Thoughts on this used welder?

[joshuabardwell]

I don't have the diagnostic tools or knowledge to design the choke/capacitor circuit that would be needed for this. I should be more specific - is such a DC converter available as a completed external 'black box'?

Ahh. Well, I have never heard of such a thing. A little Googling turned this up, though:

http://www.tractorbynet.com/forums/b...lder-into.html

All roads lead back to TBN!

EDIT: And here's the thing you're looking for. http://www.proto-power.com/dc_cheater.html

[CNC Dan]

Seems like there are welding theory gurus lurking in this thread. ...
Would there be a simple way to put an external rectifier/choke/capacitor module in the ground lead of Harbor Freight's AC flux welders to convert to DC and make them weld better?

I'll start a new thread if this is worth discussing.

Yes, it can be done. You can get ready made bridge diode modules that are big enough, or you can make one up yourself. The choke can be wound from extra welding cable. The right amount will have to be found by trial, as you can have too much with a wire feed welder.
Not sure about the capacitor value.

But while it will make improvments to the HF welder, it's still a crap HF welder.

[CNC Dan]

https://www.galco.com/shop/70HF-Vish...ecovery-Diodes
which part of the diode is the "stud"? Is it the threaded post or is it the little tab that the wire lead gets welded to?

Threaded post is stud.
If your diodes are all the same, you could replace them with the other kind. The pos. neg. output would be backwards, and you would have to reverse the capacitor(it should have a + or - on one end).
Look on the diode for the diode symbol. It looks like an arrow against a bar. I forget witch end is the cathode. You should be able too look it up.

[CNC Dan]

http://weldingweb.com/showthread.php?t=41926

Just found this. Looks like they found a good source for diodes.

[k0ua]

https://www.galco.com/shop/70HF-Vish...ecovery-Diodes

I have found what appear to be replacement diodes for my welder. One question: when they refer to "stud cathode" or "stud anode," which part of the diode is the "stud"? Is it the threaded post or is it the little tab that the wire lead gets welded to?

I have read that you can find the anode and the cathode of a diode by seeing which way the meter shows open vs. short. Only problem is that, according to the site I read, not all meters put out their test current on the red lead, and you can't know for sure unless you have two multimeters and test one with the other (which, currently, I don't). So if I was to take a 12 volt battery and a light bulb and put it across the diode, would I be correct that, when the light bulb lit up, the positive lead is touching the anode?

Apply a positive voltage to the anode and hook one lead of the lamp to the cathode. Now hook the other lead of the lamp to the negative side of the battery. the lamp should light, you have conduction and current flow. IF you hook a positive voltage to the cathode and your lamp to the anode and the other lead of the lamp back to the negative voltage your lamp will not light, you will have no current flow. I believe the stud refers to the bolt portion of that type of diode. you would put it through a heatsink and screw a nut onto the bolt "stud"

James K0UA

James K0UA

[joshuabardwell]

Just found this. Looks like they found a good source for diodes.

Yup. I have seen that very thread. And, at least on the inside, that looks to be the exact same welder that I have. Looks like it has been sold with many a different face plate over the years.

Threaded post is stud. Look on the diode for the diode symbol.

Silly me. I thought that symbol was just indicating that this was a diode. Didn't occur to me that it would also indicate directionality, although I suppose that's obvious now that I think about it. If you had a mixed pile of diodes, you wouldn't want to have to pull your meter out every time to confirm their polarity.



In fact, here's a photo from that same thread showing the diode symbol in between the I and the R on the side of the diode. It seems to be indicating that the stud is the cathode.

It looks like replacing all the diodes is going to run me somewhere on the order of $40 plus shipping. If that fixes it, I will be in for under $200 on this welder, and still consider myself to have done all right, price-wise. And what price the knowledge all this troubleshooting has brought? Priceless!

[joshuabardwell]

Apply a positive voltage to the anode and hook one lead of the lamp to the cathode. Now hook the other lead of the lamp to the negative side of the battery. the lamp should light, you have conduction and current flow.

I think you are agreeing with what I said earlier, with a whole lot of different words. When the positive lead of the battery goes to the anode, the bulb lights. When the positive lead of the battery goes to the cathode, no current flows. Right?

[California]

Yes, it can be done. ... But while it will make improvements to the HF welder, it's still a crap HF welder.

I looked at the thread you referenced; now I realize a varistor is needed to protect the diodes (and probably the welder's internal control boards) from spikes, in addition to buying / mounting the diode bridge and making a LC filter. And adding a fan, which my earlier model HF 90A welder doesn't have.

It looks like stepping up from this $74 welder to a better welder is the more practical solution.

Thanks!

[k0ua]

I think you are agreeing with what I said earlier, with a whole lot of different words. When the positive lead of the battery goes to the anode, the bulb lights. When the positive lead of the battery goes to the cathode, no current flows. Right?

Correct.

James K0UA

[CNC Dan]

I looked at the thread you referenced; now I realize a varistor is needed to protect the diodes (and probably the welder's internal control boards) from spikes, in addition to buying / mounting the diode bridge and making a LC filter. And adding a fan, which my earlier model HF 90A welder doesn't have.

A capacitor will do a lot to absorb spikes, but a varistor in addition will likely be needed if there is any real electronics involved.