Spot welder (homemade construction) made from an old arc welding transformer and a couple of fibreglass tent poles

By Dorian Stonehouse

MAKING a spot welder out of an old welding transformer or microwave oven transformer is no big deal. 

picture of old welding transformer, with two large coils

But remember: the ac output to the spot welding tool must be very high current, but low voltage capable – typically around a 1000 amps at 8 volts.

picture of secondary coil made out of welding leads

Everybody’s got an arc welder – Yea right!

So, I made my spot welder out of an old arc welder, removed the secondary winding completely, then removed the electrode holder at the end of the welding cable and used this cable to wrap around the transformer secondary – hey presto, a nice 1000 amp/8volt coil!

croc clips voltage taps attached to secondary coil

Spot welder (homemade construction) made from an old arc welding transformer and a couple of fibreglass tent poles

heavy duty solenoid switch, with foot pedal used

Solenoid Switched by foot pedal

The solenoid is the type used in lorry (truck) lifts (elevators) and is rated at 200 amps minimum ⇑⇑  I always carry out an insulation test on these solenoid switches before fitting – very important!

spot welder made out of pair of tent poles

Down to the nitty gritty

A good spot welding tool⇑⇑can be more of a challenge to make than the rest of the spot welder put together.

the spot welding tool electrodes bent in at the end

Spot welder (homemade construction) made from an old arc welding transformer and a couple of fibreglass tent poles 

Spot welding tool is joined by high temperature adhesive

Spot welder (homemade construction) made from an old arc welding transformer and a couple of fibreglass tent poles 

3mm spot welding bit

Stopping that nasty slippage

One of the challenges of this design is to stop the copper rods from moving back and forth along the tent poles. Here is one solution⇓⇓.

Two clamps used to secure electrodes inside fibreglass tube

Spot welder (homemade construction) made from an old arc welding transformer and a couple of fibreglass tent poles 

End on view of two clamps securing 3mm copper spot welding wire

Caution: with high current flowing in the fibreglass tent poles, after some time they will get very hot. 

Another end on view of two clamps and connection terminals securing electrical wires leading into the tool

Ideas from readers wanted

Ideas for the future might be to role a silicon heat resistant matt around the tent poles; or to use some other material with very high thermal resistance, so that the poles remain cooler.

Side view of spot welding tool

I have noticed that by the time the tent poles do get hot, the cables feeding the tool will also be hot, so a good time perhaps to let things cool down before proceeding with the spot welding project.

How well does the homemade spot-welder work?

Spot welded tin can as a demo

I did say at the beginning of the project that the spot-welder is capable of joining tin cans together.

So, to show you what I mean, here is an earlier spot-welded food can ⇑⇑ made into a mild steel pocket for an Edison battery.

I hope you enjoyed the pictures, so please send me your hacking ideas to be considered for featuring on electrosparkles.com

 

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