# Question about AC welding machine



## Mutt (Nov 19, 2021)

So I see a alot of videos of people making good spot welders outta microwave transformers. I took a microwave apart today (Panasonic) and it had the most ridiculously cheap transformer I have ever seen. Not even sure how it even worked. It was mostly plastic and the fewest winding of I have ever seen.  So my question is this

Since that AC transformer just loses it secondary windings  and some 2/0 welding cable  is just double wrapped it in it's place and the rest of the machine just hobbled together from scrap laying around, I got to thinking. Why wouldnt it be possible to just install a couple of tapered copper mig welding tips into the electrode and ground holders  of a AC welding machine and just use the welding machine for the current? I mean, you could make some tongs outta steel and screw the tips into it for better control, but will this work, or will the welder short circuit or something?  Or better yet, turn the tig welder on AC and be able to use the pulse (timer) function and the foot pedal or hand trigger for better control


----------



## Ulma Doctor (Nov 19, 2021)

I think the closed circuit voltage is too high and may result in some spatter 
The mot transformer spot welder i made was copied from the web, it used few turns of heavy cable to top out at about 3-4v open circuit 
It works for razor blades and thin materials 

The real deal units are DC powered


----------



## Mutt (Nov 19, 2021)

the videos I watched   most all weld 2   5/32  diameter  nails together, another  will melt a 16 penny nail in under 10 seconds.


----------



## benmychree (Nov 19, 2021)

But, why would one want to weld nails together and melt a 16 d nail?


----------



## markba633csi (Nov 19, 2021)

The Panasonic transformer you saw was probably a ferrite core high frequency transformer which are common in the new inverter designs. Totally different animal than the older iron core transformer which experimenters like to modify.
Mike is correct in that a conventional arc welder won't make a good spot welder.  You need high current but at a much lower voltage than used for arc welding- around 3 volts compared to 30 volts
-Mark
I think it requires at least two of the iron core microwave oven units to get enough amperage, and it's getting harder to find those larger scrap ovens
If you have an old arc welder you can sacrifice, that would work- change the secondary winding


----------



## Lo-Fi (Nov 20, 2021)

A cheap old transformer arc welder has the perfect transformer. I've made a spot welder this way, ended up about 3V,  1300A. I rewound it with thicker primary and a 2 turn secondary with 80mm^2 cable. Trouble is I was too successful and it draws 40A on the primary, which is way too much for a plug in appliance.


----------



## Mutt (Nov 20, 2021)

benmychree said:


> But, why would one want to weld nails together and melt a 16 d nail?


 I dont but with this power it could spotweld double 1/8" sheet metal


----------



## Mutt (Nov 20, 2021)

markba633csi said:


> The Panasonic transformer you saw was probably a ferrite core high frequency transformer which are common in the new inverter designs. Totally different animal than the older iron core transformer which experimenters like to modify.
> Mike is correct in that a conventional arc welder won't make a good spot welder.  You need high current but at a much lower voltage than used for arc welding- around 3 volts compared to 30 volts
> -Mark
> I think it requires at least two of the iron core microwave oven units to get enough amperage, and it's getting harder to find those larger scrap ovens
> If you have an old arc welder you can sacrifice, that would work- change the secondary winding


 Any ideas as to when these new ferrite transformers started being used? So most any OLD microwave will still have the iron core transformers?


----------



## RJSakowski (Nov 20, 2021)

Mutt said:


> So I see a alot of videos of people making good spot welders outta microwave transformers. I took a microwave apart today (Panasonic) and it had the most ridiculously cheap transformer I have ever seen. Not even sure how it even worked. It was mostly plastic and the fewest winding of I have ever seen.  So my question is this
> 
> Since that AC transformer just loses it secondary windings  and some 2/0 welding cable  is just double wrapped it in it's place and the rest of the machine just hobbled together from scrap laying around, I got to thinking. Why wouldnt it be possible to just install a couple of tapered copper mig welding tips into the electrode and ground holders  of a AC welding machine and just use the welding machine for the current? I mean, you could make some tongs outta steel and screw the tips into it for better control, but will this work, or will the welder short circuit or something?  Or better yet, turn the tig welder on AC and be able to use the pulse (timer) function and the foot pedal or hand trigger for better control



A spot welder typically has a very low voltage but thousands of amps.  A stick welder wouldn't be able to supply sufficient amperage.  I have a Miller spot welder that is rated at 1.5 kva.  The secondary amperage is 4,500 amps.  This is about 30x what a typical arc welder is capable of.


