Triac Voltage Control Schematic for Transformer Welder

[paddyponchero]

Switches are shot on my inherited ancient SIP MIG so was considering replacing switches with a primary side triac controller.

Trawled around for a schematic suitable for inductive transformer load found this nice one from ST for exact purpose of a welder.

Thought it might be of interest to others.

Note: The badly named and symbolised DB3 is actually a Diac.

trol Schematic

 

[Erie Fred]

Does the switch change out/in various taps on the xformer ?
if you switch over to triac control, which winding ?

 

[paddyponchero]

Hard wire triac circuit to MAX HIGH windings

 

[eddie49]

That ST Microelectronics document about TRIAC control of inductive loads was discussed in this thread:

Wire Feed Upgrade

Congratulations on all you've done so far. I have done similar mods myself to several machines and the wire speed mod really does make a big difference. Only thing I had to do was add a couple of resistors to each end of the PWM board potentiometer to get the useful wire speed range more evenly...

www.mig-welding.co.uk

It would be interesting to know how well that circuit works. Previous experiments with simple "Light Dimmer" controls seemed to only work at higher power settings.
There is also a similar idea using two SCRs:

Two SIP T100P's (T90P)

Hi, first post here and firsty thanks for the great forum. I have learnt a heap from the threads here. I may be a glutten for punishment or just plain stupid but I just won two SIP T100P's (T90P) on eBay for a song. They are "new" but each with a different fault (so the seller said), one does...

www.mig-welding.co.uk

There are two commercial hobby-level transformer-based MIG welders that use TRIAC control instead of switches - the Lidl/Parkside PFDS 120 A2 and the AutoJack 130.
There was even an early attempt at this from SIP themselves:

Sip Autoplus 120 problems

Hello, I acquired this machine a good few years ago, and whilst it hasn't been too bad after I treated it to a euro torch conversion, it has lately been a bit troublesome. Now it doesn't strike an arc. Checked the voltage at the tip and this does not change no matter what the power setting is...

www.mig-welding.co.uk

Post #24 of that thread has a diagram of the SIP TRIAC PCB.