Clarke 150 scratch start tig inverter stopped working.

[Tiggy_dorset]

Doesn't arc up. Scratching in on a job creates some very faint sparks, but no arc.
No visible signs of component failures ie. blown capacitors, scortch/burn marks.

The contact relay (just above the transformer) starts in open position and will click closed after a few seconds of the machine being switched on. Probably meant to do that, but thought I would mention it.

After I switch the machine on, the transformer feels very hot (almost too hot to touch) after 1 minute, without having done anything at all.

Is the transformer popped? The machine is about £250 to buy new, can the transformer be sourced and replaced easy enough? Would it be an economical repair if so?

Cheers.

 

[Tiggy_dorset]

Sounds to me like some of your electric pixies inside the magic box of sparkles have got the hump and decided not to play...

I guess they spotted the dodgy mushrooms growing from my workshop wall, ate them and snuffed it.

If the transformer is heating it's doing "work". This probably isn't the sort of work you want though. It could be a frazzled tranny, or it could be something downstream drawing a lot of power without passing it on like it should.

Handy with a meter/oscilloscope?

I can turn the dial on the multimeter and poke things. Oscilloscope? I have a mate with one. Not really wishing to get that deep unless it is worth it. Looking for any simple answers first before getting technical

 

[Tiggy_dorset]

I'm gonna blow it out with an airline, wiggle things and cast another eye over it. See whats happens....

 

[Tiggy_dorset]

all that, nothing.
Interestingly though, when I turn the amps to minimum I can here a very very faint...high pitched buzzing? almost a hissing sound; on for 2 seconds then off for 2 seconds, and repeats. The sound disappears when I turn the amps past 25.

Getting up close, the sound is coming from the transformer, or a component very nearby.

 

[Tiggy_dorset]

Ahhh very cunning Mr Pdg
I have just intercepted your post in the wanted section. I do believe you are withholding important information regarding the successful repair of the machine in question. Now do reveal, or feel the wrath of my deadly mushrooms.

Serious note: If I do end up getting shot of it, I will keep you in mind

 

[Tiggy_dorset]

I've never really been much of a teacher, and trying to explain how to not electrocute yourself from a distance, typing, runs a high risk of ending in tears.

I know that electrickery can hurt, I was bitten when I was younger. I poke around carefully

 

[PTvor]

I think it's a bit odd that the relay clicks on a few seconds after the welder is switched on. It's usually about half a second or less. When the welder is switched on, the big capacitors are connected to the rectified mains through a resistor. This is to stop an almighty current surge which could do damage. The 12V or so for the fan and the control electronics almost always comes through a transformer and chopper arrangement and when the capacitors are nearly charged, the relay is closed by the 12V circuit and and shorts out the resistor. Usually the 12V is done through something like a TNY255 chip and a few other components. It can be discrete parts and a MOSFET to chop the ~ 340V through the little high frequency transformer to produce the 12V. There are all sorts of other arrangements such as a normal 50Hz 240V to 12V transformer and power supply circuit and having a microcontroller sort out the timing.

I'd be inclined to check that the 12 V was around that and trouble shoot the 12V circuit. That's just my guess and there could be all sorts of other faults which would cause the symptoms you see. Dry joints and bad connections cause an awful lot of problems.

It's much easier with a circuit diagram. I don't know whether Clarke would provide one. It's almost certainly a Chinese machine anyway.

The main transformer and the choke may use commonly available cores, but will almost certainly be specially wound for the design and not something RS would stock.

Other solutions are to try Welderfix

http://www.welderfix.co.uk/

There are other fixers.

Probably a bit over a ton all told, and a dubious proposition to rescue a £250 welder, considering what you can get new with warranty for £200, IMHO.

Also there's ebay for spares and repairs - no leads. "It worked perfectly until recently but suddenly gives a very weak output, just a few sparks not a proper arc. It may be something very simple but I haven't got time to investigate it / am not an electrician". I bet you'd get £40 for it because people seem to pay more than makes sense for rubbish on ebay and Clarke inverters always seem to command a premium for some reason.

 

[Tiggy_dorset]

Cunning like a giraffe, that's me!

You want this doorstop, PDG? I cant be bothered with messing around with it. As already said, they are cheap enough to buy if I decide to get another. Not worth spending out to get it rapaired to be honest.

Its just the unit (sorry I wish to keep the leads). Not really asking for much, perhaps swap for something or owe me some kind of favour?

 

[Tiggy_dorset]

Just so long as it's a 'trousers on' kind of favour

.....Easy Tiger

Ye have a think about it, pm me when you are ready mate.

 

[Tiggy_dorset]

I reckon its that bit there thats faulty. That then makes that bit not work properly, which means that those bits over there get too hot and blow. Then that other bit sees whats going on and gets scared and starts weeping whilst the other bit stops what its doing to comfort the other bit.

Looks all a bit too technical

Great to meet you. You did pay for my pannini didn't you?

 

[Tiggy_dorset]

Looks like a winner When you bringing it back?

Seriously, its good to know that someone can make use of it. I hardly used it, I dont like scratch tig and I have a transformer for burning rods.
Well done mate.