Modding my Cosmo 130

[piehole1983]

Hello! I'm a new user and just want to say how useful I have found this site!

I have an old (ish) Cosmo 130 MIG that I bought in 2005, used once or twice and put it away until now!

Basically its almost in mint condition. It never really worked that well, overheating, wire feed etc. I thought I'd dig it out and give it a few of the mods I've read about on here.

When I opened it up to have a look inside I discovered that the cooling fan was jammed against the main transformer!

It had obviously had a good knock and bent the tranformer supports, that explains the constant overheating. The little fan motor had been pretty well cooked by being jammed so I decided to "mod" it a bit. See below!

 

[FranV8]

Nice mod! Stolen out of an old old computer?

I had a set I'd got out of an old cabinet mounted computer, used to use them in my bedroom in summer when I was younger. For some reason I thought the enormous racket they made sounded "cool."

 

[piehole1983]

I'm a fridge engineer by trade, I have odd fans kicking around so this one has been in my shed for about 3 years unused! It's a 6 inch axial job for some fridge but fits my welder much better and should keep it nice and cool now. Rated at 45W it puts a fair bit more air out than the old one!

 

[piehole1983]

More mods!

The modding continues with the addition of a new wire feed power supply. I rescued a 24v 200VA Toroidal transformer from the bin today, it has never seen mains and was perfect for my application. Maybe a wee bit overkill but better looking at it than for it

I've simply drilled a 6mm hole in the middle partition to mount the transformer on using a M6 50mm bolt. Toroids dont like to be clamped too hard is it can damage the winding insulation so I've added a lock nut to keep the bolt secure.

I kept the little inline fuse holder and added it to my MIG as well, you can never be too safe with electricity! Keeps things a bit tidier too. Next I need to source a suitable bridge rectifier.

With the transformer mounted and the fuse holder secured I powered up the transformer from a bit of flex with a plug top on the end. I measured just over 28vac on both RMS and average, a little high I think but still way lower than the 38vac I was getting from the main transformer (and as a result my PCB popped). Once I repair the PCB I'll be able to get it running! Just have to wait for the postman to bring the new TIP35C transistor.

I also made and fitted a brace to stop the wire feed from flexing, seems to keep everything nice and solid now.

To my amazement, my MIG has been factory fitted with a steel liner At least that'll save me a few £.

 

[Wedg1e]

Nice going

I'm sure in the good old days , toroidals used to come with a pair of rubber discs to fit either side when clamping.
I know: rubber discs, luxury. When I was a lad we used to sleep twelve to a bed in a shoebox in't middle o'road.
We knew we were going up in the world when we moved into that glazier's wheelie-bin etc. etc...

 

[piehole1983]

It actually does have the very luxurious rubber discs!!

The modding continues with serious use of trial and error. I had installed a smoothing capacitor to the output of the bridge rectifier, which seemed like a good idea but it turns out they seem to cause more trouble!

My problem was the wire speed would be fine for a few seconds then it would creep up and up, I can only assume this was due to the capacitor charging! I removed it and everything is ok again. It runs fine without it so I can only say smoothing the rectified supply isnt really of any benefit. My supply looks almost totally smooth on my scope without any capacitors anyway, I'd say that is largely down to the 200VA transformer!

Next step was fitting a 100R trimmer to the pcb, cost me £1 for five so it was a cheap mod! Makes setting the minimum speed a lot easier.

On the back of the wire speed issue I had (getting faster on its own) I thought of using a switched mode supply I have sitting here rated at 24VDC 2A (48W). I didnt use this one as I thought it would be under rated. I had no luck finding the actual rating of the DC motor for the wire feed so I had to test it out.

At 24V its only drawing 0.4A (9.6W) with no load and maybe 0.7A (16.8W) under a fairly heavy load. This might go up when the welder is in use, but I cant imagine a lot more. From some of the modding guides on here, I assumed it would be a lot higher than this. My current setup will supply up to 8A (192W)

Changing the voltage didnt make much difference to the power consumed. So, next I'm going to fit the switched mode supply to see how I get on. More so to prove it will run off a 2A power supply than anything else. If it works ok, I'll be removing the 200VA toroidal as it weighs a ton! I've also ordered a PWM motor controller, its going in regardless of which supply I decide to keep as the factory speed controller is poo.

 

[piehole1983]

Here's a photo of the relay I have installed to switch the 24DC supply from the transformer instead of switching the transformer on and off repeatedly. This is perfect for trying the switched mode supply as well.

 

[piehole1983]

And the progress so far! I know I'm feeding off the top of the reel when it says not to, but it feeds in better.

 

[mike 109444]

piehole1983 Do you know what size the shaft that the feed roller mounts on is? Reason is I have a bunch of used motor/gearbox assemblies from the medical equipment I work on that may suite thoses modding there machines. See attached pic. Note the shaft is only 4.9 diameter with a flat along it. The gearbox 4 mounting holes look much like the mounting of your gearbox?
They are 24v and there are two different gearboxes one type is 310 rpm output and other type is 48 rpm output.

 

[darrylp]

I use a 36 watt rated (max) 24 volt transformer from an old cordless drill charger that packed up ages ago. Also a pwm controller and relay as a brake. Runs fine from from about 1/10 inch per second up to 7 inch per sec. ( 420 inch/min ) way more range than I need. Never get any speed variation. Of course my machine cant run high amps for any real length of time. But the drive motor doesn't need any more current than what you are seeing. PS. That also me feeding from top (reversed) feed 5kg spools.