Handheld spot welder strength?

[gasket999]

Following advice on another thread, I’ve now got a lovely Tecna 7902-pulse hand held spot welder (it’s about the most powerful one I could find for single phase - 2.5KVa at 50% duty and will do 2.5mm+2.5mm steel).

Now this (with a few handmade arms) will let me quickly and easily replace a number of panels on my Range Rover Classic project and they will look factory.

But realistically, how strong can I expect each of the welds to be?

While the welds are pretty - I’m sure that the welds produced by this little handheld 240v machine would pale into insignificance compared to those produced by the giant 3-phase welding stations/robots used in a car factory…

But then again - is there much in it? Is a resistance weld ‘binary’ as in: it’s either welded or it isn’t?

There seems to be very little online regarding the strength of hobby vs industrial machines but would welcome some input. For example, if I’m going for factory strength, would I be better doing the welds at double the factory intervals?

 

[Misterg]

how strong can I expect each of the welds to be?

They should be stronger than the metal around them.

I’m sure that the welds produced by this little handheld 240v machine would pale into insignificance compared to those produced by the giant 3-phase welding stations/robots used in a car factory…

Check using a peel test - both could/should yield the same result.

 

[AKN]

I’m restoring a Range Rover Classic, if you get a copy of the original LR workshop manual for the 1990’s models the body section explains the difference between the welders used in manufacture and those available in repair shops then giving the number of spot welds to be used in repairs. You are going to have to put many more in.

 

[gasket999]

Thanks both.

AKN - I've never seen that section before, great to know - sounds like that's exactly what I need to read.

 

[hotponyshoes]

Factories will use big machines but part of that is because they run them at a much higher duty cycle than a hobby user.

If a panel requires 200a to weld it then the strength should be the same regardless if you use a 220a machine set to 200a or a 550a machine set to 200a.

The only difference is you might get the over-heat light come in after 10 welds and have to wait for a cool down.

 

[Robotstar5]

Set up on similar thickness material and tearing the pieces apart should leave a hole in one piece and a nugget on the other, known as "pulling a slug"

Don't be tempted to put the welds too close to each other, they should be at least 2x weld diameter apart to prevent "shunting" which is when some of the weld current passes through the previous weld and reduces the current weld.

 

[Morrisman]

Unless your RR is made of 2.5++mm steel I can't see why your spot welds shouldn't be as strong as factory. The factory 3 phase giant is probably turned almost to minimum to do their job.

 

[gasket999]

That's really reassuring - thanks for the advice everyone.

 

[ghound]

I had a hand held spot welder, i think it was an SIP from memory.
It was quite powerful but only was fit for a handful of spots per minute before the handles got soo hot you could hardly hold it lol, but it was fine for body repair.
I sold it because i needed a more production line type of welder, so bought a 240v water cooled pedestal type.

 

[Wallace]

If the arms are long, applying enough pressure has been my biggest problem. I keep every piece of clean scrap for testing!

 

[chris y]

Good advice here, except that there should be no reason to need more spots than factory.

Always weld some test pieces first then tear them apart, as long as you pull a decent slug its as strong as a weld from any welder.

Some differences from factory are that your machine will struggle to achieve enough pressure so a good fitup is important, dont use the welder to close gaps.
Your machine will take more time (more cycles of the 50 Hz wave) to weld it.
Your machine will do a few, then need to cool down.

 

[joebog1]

I think the OP's welder will be fine for bodywork.
Yes, you can get a bigger one, BUT if you wind the amps up too big, the welder will just vaporise the steel panels and shutdown.
How do I know??.
If I remember correctly, its more the diameter of the copper pads than the number of welds or the amperage used.
I was taught a weld should take about 2 seconds. Thats for my standard chassis corners in 1.6mm zincalume.
I now do them with a TIG as I can file/grind it down and it then looks homogenous.

Joe

 

[Neilj]

I now do them with a TIG as I can file/grind it down and it then looks homogenous.

Joe

Tell me more, are you plug welding them with a TIG? I have a bodyshell that I'd like to replicate the appearance of spot welds on and there's no way I can reach in far enough. MIG plug welds end up proud which doesn't look right.

 

[joebog1]

I can almost sweat them together. The two edges that meet at the corner. Sometimes if I get a little hot and blow a hole I need filler rod to fix that.
Setup is what makes it easy. If the joint in near perfectly aligned mechanically I only need a drop of filler rod at the end of the corner.
I do put a 10 or 12 mm return ( 90 degree lip ) that I tap and screw the bottom panel onto.

Joe

 

[Neilj]

That sounds interesting, got any pictures of them?