Chinese plasma cutter CUT-50

[gaminn]

Hi,
I purchased this cheap chinese plasma cutter CUT50 (50 amp): https://www.ebay.com/itm/Plasmaschneider-CUT-50-HF-Inverter-Plasmaschneidger%C3%A4t-bis-10-mm-230V-50Amp/202737585934

I opened this thing to check whether there is actually anything inside the box. I can see two (dirty) boards named: CUT35-2A2 and CUT35-1A2 which triggered alarm: Did I buy CUT35 (35 amp) plasma cutter nicely packed in a CUT50 enclosure?

On one board there are two pairs (total 4 pieces) of dual 15/30 A diodes https://www.onsemi.com/pub/Collateral/MUR3020PT-D.PDF Each pair is connected in parallel so they should handle 60 A.

On the second board there are two pairs of 23 A mosfets http://www.unisonic.com.tw/datasheet/23N50E.pdf . Each pair is connected in parallel to handle double of the current.

So, maybe, the components could handle declared current, but I'm still unsure whether this is really CUT50 plasma cutter. Can anyone confirm/comment?

[ace1903]

No idea about power rating but will ask one noob question.
How plasma is ignited? Can not see HF transformer on pictures?

[gaminn]

You have to touch the metal to ignite it. There is also a place on pcb where this HF transformer goes (but it is not assembled).

[TERRA Operative]

Hmm, been a few years since I used to repair this stuff...

It looks about right, you'll probably find there are a few missing transistors etc in the Cut-30.
Often they would do that for the lower spec models, customers never used to complain when we replaced a lower spec board with a higher spec one. The boards were so cheap, it was easier to just keep the higher rated ones in stock than the whole range..

Incase you don't already know, you'll need to install an oil seperator, dessicant dryer and dust filter (preferably in that order) to make the air supply as clean and dry as possible.
If the air is dirty or wet/oily in any way, you'll eat cutting tips and have inconsistent cut quality.

[gaminn]

I'm returning this plasma cutter. Did you notice that AWG14 output cables inside this CUT50? Not sure if it is visible. How much current can they handle, 5 A?

Everywhere on Youtube you can see CUT50 has 3 or 4 times more mosfets/diodes inside. I'm not saying more mosfets = better plasma cutter, but with this plasma it is clearly visible they are cheating buyers.

FYI any CUT-50 that has item location "Jenec, Czech Republic" will be this garbage.

[gaminn]

So, before I return the unit, I tried to cut 8 mm steel. It cuts, but really slowly.

I measured current via UT210E clamp meter (100 A DC range) on + wire off the unit - max reading I was able to get was 25 A on meter when the plasma cutter was set on 50 amps. Should I believe my clamp meter? On lower DC ranges it is quite accurate (+- 2 %).

[TERRA Operative]

It's probably an extremely optimistic 50A, or an outright lie.... I'd trust the DC clamp meter over the seller trying to maximise profit on cheap welding gear.