Mig 2000 and introduction

[Josh hector]

Hi guys, my first post on here but I've been a long time reader on some of the more interesting things I get linked to from other forums I use.

I've just purchased for a grand total of £50 this old heavy mig welder. It's 120a and has a euro torch and it is a heavy old monster. After some googling I've found two posts on separate forums about this welder but both turn out to be the same unit that has changed hands. I have raised my queries with both other members but am posting here as most of you guys are bound to be more experienced in matters such as this.

The welder has been played with before in what I assume to be an attempt at getting the wire feed more accurate. It has had a box of "tricks" attached to the back of the pot and the stitch timer removed completely as far as I can tell. I simply would like to get the wire feed potentiometer back to standard and the fuse and power leds wired back in properly instead of all this "stuff" as it's creating a weird motor reset/short.

I have attached images of the welder and the stuff someone has wired in. I studied design engineering and am remotely capable with a soldering iron etc but I was just wondering if there was a simple way using the three wires off the back of the pot to get this sorted.

 

[mike 109444]

Welcome Josh
Well you like a challenge...
I take it the feed motor has 4 wires going to it?

 

[Josh hector]

Thanks mike!

I never seem to do anything by halves. The welder laid down some pretty decent welds on the framework I'm making before it started shorting.

Motor has 2 wires going to it, I've removed all wires that appear to be added by previous owner taking photos of everything along the way. This leaves a central relay that is triggered by the torch and the spades that lead into the motor. Obviously without any control until the pot is added in.

Going by the pot that was listed on the other forum I need a 1k9 resistor and a 2k multi turn pot to get decent control. It's just a matter of getting the pot and motor wired in.

 

[mike 109444]

It looks like the made up circuit is a basic psu ie bridge rectifier + volt reg(s) + cap + transistor. Do you have a GOOD pic of the main pcb?
What make is this machine (2000 what ?)
Why a multi turn pot ?
What's wrong with ori ?

 

[Josh hector]

According the the other forums the original pot is 4k9 and gives a massive dead spot in the middle of the wire feed. A multi turn pot and 1k9 in that combination is what the other chap used with good results.

Identifying the machine is anyone's guess. There is no markings and no pcb, the whole thing is controlled with relays through the transformer.

Blue wires in the picture are the switch from the torch and operate 2 relays, one which opens up the gas and the second relay and the second switching relay I assume controls the wire feed as that is what is currently plugged into it (red and brown wire with spades middle left). Assuming it was originally set up as a rheostat/voltage divider? And someone has put in the psu box to better control it?

 

[mike 109444]

Think you might need to look for an off the shelf variable psu rated at the sort of current that the motor will draw. (if you hook the motor up to a 12 v psu and meter the current being drawn when you load it (rub finger on roller while running!) that should give you some indication of current (and fuse required) Note some have tried switch mode psu's but seam to have lots of issues with the start up speed. Note also that it may require some form of braking to stop over runs.
There are off the shelf mig pcb's from the likes of Technical Arc but yo would be looking at £65 ish http://www.ebay.co.uk/itm/UNIVERSAL...831?pt=LH_DefaultDomain_3&hash=item1c4a9d0197 and then there is being able to wire it in.

 

[Josh hector]

Had a go at the welder today and I found that I spent most of the time scratching my head. So I gave up and did some planing on some doors instead, much needed therapy!

I checked ebay for 24v motor controllers but from what you said previous mike I would assume that the diy psu converted a ac voltage to dc for the motor so a controller is no good unless I can get 220v input 24v output and simply wire it into the mains input?

I've been looking over the insides of my baby hobby mig and thought about pinching the control board out of that but while I could happily identify the outputs and inputs on it I probably would struggle to graft it into the other machine.

Anyone local that can help? I just want to get welding again!

 

[mike 109444]

There should be a low voltage some where in there as they would (should) not be feeding 240v through the trigger switch! It might be that there is a low (< 40v) AC being taken from the secondary side of the welding transformer (not the best ideal but not uncommon) see pic. pink and purple lines.
You will need to check the voltage marked on the wire feed motor to sus any supply for it. I did say 24v as a guess but it could be a 30 > volt DC motor, check for a label. It might be possible to use the pcb from your other welder BUT if it is only driving a VERY small motor then it's likley to fry trying to drive that big motor.

 

[Josh hector]

Mike, the card that controls the smaller welders motor is setup exactly as per your diagram, and I have found a 30v AC source off the trigger thanks to your suggestions.

A plan has hatched with off the shelf parts as I'm not going to be faffing around with building up a psu. So a 24v mains dc power source has been purchased along with a high wattage motor controller. I'll be bench testing the motor and controller before it becomes a permenant fixture in the welder.

Plan is to power up the 240VAC to 24VDC source up to the main power switch so it is always live when the welder is live. The 24VDC source will run through the switched relay that is triggered by the trigger allowing it to go to the controller and thus to the motor.

The parts have cost me £25 and are pretty much what I have seen listed on eBay and other sites as specific upgrades for SIP welders for £50-70. Only difference is I will be using the insanely oversized relay in the welder and not a new solid state one.