There is a new Version 3.1 of the Spot Welder available. It has a little improvement on the mosfet board that makes it possible to use higher CCA car batteries -> more welding current. Read more to find out the details.
Difference between V3 and V3.1
While the “old” V3 can handle 400…600CCA car batteries reliable the new V3.1 is now capable of handling up to 800CCA car batteries.
The restriction in the car battery size was not due to the IRFB7430 mosfets. These can handle an absolute maximum of 1400A pulse current. It was the TVS diode that basically has to clamp almost all the welding current to ground for a very short time (few micro seconds) at the end of each welding pulse. Since each pulse consists of 2 pulses, a short one to heat up and clean the weld spot and the second real welding pulse, the TVS diode has to “protect” 2 times on each pulse. If you are now using a higher CCA car battery usually the pulse time will need to be set lower because of the higher current. This does stress the TVS diode even more because it has to take the higher current in a shorter time periode as compared to using a lower CCA car battery where the TVS has to take less current and has a longer periode of time between the pulse ends.
The improvement in V3.1 is that it uses 4 TVS diodes in paralell on the mosfet board instaed of one in V3. The through hole TVS diode in V3 (5KP13A-E3/54) has an absolute maximum current rating of 600A. The SMD TVS diodes (5.0SMDJ13A) do have an absolute maximum rating of 300A each. So with some reduction because of paralell use calculated in, the 4 SMD TVS diodes should be capable of handling about 1000A.
When builing the Spot Welder yourself make sure to use 4 TVS diodes from the same batch or at least from the same order. This will ensure that theire specs tolerances are pretty close to each other so the current is spread evenly across the 4 diodes. If you are using maybe 2 old diodes you already had laying arround and 2 new ones it can happen that e.g. the old ones open earlier as the new ones. Then they take all the current and will fail.
Although it is now possible to use up to 800CCA car batteries i would still recommend to use only 400…600CCA batteries. These deliver enough current to weld 0.15 to 0.25mm nickel strips which should fit most applications and it will stress the components on the Spot welder much less than a super powerfull 800CCA car battery.