Author Topic: Microwave owen transformer spot welder?  (Read 13614 times)

Offline BillTodd

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Re: Microwave owen transformer spot welder?
« Reply #25 on: November 22, 2015, 04:18:00 AM »
stop over thinking it!    :hammer:

just stick with a 20A mechanical relay and stop worrying . it operates for a second or two then stops that's all!

if you want complication, add a temperature sensor and disable the thing until cool enough to restart.

Bill

Offline Fergus OMore

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Re: Microwave owen transformer spot welder?
« Reply #26 on: November 22, 2015, 04:53:58 AM »
stop over thinking it!    :hammer:

just stick with a 20A mechanical relay and stop worrying . it operates for a second or two then stops that's all!

if you want complication, add a temperature sensor and disable the thing until cool enough to restart.

I can pretty well agree.  Frankly, adequate arc welders at a give away price are available to replace the complexities of cannibalising a piece of old scrap.  As far as the spot welder is concerned, it can be a single side machine which is no more than a pressure loaded carbon arc rod tied to the arc set. Again, a couple of carbon arcs  makes what was called Limelight by Charlie Chaplin. No, it isn't a joke it is a practical  way of brazing if you have to go cheeseparing for one reason or another.

To answer the obvious question, I've done it, written about it, it was seemingly ignored and -who knows- ignored yet again.

Ah well,


Norman

 

Offline John Rudd

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Re: Microwave owen transformer spot welder?
« Reply #27 on: November 22, 2015, 05:09:31 AM »
stop over thinking it!    :hammer:

just stick with a 20A mechanical relay and stop worrying . it operates for a second or two then stops that's all!

if you want complication, add a temperature sensor and disable the thing until cool enough to restart.

Exactly,
I have an Italian Cebora unit. It is completely manual in use, plug in, place over job and squeeze the handles.....job done...

In complete contrast, when serving my apprenticeship, we had to make a tool box, the spot welder we used was bench mounted with an integral timer.....took the guesswork out of holding the handles together for too long or not long enough.... :zap:
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Offline PekkaNF

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Re: Microwave owen transformer spot welder?
« Reply #28 on: November 22, 2015, 05:11:12 AM »
stop over thinking it!    :hammer:

just stick with a 20A mechanical relay and stop worrying . it operates for a second or two then stops that's all!

if you want complication, add a temperature sensor and disable the thing until cool enough to restart.

I propably forget to mention that I have 90C bimetal switch that I was thinking of putting there for overheating....

I have been a bit sick last three days and haven't rush with a mechanical construction. Partly also, because I'm waiting 18 mm dia 500m long pure copper rod (eyeball figure).

Idle mind had some time to play with the control part. I agree that it would be easy to manually weld with a proper welder about 2/3 to 2 sec welds, but this small welder will be reserved for a) study and b) very thin stainless steel (and other foils/wires) and friend of mine has a bandsaw welding aparatus refurbished by my old very small welding transformer that welds well, but it is pretty hard to control annealing, therefore a control circuit would be higly desirable.

Spot welder it will be, but following test hast be done outside of the living room warmth. Direct orders from ministry of the deomestic affairs. She was not amused of test to saturate the core and current measurement of simulated spot welding. Women!

Pekka

Offline awemawson

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Re: Microwave owen transformer spot welder?
« Reply #29 on: November 22, 2015, 05:59:46 AM »
Pekka,

I don't think you need to 'over think' the design. Just make sure that your solid state relay is well over specified. At the end of the day SSR's are cheap as chips - if you fry one it's not the end of the world. Just replace it with a bigger one :)
Andrew Mawson
East Sussex

Offline BillTodd

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Re: Microwave owen transformer spot welder?
« Reply #30 on: November 22, 2015, 07:54:03 AM »
Just in case you haven't already seen this:

BTW his spotwelder is very powerful so his timings are in cycles (20mS - I guess)

https://www.youtube.com/watch?v=82Iil0fFN9Y
Bill

Offline PekkaNF

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Re: Microwave owen transformer spot welder?
« Reply #31 on: November 22, 2015, 01:15:01 PM »
Thanks, I saw it. His unit is pretty ideal to him, 15KVA I think, his reasoning being that on thin steel plate you can weld well with MIG after this machine gets small.

And NO, I'm not over complicating it. I'm trying understad enough of instead of over simplifying it. Just got 400 VAC welder, single phase all out 180A...This could be tranny donor to next spot welder....but this thing first - baby steps.

Pekka

Offline PekkaNF

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Re: Microwave owen transformer spot welder?
« Reply #32 on: November 25, 2015, 02:02:20 PM »
Got yesterday 20 mm copper rod and big enough CU/AL connectors. They are pretty nice, all data is available down to screw torque.

