Murex Miget-Carrying on where Pauly left off.

[Mattycoops43]

The other approach i thought of was to put the ac mains into the rectifier unloaded, with the outputs insulated and disconnected from the welder,with an ac current clamp monitoring the load input on the live only. in theory there should be no current being consumed ,but due to efficiency losses it may draw something. if however it was sucking loads of juice,say above 1amp at 240v ac then it would be clear that the rectifier is partially shorting and wasting power. You could put a bulb across the output,ive never tried lighting up a bulb at 240 volts on dc. Beware!!!! anybody else have any thoughts?

I understand that, I think I would like a second opinion as to whether that is ok to do purely because that is kind of on the limit of what I would understand. I would be quite happy to do it safely, just whether I am likely to blow something up!

 

[baldy]

if you look at the rectifier from technical arc and the one from from wasp supplies ,youll note the picture is the same.If you want to you could up the power performance to around 200a to increase the duty cycle. id bang one of those on. dont get hung up on he size of the unit,new technology is smaller and lighter.

 

[baldy]

I understand that, I think I would like a second opinion as to whether that is ok to do purely because that is kind of on the limit of what I would understand. I would be quite happy to do it safely, just whether I am likely to blow something up!

Scrap, that , thinking about it,the transformer feeds a much lower voltage into the recifier,feeding it 240 would fry it. Poof, bang ! The other thing which i thought of was to watch the load into the rectifier with a current clamp when the torch switch is operated when the mig was in its operational mode.The other way is just to bang on a 200amp rectifier in place of the original and try it.

 

[Mattycoops43]

if you look at the rectifier from technical arc and the one from from wasp supplies ,youll note the picture is the same.If you want to you could up the power performance to around 200a to increase the duty cycle. id bang one of those on. dont get hung up on he size of the unit,new technology is smaller and lighter.

Ok, that sounds right. In all honesty, I was looking at the pics of the new ones and thinking 'crikey, they look a bit wussy' compared to what's in there, but as you said, it is old tech. I think I'll try a new one and see how it goes. I will test the switches etc first as has been suggested to rule things out.

 

[baldy]

Dont try shoving 240 v into the rectifier, although its ac going in, its probably under 100 volts off load.240v would fry it , big time.Lots of aloud thinking going on here!

 

[baldy]

The other option is to ring Technical Arc and get them to recommend a rectifier unit for the Murex.

 

[eddie49]

As you have found, the plates with rounded ends on the rectifier are connected to the "wire" ends of the "diode-quads" during manufacture ( perhaps by soldering ? ), and the other ends of these plates are actually bolted together, so it's OK that they are touching.
It's great that baldy has found the circuit diagram; that makes it a lot easier than just guessing. The diagram shows that the 6-position power switch is just one pole in and 6 ways out. Simples ! The input is mains power from the Live, and the 6 outputs are tappings on the primary winding of the large transformer.
These switches can burn, melt, and short-circuit internally. To take the switch out of the picture, label all the 7 wires and carefully note where they go to on the switch. Check which position the switch is in when you start, and leave it in that position. You may have to unscrew the switch from the front panel to make it easier to get to.
Trace the wire that brings the power in to the switch - from the main contactor ( large black heavy-duty relay ). Disconnect it, then disconnect all of the 6 output wires from the switch - they all go to the main transformer. If there are short link wires that join segments of the switch itself together, leave them in place.
Select one of the 6 tapping wires, join it to the input power wire, and insulate that joint ( it's 240v mains ! ). Insulate the 5 remaining tapping wires, and keep them apart from each other and the case.
With the rectifier back in, you can then test the welder. It will have one power setting, and the possibly-faulty range switch will no longer be used at all. Check if the breaker trips, and if the welder has sufficient power.
If it looks promising, you could power off, open that wire joint, and repeat this process with each of the 5 remaining transformer power tappings in turn.
If these tests fail, it's not the switch. It could be the main transformer - but they don't tend to fail that often. It could still be the rectifier. Instead of buying a new one, you could post it to me and I'd be happy to test it ( with a meter, and also on-load in a welder ).
Do you have a multi-meter, or could you maybe borrow one?

 

[Mattycoops43]

As you have found, the plates with rounded ends on the rectifier are connected to the "wire" ends of the "diode-quads" during manufacture ( perhaps by soldering ? ), and the other ends of these plates are actually bolted together, so it's OK that they are touching.
It's great that baldy has found the circuit diagram; that makes it a lot easier than just guessing. The diagram shows that the 6-position power switch is just one pole in and 6 ways out. Simples ! The input is mains power from the Live, and the 6 outputs are tappings on the primary winding of the large transformer.
These switches can burn, melt, and short-circuit internally. To take the switch out of the picture, label all the 7 wires and carefully note where they go to on the switch. Check which position the switch is in when you start, and leave it in that position. You may have to unscrew the switch from the front panel to make it easier to get to.
Trace the wire that brings the power in to the switch - from the main contactor ( large black heavy-duty relay ). Disconnect it, then disconnect all of the 6 output wires from the switch - they all go to the main transformer. If there are short link wires that join segments of the switch itself together, leave them in place.
Select one of the 6 tapping wires, join it to the input power wire, and insulate that joint ( it's 240v mains ! ). Insulate the 5 remaining tapping wires, and keep them apart from each other and the case.
With the rectifier back in, you can then test the welder. It will have one power setting, and the possibly-faulty range switch will no longer be used at all. Check if the breaker trips, and if the welder has sufficient power.
If it looks promising, you could power off, open that wire joint, and repeat this process with each of the 5 remaining transformer power tappings in turn.
If these tests fail, it's not the switch. It could be the main transformer - but they don't tend to fail that often. It could still be the rectifier. Instead of buying a new one, you could post it to me and I'd be happy to test it ( with a meter, and also on-load in a welder ).
Do you have a multi-meter, or could you maybe borrow one?

