Protecting diodes with Century High-freq box

admin

I just picked up a Century high-freq box, that I will attach to my AC/DC225, to try out some light TIG welding.The internals of the box are pretty simple:-transformer to inject the high freq onto the torch lead-transformer to power the spark gap-spark gap itself-capacitor from welding ground lead to wall outlet ground-capacitor+resistor from welding supply lead to wall outlet ground-power switch in series with power supply to spark gap.I observe that filtering to prevent the high voltage from reaching the welding power supply via the torch lead power input appears fairly minimal.This is a concern since the AC/DC 225 has diodes inside it, the exact wiring and specs of which are unknown to me at this time.Does anyone here have experience with this?  Has anyone used one of these boxes for an extended period of time?Lincoln apparently used to make a kit to go with their high-freq unit that is no longer available.Side question: The unit came with a "best welds" torch, is this a Chinese off-brand?------------------------------Lincoln 175HDLincoln AC/DC225Smith O/A
Reply:Miller HF boxes used to have a 10uf capacitor in series with a 10ohm capacitor across the power input terminals.There was also a 10k resistor across the capacitor terminals.If you are comfortable with schematics.:http://www.millerwelds.com/om/o611u_mil.pdfR1,R2 and C5 are the snubber on this unit.I was nervous about the small amount of leakage and added a 5uf motor run capacitor across the power in terminals,of the stabilizer box..It seemed to drop the leakage to a more manageable level.
Reply:Thanks.That makes sense.    Looks like the 10K is there for safety reasons.Not a bad idea, and something the century box doesn't have.That manual is great.  Miller and Lincoln have some of the best manuals I've seen.------------------------------Lincoln 175HDLincoln AC/DC225Smith O/A
Reply:I made a homemade TIG with a Century HF box and a 230A buzz box (not a tombstone, but the same idea), with a set of 500A, 500V diodes in the middle that I got from fleaBay, and never had any issues.  YMMV, but it worked just fine for me.  Still, I ended up buying a real TIG unit after that experience.
Reply:You can put a couple of .05uf @ 500 VDC disk capacitors from your weld terminals to the case. Inside your welder. This will give the HF a path around the welder and not through it.The century box does not have a start circuit to turn the HF off  It runs all the time.this is ok for AL but for steel you want to be able to turn the HF off. Some guys put a foot switch on it and just tap it to get the arc going.