a reference for others. I will reverse engineer the design.

The processor has had its ID removed by laser etching but I think there are pictures of the MK1 with the chips ID visible.

Fraser

Fraser:
Pictures continued.....

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