Indubitably
100 W
- Joined
- Jan 9, 2010
- Messages
- 126
I've been on a DIY how to build "absurdly expensive shop tool X, using off the shelf parts" kick lately, and while sourcing aluminum for a cnc router project, I realized that it would be much easier to build the router if I built an AC tig welder first. It then occurred to me that the PWMed output of a beefed up ebike controller would make for an ideal current throttling device in my welder. I've only recently begun the process of attempting to wrap my brain around this tech, so bare with me if for a moment if I say something that is completely off base, but my understanding of the way a controller works, is that it modulates the pulse width of a square wave so fast that it looks like a sign wave to the motor, and as this simulated sine wave passes through the windings of the motor an alternating magnetic field is created, which in turn (no pun intended) pushes against the magnets in the rotor so that they "slip" back at a speed that is slower than the rotating field, subsequently creating torque on the wheel. Now, I am told that because PWM is not a true sign wave, it is not suitable for welding aluminum, but my thinking is that if we can create an alternating magnetic field by passing the PWMed wave through the windings of a motor, then we should be able to create an alternating magnetic field by passing that same wave through the primary winding of a one to one transformer, and that as far as the tig gun is concerned, the alternating current induced in the secondary winding of the transformer should, effectively, be indistinguishable from any other source of AC.
At any rate, if you think about it, the throttle on an ebike does almost exactly what we want a welder to do, only backwards. With an ebike, you want high current at low voltage that will gradually ease into low current at high voltage, where as you want a welder to arc at high voltage and low current then ease into low voltage at high current. I'm guessing that this effect is controlled by varying the frequency of the simulated sine wave in response to a combination of input from the hall sensors and the throttle, so that by manually feeding the hall sensor input a signal, we should essentially be able to trick the controller into thinking that we are on the flat at speed when we want to establish an arc, and then convince it that we are trying to climb a hill when we want to weld. We' should be in the right voltage and amperage range though, since you usually want about 70v to establish an arc, and about 15 to 20v at 100 to 200 amps to do your weld. I imagine that some sort of active cooling for the fets would be necessary, and I'm not sure what frequency a tig welder needs to operate at it in order to penetrate the aluminum oxide layer, so its possible that we may needing fets that are faster in oder to simulate it, but if it can be done, we would have an inexpensive way to turn a charger and a controller into a portable light duty AC welding machine .
At any rate, if you think about it, the throttle on an ebike does almost exactly what we want a welder to do, only backwards. With an ebike, you want high current at low voltage that will gradually ease into low current at high voltage, where as you want a welder to arc at high voltage and low current then ease into low voltage at high current. I'm guessing that this effect is controlled by varying the frequency of the simulated sine wave in response to a combination of input from the hall sensors and the throttle, so that by manually feeding the hall sensor input a signal, we should essentially be able to trick the controller into thinking that we are on the flat at speed when we want to establish an arc, and then convince it that we are trying to climb a hill when we want to weld. We' should be in the right voltage and amperage range though, since you usually want about 70v to establish an arc, and about 15 to 20v at 100 to 200 amps to do your weld. I imagine that some sort of active cooling for the fets would be necessary, and I'm not sure what frequency a tig welder needs to operate at it in order to penetrate the aluminum oxide layer, so its possible that we may needing fets that are faster in oder to simulate it, but if it can be done, we would have an inexpensive way to turn a charger and a controller into a portable light duty AC welding machine .