Small DC TIG welder remote switch needed

[Clambake]

Hi -first time here!

I have a small 120V DC inverter welder that I use to do small TIG welding projects -mostly small tacking jobs. It works great for what I need it for, but I would really like to add a remote torch on/off switch.

My thinking was that it would be best to add the switch into the thermal protection circuit so that when open (or closed) an overheat condition is simulated. This way everything stays on except power to the torch itself. I figured I'd just open it up, find a thermal sensor and go from there.

Trouble is I'm not finding anything that looks like a dedicated thermal sensor, and the schematics are not available. I did notice that big ceramic fuse (7w4r7j), but I'm thinking it's not the resettable kind, so maybe not the right component. Maybe I'm wrong.

So I thought I'd post my dilemma and some photos of the machine's innards in the hopes that someone here could help.

Any help would be much apprieciated!

 

[73's de Edd]

.


Sir Clambake . . . . . . .

I initially was surprised to see an Amerikanski sourced posting using a "torch" reference.
If the purpose is to illuminate a proposed pre observed welding position before initiating the weld, wouldn't the problem highly be simplified
by the use of the HIGH illumination level provided by a small halogen lamp contained within a mirrored parabolic reflector.
You then use a FOOT activated momentary contact switch to activate lighting for a required observation interval while moving into close position for your weld.

Of your pictures I am only seeing a particular do-nut toroid that is being used for current sensing.
Any co utilization of that type of sensing would only have lamp activation activation AT and DURING weld activity and NOT just prior to it.

HIGH . . . . . . intensity halogen lamp light source . . . . .

Did I read between the lines on what you are wanting to accomplish ?



73's de Edd


,

 

[Clambake]

Sorry Ed -I really did mean the American version of a torch -the part of a TIG welder that does the work of welding! The zappy part.

 

[CDRIVE]

I don't even see an On - Off power switch on the front panel! Probably couldn't fit one in there. Damn,.. that's the quintessential definition of the "10 pounds of sh!t in a 1 pound bag" thing!

The good news is there's definitely a low voltage low current control circuit in there.... Somewhere!

Chris

 

[Clambake]

I don't even see an On - Off power switch on the front panel! Probably couldn't fit one in there. Damn,.. that's the quintessential definition of the "10 pounds of sh!t in a 1 pound bag" thing!

The good news is there's definitely a low voltage low current control circuit in there.... Somewhere!

Chris

The pot on the front panel is switched Chris.

I admit it was an inexpensive little welder, but it serves my purposes perfectly -all but the remote switch I'm trying to add. Can you help find the thermal sensor? You talk like you should be able to spot it blindfolded!

 

[CDRIVE]

Then if the pot has an integral switch at the extreme CCW position then that's where I'd check first using a DMM. Check to see if it's switching the mains power (120VAC) or something else.

If it's switching the mains (most probable) you can break one leg and insert relay contacts in series. The relay coil would be powered from LVDC tapped off the PSU powering all that solid state I see in there. This way the push button torch switch will be carrying only low voltage control current.

Chris

 

[Clambake]

Then if the pot has an integral switch at the extreme CCW position then that's where I'd check first using a DMM. Check to see if it's switching the mains power (120VAC) or something else.

If it's switching the mains (most probable) you can break one leg and insert relay contacts in series. The relay coil would be powered from LVDC tapped off the PSU powering all that solid state I see in there. This way the push button torch switch will be carrying only low voltage control current.

Chris

Thanks for the idea Chis -with a remote switch, I was hoping to keep everything but the torch powered including the cooling fan -that's what was behind my idea of interrupting the thermal protection circuit. Would your idea do that or just shut the whole thing off?

 

[CDRIVE]

It would shut the whole thing off.

OK, here's another thought. Since we don't have a schematic we're lacking a decisive point within all your low voltage circuitry (which is appreciable) to logically tap into. There is one point that is obvious though. That would be the Pot itself.

