Monkeypeas
Member
- Messages
- 156
- Location
- Staveley/Creswell, North Derbyshire, UK
When you turn the machine on, mains voltage is fed to the small PCB transformer, giving a 12 vac output that is then fed through a diode to give 12 vdc, which is used to power the relay when you press the trigger to send mains voltage through the welding transformer's primary winding.
It is easier to work off the board as the schematic is too simplistic. You can see the two pins with 240 vac and those opposite are the 12 vac, so you have the four positions of the fly leads you need.
Thanks that makes alot of sense, if for example I was to add a normal (non switching type) 24v ac transformer and rectifier would I just take the power from that into where power currently goes into the control board from the main welding rectifier, would it still have to be switched somehow? or would you just connect the input of the aux transformer to a switched 240v supply like people do with gas solenoids to make the whole thing switched?As a111r said, the plastic-encapsulated transformer on the PCB implements one of the functions of the "auxiliary power supply" that I mentioned in post #16 - it controls on/off of the main welding transformer when activated by the torch trigger switch. This small transformer is only rated at about 2 Watts, so it cannot run the wirefeed motor, it only powers the coil of the on-board relay.
The other components on the PCB form the speed controller for the wirefeed motor. This is a second function of the board, but it is completely separate and takes no power from the small transformer.
When a new dedicated power supply is added to run the wirefeed motor, it is often an electronic switch-mode unit. These are best powered-on constantly, rather than being enabled at every press of the torch trigger. Therefore the mains input of the PSU would be wired to the welder's On/Off switch S1. It is the output of the new PSU that gets switched, by a double-pole relay, as described in post #16. The relay coil could be 12v, paralleled to the coil of the on-board relay, or 24v, across the welding transformer output, or 230v, switched by the on-board relay contacts.
I know most people use switching psus when modifying (which as you say don't like being flicked on and off) but I've seen several higher end and older welders use normal transformers and rectifiers for auxullary power so was interested in how you'd retro fit something like that, especially since I have a couple of old 230-24v transformers hanging around, including the Siemens one I showed above with the on board rectifier and dc output