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Author Message | Next Topic >> Gizmo Admin Group   Administrator Joined: 05 June 2004 Location: Australia Online Status: Offline Posts: 4380 Posted: 02 January 2008 at 7:39pm | IP Logged  Hi all. After reading Vasi's thread on home made welders built from microwave oven transformers, I got the idea to make a spot welder. Lately I've been making a few tools for the workshop, and having access to a laser cutter has make the job easy. Below is my disc sander and belt sander, using old induction motors I've had sitting on the junk pile for may years.   Next is a spot welder. I already have a mig welder, but a spot welder is so easy to use on those quick light steel jobs. I found a heap of info on the internet on home made spot welders using microwave transformers, but I wanted something with a little more grunt. I found this PDF http://www./junkyardprojects/FreeWelderPlans/ SpotWelder%232.pdf which describes an old machine, but old is good.  A quick search through the junk pile turned up an old Nikko UPS with a dirty great transformer inside. I cut off the secondary winding with a hacksaw, then wound some heavy welding wire around the primary. A quick test showed 4.2 volts AC output, perfect! Next I'll make up the clamp arms with brass tips, and the control circuit. For control, I was going to use a NE555 timer so I could adjust the weld period to get consistant results, fired by a foot switch. The lighter is there for size comparison, since I gave up smoking I seam to have lighters everywhere   So any idea's or input would be appreciated, I havn't used a spot welder for over 20 years so if anyone has a few tips on use or construction I would appreciate it. Glenn __________________ 'If it dont fit, use a bigger hammer.' The Back Shed JAQ Software Back to Top    Gizmo Admin Group Administrator Joined: 05 June 2004 Location: Australia Online Status: Offline Posts: 4380 Posted: 03 January 2008 at 8:13pm | IP Logged I drew up and lasercut parts for the spot welder 'pincher' today. The parts were cut from 12mm and 5mm steel plate. Once I got the parts home, I used the side plates as templates to cut some 3mm fibreboard. The laser can cut this stuff, but its messy and leaves a carbon rich burnt edge. As this fibreboard was to be used as a insulator, I didn't want any carbon edges, so it was easier to cut the fibreboard manually. I also used a hole saw to make up some washers. A bit of welding, and I put the bits together as a mock up to make sure it will work. Looks good. The lever at the top is to clamp the tips together, I need to add a sping at the back to pull the tips apart. Glenn __________________ 'If it dont fit, use a bigger hammer.' The Back Shed JAQ Software Back to Top dwyer Guru Joined: 19 September 2005 Location: Australia Online Status: Offline Posts: 531 Posted: 03 January 2008 at 9:47pm | IP Logged Hi Gimzo Bloody good ideas about spotweld as l all way want one and never through about mirco waves transformer however l work for a company and built Australia made stud welder that useing copacitor discharge when i was electronic wireman at the time around 1968 in melbourne anyway l can get many tranformer if the rubbish tip for free Glenn let me know if you need some regard ian Back to Top Gill Senior Member Joined: 11 November 2006 Location: Australia Online Status: Offline Posts: 669 Posted: 03 January 2008 at 10:49pm | IP Logged G'day Glenn, That'll be a good sized unit when it's finished. I scored an old mini spot welder 6 months ago. I checked it out and mostly seems fine. The only fault seems to be 2 x 480MFD caps the worst for wear. Tried to substitute a couple of junk box caps of much larger capacity but poor result. I feel it is made for say spotting the tabs on batteries. Very small stuff. Could not do a broken off sausepan handle lug. Fell off before it made it to the kitchen. Tried to find the circuit diagram I made of it but the gremlins have hidden it.(Their favorite game at my place). As I recall, there were 2 transformers. An initial voltage drop and current boost with 4 selectable voltages. This charged up the two big caps. Then, only when the pincers are clamped together can the WELD button be pressed. This disconnects the caps from incomming voltage and shorts them through the second High current transformer(primary). The secondry of the high current tranny is a circuit through the pincers. And Voila... Zitt ! So you'll have to post your circuit and modified components list too. Yeh? Mine has heavy braid wire supplying both pincer arms of brass with pincers of copper. With your arms of steel, will you run a braid wire along the arms to the pincers or will the steel arms carry the current? And what are the pincers (I don't know the real trade name for them but pincers sounds perfectly descriptive to me)to be made of? Looking good so far. __________________ was working fine... til the smoke got out. Cheers Gill _Cairns, FNQ Back to Top Gizmo Admin Group Administrator Joined: 05 June 2004 Location: Australia Online Status: Offline Posts: 4380 Posted: 04 January 2008 at 7:14am | IP Logged The circuit for mine will just consist of a one shot NE555 timer with a duration adjustment on the front case. This will switch a contactor in series with the transformer. The transformer itself has two primary windings ( actually they were the secondary windings when it was a UPS ), If I connect them in series I get just over 2.1 volts on the secondary, in parallel I get 4.2. I'll use a Hi Low switch so I can change between the two combinations. I figure with the Hi Low switch and timer I should be able to adjust the machine for any thickness up to say 1mm plate. I did intend to make the arms from aluminium, but a phone around this week and every single bloody steel merchant or aluminium welder in this town is closed for the Christmass period So I went for 12mm steel, and added a lot more cross sectional area to help cary the current. I think it will be