-----Original Message----- From: Bill Blackburn To: lilel@toastmaster.com Date: Monday, March 08, 1999 7:02 PM Subject: Spot Welder Bill wrote: >I noticed your note on the PIC list on building a spot welder. I just >finished building one and I ended up using one electronic timer & relay >to control the transformer. The electronic timer is the adjustable >type. It is adjustable from 1/4 to 4 seconds. I use a foot switch >for activation. This frees up both hands to hold the work. Not sure >whether a pic is needed for this joe. Unless of coarse it is for >experience I'm probably going to use a PIC. One of these will replace a finicky homebrewed control on an existing welder. This welder only needs to run for 30 - 300 milliseconds. Millisecond control is not something I trust a relay to be able to handle very well. I kind of want this item to be very repeatable. Roland wrote: >Lawrence, have you considered just replacing the footpedal switch with a ?fet/bjt/relay? May be easier than getting onto the HV side of things.. The footpedal will probably be a low voltage switch. It helps to have a footpedal because your hands are usually busy holding parts. This is in a prototype shop where each weld is different, and there is not enough justification to make fancy holdingfixtures. On the HV side, a relay would be simpler than Triacs, though. Just how fast can a 50 amp contactor operate? Probably pretty slow. I'd be surprised if such a contactor could close and open in less than 0.2 seconds. That's WAY too long for welding thin sheet metal. Besides, I can probably lean on somebody for samples of a triac!