Murex tradesmig 160

[Welder Wilk]

Having removed the cover panels on the welder today to give it a bit of a clean out I found this only connected at one end?
Im not sure what I need to look for as a replacement.
Any help would be appreciated.
Ive attached a picture of offending item
Thanks

 

[Bobbes]

That is a resistor. I can reed 16 Watt. Turn the resistor a littlebit. So we can se the value of the resistor.

 

[Welder Wilk]

Hi Bob, whats on the paper is whats on the resistor... thats all there is
the next bit underneath is ..79 2

 

[Bobbes]

I din't reed the papier. Sorry. The resistor is 24 Ohm and 16 Watt. There must be an empty place on the board I think.

 

[Welder Wilk]

It wasnt on the board its attached to the switching gear that operates when you close the trigger

 

[eddie49]

It is a bleeder resistor, used to drain the voltage from the DC capacitors.
There may be two thin wires attached to the capacitor bank ( as opposed to the heavy bus bars there ) which go to a pair of normally-closed ( NC ) contacts on the main contactor ( heavy-duty relay ). The resistor should be connected on the other side of that pair of contacts. When you press the torch trigger, the contactor pulls in, this pair of contacts opens, taking the bleeder resistor out of the circuit, and the capacitors charge up. When the trigger is released, the contactor lets go, so the NC contacts close, putting the resistor back across the capacitors and draining them down. This ensures that there is no residual voltage, which would otherwise cause a "live torch" effect, and give a small spark at the end of the MIG wire before you press the trigger.
The vibration of the contactor clacking in and out often causes the solid copper resistor leads to fracture. If you look carefully under the screws on the contactor, you should be able to find the broken resistor leg still clamped in there.

 

[Welder Wilk]

Hi Eddie
Yep I think you hit the nail on the head with that, I did find the other end of the wire at the time, so next question.. what is its full title so I can search for a replacement?

 

[Bobbes]

In this case you can allso use a standaard value of 27 Ohm and at least 16 Watt or more.

 

[eddie49]

As Bobbes said, the standardised resistance value that is the nearest replacement to this component is 27 Ohms, rather than the 24 Ohms that your machine was fitted with. Either one will work, it is just there to drain the charge from the capacitors.
This type of component is called a high-wattage wirewound resistor. Basically a ceramic tube wound with high-resistance nichrome wire.
Often mounted inside a finned aluminium heatsink, then it's called a "cased wirewound resistor".
That version has the additional benefit of an aluminium case with mounting lugs, so it can be rigidly mounted somewhere close to the original location at the Contactor, and connected to the screw terminals on the Contactor with flexible wire. The resistor will not be vibrated, and the flexible wires will not fracture, so it will be better than the original design.

You could replace the damaged resistor with a 24 Ohm 25 Watt cased wirewound resistor from here:
https://www.ebay.co.uk/itm/0-01-5k-...e-Wirewound-25-50-100W-Resistor/183603453219?
Select 24R and 25W, price £0.99 plus postage.

 

[eddie49]

There may be two thin wires attached to the capacitor bank ( as opposed to the heavy bus bars there ) which go to a pair of normally-closed ( NC ) contacts on the main contactor ( heavy-duty relay ). The resistor should be connected on the other side of that pair of contacts.

Actually, there may be two pairs of contacts, so that both ends of the resistor are switched on or off from the capacitor bank when the Contactor operates.

 

[Welder Wilk]

Hi Eddie

Cheers for that, I will mount it on the frame and not on the switch where it can vibrate, I hope the delivery isn't to long as I need to get welding asap.

Many thanks. Clive

 

[eddie49]

You could still use the welder, if you have to, it's just that when you first touch the end of the wire against the workpiece you will see a spark, which is due to the remaining charge in the capacitors. This will be just before you press the torch trigger, it can be a bit disconcerting, and long-term it is better for the capacitors to be discharged through a resistor rather than with a dead short.
If you scrape the paint off the end of the old resistor you may find a brass end-cap, to which you could temporarily solder a wire.

 

[Welder Wilk]

Ive been just tacking up my repair plates as it is a bit of a pain when it sparks and sticks..

 

[Welder Wilk]

You could still use the welder, if you have to, it's just that when you first touch the end of the wire against the workpiece you will see a spark, which is due to the remaining charge in the capacitors. This will be just before you press the torch trigger, it can be a bit disconcerting, and long-term it is better for the capacitors to be discharged through a resistor rather than with a dead short.
If you scrape the paint off the end of the old resistor you may find a brass end-cap, to which you could temporarily solder a wire.

It took a bit of doing as there really wasnt a lot to solder too but its done and working, will get the new one fitted as soon as it arrives

 

[Steveh101]

I have same resistor hanging about, nothing to solder to at all, link for resistor is long gone, can someone point me in right direction?

 

[Steveh101]

https://www.ebay.co.uk/itm/404272630206?var=674171847252

Would that do the job?

 

[eddie49]

Hello and welcome to the Forum !
Yes, the 25 Ohm 25 Watt resistors in the link that you provided will do the job. You only need one, priced at £2.18 plus postage.
This 24 Ohm 50 Watt at £3.74 inc. postage from Somerset may be faster delivery:

https://www.ebay.co.uk/itm/264693744396

 

[Hopefuldave]

https://www.ebay.co.uk/itm/404272630206?var=674171847252

Would that do the job?

That'll do the job, the wires will go from it to the contactor NC contacts with the capacitors on the other side, to bleed the voltage on them off when you release the trigger - circled in red below!

 

[Steveh101]

Many thanks, ordered, i hope it helps, i have a Tradesmig 130 and its not welding properly, only works on settind 7 and 8, opened up and look like it had yrs of bodyshop filler dust in it, cleaned as best as I can, emptied a can of contact cleaner in it and checked diodes and capacitors, all look good. Orderd new earth lead and euro handle/nozzle, hope that works or im gunna looking for a new 2nd hand welder.

 

[eddie49]

Like all Murex machines, a Tradesmig 130 should be a good welder. To diagnose the reason why it is not working properly, I would start by looking for loose, burnt, or corroded joints and connections in the low-voltage high-current secondary circuit - i.e. the transformer secondary, the rectifier diodes, the choke ( inductor ), and the torch connector and work clamp & return cable. If that does not solve the problem, then measure the DC output voltage from the torch tip to the work clamp at each of the settings on the rotary power switch. This should vary in equal steps from about 15 to 30 volts.