ok, see how it goes. If the steel gets too hot I'll buy some more welding cable and run it straight to the tips. The tips in the picture are there just for show, I need to buy some brass thread, or even copper if I can find it. Glenn __________________ 'If it dont fit, use a bigger hammer.' The Back Shed JAQ Software Back to Top Gizmo Admin Group Administrator Joined: 05 June 2004 Location: Australia Online Status: Offline Posts: 4380 Posted: 04 January 2008 at 7:16am | IP Logged I should add, if anyone wants a copy of the DXF file I used to cut the parts then let me know. But I would wait to see if it all works first. Glenn __________________ 'If it dont fit, use a bigger hammer.' The Back Shed JAQ Software Back to Top herbnz Senior Member Joined: 18 February 2007 Location: New Zealand Online Status: Offline Posts: 256 Posted: 04 January 2008 at 10:16am | IP Logged Hi Glen In welding transformers the output current is limited by the loose coupling between the pri and sec windings. If you find you draw to much current try sec winding 1/2 on each outer leg core. I have a small portable unit here that is very handy it has the handle controlling initial clamp then weld not timed you just observe then press harder and it shuts current off and holds pressure on. I could if you wish remove covers and take pic to show how it is set up. Herb Back to Top Gill Senior Member Joined: 11 November 2006 Location: Australia Online Status: Offline Posts: 669 Posted: 04 January 2008 at 12:34pm | IP Logged Glenn, By my estimations you're expecting to get from 850 to 1500 amps per Zapp, is this about right for these things? I'm thinking the primary of an UPS would be a fairly solid wire, this doesn't seem the kind of project a microwave transformer would be suitable for. Maybe a smaller version more like mine? Two in parallel might be better. I don't expect I could run one of these designs because I'm off grid and the generator protests every time the arc is struck with the welder. Always a lag for the revs to build up to max before you can settle in to the weld run. I can supply a saucepan and handle for the test run if you're short of jobs. Ha.ha. Edited by Gill on 04 January 2008 at 12:40pm __________________ was working fine... til the smoke got out. Cheers Gill _Cairns, FNQ Back to Top Dinges Senior Member Joined: 04 January 2008 Location: Albania Online Status: Offline Posts: 510 Posted: 04 January 2008 at 10:12pm | IP Logged Hello, My first post on this board but have been reading for a while. A few months ago I built a small spotwelder too, using an old microwave transformer. I really wanted to build a capacitor discharge spotwelder (see links below) but don't have the right caps at the moment (~1F @ 30-40 V), so decided to make a transformer spotwelder first. It uses an old microwave transformer, a NE555 timer with front timing potmeter, driving an Opto22 solid state relay. Schematic can be found here: http://www./gallery/dinges/spotwelding_machi ne?full=1 Here are some photos of the welder (without the clamps), I used an old welding inverter case (which already had convenient welding fast-connect connectors. http://www./gallery/dinges?page=13 It works, but only for very thin stainless steel metal as the current is too small (~500A); I have too much resistance in the connecting wires. I plan to build a new, bigger one when I can find a suitable 2 kVA transformer with inner primary (and an easy to remove secondary). The new one will have the welding thongs connected straight to the transformer, without wires. Resistance kills quickly in this application (I think my total wire resistance was 12 milli-ohm, which limited current to ~500 A). Here are some links to other projects, for those interested: http://www./welder.htm http://www.philpem./elec/welder/?elec/welder http:///site/pages/products (products that make me drool...) I'll be following your experiments with interest! Peter D. Back to Top Gizmo Admin Group Administrator Joined: 05 June 2004 Location: Australia Online Status: Offline Posts: 4380 Posted: 08 January 2008 at 7:46pm | IP Logged Thanks for the links Peter. Finished the welder today. Made a foot switch from some 1mm zinc plate and a couple of DSE switches. Below is the circuit, I need to draw it up. It uses a NE555 as the timer. I had to add a lot of spike protection, the back emf from the contactor and transformer was causing false triggering. I still need to tidy up the wires with cable ties. The finished machine. And some test welds, 1mm zinc plate. I do need to replace the steel arms with aluminium, the steel gets very warm after a couple of welds, and this means I'm loosing a lot of the available energy in the arms. Glenn __________________ 'If it dont fit, use a bigger hammer.' The Back Shed JAQ Software Back to Top vasi Guru Joined: 23 March 2007 Location: Romania Online Status: Offline Posts: 1697 Posted: 08 January 2008 at 11:46pm | IP Logged Great job as usual. How strong is the 'connection' between plates? Maybe the schematic will have his page on info/projects ? Back to Top Tinker Guru Joined: 07 November 2007 Location: Australia Online Status: Offline Posts: 1077 Posted: 13 January 2008 at 1:18am | IP Logged Gizmo wrote: I do need to replace the steel arms with aluminium, the steel gets very warm after a couple of welds, and this means I'm loosing a lot of the available energy in the arms. Glenn May I suggest not to bother with alu arms as your results will even then still lack 'ummph'. Try to get some suitable size flat braid copper and connect it directly to the back of the tip electrodes. As was mentioned elsewhere in this thread, resistance in the wrong places kills a spot welder. Ideally, you want 99.99% of the resistance at what's clamped between the electrodes. Commercial small spot welders I used (years ago) had about 25mm dia copper rod for the pincer arms, one even had the arms water cooled. Klaus __________________ Klaus Back to Top |
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