For posts specifically relating to fusor design, construction, and operation.
2 posts • Page 1 of 1
- Carl Willis
- Posts: 2841
- Joined: Thu Jul 26, 2001 11:33 pm
- Real name: Carl Willis
- Location: Albuquerque, New Mexico, USA
Yes, I'm aware this has been a trivial issue for just about everyone else. But the spot welding problem has been frustrating me for a long time, until this week when a surprisingly crude lashup of capacitors and a transformer did an awesome job of assembling my first fusor grid. The welder is composed of eight 2900 microF / 200 VDC computer-grade caps obtained from brigarelectronics.com for $2.50 each, connected in series-parallel to form a total capacitance of 5800 microF / 400 VDC; these are switched through the primary of a microwave oven transformer (MOT) with a foot pedal switch, and charged through a current-limiting resistor with a B+ supply. The MOT's secondary is removed, as well as the two small shunts, and a 5-turn winding of very heavy stranded wire is made in its place. Welding electrodes do not really outperform special bent pieces of copper refrigerator tubing as electrodes. Only 100 J or less is really necessary for good welds. Full energy, not surprisingly, blows the wire apart. The user must remember to put the pedal down for at least a second to prevent destructive arcs at its contact. A relay would no doubt be better. I am posting this in case there are any other spot-welding-illiterate folks who come along. I'd hate anyone to land in the several-months-long rut of frustration with other setups that I have experienced. Thanks to those who helped me with this issue. Hopefully some star-mode discharges will ensue imminently...