Thanks Eddie, that is really helpful.

I would be very keen to send it to you, if you don't mind testing it for me? I could probably find my way through, but then I cant guarantee I wouldn't do something wrong and get a false result, or damage something. I will take the switch out and test it for short circuits etc, just struggling for time at the moment.

Matt

 

[eddie49]

Yes Matt, sure, I will gladly test it. PM sent with my address.
Please take care with the range switch connections - this Forum is full of horror stories about mis-wired, exploded and self-destructed switches ( however, this 1-pole 6-way is actually an easy one ).

 

[Mattycoops43]

Yes Matt, sure, I will gladly test it. PM sent with my address.
Please take care with the range switch connections - this Forum is full of horror stories about mis-wired, exploded and self-destructed switches ( however, this 1-pole 6-way is actually an easy one ).

Brilliant!

I have a history of 12v auto electrics, I'm pretty good at it, but I don't take anything 240v lightly. I will test the switch without power, I can test to make sure things that are meant to be isolated are, and the correct pathways do connect when the switch is turned.

Matt

 

[baldy]

Whats the latest then? Im itching to know youve fixed it !

 

[Mattycoops43]

Eddie had almost finished testing the rectifier and had found no fault so far, so it could be a simple as the switch or something similar. I was so convinced it was the rec I haven't even looked at anything else yet. Bit nuts at work, I'll get into it as soon as I get a chance.

 

[eddie49]

The rectifier is OK. I tested it with a meter, a 12v supply and a bulb, and then in my SureWeld 140 MIG. It changes 23.7v AC to 32.3v DC, does not short, burn, or heat up, and welds fine.

I have now posted the rectifier back to Matt. The next troubleshooting step, I'd suggest, is to try bypassing the 6-way power switch.

 

[baldy]

Well done that man! , Matty you could try cleaning the switch with contact cleaner, it has been un-used for a while after my brother contacted Parkinsons, that could be it.Also maybe contact Technical Arc, to see if they have a new switch ?

 

[Mattycoops43]

Yes, that is the next step. Still snowed under here with work, I'll report back as soon as I get somewhere.

Matt

 

[baldy]

At this rate, youll fix that Murex before my new oxford rocks up, its been near on a month, but i did order some xtra gadgets, so ill have to wait i guess.

 

[baldy]

Well its arrived,new oxford Migmaker 180-1 is living in our abode.What have i learned today?. Well, i tried the same test i did with the Murex,operate the torch, no load, no wire, no gas ,power level 1ok, 2ok, 3ok, 4ok ,5ok. 6 bink lights out. it does exactly the same as the murex did. So i suspect Matt, theres bugger all wrong with the Murex that a bit of love wont fix.The new oxford does have capicitors fitted, so the welds are creamy nice. but theres nothing stopping you adding them to the Murex.im quite surprised how little there is inside the Oxford to be honest.1 little pcb, a sod off big transformer, a 6 pole switch,a gas valve, and numerous connections.I took the side of to extract a shed load of polystyrene which was inside.I was quite shocked at the lack of wizardry to be honest.But if it welds ok, it doesnt need it i guess, less to go wrong anyhow ! Im off now to seek a separate 16 amp mcb of the d type and stand alone fuse box.The c type doesnt cut it.

 

[eddie49]

Baldy, I should mention that when we tested the Murex rectifier, the only issue was that it had been wired Electrode Negative - i.e. as for gasless wire. Luckily, I found that out before testing the rectifier in my Eland MIG, or else the 6 x 10,000uF electrolytic capacitors would have gone bang.
Having the torch/electrode negative gives more heat in the electrode/wire and less in the work, so maybe that would explain why the Murex seemed low on power.

 

[baldy]

Ah thats interesting,that was pre wired and pre made by Murex,my brother never used gas less wire.Always Argoshield 5 and regular wire.I had never removed the rectifier only disconnected one terminal at a time trying to figure out why the mcb kept goin out. so rewire that recifier torch positive and negative ground and she should be good to go.

 

[Mattycoops43]

Hmm interesting.

I wired it up as was from the factory, and it's working totally fine. I even got a short burst on power 5 and then 6 on my normal plug socket without tripping the circuit. When I used it to try a job on power 5 it did trip out after 10 minutes but I think that's normal.

Only issue I had was the murex tip had massive tip stick out. I was getting random holes appearing in the weld at all powers which I think was the gas dispersing. I tried to plug my mb36 torch in and the murex euro torch connector is not the same as other euro torch connectors.it seems like the gas connection won't fit into the socket.