A project log for Pulsed Capacitive Discharge Power Supply

Pulsed-discharge power system suitable for welding, plasma cutting, laser driving, and other high-power equipment.

Jakob WulfkindJakob Wulfkind 06/03/2014 at 17:460 Comments

So I haven't been keeping up with my planned once-a-week project log schedule, and there's a lot of development that's already gone on. Here it is in a nutshell:

This build started two weeks ago while I was waiting on the CNC machine to become available for my other project, the hybrid axis wind turbine (I also haven't been posting logs there as diligently as I should have. Suffice to say there has been progress there as well). I had been thinking about mounting solutions for the wind turbine, specifically concentrating on steel lattice support structures, and decided to try making a quick-and-dirty capacitive arc discharge welder out of a few supercapacitors lying around in the lab.

The old standby of charging a cap for a few seconds and then using it to melt a hole in the side of a coke can was well and good, but the novelty wore off quickly, and it was clear that I wouldn't be able to use that method to create durable structures . Also, I made the discovery that you shouldn't use a plasma discharge arc on a soda can that hasn't been opened.

It occurred to me that by manually charging and discharging the cap, I was in essence using a very primitive form of PWM. I then realized that if I could automate the system to  charge to a particular voltage, then discharge until it dropped down below a threshold voltage, that the size of the capacitors wouldn't matter, since I would be outputting the same wattage over a long enough time. I switched from a 3.1F audio capacitor to four 1000 uF capacitors. 

...I'm now down to three 1000 uF capacitors. Kids, always remember to check the polarities when wiring a high-wattage circuit.

But the concept was a sound one! I got just as much sparking and pitting from 3000 microfarads on an automated charge-discharge cycle as I did with 3 Farads discharging by hand! I don't have any photos, unfortunately (it really isn't safe to be handling a high-wattage system with one hand and photographing it with the other), but I expect to have a few posted on my next build log.