There has been at least 4 versions of the CheApo Red spot welder going back 5 years now.
The one I got was slightly different than any I saw modified online. I used it a bunch without any modifications.
The early recommended modifications were designed to keep low weld battery voltage from frying the mosfets. There is also the inrush current blowing up a diode after a few power ups. The mods were largely add a capacitor here, add a resistor there or desolder it and change its value.
I performed no capacitor or resistor modifications to my Red, or purple cheapo spot welders
I swapped my Zee lipo from xt60 to Xt90s.
I used a second 12v battery to power circuit board, also via an xt90s antispark connector. These seem to eliminate the major FET frying issues.
I found my Purple spot welder to have about 40% more power than my red one using the same welding pens and weld battery. Im thinking about acquiring a backup purple welder, if/when I next build a battery, just in case. There is a newer double pulse purple welder out now too.
More info on the cheapo spot welders here:
Neither of my cheapo welders had issue with 0.15 pure nickel, but 0.15 copper with 0.1 nickel plated steel sandwich was not happening at all with the red, and had about a 30% success rate with the purple.
The red had about a 30% successful weld rate on 0.1 copper, 0.1 nickel plated steel sandwich with a 99 millisecond pulse. The purple had a 100% success rate on same at 85 milliseconds. I switched out the 10awg on welding pens to 8awg, and got this down to 70 to 75 milliseconds.
I’d like to do 0.15 copper, 0.1 nickel.plated steel. I think a better weld Lipo, or a second in parallel would allow it.
I tried a third chePo spot welder, black circuit board. Same leads to and from as purple and red. Maxxed out it could not reliably do 0.15 pure nickel.
I tried it with 2 large 6v AGM Lead acid golf cart batteries in series, and it went full spark throwing machine gun on me, tried to drill a hole into the battery can. Mosfets shorted closed.
I think there is a goldilocks sweet spot on weld battery size/power with these cheapo spot welders. Too little will definitely fry them. Have not tried the big AGMs again as the weld battery.
Obviously it is far better to get a malelectics.or Kweld or Glitter. These cheapo welders can be more miss than hit and might even be dangerous.
My black welder browned my underwear.