----------



## markba633csi (Nov 20, 2021)

I think Panasonic introduced the inverter microwave around 20 years ago, so you have to go back a ways.
Usually, the iron core models are heavier though so that's one way to tell
-M


----------



## RJSakowski (Nov 20, 2021)

When looking for a suitable candidate for a transformer, I would want one with power rating of 1 kva or more.  This would be equivalent of an input current rating of around 10 amps.  A lower rated transformer wouldn't have sufficient iron in the core and and the flux would saturate. In addition to a microwave transformer, a large battery charger transformer might work well. I have one with a 25 amp intermittent rating, so good for 3 kva in a low duty cycle mode.  A spot welder is tupocally low duty cycle so it would be a good match.  A thrirf possibility is a Variac.  Replacement brushes are insanely expensive and many of the old Variacs are  just scrapped.  A 2 kva Variac should work well.  The toroidal construction makes adding a high current secondary winding simple.  Just strip off all the hardware and add the cable winding.

As to using MIG tips for the contacts, they will probably not work well.  They have too much resistance for the amount of current required and would heat up excessively, causing distortion of the tip.  You can buy spot welding tips on Amazon.


----------



## Mutt (Nov 20, 2021)

markba633csi said:


> I think Panasonic introduced the inverter microwave around 20 years ago, so you have to go back a ways.
> Usually, the iron core models are heavier though so that's one way to tell
> -M


Thanks. A friend of mine had a few old microwaves laying in the scrap pile. I picked up one and it didn't seem very heavy. Picked the other up and it was much heavier. Yanked a few screws and there it was. Got it out and fixing to start building the spot welder.


----------



## markba633csi (Nov 21, 2021)

One thing to be aware of:  The magnetron unit contains beryllium spacer pieces (usually pink or white) which are carcinogenic if broken and particles are inhaled
Try to avoid damaging the magnetron- it's the box-like thing with the cooling fins near the transformer
Also be careful of the large high voltage capacitor nearby it may still have some charge
-M


----------



## Mutt (Nov 21, 2021)

I only remove the transformers and momentary switches out of them. The rest got to the scrap yard


----------



## AGCB97 (Nov 21, 2021)

I built one that didn't work very well. Now I have a harbor freight 220 volt


----------



## Mutt (Nov 21, 2021)

AGCB97 said:


> I built one that didn't work very well. Now I have a harbor freight 220 volt


all this one has to do is spot weld 2 pieces of .060" steel together in 3 places. I have $14 tied up in it total. 

So has anyone ever been actually been inside their  110v and the 220v from HF? They both look the same from the outside. I'm just curious if the only difference is the actual plug   !!!!!!!!!!!! I mean, a coil of wire is a coil of wire.


----------



## woodchucker (Nov 21, 2021)

markba633csi said:


> One thing to be aware of:  The magnetron unit contains beryllium spacer pieces (usually pink or white) which are carcinogenic if broken and particles are inhaled
> Try to avoid damaging the magnetron- it's the box-like thing with the cooling fins near the transformer
> Also be careful of the large high voltage capacitor nearby it may still have some charge
> -M


I thought the beryllium is only dangerous if filed or sanded... dust being the problem?  many tools are made of beryllium for use around MRI machines..


----------



## AGCB97 (Nov 21, 2021)

Let us know how it works.
Aaron


----------



## Weldingrod1 (Nov 21, 2021)

I have a switch to run my 220 HF spot welder on 120 vac when I want to be gentle. Works fine.
I've never played with the 120 version.

Sent from my SM-G892A using Tapatalk


----------



## Lo-Fi (Nov 21, 2021)

The audio is not great, but this is a half hour of solid gold on spot welding:


----------



## G-ManBart (Nov 29, 2021)

woodchucker said:


> I thought the beryllium is only dangerous if filed or sanded... dust being the problem?  many tools are made of beryllium for use around MRI machines..


The problem with beryllium happens when it can be inhaled....anything that can create dust or fine particles should be avoided.


----------

