kylebosch808 said:
Hi i was reading your post on the alternator welder and i was thinking, Couldnt you use a dimmer swtich, like the ones you use in your house to dime the lights down??? i would think that would work because your not adjusting the speed of the alternator. Tomorow im going to go and take the alternator out of my old feild car and make one for my dads garden tractor and il try the dimmer switch and il reply back
I have been sidetracked for a bit and forgot to come back and post some updates.
To date, I have over 110 hours of run time on the old junk yard alternator that I originally bought to try out the concept. I cannot blow it up. I even connected the welding leads through a piece of angle iron (dead short) for 2 tankfuls of gas. The alternator just will not quit. The only item I have had fail was a cheap mower belt that has since been replaced with a automotive belt and now I have had no issues.
As for the excitation to the alternator, a dimmer switch would work in theory, depending on the resistance of the field winding. You will find that with a rheostat, you will get a ton of heat build up. For that reason, the "simple" approach that I took initially was a rheostat and a couple of power transistors. Much more efficient and precise to control. Even this arrangement produced a significant amount of heat.
I have since moved on to Pulse Width Modulation that uses a Mosfet and PWM to precisely tailor the weld output with no heat output and I have also managed to really crank up the frequency--to the point that I can scratch TIG, run a wire feed, etc..
So, like I posted earlier, you can produce a welder very easily, but if you want to have a unit that will last a long time and produce consistent, quality welds, you should really get more sophisticated by going the power transitor approach or PWM. The power transitor approach is no more difficult than wiring up the dimmer that you mentioned. All in all, this has been a wonderful project that has taught me volumes.
