CUT50 Plasma cutter repair

This is somewhat a break from the normal type of post for me but I thought I would share by experiences of fixing my plasma cutter..

Firstly it went with a 'bang' and stopped working mid way through cutting a panel of a car body shell.


On inspection some of the mosfets (Toshiba K2837) had disintegrated, which appears from looking online to be a common problem. I ordered some more in (chinese variety as its all I could find) and we replaced the faulty ones after testing them. You can test mosfets in a number of ways (google will help here)
Once the mosfets had been replaced the unit powered up, I plugged a torch in and tried it - bang the breaker tripped.

I stripped it down again and did some googling and I found something listed here 

To summarise from the post within that thread:



Set the meter to the diode test position



Connect the test meter with gate (+) and source (-) Meter should read around 735. Reverse the meter connections and it should read infinity.

Next connect the meter with source (+) and drain (-), the meter should now read about 450. Reverse the meter connections and it should read infinity. (It might take a couple of seconds for the reading to settle)

If any of the readings show a short circuit this indicates there is a fault with any or all of the 3 MOSFETS and possibly the zener diode.







I had at least another 3 dead mosfets again.. I ordered some more chinese ones in and these ones were suspect - the legs were thin and fragile and there was no way they would take the current. I started looking around for something comparable available from uk suppliers and found this 

within this thread the IGBT IRG4PC50UPBF is mentioned - I ordered these Infineon parts from farnell in the UK - they are no longer manufactured. I decided to take a punt and replace the mosfets with these (mine needed 12 - as you need to replace all of them).

I also tested the switching diodes on the bottom board, all of these checked out ok, which is nice - however I had also ordered some of them in so I have spares if needed.

After a bit more searching I also found this https://www.youtube.com/watch?v=Yhza65nWBZY youtube video, it's quite interesting if you can ignore the soldering skills.


I checked the 12 gate resistors they were not 4.7Ohm as mentioned in the linked youtube video but 7 ohm - hardly much difference but I used the correct values, some of mine we looking suspect so I decided to replace them all (with 7 ohm still), as you can see in the photos I managed to lift some tracks slightly when desoldering components - this is all fixed now.

When I tested the zeners on the driver board one was shorted. - They weren't 3.3v as on the video but 5.6v - confirmed this by removing one of the working ones and added a 1k resistor in series and then connected across a psu and measured the voltage across the diode.
So mine were a 5.6v Zener in Mini MELF format (manufacturer part used was TZMC5V6-GS08, farnell order code 1612412)

This was an easy replacement (D12) using my hot air rework station, but I suspect easily done with a soldering iron and tweezers.

After replacing the gate resistors as they looked crap, a zener diode and all the mosfets with IGBTs I'm now back up and working - although I've only done a quick test so far.



If you are going to repair your own then the usual disclaimers apply around the high voltages present inside the device - and remember they are higher than the input voltage due to the HF arc.

Existing Setup

I started out in the homeautomation hobby after fully stripping out a house and refurbishing it from bare brick. I rewired it in the traditional UK sense. ring mains and   a radial for the lights with the neutral at the ceiling rose and not at the switch. I included around 40 cat 5 outlets all over the house wired back to a small rack in the loft. 

having then bought a raspberry pi the day they were released. I had a little bit of prior experience using Linux with Ubuntu so didn't see this being too much of a problem

I got the hardware and started playing, flitting from one project or idea to another,  I played with interrupts and gpios then going on knock up a deamon up in c or c++, can't remember which of the two or was!

nothing was doing exactly what I wanted and I didn't want to be adding more motion sensors in rooms when I had perfectly good alarm with sensors - or so I thought..

I dropped an email to texecom and asked if there was any way of getting this data out of the alarm.. they suggested I upgrade to the Premier elite range as this has multiple options for integrating, this landed about the same time as I finished building the garage and decided that if I upgraded I could have the garage as a seperate area rather than a completely seperate alarm system.

I replaced the alarm and wrote some python code to decode some of the data coming out, coupled with the nest thermostat api to control the heating.

This approach worked but it was fragile and had some issues, which I eventually resolved or worked around.

I then stumbled on homegenie which I liked as I could develop in c# which in more confortable in.. I know I could have done this previously using mono but it didn't feel right which is why I avoided it.

so once I started with homegenie I ported over a lot of existing code and had something that worked very well for what I needed. I had it integrated with a lot of things and was very happy..

I then started looking at how to automate my lighting.. I bought the ikea tradfri kit and integrated homegenie with that, but it didn't give me the control or logic.. I want to know if someone in a room turns a light on. I added some functionality to the coap library I was using to poll devices for their status but it still wasnt going to do what I wanted which was using existing switch locations.

I set about playing with esp8266s and later esp32s which would be mounted behind the switch and use a relay to mimic the existing switch. I had code working sending messages via mqtt and all worked well in theory.. ota updates.. if homegenie went down switches worked fine as they controlled the relay locally and sent the state change via mqtt.

We then decided to redecorate the whole house, so I had an opportunity to get cat5 to most of the ground floor switches via a crawl space and creative fishing behind the dot and dabbed plasterboard that I fitted a few years before..  my box containing the pi was on the ground floor and had a route for the cables so that works.. I had no route possible from first to ground though so took those up into the loft, I left them all coiled up to deal with when I had more time to revisit, but at least it was done prior to decorating

we then got married, and decided to move home!

Enclosure Sorted

Just bagged a Future Automation LXN4 Enclosure on ebay for close to half of the price new.

Hopefully its in good condition, it's advertised as new and the original packaging is unopened.

This may give a clue to the direction I am going in.

New Home - New Home()

I bought this domain name a while ago with the intention of documenting my current home automation setup, but since then I got married and we were looking to buy a new house together, rather than living in a house that would always be referred to as my "house".

This was music to my ears as it meant that everything I did wrong with this house in regards to homeautomation could be rectified in the new house, and my requirement for the house was a large garage (or room to build one) and something that needed work doing. My wife had other requirements - No local shootings, an area she wasnt scared to walk around the block, nice views, a country feel and detached.

We have now found a new house that meets all our requirements and the Sale / Purchase is currently in progress! And a big renovation will follow shortly after (planning permitting obviously) . More details on that later.

I'll also post up a bit more detail later on the current system that is in use, the proposed system (and why the change in direction) and more information on the custom software I have developed along the way and also hopefully blog the progress of the renovation too.