So the first thing to think about is exactly how will this welder converter connect to the existing welding transformer that I (and you if you're wanting to build this) have.

Somewhere near the top of the list of concerns when dealing with anything that plugs into the wall is (or should be) safety.

It is tempting to just have a couple of bolts sticking out the back pf the converter box to just attach the electrode holder to and the earth clamp to. (literally clip them on), but that's not fantastically safe, and likely to come off half way through doing something, more than likely at some sort of critical stage...

Something that I will say is, you can just attach a connector to this and bolt is directly to the back of the machine, or even take the existing electrode wire and earth clamp and cut them up and permanently install them into the converter box hard-wiring the cheap transformer to this box.

However I'm going to go a route that will "look" a bit nicer, but serve no other functional purpose.
The connectors used on the higher end welding machines are like bayonet connectors, and are made by a company called Dinse -therefore I'll refer to the connectors as "Dinse connectors".


These come in various sizes, all in mm2 size ratings, - which will determine the current handling capability of the actual connector.

to decide on the size of connector you need look at the maximum current rating of your machine, and pick the next biggest size.

For example: if your welder has a maximum welding current of 120Amps, then a 10- 16mm2 connector will be enough.

If you plan to put a 250Amp supply onto the converter box, then you'll want to go with the 285 connector 35 - 50mm2


For my welder, the cables are fixed to the transformer. -this will be true of most "cheaper" welders.

I'll need to cut the cables, drill the control panel and install Dinse type connectors on the main transformer, and attach connectors to the existing earth clamp and electrode holder.
(so after that I'll have the same capacity stick welder, but I can pack it away a bit neater!?)

In order to make it so it only works one way I'll install chassis plugs onto the tig converters back. which means that the connector attaching to the weld transformer needs a plug at one end, and a socket at the other. this means that you can't plug the transformer into the welder output.-so I essentially get a bit of an extension cable for my existing welder setup also.


I'm going with the Dinse type connectors, but will buy off brand copies in order to reduce costs for myself.

Welding Transformer
2x chassis Socket

Connecting lead
2x inline plug + 2x inline socket

Tig box input
2x Chassis plug

Tig box output
2x Chassis Socket
so, four chassis sockets, two chassis plugs, two inline sockets and two inline plugs.
Individually, (and in the size I want) these start at around £5 each on ebay.

but scroll down the listings and you'll find some people list sets. I've just seen set of 2x chassis sockets and 2x inline plugs for £13 (free P&P) this puts the cost down to £3.50 each.

it's also worth searching for CK size, in this case CK35-50

At this price that's £35 for the set up I want.


Next cables need to be looked at
Again a simple table

(weirdly the American wire Gauge doesn't go high enough to express the chunkiest cables required!)

the table shows the crs sectional area, under that the diameter of the cable in mm, and under that the American wire gauge and standard wire gauge (other wise known as imperial or British) 

Again I'm looking for a max capacity of 250Amps, so will look at the 300amp row. I'll only need a few meters (less than 10!) so only need 50mm2 conductor cross section. (this is clearly the biggest cable I could use with the 35 - 50mm2 dinse connectors (if I wanted a longer weld cable then I could use a 70mm2 conductor, but would need bigger plugs.)

A quick look around shows this wire to be seriously expensive when bought in rolls.

However, you only need a short length (to connect the welding transformer to the converter box), in order to find this wire in convenient sizes search for 300amp jump leads. Which I've seen for £5.


As for getting my budget of sub £100...
theses connectors are NOT included.

why?
well I could easily take the price to well over the target budget with non-essential fluff. Laser cut aluminium case? with logos, powder coated?
why not? and if I'm really happy with what I've done then I'd happily spend some time and money giving it a good case.

At the moment, the only thing "needed" will be 2x Dinse plugs for the output to mate the TIG converter to a torch.
and even they are non essential as you could cut off whatever plugs came with a torch and hard-wire it to the converter box. or use some bolts and some lugs and nuts...

basically, there is a £40 spend I'm going to make now (plugs and wires) I expect that if you want to save money you'll just cut off the electrode holder and hard-wire the transformer to the box at zero cost for connections. -in the end it's your device and your choice.

It might be cheating, but the project goal here is to get a TIG converter for £100, not get a nice looking one.
(I'll keep track of both essential and non-essential budgets in a BOM round up.)