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View Full Version : spot welder from old microwave really interesting and seems easy too



Alistair Hosie
02-21-2015, 05:14 PM
See some of the things this guy does but the spot welder is a great idea for me.Alistair



https://www.youtube.com/watch?v=vrlvqib94xQ

chrisinestes
02-21-2015, 06:41 PM
I like it... I didn't even know I "needed" a spot welder till now.

Thanks for posting that,
Chris

Willy
02-21-2015, 07:17 PM
Thanks for posting this Alstair, looks interesting. Very good video as well, clear and to the point.
Not easy to put a professional looking video together.
Not only that but clicking on his link (The King of Random (http://www.youtube.com/channel/UC1zZE_kJ8rQHgLTVfobLi_g)) opens up a whole other world of interesting projects to keep me and the nieghborhood kids amused.:)

PStechPaul
02-21-2015, 07:18 PM
I've seen that before, and it looks simple to build and useful. It's better to use DC, but it would require some huge rectifiers to get the 1000-2000 amps that this probably puts put, and two turns on a MOT is probably only 2-4 volts, so a silicon bridge rectifier would drop about half that. But there are advantages to DC:

http://journalamme.org/papers_vol24_1/24143.pdf

alanganes
02-21-2015, 07:37 PM
Most typical spot welders are AC, aren't they?

PStechPaul
02-21-2015, 08:09 PM
They probably are. The $170 Harbor Freight version (http://www.harborfreight.com/welding/spot-welders/120-volt-spot-welder-61205.html) is just a transformer and switch:

http://manuals.harborfreight.com/manuals/61000-61999/61205.pdf

http://www.harborfreight.com/media/catalog/product/cache/1/small_image/135x/9df78eab33525d08d6e5fb8d27136e95/i/m/image_23692.jpg

Some of the larger industrial and professional types use a higher frequency than the mains, in order to make the transformer smaller and lighter. The higher frequency current through the weld might improve quality, but I don't know for sure.

vpt
02-21-2015, 08:28 PM
There is a microwave in the snowbank outside...

gld
02-21-2015, 09:14 PM
I built one several years ago, and it works great. Did not use the timer. Just a foot operated micro switch. Nice thing is you can build the welding tips for what ever your need is.

alanganes
02-21-2015, 09:14 PM
There is a microwave in the snowbank outside...

And the longer it sits there, the more it looks like a spot welder...

Mike Amick
02-21-2015, 09:33 PM
I tried doing that hack .. and had a heck of a time getting the xformer apart. Actually
ruined it trying.

rdfeil
02-21-2015, 10:58 PM
and the longer it sits there, the more it looks like a spot welder...

+1

r

J Tiers
02-21-2015, 11:43 PM
There's a bit more to a spotwelder than it seems.... as the crappy non-welds he got clearly show.

If there was actually a "weld", there should have been no way to break the washers apart. There should have been a "nugget" of melted-together metal at the weld, fusing the washers so that they would have to be broken through to separate any part of one from the next.

Now, the washers appeared to be zinc plated, which would affect the weld somewhat, but I think there should still have been an actual weld, which there evidently was not.

With a decent spotwelder, such as even the HF 120V unit, you can easily spot-weld steel together in a virtually unbreakable bond. The process only slightly resembles that "science project toy". It takes under a second, usually.

I have even done spot welds in 0.030 aluminum using an HF 120V welder, on a low volume production basis. That was to do 8 welds per each aluminum cover for a custom VFD supplied to the Navy. We worked out the tong pressure, and the timing, used a time-delay relay to set the pulse length, and did quite well with it. Every "X" number of welds, we did a coupon and checked to verify the way it broke when pulled apart.

That "gizmo" might weld something, but not much.

JRouche
02-22-2015, 12:10 AM
Thanks Alistair. I like some of his other vids also. He didnt show how he modified the transformer. Like how to split it to remove the secondary and install the new secondary. But I like the fast paced wordage he uses, prolly post added.

Umm re: the HF spot welders?? I have one, the 220vac unit. I did a review of it and posted my opinion here, was a few years ago. Its a great welder, specially for the money. And like Jerry said, it should not be-able to be broken, the weld. With mine the base metal rips before the weld comes apart.

I dont think a lack of power was the issue with his washers, the unit obviously has the ummph to melt the washers. I think the zinc coating caused the "adhesion" issues. He clearly shows the transformer has the ability to completely melt the washers if need be.