I found out that grounding "copper" rods are steel rods, that are plated with copper....

Found out place that sells spot welder electrode rods by metre (or even pieces). They have 8,10 and 12 mm at the small end.

Postal service is on strike......

Pekka

Offline Fergus OMore

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Re: Microwave owen transformer spot welder?
« Reply #33 on: November 27, 2015, 04:05:56 PM »
I've just found out that my earthing rod is also coated steel. Happily, I have found a possible source of small quantities of  scrap copper to cut up. I'm now looking for insulation for the welder arms. I have, like the other Atkinson cousin , a cunning plan.

Offline PekkaNF

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Re: Microwave owen transformer spot welder?
« Reply #34 on: December 17, 2015, 02:51:48 AM »
Ok. Got 1 metre of 10 mm spot welding electrode rod and 1,5 metres of 12 mm diameter. Those were smalles amount (cutoffs....) from the welding supply shop that deals with individuals here.

So I must build something. Work has kept me busy, but maybe in Christmas time I can squise some time off.

Next I need to build mechanics, I think I have all in the junk er.. materials pile. Probably will use circuit board for insulation.

But my mind is in timer/counter. I want something like 2-100 mains cycles. Or from 20 ms up to sec or two. Any suggestions to ready made timer/counter that would keep the count between power up/down cycle and has PNP/NPN output. Maybe with BCD switches.

Pekka

Offline SwarfnStuff

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Re: Microwave owen transformer spot welder?
« Reply #35 on: December 18, 2015, 12:06:34 AM »
Hey Bill, Thanks for posting Dan Gelbart's spot welding tutorial. I went to check it out and recalled that he has many very good tutorials on prototyping which in a way is what we get up to in our play-pens.
Or, at least I seem to, even if I have plans I seem to adjust / modify them for the materials at hand or more often because I messed up on some part.

I have added his page to my bookmarks figuring from there I can wander off to his many other topics.
John B
Converting good metal into swarf sometimes ending up with something useful. ;-)

Offline PekkaNF

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Re: Microwave owen transformer spot welder?
« Reply #36 on: December 25, 2015, 08:01:52 AM »
Been busy with the work and flu&other seasonal hinderaces....

I have a concept for mechanics, I was going to rocker type. Mainly because of the simplicity and I don't need high cycle time. However the pneumatic cylinder I have is too smal for normal rocker, I need to make swing arm to have eneough force and to keep the whole contraption compact.

I have two problems:
1) How to hook up the current from tranny to electrode holder
2) How to make the electode holder adjustable and I would like very much to able to adjust the holder position and to swap the holder and to turn it over (other end having 90 degree mount for electrode and other 45 degree or special).

Both would be simple if I had two big chuncks of copper. Big square piece, 20 mm bore for electrode holder and four bolt mount. Really elegant solution. Copper has excelent electrical and mechanical properties for this part. But I don't have it, nor I can easily get one!

I was considering similar construction of aluminium, I have it, easy to machine and I have a special clamps to connect copper cable to aluminium. Main problem I have is that I don't believe there is a good enough electrical contact between this aluminium bar and 20 mm copper bar (electrode holder).

I was thinking of "tinning" the 20 mm hole (for electrode holder) in this aluminium block, but I never have soldered aluminium and googling it produced mainly special fluxes and solders that seems proprietary, expensive, dubious mixtures of mainly tin and rest of it mainly zink....resulting in about 25% conductivity of the aluminium. Could aswell use steel or brass....equally bad results and wole lot cheaper.

Only way I can think of using the aluminium mount, is to make a sleeve of copper tube. Standard sixe OD22, ID 20 would be close enough and probably could get two metre piece without breaking the bank. This thin sleeve should work well when clampd between rod and split block, and still have enough of cross section area to conduct the current.

There might even be insulator material that would survive between the copper sleeve and aluminium block?

Is there a problem I don't see or would this work?

Pekka

Offline awemawson

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Re: Microwave owen transformer spot welder?
« Reply #37 on: December 25, 2015, 08:15:02 AM »
Pekka,

Seasons greetings to you.

It's notoriously hard to get good very low resistance contacts reliably on aluminium due to the inevitable oxide film that grows. It can be done, and contact surfaces need covering with petroleum jelly or similar to exclude air as far as possible. At the currents you are probably using I would anticipate problems.

Bite the bullet and buy some copper block or find something that can be 're-purposed'
Andrew Mawson
East Sussex

Offline PekkaNF

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Re: Microwave owen transformer spot welder?
« Reply #38 on: December 25, 2015, 11:31:11 AM »
Thanks. Ham and turkey to you too!

