Home made SPOT welder

[graffian]

If you do mess around with microwave transformers bear in mind the secondary delivers about 2000 volts, that at 800 watts is lethal. Also there is a large capacitor in there which can hold a lethal charge even after the unit has been switched off.

I tried spot welding with a microwave transformer. I made new steering box covers for my landrover and they have stayed together, amazingly. I can't remember how I squezed the tips together. I did use proper berylium copper tips, they were on sale in bucknhickman, something like 50p a piece. I did approx 1/8 diam spots.

 

[rtbcomp]

I tried spot welding with a microwave transformer......

Presumably you just used the primary and wound your own secondary?

 

[graffian]

Secondry was a single winding of busbar[copper flat stock]. The output was around a volt.

The clamp was cobbled together but put a fair bit of pressure on the tips. I found a larger spot and the weld wasn't always good. The boxes have been on a rattly diesel land rover for 9 years and haven't fallen apart yet.

 

[rtbcomp]

Can you remember the wattage of the microwave? I feel a project coming on!

 

[graffian]

No. It was one of the big late 70's Philips things. Tell you what I still have the transformer, was running my parts washer off it recently. I can take a photo of the label, it's still readable.

After I did it I found a load of stuff on the internet about doing things like it.


If you strip a microwave I wouldn't mind the capacitor, I have just found a use for the one from mine. I used it to run the three phase oil pump on my milling machine and I have a few other small three phase motors to run.

 

[rtbcomp]

I'll have a look for you, I collect old domestic appliances for parts for projects.

BTW some microwaves have aluminium primaries, not much good in the copper scrap box!

 

[madkayaker]

the price of copper is rubbish at the moment any way

 

[classic2cv]

I did wonder if it's OK to pre-clamp and apply pressure before applying current, and then turn off current before releasing the work piece. That way there would not be an arc or spark

thats exactly how a spot welder works

i like the idea of using a microwave transformer

how about modding one of these to apply the pressure needed for making the welds

make some arms to hold the tips and add a big switch (or a relay) for the current all done

 

[rtbcomp]

You may even find a suitable relay in an old microwave too.

 

[GeorgeB]

Thank you for all the recent postings. Perhaps I gave up too early! I used 4 turns for 2.4V and possibly 2000 amps. Both my voltage and total AV output was a tad low compared to the proprietary spot welders. I didn't think of trying 2 turns for 1.1V and perhaps 4000A in my case. Perhaps that would have worked better.

Graffian's Land Rover spots look excellent. Perhaps the proper copper alloy electrodes do make a difference, too. I used MIG tips to help keep costs down, as the cheapest spot electrodes I could find are almost £10 EACH and I'd have needed two.

I have some quite large microwave oven transformers but they are small alongside the arc transformer which I used so I can't see how my transformer core was a weak point, but who knows?

I never did try applying pre-pressure. Classic2CVs clamp idea sounds much better and I'll try something like that next time.

The other bit of bad news is that I bought the arc welder for only £19 during a special offer in 2007 or 2008. It was brand new when I dismantled it. They now sell on eBay for £55, and all I have is a pile of parts! It was quite a costly exeriment but perhaps it can still be made to work.

 

[graffian]

I pulled apart a virtually unused 180A stick welder to try this with just before I tried the uwave transformer. I had no luck at all with the stick transformer, but I was trying to weld with bus bar as tips and didn't get a lot of pressure on the tips. When you get much pressure on copper it deforms and the tips end up to big. I went to a lot of trouble to get the ones on the landy parts like that. As soon as I did that part a mate lent me a proper spot welder, wish I had bought more tips when they were cheap as his welder has really ****e tips.

I did look at the transformer, I couldn't remember the microwave power.
the transformer is marked
Advance transformers
8512M44-90
AC-180-3
Secondry
2340V .7A
315V 15A

 

[terry_09]

Question...

making a home a homemade spot welder out of two mots using a set of jumper cables wires for the number four wire Ask like its not getting enough power got spark but it is not heating up hot enough to melt. Any info reply back to terry_09

 

[graffian]

make the contact tips really small.

 

[terry_09]

Home made spot welder...

They are small only a 1/4 inch. if not a little bit smaller... so if anybody has any ideas please respond.

Thank you..

 

[terry_09]

does 4 gauge wire and battery cable is their any differences? because the jumper cables have coating around them.

 

[terry_09]

does anyone have any advise for me?

 

[graffian]

1/4 inch is far to big.
I used around an 1/8.

 

[terry_09]

is that why im not getting enough power?

 

[graffian]

probably.
Did you take the shunts out of the transformer. I can't remember if I did or not.

 

[terry_09]

I cant remember if i did or not i am using a pair of jumper cables wires what im trying to do is make a spot welder for auto body im am using a 115 and a 220 transformer what would be better to hook to?