Thoughts on this used welder?

[CNC Dan]

Its un-filtered DC. If you were to use an osiloscope(sp?) to view the waveform it would look like cursive 'm's all strung together.
Think of the usual AC sine wave, but flip the lower parts up to the upper half.

The AC that you are measuring is the ripple of the preaks and valeys.

 

[joshuabardwell]

Its un-filtered DC. If you were to use an osiloscope(sp?) to view the waveform it would look like cursive 'm's all strung together. Think of the usual AC sine wave, but flip the lower parts up to the upper half. The AC that you are measuring is the ripple of the preaks and valeys.

Interesting. So the AC component can be ignored then? What about the fact that the DC voltage drops with the bulb in circuit on DC, but not on AC?

 

[joshuabardwell]

Also: I thought the whole point of DC welding was that the voltage didn't pass through zero 60 times a second. But the image above shows the rectified DC hitting zero just as often as AC--just not ever going negative.

 

[CNC Dan]

Also: I thought the whole point of DC welding was that the voltage didn't pass through zero 60 times a second. But the image above shows the rectified DC hitting zero just as often as AC--just not ever going negative.

Thats unloaded output. Put a heavy load on it and the inductance of the choke (coil) will keep the Current going. Kinda works like flywheel.

Plus, the Voltage waveform and the Current waveform won't be in sync.

Isn't AC fun? You should see all the math that goes with it.

 

[CNC Dan]

Interesting. So the AC component can be ignored then? What about the fact that the DC voltage drops with the bulb in circuit on DC, but not on AC?

That's what happens with an un-filtered, un-regulated supply.

The meter is reading the peaks of the un-filtered DC. But those peaks are narrow so they can't provide much current. Under load, they flatten out.

 

[joshuabardwell]

Thats unloaded output. Put a heavy load on it and the inductance of the choke (coil) will keep the Current going. Kinda works like flywheel.

Fascinating.

That's what happens with an un-filtered, un-regulated supply. The meter is reading the peaks of the un-filtered DC. But those peaks are narrow so they can't provide much current. Under load, they flatten out.

I'm confused though. The welder ought to be able to provide up to its rated 140 amps when welding, right? Does that not count as "under load"? Maybe not, since welding basically creates a short between the rod and the work piece.

Sounds like you're saying nothing is very anomalous about my readings. Yes?

 

[CNC Dan]

Fascinating.

I'm confused though. The welder ought to be able to provide up to its rated 140 amps when welding, right? Does that not count as "under load"? Maybe not, since welding basically creates a short between the rod and the work piece.

Sounds like you're saying nothing is very anomalous about my readings. Yes?

You are right, it should be able to provide rated amps, but not at the OCV. Usualy they are rated at 25 volts.

Can't figure whats going on with the super low volts at startup though.

Check all the connections on the DC side of the diodes. I still think something simple is out of whack.

 

[joshuabardwell]

Can't figure whats going on with the super low volts at startup though.

Just to reiterate, the super-low volts are the AC volts, not DC. As far as I can tell, we have concluded that the AC voltage is just the result of the non-regulated rectified DC, and so it is not a problem or worthy of further investigation.

If the welder is rated at 25 volts, then I believe everything is nominal, since it drops to 27 volts with the bulb in circuit. What it seems we are shaping up to is that voltage is correct and the diodes test out good, but something in the circuitry is preventing delivery of full amps when welding. Someone made a suggestion to stick a rod on max output for ten seconds, then un-plug the welder (for safety) and look for a spot inside the welder that is hot. I think that may be the next step.

 

[CNC Dan]

Someone made a suggestion to stick a rod on max output for ten seconds, then un-plug the welder (for safety) and look for a spot inside the welder that is hot. I think that may be the next step.

I've done that on cars that wouldn't start due to a bad connection.
Have the welder all opened up so you can get to all the suspect connections quickly.

 

[joshuabardwell]

Well, I made something useful today!



I had some hooks from some ratchet straps that had to be retired, so I put some screw threads on them so they could screw into the wall and hang tools from and such.

Don't bother critiquing the welds. They are total crap and I know it. But I twisted and pulled on them and they didn't wiggle, so I think they'll do.

BTW: AC 1/8" E6011 at about 120-130 amps.