I have scoured local scrappies, small shops and put some adds on local bulletinboards. I haven't got a piece of reasonably copperish copper yet.

I put two more adds on local hobby boards, but if I don't get answer on few days I'll try something else. Like copper sleeve as a conductor and aluminium or steel block as a support.

I have some AL/CU connectors and I have seen propper electricias using them/grease/torguewrench and works. Not really something I'd like to rely on low voltage/high current application.

Pekka

Pekka

Offline JHovel

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Re: Microwave owen transformer spot welder?
« Reply #39 on: December 25, 2015, 09:51:41 PM »
Merry Christmas!
It is possible to tin aluminium properly - against mine and others' 'common sense' - and I have been shown, taught and done it, all the while shaking my head in disbelief.
The process is to heat the aluminium to soldering temperature (using an oxy torch in mine case, because the aluminium moves the heat away so fast, you have to keep pushing more in fast). While it is hot, vigorously brush the surface with a stainless steel brush to remove the oxide layer. Apply ordinary tinning flux to this shiney hot layer and add solder/tinning rod. This sort of floats on the hot surface without seemingly joining the aluminium. Vigourously wirebrush the solder/tin into the aluminium surface until you see it actually 'mixing in' and suddenly it 'alloys' with the hot aluminium surface. You can then add solder/tin to that surface and it flows like ordinary soldering does. However, the last step only works for a very short time! It seems that the aluminium insists on putting an oxide layer between the pure aluminium and the alloyed layer if you keep it hot enough.....
Once you see it all happeneing in front of your eyes, you will shake your head in disbelief like I did and then use the process whenever necessary.
Cheers,
Joe

PS: I learnt about this while doing a course on leading car panels, including aluminium car panels.
Cheers,
Joe

Offline PekkaNF

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Re: Microwave owen transformer spot welder?
« Reply #40 on: December 26, 2015, 08:44:11 AM »
ONE person said that he has 30*10 mm copper buss barrs....length 2400 mm! I'm pretty sure that is pricey. But it's only 90 km (one way). Not too bad.

Now...If I would cut a 40 mm piece of that bar and make a v-groove for electrode holder. Multistrand cable is easy to attach on that coppe piece, no problem there, but would this two 40 long line contacts give enough cross sectin for the current? Probably yes.

Another idea is to make close fitting 20 hole + slit other side onto piece of this buss bar for the electrode holder and cut a little (17*10*20 mm) lug for the cable connector. This would only work as an connector and there would be a separate mechanical split holder for the arm.

Tonight I'm going to order some electrical parts for the controller.

Pekka

Offline sparky961

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Re: Microwave owen transformer spot welder?
« Reply #41 on: December 26, 2015, 09:32:12 AM »
I'm having a bit of trouble picturing your current troubles, but I've thrown in some possibly useful idea starters below.

Have you checked your local building store for a solid copper grounding rod?  No idea of the alloy or quality but you'd hope it would conduct well considering the application.  Maybe you guys use something different there?

Near the grounding rods you should also find heavy grounding cable.  Here it's used for grounding 100A and 200A electrical services.  It's not the most flexible stuff to work with but if you're considering bus bars already then flexibility doesn't seem a big concern.  You can put them in parallel if you need something with even less resistance.

Do you or any of your friends have a furnace that's hot enough to melt copper?  The melting point is almost double that of aluminum, but not outside the realm of home foundry setup.  Scrounge whatever small pieces of copper you can (plumbing, electrical, whatever) and cast your own large block whatever size you need.

Offline PekkaNF

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Re: Microwave owen transformer spot welder?
« Reply #42 on: December 26, 2015, 11:49:13 AM »
I'm having a bit of trouble picturing your current troubles, but I've thrown in some possibly useful idea starters below.

I am electrical engineer and I have some experience on various systems. Therefore I'm little apprehensive when I push componenets beyond their intended use. The way low voltage circuit works on resistance spot welding machine is simple on most of the aspects, but there was very little at the university that prepared me to work few volts and thousands of amps...

Right now I'm consentrating on a bit that connects secondary coil conductor on the stationary and moving electrode holder.

The conductor has very fine multistrand braid, about 35mm2, should be fine for short pulse of 1100A.

Electrode holder is 20 mm pure copper bar used on electrical cabinet construction.

This piece has two functions:
1) To connect tranny secondary to electrode holder with minimal resistance, this is not one time operation, but must allow mechanical adjustment.
2) Mechanical: Attach mechanically bar to arm.

This is a small part, maximum linear dimenssion 40 mm, 20 mm hole trough it.

Have you checked your local building store for a solid copper grounding rod?  No idea of the alloy or quality but you'd hope it would conduct well considering the application.  Maybe you guys use something different there?