I like this guys post editing of his vids. Not alot of dead time. Im subscribed :) JR

Found my review of the HF welder if interested ---> http://bbs.homeshopmachinist.net/threads/13691

macona
02-22-2015, 02:51 AM
The only DC spot welders are capacitive discharge. I use one to weld the filaments for my SEM.

https://farm8.staticflickr.com/7527/15656903079_d023597e29_b.jpg (https://flic.kr/p/pRxHNP)Capacitive discharge spot welder (https://flic.kr/p/pRxHNP) by macona (https://www.flickr.com/people/67292116@N00/), on Flickr

darryl
02-22-2015, 03:50 AM
Regarding the transformers- no need to take them apart. The secondary is physically separated from the primary, and can just be cut apart and knocked out. Knock the shunts out also, then thread the welding wire through. It's only two turns or so.

Willy
02-22-2015, 04:37 AM
I think one has to keep things in perspective here. This is not a high tech spot welder, hell it isn't even a low tech spot welder. What it is, is a no-buck spot welder capable for clean light guage sheet metal at best, not cadmium plated .0625 washers.
As professional as I thought he did in the production of this video, I was amazed that he chose this material as his demonstration coupon. Two pieces of clean 24 ga. sheet metal would have made his project look so much more credible.

However I believe the whole idea of this little project goes much further than building a tool one would use in an industrial environment on a daily basis, than it does as a project to stimulate the mind into using one's imagination discovering possibilities.
I still like his concept and the message he conveys, as I think most here will as well.

macona
02-22-2015, 05:12 AM
Here is a old site that shows a MOT spot welder:

http://www.5bears.com/welder.htm

J Tiers
02-22-2015, 11:02 AM
The HF spotwelds zinc plated material together perfectly well. I've done it. (Stayed out of the smoke, though). And that was the 120V version.

Automakers do it all the time. Auto sheet metal is commonly electro-galvanized these days.

Point was NOT that the M.O.T. version could never work.....

Point is more that with clipped-off ends on the skinny tip wires, nonexistent tong pressure, marginal current (due to other conditions), etc, you do not get a good weld. He got the washers hot, but it took quite a while, probably a count of 2 or 3 before it got to full temp.

With the HF, we were using a timed pulse of 0.4 sec, and getting a good weld in aluminum. Steel is 12x easier. It's much harder to FAIL with steel, compared with aluminum, and it does not take as long with the pulse.

The spotwelder as a concept is fine, the problem is with all the details that affect how much current you actually get, etc. With the low voltages, what might be considered a tiny and "insignificant" resistance in the joint means you don't weld properly.

With the cut-off ends of wire, just left as-is, it purely, plainly, isn't gonna happen. There is a reason why spotwelders are made the way they are. And why you have to dress the tips off right, etc, etc.

https://www.millerwelds.com/pdf/Resistance.pdf

chipmaker4130
02-22-2015, 11:23 AM
If you guys look past the 'defects', you might realize that the vid-maker never intended this to be a great working machine. He's trying to show what one can do with junk! He's trying to inspire people to be creative, and think and dream. Look at some of his other videos. He's selling enthusiasm and creativity.

Luke55
02-22-2015, 11:34 AM
I built one couple years ago. It work pretty well on 22 ga an over. Only problem I had is to keep electrodes alignment. For the price it is good

MaxHeadRoom
02-22-2015, 11:51 AM
A couple of possible enhancements to bring it more in line with a commercial unit would be water cooled tips, and a timer and a phase angle controlled pulse(s) on the primary in the form of Triac or two SCR's back to back.
Also higher pressure at the tip points.
If doing any kind of small production oriented or repetitive work these are essential.
Max.

vpt
02-22-2015, 12:55 PM
And the longer it sits there, the more it looks like a spot welder...



It is all stainless so it look nice sitting there in the snow. My kids use it as a hiding spot for "things".

J Tiers
02-22-2015, 03:55 PM
If you guys look past the 'defects', you might realize that the vid-maker never intended this to be a great working machine. He's trying to show what one can do with junk! He's trying to inspire people to be creative, and think and dream. Look at some of his other videos. He's selling enthusiasm and creativity.

Well that's fine.

Now let's see the next one.... "Making the cheap spotwelder actually work".

Creativity is fine. but at some point you either put aside the "proof of concept" item, OR you make it work. Paper airplanes are creative... the number of times they are actually USEFUL is very low.

It's basically a toy... a dangerous one, but still a toy. Looks kinda like a real one, kinda acts like a real one, but doesn't really work like a real one. Realize that, and there isn't any problem.

kf2qd
02-22-2015, 09:02 PM
Wonderful attitude. +1 for you.

If someone presents an idea, even one needing refinement he is a fool and wasting his time. Meanwhile others have suggested refinements and such that might be beneficial.