Please take a clear shot of the Pot. It may be possible to break the wiper lead circuit and insert your switch in series.

Chris

 

[Clambake]

Here's the best I can do front and backside. Actually I did try breaking the wiper leg in an earlier attempt -torch was still live. Maybe I didn't do it right:

 

[CDRIVE]

Hey, I had a near accident earlier. An open bottle of Vodka fell over and nearly spilled all over my wood floor. Fortunately my lightning reflexes caught about 98% of it with my mouth. Consequently I'm having trouble keeping my eyes open.

So before I sack out let me ask.. Do you own a DMM? If so we're going to do some sleuthing by wringing out the pot circuit.

Be back in the morning.

Chris

 

[Clambake]

Hey, I had a near accident earlier. An open bottle of Vodka fell over and nearly spilled all over my wood floor. Fortunately my lightning reflexes caught about 98% of it with my mouth. Consequently I'm having trouble keeping my eyes open.

So before I sack out let me ask.. Do you own a DMM? If so we're going to do some sleuthing by wringing out the pot circuit.

Be back in the morning.

Chris

Sounds good. Yes I have a DMM -thanks for the help!

 

[CDRIVE]

How difficult would it be for you to pull the board that contains the Pot so we can see clear photos of both sides of the board?

Needless to say make sure the unit is unplugged from the mains.

Chris

 

[Clambake]

How difficult would it be for you to pull the board that contains the Pot so we can see clear photos of both sides of the board?

Needless to say make sure the unit is unplugged from the mains.

Chris

The pot is mounted to the main board and would require a lot of desoldering of other components to show all it's traces. The backside of the board is pretty clear, but the front is really cluttered. Is pulling the board the only way?

 

[CDRIVE]

Try to get a clear photo of the bottom of the board.

Chris

 

[Clambake]

Try to get a clear photo of the bottom of the board.

Chris

I will try for a good photo when I get home this evening.

Another idea I just had was to use a 3 pos momentary switch and 10k resistor to interrupt the (10k) Pot.

I'd break and insulate the #3 Pot leg from the board, and run a wire from that spot on the board to the Common leg of the switch. I'd then run a wire from the #3 Pot leg to the NO switch leg and run a wire with resistor from the Wiper to the NC switch leg.

Would that work in theory?

 

[CDRIVE]

We speak schematic here so this is what I'm hoping your Pot circuit looks like and how we'd modify it but it's purely speculation.

Chris

 

[Clambake]

We speak schematic here so this is what I'm hoping your Pot circuit looks like and how we'd modify it but it's purely speculation.

ChrisView attachment 25507

Ok -well here's the best I could do given the shiny varnish on the board. I hope there's enough there to make sense of. Thanks again Chris.

 

[CDRIVE]

Where's the Pot's pins located In that photo? I know it's near a corner of the board but which one? Upper right, lower left,....?

Here's some DMM test to do.
(1) While unplugged from the mains, measure the resistance from the case and each Pot pin.
(2) Measure the resistance from the Hot blade (smaller blade) of the power plug and each pin of the Pot's switch.

Post your results.

Chris

 

[CDRIVE]

I think I found it! Is it the lower left corner of the board bottom photo? If I'm right I don't think the switch is switching the mains.

Chris

 

[Clambake]

Where's the Pot's pins located In that photo? I know it's near a corner of the board but which one? Upper right, lower left,....?

Here's some DMM test to do.
(1) While unplugged from the mains, measure the resistance from the case and each Pot pin.
(2) Measure the resistance from the Hot blade (smaller blade) of the power plug and each pin of the Pot's switch.

Post your results.

Chris

Yes the lower left group is the Pot

Ok so from the Pot power switch pins to the hot blade I get ~5MOhms for the lower in the photo and ~10MOhms for the upper

For the case to the Pot pins I get no resistance reading and no continuity

Does that make sense?