Resistance-No Resistance wire welder

[Mad Scientist]

Thicker, or most conductive (iirc)

If the electron bombardment theory holds, it would be the thicker regardless of the resistance. The pole the resistance is on won't effect the electron bombardment heating at the arc. Current flow through the resistance wire i.e. joule heating will be effected by resistance of course. The proposition here is that is not the controlling factor for the weld. I guess that would be the experiment to find out.

 

[awsum140]

It figures, if anything, I always do things backwards. I've been welding with the thicker wire, 30ga, in the negative electrode and the thinner, resistance wire, in the positive electrode. I was having a lot of failures the other way around. There are still failures, but not as many. Now I've got to revert back and see what happens.

 

[Mad Scientist]

It figures, if anything, I always do things backwards. I've been welding with the thicker wire, 30ga, in the negative electrode and the thinner, resistance wire, in the positive electrode. I was having a lot of failures the other way around. There are still failures, but not as many. Now I've got to revert back and see what happens.

Interesting. Next time you weld some let us know what you observe.

Here's a thermocouple welder in operation. Thermocouple Welders and Data Logging Equipment by DCC Corporation

 

[yo han]

OK 1 more modification;
By using a 3PDT switch the caps always bleed down R2 when set to measuring mode.
Not sure if it's of any use but it won't hurt either

 

[awsum140]

As I see that, none actually bleed down and the negative side of C1 is above ground through R@. I'm not having a very good day, so don't take my word on this one!

 

[yo han]

But switching S5 to the resistance meter will do the same as pressing S2...

 

[Mad Scientist]

OK 1 more modification;
By using a 3PDT switch the caps always bleed down R2 when set to measuring mode.
Not sure if it's of any use but it won't hurt either

You're very close. The way you have it set up now, C1 will fire current limited by R2. Ground the negative side of C1 same as C2 and C3 and place the "discharge" pole of your 3 pole switch in parallel across your discharge switch -- one way to do it.

 

[yo han]

I don't get it. As I see it, the discharge pole of S5 is already the same as S2...
S2 is meant to bleed the caps right? S5 is doing the same now when switched to that position.

 

[awsum140]

I think you need to move the connection now showing at the junction of S2 and R2 off of the negative lead of C1 and run the negative lead of C1 to ground. Again, I'm having a bad day and have a splitting headache, but that should fix it up fine.

 

[yo han]

Gosh, my lack of knowledge really kicks in. My previous circuit was exactly the same and was OK.
Now all I've done is add a switch in parallel with S2 and it's not right anymore. Sorry guys, I'm trying to learn but can't see the logic.

 

[Mad Scientist]

I don't get it. As I see it, the discharge pole of S5 is already the same as S2...
S2 is meant to bleed the caps right? S5 is doing the same now when switched to that position.

The way it is drawn, the discharge pole of S5 is a dead short across C1 when closed; C2 and C3 will bleed through R2. When open, the return path of C1 is through R2 when you "fire" it to weld your wires, which will limit current from C1 and likely fry R2. Do exactly what awsum140 suggested.

 

[yo han]

OK but wasn't S2 a dead short in awsum's orignal drawing as well?

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[Mad Scientist]

Gosh, my lack of knowledge really kicks in. My previous circuit was exactly the same and was OK.
Now all I've done is add a switch in parallel with S2 and it's not right anymore. Sorry guys, I'm trying to learn but can't see the logic.

The previous circuit had the same flaw with C1 using R2 in its ground return path. I didn't look at it closely enough to notice -- I thought you had something else in mind and didn't analyze that section carefully. For logic, think about why you drew it with the negative side of C1 different from C2 and C3. There is no reason for a difference and the negative side of C1 should return directly to ground, same as C2 and C3. Your discharge switch should just pull the positive sides of the caps to ground through R2. There is no reason to involve the negative side of C1 there.

 

[Mad Scientist]

OK but wasn't S2 a dead short in awsum's orignal drawing as well?

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Yes, but he is using C1 as a filter for the DC input which, in the circuit as drawn, has no purpose (my assumption is C1 in this drawing is a small value cap). For some types of DC to DC converters, a cap on its output helps to prevent the supply from oscillating, although the resistor R2 turns it into more of a low pass filter than a bypass cap. Any higher frequency oscillating component in the DC input will pass through the cap and R2 to ground. Either way it has no useful purpose because it is not in the circuit when not in the "charge" mode. My guess is it was copied from a circuit that needed it or it's just a mistake.

 

[yo han]

Ah ok, thanks. Will update my drawing once more tomorrow and hopefully it will be ok then

 

[awsum140]

A picture is worth a thousand words. Yo Han, pardon my butchery of your schematic, but try this -


Incidentally, C1 in the original drawing is a suppressor cap to mitigate sparks on the discharge switch. In my case, a filter capacitor isn't needed on the output of the bridge, but with the LM2577 it's probably a good idea.

 

[yo han]

Yes, that's what I had in mind from what you were saying. Like I said, I'll update tomorrow.
Thanks again for all the help!

Again, I'm having a bad day and have a splitting headache....

Get well soon buddy. Hope you're feeling better tomorrow.

 

[Mad Scientist]

A picture is worth a thousand words. Yo Han, pardon my butchery of your schematic, but try this -


Incidentally, C1 in the original drawing is a suppressor cap to mitigate sparks on the discharge switch. In my case, a filter capacitor isn't needed on the output of the bridge, but with the LM2577 it's probably a good idea.

It won't mitigate a spark on close and with the main caps discharged, there is no potential to be mitigated when it opens. Do you close and open it with the main caps still charged to "tap" down the charge on the main caps?

 

[yo han]

Yes, that's the idea behind S2.
By the way, I'm going to use a 12V wall wart. How much mA does it need to be?

 

[Strangebrew]

Not welding wire any longer... going to give away