Where do I get the thermal switch in the Uk

[theprofessor]

I just purchased a wolfweld 140 for repairs... found 2 problems with the unit. 1. The thermal switch is bad, see photo below.

2 the circuit board transformer shows signs of being burnt.

Where can I get these 2 items in the UK.
The transformer does not seem to have a part number. Any ideas?

 

[Tigman]

RS ?

 

[zzr1200]

CPC Farnell

 

[theprofessor]

Neither one has them on their online catalog that I can find

 

[eddie49]

Hello and welcome to the Forum !

The 125 C thermal cutout switch will normally be closed. It is probably glued to the side of the main transformer...? Tapping or hitting it may help it to close again. If it has failed open-circuit, you could bypass it by joining the two wires together. For a replacement, search eBay for "thermal cutout switch".

The small transformer on the board drives the relay when the torch trigger switch is pressed. The relay is marked "18v DC", so you need to search eBay for "PCB transformer 18v". To confirm that the component actually has failed, check for AC voltage across the secondary when the welder is plugged in and powered on ( and the thermal cutout is closed ), or for continuity of the primary and secondary windings. The resistance of the primary ( which is the most likely to have burnt out ) may be surprisingly high - up to 3k Ohms, and a couple of hundred Ohms for the secondary.

Post #3 of this earlier thread may be a circuit diagram of the welder:

WOLF WELD 140 NO WIRE FEED!!!!

Hi all! was using my welder yesterday and all of a sudden the wire feed stopped! I’ve hooked up the motor to a battery and it works with a 12v feed but when I try it with the machine wires there isn’t even a 1v feed. You can hear the relay click but no wire movement!

www.mig-welding.co.uk

and this may be the circuit diagram of the PCB:
https://easyeda.com/Tonyataintree/wolf-weld-wire-feed-control-pcb

 

[theprofessor]

Hey Eddie, I looked on ebay.co.uk, for the thermo cutoff switch and they have only dinky buggers like 10 amps, this one is a 40/ 60 amp one. I'm having a begeezer of a time finding one. As for the transformer, it is no question it's smoked, 240vac in, and I'm getting 135vac out...

Hello and welcome to the Forum !

The 125 C thermal cutout switch will normally be closed. It is probably glued to the side of the main transformer...? Tapping or hitting it may help it to close again. If it has failed open-circuit, you could bypass it by joining the two wires together. For a replacement, search eBay for "thermal cutout switch".

The small transformer on the board drives the relay when the torch trigger switch is pressed. The relay is marked "18v DC", so you need to search eBay for "PCB transformer 18v". To confirm that the component actually has failed, check for AC voltage across the secondary when the welder is plugged in and powered on ( and the thermal cutout is closed ), or for continuity of the primary and secondary windings. The resistance of the primary ( which is the most likely to have burnt out ) may be surprisingly high - up to 3k Ohms, and a couple of hundred Ohms for the secondary.

Post #3 of this earlier thread may be a circuit diagram of the welder:

WOLF WELD 140 NO WIRE FEED!!!!

Hi all! was using my welder yesterday and all of a sudden the wire feed stopped! I’ve hooked up the motor to a battery and it works with a 12v feed but when I try it with the machine wires there isn’t even a 1v feed. You can hear the relay click but no wire movement!

www.mig-welding.co.uk

and this may be the circuit diagram of the PCB:
https://easyeda.com/Tonyataintree/wolf-weld-wire-feed-control-pcb

 

[theprofessor]

Alternatively I was thinking of using this https://amzn.eu/d/3BcJ2c2 it is a programmable unit that you can connect a relay or SSR to as big as you want. Then use a off board transformer... but I much rather keep OEM...

 

[eddie49]

Even if it was in the supply circuit for the primary winding, a 10 Amp thermal cutout would actually be able to supply 2,300 Watts, which would be enough to run the output of a MIG welder at 100 Amps. However, as per the diagram I linked above, the cutout is only in the circuit for the primary winding of the small control transformer, so a rating of 10 Amps, or 40 Amps or 60 Amps is unimportant.

However, on closer inspection of that diagram, I was wrong about the cutout being normally closed. It should be open, and at high temperature it will close and light the Overtemperature indicator. Is your cutout open or closed, and is that light on or off?

