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Small DC TIG welder remote switch needed

73's de Edd

Aug 21, 2015
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Sir Clambake . . . . . . . . . .


Ahhhhhh Sooooooo, you are now coming forward with the much needed info.

REFERENCE:
3QQgjhF.jpg



That pot assemblies switch connections are the YELLOW CIRCLES, the RED circles were just differentiating from the non significant pot support mounting brackets.

Mamma- san certainly done some SLOPPY soldering on ALL of those joints around that area.

Looking at the GREEN path and my broken trace X in YELLOW, see if your opening of that circuit and using the closing of that circuit path doesn't then accomplish your desired
remote controlling .

Except this time if you have the remote switch closed and adjust the pot for optimum /desired setting, afterwards, the unit should come on as soon as the remote switch is closed.
AS the unit was . . . . that setting would have to be run up and approximated EVERY time you turned the unit ON with that pots adjunct main power switch.
From the minuscule size of that GREEN trace run . . . . . we can see that is being a a minor switching function . . . . .with the REAL POWER switching done elsewhere with a secondaryPOWER device..




If somehow that shuts down more than desired, the second suggested procedure's roadmap is as shown below.
It is effectively running the pot down to its minimum setting every time the YELLOW X path is opened with the remote switching.

Plan II:
2cCM1p8.jpg






73's de Edd




.
 
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Clambake

Mar 8, 2016
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Sir Clambake . . . . . . . . . .


Ahhhhhh Sooooooo, you are now coming forward with the much needed info.

REFERENCE:
3QQgjhF.jpg



That pot assemblies switch connections are the YELLOW CIRCLES, the RED circles were just differentiating from the non significant pot support mounting brackets.

Mamma- san certainly done some SLOPPY soldering on ALL of those joints around that area.

Looking at the GREEN path and my broken trace X in YELLOW, see if your opening of that circuit and using the closing of that circuit path doesn't then accomplish your desired
remote controlling .

Except this time if you have the remote switch closed and adjust the pot for optimum /desired setting, afterwards, the unit should come on as soon as the remote switch is closed.
AS the unit was . . . . that setting would have to be run up and approximated EVERY time you turned the unit ON with that pots adjunct main power switch.
From the minuscule size of that GREEN trace run . . . . . we can see that is being a a minor switching function . . . . .with the REAL POWER switching done elsewhere with a secondaryPOWER device..




If somehow that shuts down more than desired, the second suggested procedure's roadmap is as shown below.
It is effectively running the pot down to its minimum setting every time the YELLOW X path is opened with the remote switching.

Plan II:
2cCM1p8.jpg






73's de Edd




.
Hi Ed -thanks for the input!

Your plan #1 is what I plan to use if I can't find anything better. My problem with it is as you said -it shuts the whole thing down, including the cooling fan.

I like your plan #2, but that sloppy soldering is in fact mine from when I desoldered the pot and tried switching that leg a while ago -my eyes aren't what they used to be -and actually, that real bad looking spot is a flake of board varnish standing up. When I tried switching that leg, the result was the torch was still hot, BUT I do admit I did not notice if it matched what would be the result of turning the pot all the way down or not.

Do you think if I tried plan #2 again but put a resistor in line that would cut the power at the torch to zero?
 
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CDRIVE

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Well I've spent most of my morning coffee time watching youtube inverter welder vids and searching through endless google image schematics until my eyes threatened to bleed.

Here's your next two tests.. Measure the resistance of the two outer terminals of the Pot when at extreme CCW (0) position but just prior to switching it off. Then repeat this at the max CW (80) position.

Conditions: Disconnected from the Mains.

The purpose of this test is to see if the Pot is configured as a Pot or a Rheostat (Variable Resistor). Unfortunately this isn't a conclusive test because it's only valid when the designer commits the wiper to one of the 2 outer (fixed R) terminals. Designs that do commit a fixed pin to the wiper do it to as a safeguard to guarantee at least the fixed (outer terminals) resistance if the wiper ever failed or becomes intermittent. It can also mean that completely breaking the circuit
could cause harm to the circuit but this is not carved in stone.

If you're curious... The functional difference between a Pot and a Rheostat is that unlike a Rheostat a Pot's three terminals form a resistive voltage divider, while a Rheostat doesn't.

Conditions: Connected to the Mains and Powered On.

With the Pot at extreme CCW position (without turning unit off) measure the fixed (outer terminals) voltage. Repeat at extreme CW position.

Be Extremely careful!!! Do not let any part of your body come in contact with the chassis or circuitry!!! Don't let the probes slip and bridge any adjacent traces!!! Don't make SMOKE!!!!!!!

