Spot welder not working.

[Scrounga]

Hi all, I have a spot welder, pictured below with the covers off, but I can’t get it working.

When I tread on the lower lever I can hear the transformer hum but no weld. I have cleaned EVERY contact between the power plug and the welding tips including the brass clamping blocks. It has three voltage settings selected by this switch…

and testing the voltage at the tips shows 1 volt on low, 1.3 volts on medium and 1.7 volts on high but I don’t know if this is too low. I tested this by measuring the volts at the tips by engaging the transformer without the tips touching. The specs on the manufacture plate says 240 volt, single phase, 15 amp so it’s very desirable as most welders of this size are 3 phase which I don’t have. I also like the stand which puts it at waist height for me. The windings are made of multiple copper straps about 40-50mm wide.

To me my last option is to unwind the copper windings but I’m not sure what I’m looking for. After that I have a cheap Vevor spot welder I’m thinking of pulling the transformer out of to fit into this machine. While the Vevor machine works it has some shortcomings like 150mm arms which really limits reach. You need one hand to operate it making parts alignment awkward and the tips are just plain copper so they mushroom very quickly. Good quality tips are made of a copper/ chrome alloy to stop this. Yet another option is to use two microwave transformers. I’ve done this once before with a single transformer and it worked well as an experiment to melt screws etc but I didn’t make a welder. I guess if all else fails I could put it into a welder repair shop. Any ideas are welcome. Just as an aside, I paid $200 for this machine but was unable to test it as the seller (who I presume knew it didn’t work) didn’t have a 15 amp socket. These type of machines sell for around $2500 at the second hand machinery suppliers and around $5000 to buy new so I’m not complaining as I don’t have a lot of money in it, it’s the lies that makes me mad. Two main questions are, is the voltage high enough, and how can there be voltage without current. Thanks all, Stu. Australia.

 

[eddie49]

G'day and welcome to the Forum!

The secondary voltages that you have measured - 1.0 / 1.3 / 1.7 - sound about right. The flat copper windings should be carrying two or three thousand Amps.

If you have a clamp-on AC current meter, check if the primary current approaches 15 Amps when you operate the welder. I guess that it will not, and that may be due to a high resistance somewhere in the primary circuit.

Between live and neutral the total resistance may be as little as 1 Ohm, and as you step up the Low/Medium/High power switch that resistance will drop. A normal digital meter with 0 - 200 Ohms range may not be accurate enough to show that.

You could bypass the 3-way switch and wire the power cord directly to one of the transformer primary tappings.

Some notes about welder primary resistance in Post #6 here:

Dent puller spot welder.

Afternoon all I have a little eBay dent puller spot welder. I blew a varistor on the board and the company did sent me another spare board. Problem is that the moment i connect the transformer to the board it trips the breakers. I measured the primary winding on the coil and it measures...

www.mig-welding.co.uk

 

[Scrounga]

Hi Eddie and thanks for your reply. While I’m confident with house hold electrical it’s the high amps here that makes me nervous. I will try your suggestion and bypass the switch just to see what happens.
Cheers mate, Stu.

 

[eddie49]

With less than 2 volts available, the resistance of your body will not allow any current to flow, so there is no danger of getting a shock. However, during a spot weld operation a high-current or high temperature burn is possible.

 

[Scrounga]

Hi all, just an update to explain how I fixed my spot welder. I’m posting this hoping it may help someone else. I kept thinking about the voltage but no current issue and on closer examination I realised there was a contact I hadn’t checked and that was the electrode tips in their holders. I had no idea how they were held in place so I spun them down on the lathe to reveal they were actually a taper press fit. The corrosion, especially in the copper holder, shows the problem.

Rather than mess around with these and as I had the materials anyway I made some new ones. The tips are copper / chrome alloy which are tapped and threaded into the copper holder never to come out. Copper is very soft and gooey to machine so when the pieces are screwed together they tend to gaul permanently joining them. In my case this isn’t a problem as I have plenty of material left to make new ones and it’s not going to be used too often.

The result was a big relief and made my day. This spot weld took about 2 seconds and I couldn’t get it apart.

Now I can carry on to restoring the whole machine and I’ll probably add water cooling. Sucks to the liar that sold it to me. It was nice to have a win. A big thanks to the forum for allowing me to post.
Many thanks, Stuart, Australia.

 

[Scrounga]

With less than 2 volts available, the resistance of your body will not allow any current to flow, so there is no danger of getting a shock. However, during a spot weld operation a high-current or high temperature burn is possible.

Hi Fred, I found the problem and have posted the result hopefully for others to use. I had to put it under your answer as there is no edit option showing on my original post.
Thanks again for your help, cheers mate, Stuart.