Here is an example of an eBay listing for the small transformer:

Pardon our interruption...

This may require extra holes and wire links to allow fitting to the board.

 

[theprofessor]

Hey Eddie, the light is off when it's cold, and on when hot. When I took the switch out and inspected it, it appears to be in the normally closed position while cold, and open when hot.

Even if it was in the supply circuit for the primary winding, a 10 Amp thermal cutout would actually be able to supply 2,300 Watts, which would be enough to run the output of a MIG welder at 100 Amps. However, as per the diagram I linked above, the cutout is only in the circuit for the primary winding of the small control transformer, so a rating of 10 Amps, or 40 Amps or 60 Amps is unimportant.

However, on closer inspection of that diagram, I was wrong about the cutout being normally closed. It should be open, and at high temperature it will close and light the Overtemperature indicator. Is your cutout open or closed, and is that light on or off?

Here is an example of an eBay listing for the small transformer:

Pardon our interruption...

This may require extra holes and wire links to allow fitting to the board.

 

[theprofessor]

Unless it has failed in the closed position.
When I first tested the switch on the transformer there was no continuity, when I took it off, and popped the cover it had continuity and was in the closed position.

 

[theprofessor]

Also the switch had tension on the tang in the closed position, when you depressed it, it immediately sprung back to the closed position rather than sagging into the open position.

 

[eddie49]

Usually the thermal cutout switches used on MIG welders are Normally Closed ( NC ) and wired in series. There may be one on the main transformer bobbin, and one on the fins of the rectifier. They open when hot, cutting AC mains power to the primary of the small transformer on the control board. With no supply for the coil, the relay drops out, or cannot close, so the welder switches off and will not restart until the cutout cools down and closes. The Overtemperature indicator is often a neon lamp, wired in parallel with the thermal cutout. When the contacts of the NC cutout open, the voltage across them lights the indicator.

According to the diagram, this Wolfweld MIG has a Normally Open ( NO ) thermal cutout which is only wired to light the Overtemperature indicator if it closes. It does not switch the welder off or prevent it from working, it relies on the operator noticing that the indicator is illuminated.
Since you are going to buy a new cutout, I would suggest getting an NC one and changing the circuit so that AC mains power to the primary of the small transformer is cut on overtemperature.

 

[theprofessor]

I will check tomorrow which way it goes, I will heat the collector up with my heat gun and see what happens.

On my unit I believe that it is NC, and does like you say cuts the small transformer... I don't see any wires going to the rectifiers just the main heavy copper ones.

 

[theprofessor]

The reason I think this was because there was NO power to the coils when there was no continuity across the thermo switch when it was cold. After I popped it out and opened it, then I had continuity, and I assume will have power to the coils now, but haven't tested it yet.

 

[Nomad]

For the temperature switch I normally search for *kick stat* ( trade name, used in ovens microwaves cars...)

They come on 2 options, normally open or normally closed

 

[Dragnet]

They are generic, and a common item. I just got one from my local motor repair place. They also sell other accoutrements like start and run capacitors. A quick search throws up Rotamec in Exeter who will probably have boxes of thermal cutouts. It can also be very helpful to have a conversation in person with the old bit in your hand, as they'll be able to say 'aha! you need...' there and then.

 

[theprofessor]

Ok I am making some progress, the thermal switch is working fine, I heat up the metal disc and it pops to the NO position.
The problem before was a broken spade connector on the thermal switch.

So now I get the top orange light to come on when I switch the power on. My question is should the fan come on immediately, or should the fan come on when the thermal switch kicks to the NO position?

When the thermal switch is heated, the overload light does not illuminate, however by connecting the wite directly to the power supply wire, it will come on.

When the thermal switch is heated up and pops, should it cut all power to the machine, or should the overload light and fan come on while cutting the power to the wirefeed motor?

I am still not getting any wire feed motor to work, however by connecting a 9v battery to the 2 wires, it will spin up.


Thoughts?

Thanks everyone.

 

[Hutcho]

Fan should be on all the time
Depending where the thermal is - some cut the torch trigger and others cut power to the transformer - but the machine will remain on for the fan to cool it down .