Chris
 

CDRIVE

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I've just read Ed's post and your reply. I would be remiss if I didn't state that your reply pissed me off just a tad. Finding out (NOW!) that you've messed with the Pot before this topic was created is a real A$$ burner!

Also I assume you realize the Pot's mounting ears (as Ed pointed out) have nothing to do with the electrical characteristics of the Pot and that was NOT one of the points that you were measuring during your resistive tests??

I'm going for a long bike ride!
Chris
 

Clambake

Mar 8, 2016
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I've just read Ed's post and your reply. I would be remiss if I didn't state that your reply pissed me off just a tad. Finding out (NOW!) that you've messed with the Pot before this topic was created is a real A$$ burner!

Also I assume you realize the Pot's mounting ears (as Ed pointed out) have nothing to do with the electrical characteristics of the Pot and that was NOT one of the points that you were measuring during your resistive tests??

I'm going for a long bike ride!
Chris

I'm sorry there was a misunderstanding Chris.

Actually I did mention earlier experimentatiin with the Pot back in comment #9, in reply to your idea of breaking the wiper leg -just before your vodka accident.

I will try those two Pot tests you suggested as soon as I can get away from my pesky livelyhood stuff.

Thanks again for your help!
 

73's de Edd

Aug 21, 2015
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Sir Clambake . . . . . . .

Some observations and info that I need feedback from you on, in an eyball observation of board details.
Good job on the photos supplied as that is 'soitanly one densely packed "brick".
I am hereafter assigning them #'s from top left corner to bottom right corner .

As per the mentioned quandry of is it a potentiometer / vs / rheostat utilization of the control pot.

Reference . . . . .using the bottom photo of my #21 post.

Pot Lo foil path:

Looks like the Pot Lo foil path drops down and loops thru the open path of a IK SM resistor and then passes up to catch the emitter of a SM transistor *.
* See if you can get the alphanumeric marking on that unit, as its base seems to flow down and to the right, and then tie into another SM transistor, with
that transistor then interfacing into the IC function to its right.
Then it routes to the right to drop down and catch the emitter of another SM transistor . . . . . .after it passes upwards to that 10K SM resistor , that's where
not having the board in my hand, for close inspection, looses the flow.
IF . . . it somehow is routed around that 10K, it seems to then logically go up and catch two more SM resistors (2.21K and 4.7K ) and then flow UNDER the 3.3K to their
right and end up tieing into the then widened ground ? buss to the right . . . .? OR ?. . . . . .that larger trace might be a LVDC power buss ?
By all means, get the numbering on that flat pack IC partially covered up by the YELLOW wire.
Relating connections being made to its power supply pins will straighten out that prior mentioned buss . . . . .as well as to establish a given ground metering point for later measurements .

Pot Rotor foil path:

Moves to the right to "RED Sharpie marked" junction then to pass down to collector of SM transistor and also, upwards to 10K SM resistor to feed thru via for power.
from other side of the board.

Pot Hi foil path:
Moves up and then slants over to the right to pass thru and between the 10K SM resistor end terminals. It the passes to the right to then be lost under the blob of hot glue.


Sooooooo . . . . . . . the result . . . . . it "reads" as to be used in a potentiometric function.

OBSERVATIONS:



At the very rear of the unit is a cooling fan that cools a massive heat sink, associated with the units SMPS (Switch Mode Power Supply)
AC line input comes in and then passes to what I think will be a sloppy white tin oxide covered 4 terminal Full Wave Bridge rectifier unit, mounted on the bottom of that frontal large aluminum plate .
Its raw DC then passes on for filtering via the massive 1500 +1500 ufd @ 250VDC rated capacitors.
That approx 170 VDC power then passes over the large heat sink with its mounted electronics which then converts that voltage down to a low voltage HIGH current output with that black SMPS power transformer that you see just inward of that boards components side.
I see at least . . .minimally . . . .two hefty power Mosfets mounted to that PCB's bottom.
Get us that flat pack IC's number on the top PCB . . .I'm expecting a SC3842/3/4/5/ series of SMPS controller IC somewhere in that boards cluster of parts.

Here is the units operational info . . . . . . for any Peanut Gallery observers:
http://www.harborfreight.com/80-amp-dc-120-volt-inverter-stick-welder-61749.html

It certainly seems to me that the overload aspect is being detected electronically,rapidly, instead of using any "slow" electro-mechanical Klixon type of thermal sensing .

