DIY Spot welder

[oddbob]

My cheapenese spot welder has died on me ...my own fault, think I cooked it.

I've seen those 'build your own' vids on Youtube using a rewound microwave transformer, but can't see how such a tiny thing could be up to the job.

I do have an old 160amp buzz box and am wondering if i could use that ...rewind the secondary to achieve around five volts, re-use the arms and clamping mechanism from my old machine. Anyone done anything like it? ...or any thoughts?

 

[rikrobson]

you can get spot weld guns for arc welders. it holds a carbon electrode, but it doesnt squeeze the parts together.

The current on a buzz box should be ok. I dont see why you'll need to drop the voltage though. They are stray field transformers and are adjusted with an iron core being wound in and out, hence the knob on the front.
it will be a pita to rewire i expect.

if you make a pair of jaws or reuse the old ones and add a timer, that should work.

 

[The_Yellow_Ardvark]

The dead spot welder may have a thermal fuse in it. Or the Xforner may have a fusible link.
have a nosy round inside with a multi meter.

 

[The_Yellow_Ardvark]

I did the U tube thing and built a "Spot welder" or "metal melter" from a dead microwave.
It worked, it was a learning experience.
But for practical use, nope.
go buy one.

 

[Jim Davey]

They work. But really you need a much bigger transformer to cope with repeated spots or thicker material, say 2+2mm.
There is a reason the transformer in a 25kva spotwelder is the size of a football.
Before you say it, 25kva sounds a lot, but it's not for a spotwelder.

 

[oddbob]

They work. But really you need a much bigger transformer to cope with repeated spots or thicker material, say 2+2mm.

That's why I was thinking about trying the buzz box transformer. The thickest material I need it to work on is only 1mm, or maybe just over.

The dead spot welder may have a thermal fuse in it. Or the Xforner may have a fusible link.
have a nosy round inside with a multi meter.

Sadly no internal fuse ...it's a pretty basic bit of kit. Looks like a copy of the Miller LMSW-52.

 

[The_Yellow_Ardvark]

@oddbob
The thermal fuse does not look like a normal fuse, the ****** ones also never show fused links, thermal fuses on wiring diagrams.

A Few examples.

 

[WorkshopChris]

With a spot welder you will be looking in the region of a 2000a requirement, depending on electrode diameter and material thickness.
I have worked with big spot welders on production lines, we have a big national grid substation for part of the southeast locally.
You could watch the pulse on an oscilloscope directly at the substation, and that was with a hv supply right into the switch room.

 

[oddbob]

Bit of an update.





Buzz box was a 160amp Silverline jobbie, that I bought years ago to get get me by for a while, and only used once, so as new really. The stand I had made for the old machine some time ago, but it needed serious modifying so that I could hang the buzz box off the back (if I'd been starting from scratch I'd have made it much simpler!).

I rewound the secondary with two turns of 95mm2 flexible cable (600 odd strand copper) which gives me a little over 2 volts, and fitted a 20amp microswitch to trigger the primary. Alas, aluminium winding on the primary, but the wire is at least three times the thickness of that of my dead spotwelder (which was also aluminium). I took the sliding shunt completely out as it still reduced the output even with it wound as far out as it would go ...bit of a shame I couldn't leave it as I liked the idea of being able to drop the output for spotting wire and the like. Removing it made an enormous difference though. The old spotwelder struggled with much over 1.2mm+1.2mm, this manages 2mm+2mm with no problem. I'll have to get hold of a clamp meter and see exactly how many amps it pushes out.

It could do with some heavier arms and electrodes, which I will sort sometime. I may even get round to fitting a timer.

 

[Jim Davey]

You'll struggle to get a reading on the average clamp meter, very high current is beyond the 1000 amps most clamps show, and it's over and done with before most meters show a reading.
You might be able to work it out using ohms law, but you'd need to know the exact resistances in the circuit.
Nice setup though, I like a well thought out self build.

 

[arther dailey]

the largest spot welder I rewound (back in the day) had solid copper secondaries, about an inch thick,bored for water cooling, primary was wound flat copper maybe an inch wide about 3/32 thick.

 

[Robotstar5]

You'll struggle to get a reading on the average clamp meter, very high current is beyond the 1000 amps most clamps show, and it's over and done with before most meters show a reading.

The weld techs at Longbridge had purpose built meters with a strap that wrapped round the electrode arms, it captured current, cycle times, pulses etc.

 

[oddbob]

You'll struggle to get a reading on the average clamp meter, very high current is beyond the 1000 amps most clamps show, and it's over and done with before most meters show a reading.

Glad you said that ...I was about to buy one. Better get Googlin' ohms law.

 

[WorkshopChris]

I rewound the secondary with two turns of 95mm2 flexible cable (600 odd strand copper) which gives me a little over 2 volts,

Have you any problems with the cables moving or repelling each other under load?

EDIT:- link with reference to low resistance testing.
http://www.testequipmentdepot.com/megger/pdf/low-resistance-testing.pdf

 

[oddbob]

Have you any problems with the cables moving or repelling each other under load?

Luckily the cable is very tight in the available space (it's around 20mm diameter), so no sign of it moving. Getting it wound in there wasn't these easiest thing I've ever done. If I'd had to up the voltage I'd have been st*ffed!

 

[Robotstar5]

Have you any problems with the cables moving or repelling each other under load?

The cables used to jump about on our spot welding machines, for the hand operated welders we used a "kickless cable" to feed the gun, the supply and return cores were spiral wrapped inside a water cooled cover.

I recently found some pictures I took inside the BIW (body in white) building at Longbridge, this one's a spot welding transfer line which assembled the floor and front end, welding sparks visible in the middle

This machine cost 7.5 million in 1979 and there were 2 identical ones.

 

[chris y]

Bit of an update.

View attachment 93751

View attachment 93752

Buzz box was a 160amp Silverline jobbie, that I bought years ago to get get me by for a while, and only used once, so as new really. The stand I had made for the old machine some time ago, but it needed serious modifying so that I could hang the buzz box off the back (if I'd been starting from scratch I'd have made it much simpler!).

I rewound the secondary with two turns of 95mm2 flexible cable (600 odd strand copper) which gives me a little over 2 volts, and fitted a 20amp microswitch to trigger the primary. Alas, aluminium winding on the primary, but the wire is at least three times the thickness of that of my dead spotwelder (which was also aluminium). I took the sliding shunt completely out as it still reduced the output even with it wound as far out as it would go ...bit of a shame I couldn't leave it as I liked the idea of being able to drop the output for spotting wire and the like. Removing it made an enormous difference though. The old spotwelder struggled with much over 1.2mm+1.2mm, this manages 2mm+2mm with no problem. I'll have to get hold of a clamp meter and see exactly how many amps it pushes out.

It could do with some heavier arms and electrodes, which I will sort sometime. I may even get round to fitting a timer.

That's great. Do you have any more pics, especially what you did inside the boxes.

 

[oddbob]

That's great. Do you have any more pics, especially what you did inside the boxes.

'Fraid I don't. To be honest there's not much to see inside. The only major changes are the rewinding of the secondary and removal of the sliding shunt. The box on the top is purely to attach the arms and clamping mechanism to and has nothing in it except an extra axial fan in attempt to keep it all as cool as possible. If I hadn't been reusing my old stand I would probably have attached the arms to the front of the buzz box in some way. It's a very simple mod/build really, and would still be so even if you didn't have an old spot welder to cannibalise. I've definitely ended up with a machine at least comparable to the one that I originally trashed ...and probably better!

 

[mikejack]

that looks spot on ! (sorry)