The anal retentive type of responses don't encourage others to try, because they just know they will be called useless and stupid and a waste of oxygen. Have you EVER presented any ideas on building a device that might be able to do this? It is easy to make sure that everyone knows how stupid you think they are, but such responses rarely encourage anything other than going back to hide under a rock.

J Tiers
02-22-2015, 09:48 PM
Wonderful attitude. +1 for you.

If someone presents an idea, even one needing refinement he is a fool and wasting his time. Meanwhile others have suggested refinements and such that might be beneficial.

The anal retentive type of responses don't encourage others to try, because they just know they will be called useless and stupid and a waste of oxygen. Have you EVER presented any ideas on building a device that might be able to do this? It is easy to make sure that everyone knows how stupid you think they are, but such responses rarely encourage anything other than going back to hide under a rock.

Well isn't THAT an intelligent response.......

It's a fine "proof of concept" device, AND I SAID THAT.

The only one of us who has used the word "fool" up to this sentence is YOU, "kf2qd".

If you want to call it a "spotwelder", then there is some more work to do. So far, he has not demonstrated it actually welding..... it stuck some washers together, and they broke apart...which wouldn't happen if they were *welded*. And the reason for that is the things that he did NOT do. As well as trying to use too thick a material for the machine to weld.

If you leave it at the "demonstration electric motor" stage, that's fine.... so long as you realize it is just a demonstration. As a demonstration, it's fine. And IF I had to spotweld some things in a situation where I had nothing to work with, I'd probably make something very much like that.. but I'd have to get it to actually WORK, which seems to be where he left off. Which, again, is fine for a demonstration device.

It might actually weld reasonably, IF it had dressed tips, and if he used thinner workpiece material. There was mention of 800A, which I don't know is true... but is possible. That's a bit light for the thick washers he used as a demo. It would probably do some welding at 22ga.

The problem is NOT with the youtube guy, but with others calling it a "spotwelder" (meaning general purpose), and perhaps thinking they can make one for the shop just like it.

The thing that works will LOOK like that, but it won't BE that.

daveo
02-22-2015, 10:16 PM
Tag, to read all of the bickering later....

vpt
02-23-2015, 07:55 AM
I didn't watch his other video of the apparent "making of" the power source. But I did notice in his video that he had the "leads" only wrapped around the "power source" magnet only one time?

John Stevenson
02-23-2015, 08:28 AM
There is a microwave in the snowbank outside...

Can't be any good or it would have melted the snow.......................

J Tiers
02-23-2015, 08:28 AM
I didn't watch his other video of the apparent "making of" the power source. But I did notice in his video that he had the "leads" only wrapped around the "power source" magnet only one time?

Nope, he has two turns on it. Which is probably good, it takes some voltage to produce the currents needed, and any transformer has a certain "volts per turn" depending essentially on the core size.

The MOT has another advantage over the standard transformer in a spotwelder, which the HF is typical of.....

Most commercial portable spotwelders have a transformer that is long, forming the long portion of the case behind the tongs. They stack up a long length of laminations. The "stack" of laminations may be 2 or more times the width or height of an individual lamination. A normal transformer would use a "stack" generally no more than about equal to the smallest outside dimension of a single lamination (it's usually based on the center leg size).

This does get a lot of core area (more volts per turn) into a shape that suits the mechanical needs of the application. With lots of core area, you can use fewer turns on the primary, of heavier wire, and you may need only one large "turn" of wire for the secondary. With only one turn needed, you can use all the remaining area to put in large wire, for low resistance and maximum current capability.

But the problem is that the long transformer uses a long length of wire per turn, so the resistance is larger. With only a small voltage to drive it, and wanting well over 1000 amps, you can't have much resistance. At some point the thing becomes self-limiting, and you have to go to a larger dimension of core lamination, so the case gets larger.

With the MOT, the length per turn is short, so more effective use is made of the wire composing the turns. You can use the shortest length of wire possible for the power capability of the transformer. Of course, the long wires coming FROM the transformer eat up some of that.... In the standard 'caterpillar-shaped" transformer, all that wire up to the tongs is used in the transformer, and it is contributing to output. It's a trade-off.

He could stack two MOTs, with one turn through each, and get two effective turns, of wire double the size (or two parallel wires the same size). With the primarys parallelled, he could get more output.

Lew Hartswick
02-23-2015, 09:09 AM
Nobody has commented on his woodworking ability. I thought he did a pretty good job on that part of the construction. :-)
...lew...

CCWKen
02-23-2015, 05:34 PM
Well, now I'm waiting for someone to go out and buy a HF spot welder and turn it into a microwave oven. :)

By the way, I have two of the HF 240v spot welders and couldn't make it through the week without them.