AC to DC, spot welding board

The easiest way it seems would be a rectifier. But will it be able to handle high enough current's in the 100-200A, even if it's just for few ms ?

You already know the answer - however, if you have to ask such a question you shouldn't be playing with anything as dangerous as an MOT - it's a highly lethal device.

As for a rectifier, you need a LARGE one.

I agree, it's very dangerous Right now i have it hooked up as a spot welder for metal

The rectifier would have to be built out of something like these:

Paralleling the two diodes in a module makes it capable of 400A (on a good heatsink).

Four such modules in a bridge could take 800A continuous, or rather more in short pulses.

It could be cheaper overall to buy some high current supercaps & use a normal DC supply?

(That's what my Chinese spot welder uses, two monster 3000F in series; input The power source is 12V from a 5A power supply via am internal regulator to charge it to 5.5V, though it does take quite some time to reach full charge for the first weld!)

Yeah, those aren't cheap.

I already have a little battery powered spot welder, its good for 0.12 and passable for 0.15. I really wanted something heavy duty for 0.2 that is instant use. I have 2 2.7V 500F caps, but this board has a flaw and its easy to burn mosfets when voltage drops. Thats why i thought it would be perfect to run it from 12V source.

Now, i could just make arduino controller and use that 12V AC, its easy to program. And for the spare board i guess i could just buy a car battery or some small lipo.

Smaller 20A diodes are dirt cheap though, 50pcs for few bucks. Could i just parallel a bunch of them and add some heatsink with a fan ? I don't expect i will need more than 200A to spot weld 0.2, and its miliseconds of current going through for each weld

What about something like this ? Pretty sure i can find similar priced one thats 200A ?

link

Lots of youtube videos rewinding these transformers for low voltage.


I would start out with a xfmr from a higher wattage microwave, not the small
shelf type, in order to get the currents needed. Maybe on youtube someone has
measured the current for their case.


Regards, Dana.

SentinelAeon said:

Yeah, those aren't cheap.

I already have a little battery powered spot welder, its good for 0.12 and passable for 0.15. I really wanted something heavy duty for 0.2 that is instant use. I have 2 2.7V 500F caps, but this board has a flaw and its easy to burn mosfets when voltage drops. Thats why i thought it would be perfect to run it from 12V source.

Click to expand...

The most likely cause of the behavior you describe is the mosfet gate voltage falling to a level to low to keep the mosfets fully on.

I would look at the board and see if you can separate the control voltage from the power voltage. running the mosfet gates at 10V or greater will likely solve that problem.

The problem at hand is converting AC to DC, everything else is taken care of