Sealey Mightymig 100 Refurb




Introduction: Sealey Mightymig 100 Refurb

Here is my Sealey MightyMig 100 welder it was from the 1970's and has been an on and off project for about a year now.

I was given it by a friend of mine as most people know I like to try to fix or re use most things.

When I got it it had a broken gas valve and a torch without a trigger.

I decided to re wire it for flux cored wire so I rang the local Sealey Engineers and asked them for advice and as expected they really didn't know if it would work or not so I went ahead and got started.

Step 1: Re Wire to Swap Live and Earth

I undid the case and followed the live and earth wire back to the sources and simply cut the wires and crossed over the wires and crimped and shrink wrapped them to their opposite. Live to Earth visa versa.

With my fingers crossed I put the case back on and plugged it in and Prayed for the best.

Well the power worked and their was an arc but it wasn't all good news.


So I now had to find a suitable replacement for the 45 year old board.


Step 2: Fitting and Wiring the PWM Board

I learnt from research that the wire feed motor controller is called a Pulse Width Modulation board (PWM).

The PWM board was found on Ebay for approx £3

I wired up the motor and the power to the board and gave it a whirl.

When welding no matter how I changed the power or wire feed settings it was still stuttering or didn't seem to have the power to pull the wire through.

I quickly realised it was wired in the opposite as I changed over the supplies early so I swapped them around and to my dismay it still didn't work.

So scratching my head and thinking hard I checked every connection tested the motor and supplies and it finally came to me


Now I had to supply the PWM with DC power.

I chose to use an old PC Power Supply over a wall wart as a power supply is a more sensitive regulated power supply that a wall transformer.

Yellow is +12v

Black is Negative.

After wiring it all together it worked a lot better so all I have to do was find a new trigger.


Step 3: Trigger Vs New Torch

I searched for a new trigger button and with the welder being so all all torches had changed in shape and their workings so it came to no luck.

Although I am trying to build a 3d printer through weekly subscriptions I haven't got one yet so it was out of my grasp to make one.

I decided to buy a new lance and torch and with Euro torches being cheaper than new hard wired one I went for the euro choice.

The euro conversion was an extra £30 so i decided to hard wire the euro torch.

Step 4: Hard Wiring a Euro Torch

To hard wire a Euro torch

1. I cut off the Euro plug of the end of the lance.

2. Stripped the insulation back and crimped the wires that go around the gas and wire supply together.

3. Cut off the Binzel end of the wire liner and attach it to the wire feed unit and thread it back to the end of the torch.

4. Wire the crimped cable to the Negative which is the torch supply now if you remember.

5. Insert the wire and refit all nibs and shrouds.



Step 5: ALL DONE

Now Make sure all Electrical connections are correctly crimped or tightened and the casing is correctly earthed.

I have nearly finished all to do now is change the wire liner and its good to go.

I accidentally fused wire inside it by trying to keep the Euro plug on the end of the lance and using a PVC pipe to insulate it.

IT DIDN'T WORK TOO WELL (and looked awful).

Right so now I changed the wire liner re - inserted the wire and I put some test welds down on 4mm thick stainless steel plate and the overall weld was good, better that a car sill repair I once had done from a garage but saying that I also attempted to weld 1.2mm mild steel sheet and with the lowest power setting being 50A it just blew holes everywhere as the weld pool wasn't sustained for long enough to warrant travel.

With a proper welding mask and gloves and not holding a piece of glass in one hand and the torch in the other it would be good enough for small repairs on 2mm to 4mm (with a v) which is perfect for what I need.

Thanks for reading.

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    7 years ago

    I've got an sip handy mig, that from the factory they seen to have been designed as a hackers paradise, due to many design faults. anyway, lots of mods, but in my research I came across a handy little idea. for the liner, one of those stretchy wire curtain spring things fits perfectly, and gives you a write liner rather than plastic. I'm not sure if the inside diameter is larger than those designed for the purpose, as there is a bit of slop in welding wire.

    Not sure if it will fit yours, but worth a look i reakon. $3 fix compared to$20 for me


    Reply 7 years ago on Introduction

    I have an engineering friend who told me that most welders like sip sealey and snap on are all made by the same people and just look a little different i dont know if it is right but might help someone if they have one and its a bit like fiat and Citroen same parts but Citroen is a lot cheaper (gear selector cable we replaced on the car £100 cheaper)


    Reply 7 years ago on Introduction

    That is a good idea and with it being coated there is some insulation there aswell.

    Thanks Discostu956


    7 years ago on Introduction

    This looks a lot like my little 120V MIG welder. Except mine is green. Why did you need to reverse the polarity of the torch?


    Reply 7 years ago on Introduction

    Pfred2 - When speaking to the Sealey engineer he said that the parts inside wasn't made to withstand the polarity swap needed so with a bit of research flux cored welders have opposite polarity it does work without swapping polarity but it welds neater with it swapped


    Reply 7 years ago on Introduction

    Yeah I can't remember what polarity my welder is. I have tested it, because I have used it to zap Ni-Cad batteries. I think the stinger might be positive? I'm just guessing. When I stick weld I do prefer DCEN.

    One thing I did with my welder was I cut the end of the stinger off, and brazed on an end that can accept common Tweco MIG tips. It used these tiny tips that were proprietary to the machine I believe. I also changed the cup to a 3/8s brass barb fitting. It is electrically hot when it runs, but again it is an easy part to get now. My brass barb is really small diameter too, so I can get tight into jobs to weld them. Really having the tip hot has not actually caused me any problems. I've never changed the cup from the first one I put on it ever either. Although I have worn it down a little now.


    Reply 7 years ago on Introduction

    I know this welder is electrically hot as well the old hobby shroud was nice and small compared to the euro generic shrouds which i know from experience cause a lot of problems in tight gaps.