It's all very well to talk about converting this plasma cutter to [pilot arc (so it's usable on a CNC machine) but that would be unforgivably rude to proceed any further without taking it apart to see what we have in front of us.
Here's a picture of the thing before I got my tools out. Haven't tried it yet but I assume at this stage it is still working:
As well as removing the screws on the sides and top of the casing, the font bezel thing has to come off, to free up the cover.
And here it is without its clothes on. At first glance it doesn't look too concerning. Being a Parkside product, I expect it has actually been through TUV or similar approvals.
Here's the little PCBA that is fitted to the front panel. It's got the only user controls on it. The pot sets the output current.
No, that's no micro. There isn't anything resembling a brain on this thing. The wide body SOIC is simply a TI Unitrode UCC 3846 ie a push pull current mode SMPS controller.
Underside there's a ribbon cable that takes the PWM signals down to the power board. The large resistors are voltage droppers for the arc voltage sensing circuit. There are 2 identical circuits, alog with 2 pairs of sense wires. This is almost certainly for safety redundancy, in case on circuit fails or a sense wire falls off.
Here's the main power PCBA
The smaller board is a filter/rectifier for the compressor which clearly uses a DC brushed motor running from rectified mains (ie 340Vdc) through a relay and soft start / inrush limiter.
It's clearly known as a "Unicut 45". Parkside describe it as 40 (European) amps, which presumably correspond to 45 Chinese amps.
The torch connection has an air hose coming out the back and the power connection made through a crimped wire of perhaps 10-12AWG. You can see the dual red and black voltage sense wires here
Top right, working down:
- Input (soft start) relay
- Input rectifier (on heatsink)
- Half of the power bridge (2 MOSFETs on heatsink)
- Housekeeping PSU
- Bus caps
- Toroidal power transformer
- Toroidal output inductor
- Gate driver transformer
- Toroidal HF transformer
Top left, working down:
- The other half of the power bridge (on heatsink)
- Output diodes (on heatsink)
- HF generation transformer, spark gap and caps
Closeup of the HF circuit:
- Spark gap
- HF transformer
- Coupling transformer
- HF caps
Top right of the PCBA, left to right, then top to bottom:
- Gate driver transformer (just off the screen)
- Housekeeping PSU
- 7815 and 7915 linear regulators (7815 has heatsink)
- Primary current transformer
- HF relay
Half of the power bridge (another FET on the other side of the heatsink). And the output diodes.
Here's a nice shitty solder joint!
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