Here copper grounding rodds are steel core, copper cladding.

Near the grounding rods you should also find heavy grounding cable.  Here it's used for grounding 100A and 200A electrical services.  It's not the most flexible stuff to work with but if you're considering bus bars already then flexibility doesn't seem a big concern.  You can put them in parallel if you need something with even less resistance.

Yesh. We have that type cable too, often consumer grade is 16mm2, not sure of it's composition.

Do you or any of your friends have a furnace that's hot enough to melt copper?  The melting point is almost double that of aluminum, but not outside the realm of home foundry setup.  Scrounge whatever small pieces of copper you can (plumbing, electrical, whatever) and cast your own large block whatever size you need.

I'm trying to avoid printtin or castig at this point. Too much to swalow at this point - would set me back months instead of weeks :lol

Pekka

Offline philf

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Re: Microwave owen transformer spot welder?
« Reply #43 on: December 26, 2015, 12:54:25 PM »
Pekka,

I can't picture exactly what you're trying to do but why can't you connect the cable directly to one end of your 20mm copper electrode holder?

 :beer:

Phil.
Phil Fern
Location: Marple, Cheshire

Offline sparky961

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Re: Microwave owen transformer spot welder?
« Reply #44 on: December 26, 2015, 01:11:49 PM »
I'm little apprehensive when I push components beyond their intended use.

Isn't that what this forum is all about?  :dremel:

If you're the only one that will be using it and you've designed in enough safety that you're comfortable with it then I say it's well-built for the application.  Maybe there's an understood but undocumented limit on the duty cycle, or certain parts of the system that aren't quite to electrical code, but you are aware of them so it isn't a problem (as long as you keep it secure from other people's use).  We have all done some risky things with the potential for burning down a house or two, but most people with enough of a brain to succeed with these projects has enough sense to have things in place to prevent catastrophic failure.

If you're building this for someone else, it's a different story entirely.

Offline PekkaNF

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Re: Microwave owen transformer spot welder?
« Reply #45 on: December 26, 2015, 02:25:05 PM »
Pekka,

I can't picture exactly what you're trying to do but why can't you connect the cable directly to one end of your 20mm copper electrode holder?

 :beer:

Phil.

That was my original plan, but then I need to mill a lug where the connector fits. This prevents me from using both ends of the bar 90 and 45 degree angles.

But it would work and is plan "B".

Pekka

Offline PekkaNF

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Re: Microwave owen transformer spot welder?
« Reply #46 on: December 28, 2015, 04:53:33 AM »
Made almost full recovery...just before starting a new workweek.

I ordered some electronics stuff. I think thyristors will be fine....just about...ordered some spares and then one size bigger, takes more current, but gate current is higher too. have to check if the opto will trigger it. it looks like it does. Ages when I measured voltage/current with scopes.

Now the happy situation is that electrical components will come in a week or two and in meantime I can start to play with the mechanical part, which I think will be more straightforward!

Oh, and I got a piece of copper tube ID 20 mm and outside 22 mm, tried and it is a nice sliding fit. About 66m2 of cross section area if I need to go that way.

Pekka

Offline PekkaNF

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Re: Microwave owen transformer spot welder?
« Reply #47 on: January 04, 2016, 03:38:10 PM »
Got electrical board ready and tested on open secondary. Seems to work.

Has been too cold to work on mechanics.

A little progress.

Pekka

Offline PekkaNF

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Re: Microwave owen transformer spot welder?
« Reply #48 on: January 05, 2016, 01:19:55 PM »
And the electrical parts looks pretty much like this.

Just wonder how to measure thysristors on the circuit. Have to take oscilloscope out of the shelf and power it up.

* Osciloscope does not syncronize...No trigger function works....old philips 10MHz unit.

Any ideas for a new scope. I don't need it that often, but when I do, I really need it.

Pekka
« Last Edit: January 05, 2016, 03:29:18 PM by PekkaNF »

Offline PK

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Re: Microwave owen transformer spot welder?
« Reply #49 on: January 05, 2016, 05:16:12 PM »
Really silly good bench DSO's are quite cheap if you avoid the premium brands. Check out the Rigol range.
If you are doing mostly power electronics, then an isolated scope is just the ducks nuts (as we say in my country). We recently bought one of these: http://siglent.com/ENs/pdxx.aspx?id=93&T=2&tid=2
As a scope, well it's OK, low res screen and a slow UI. But I can poke probes into a live panel with a reasonable chance of survival, which I quite enjoy.

Nb, the non isolated variants are dirt cheap, but then you have a non isolated, slightly crappy scope! You're better off with a bench scope.