That overload condition is additionally signified with the lower orange ? LED on the front panel lighting up. . . . . .considering that you could even SEE it for awhile,
if just recently having "welders eyesight".
Bringing up a possible second question, perchance is that Piezo speaker at the rear on the heat sinks top PCB, also sounding off during overload condition?
What I think might be your saving grace would be that BLUE relay at the front of the unit.
I am thinking that the "overload " electronics control is being switched with that relay.
A 24VDC coil that switches on its DPST or DPDT set of contacts .
In that relays inactive condition, with no coil voltage , operation of the welding unit is being normal, if overload sensing detection comes into play, then that relay coil receives
activation voltage, it shuts down power to the electrodes, (with a secondary relay contact engaging some solid state POWER switching device).
Meanwhile, times passage and the fan action gets the SMPS cooled down and sensing circuitry then drops the relay coil voltage, so that the welder unit is then ready to go again.
BTW have you ever caught the fan NOT running, I would sort of expect it to run at all times that the unit is plugged in.

Tracking the solution:


Temporarily solder tack on two hookup wires across the relay coil to travel outside of the housing . . . . in order to be able to take coil voltage measurements . . . . and either "stick" a rod or do some heavy work to get the unit into "overload" condition to see if the relays coil functioning is just as was surmised.

If so, then it looks like activating the relay would accomplish what you wanted, since we know that the fan would have to be operating in that function as well as the SMPS, but having the electrode supply disrupted..

Thassssit . . . . .


73's de Edd


.
 
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Clambake

Mar 8, 2016
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...Looks like the Pot Lo foil path drops down and loops thru the open path of a IK SM resistor and then passes up to catch the emitter of a SM transistor *.
* See if you can get the alphanumeric marking on that unit...

.

Edd

The markings on that unit are T8W54. Luckily I have one of those "appscopes" for my phone or I would never been able to read it.
 
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Clambake

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...Get us that flat pack IC's number on the top PCB . . .I'm expecting aSC3842/3/4/5/ series of SMPS controller IC somewhere in thatboards cluster of parts.



.

Do you mean this guy next to the buzzer?
 

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Clambake

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BTW have you ever caught the fan NOT running, I would sort of expect it to run at all times that the unit is plugged in.


.

The fan only runs with the control pot turned "on" -I suppose it might run on "off" when overheated, but I have never overheated it.
 

CDRIVE

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Ed, when you leave this earth donate your eyes to science. They're amazing! It's either that or I've long forgotten what I used to be able to see. :(

Chris
 

CDRIVE

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I'm sorry there was a misunderstanding Chris.

Actually I did mention earlier experimentatiin with the Pot back in comment #9, in reply to your idea of breaking the wiper leg -just before your vodka accident.

My Apologies! So you did. I guess that Vodka save didn't improve my reading comprehension. :D

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.

Thanks again for your help!

Though I like Ed's approach of tapping into the overload relay coil I think I should mention some points about your previous attempt to break the wiper connection.

Since breaking the wiper connection to the board didn't kill the torch power I can't help but believe that you missed two more tests. These would have been adjusting the Pot to center then shorting the wiper to each fixed terminal one at a time. Then testing the torch for change in arc or none.

In short, if breaking the wiper connection didn't turn off the torch or at least reduce the torch current then it's only logical that the reverse must be true! Get it Watson?

That said, Ed's relay approach would be more orthodox.

Chris
 

Clambake

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These would have been adjusting the Pot to center then shorting the wiper to each fixed terminal one at a time. Then testing the torch for change in arc or none.

Thanks Chris -I'll try that. I like the simplicity of a couple wires and a switch
 

CDRIVE

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Hey Ed, after examining the photo closer I see (what appears to be) a center pin on the Pot switch. Now I'll admit that I've never (in over 58 years) seen an integral SPDT Pot switch. This pin is connected to the Pot wiper. See what the "?" is pointing to.

Chris

upload_2016-3-11_8-8-24.png
 

Clambake

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I see (what appears to be) a center pin on the Pot switch.

Hey Chris -that pad is just a pad. There's no pin or hole for one.

(Edit) There's another blank pad to the left of the pot pin group with a short trace to Pot lo
 

CDRIVE

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Hey Chris -that pad is just a pad. There's no pin or hole for one
Ah, I see but why does it stand proud like that?

Also, have you tried my last posted test yet?

Chris
 

Clambake

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Measure the resistance of the two outer terminals of the Pot when at extreme CCW (0) position but just prior to switching it off. Then repeat this at the max CW (80) position.

I got 5.44 kohm both readings
 

Clambake

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Ah, I see but why does it stand proud like that?

I don'know -maybe it creates an intersection? Maybe those traces undernieth don't meet without it. Maybe it enables an optional configuration. That other blank pad in the board's margin stood proud too until I desoldered it.
 
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CDRIVE

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you missed two more tests. These would have been adjusting the Pot to center then shorting the wiper to each fixed terminal one at a time. Then testing the torch for change in arc or none.

Chris

I meant this test. Make sure the Pot's at mid range. It insures that this test can't pop anything because the opposite fixed un-shorted terminal will always see some resistance between it and the wiper.

Chris
 
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