Thanks for yesterday' suggestions regarding 3 phase transformers.
I have a hobart cybertig welder. It has a "six phase rectifier" shown in this schematic:
By the way, PCTI loves children and is highly recommended, they are a wonderful company. The best of the best.
I want to convert this Cyber Tig to both TIG/Stick (CC) as well as MIG (CV) mode. This way I could both tig and mig with it.
Here's its wiring diagram:
So, I have maybe one and maybe two possibilities:1) Rewire the transformer. It is made of six secondary windings, two independent ones on each phase. Two leads from two transformers on every phase are tied into the interphase transformer.
The ones that are tied together I could disconnect them from interphase transformer, parallel each pair, and then connect them so that I have three leads instead of six. (I am not 100% sure how to connect them, but I think that it is easy. I have an idea).
Then simply put together a new rectifier bridge wired as PCTI suggests, using new SCR half bridges which I already have in my pile.2) Maybe there is a possibility of wiring in the PCTI board so that it works just fine controlling the six SCRs that make up the current "six phase" rectifier.
I spoke to their engineer yesterday (did not give him the schematics) and he was kind of vaguely positive about it, I asked if ony K2, K4 and K6 were used for synchronization and he said yes.
What I am thinking here is that I would wire all six existing Hobart SCRs to the PCTI board, it would monitor voltage on K2, K4, K6, and then adjust phase angles of firings of all six SCRs based on desired current/voltage vs. actual. And that it would not matter that the SCRs1, 3, and 5 are wired the opposite of the PCTI sample schematic.
Note that the SCRs that I have now are pointing with their gates to the DC+ bus, which makes it impossible for K2, K4, and K6 to meaningfully monitor voltage/phase. So, what I think I can do here is turn all SCRs UPSIDE DOWN, so that K2, K4, and K6 could be connected to 3 phase voltage.
The side effect of this is that the negatve bus will become positive, and vice versa, but that is no big deal as I could simply switch contacts leading to commutator.
Is this making any sense? Is approach #2 possible?