Hello All,
I am looking to make a whole house fan. I have a 1.5hp 115V single phase motor. Nominal rpm is 3600. I have fan blades for it from a 220v 1/10hp that is 800 rpm. I would like to control the 1.5hp motor to a max of 1000rpm, but also be able to have a low speed (maybe 300rpm).
I would like to do this using a PIC controlling a relay that would open and close as necessary for the PWM. I don't have any experience using any of this, so opinions on the setup would be appreciated.
It seems as if a PIC would have no problem switching power on and off to the relay quick enough, but would the relay respond fast enough? I will have to test, but I think it will have to cycle maybe 5 to 10 times a second to control the speed properly. Is a solid state relay the best choice or is there another type that I'm not aware of that would work better?
Other issues I have to work through is that this motor has start and run capacitors. Obviously I have to remove the run capacitor, but I worry about amp draw when the relay switches on. Shouldn't be too much with the shaft free spinning already. Since I'm slowing the motor down, I may have to have another relay disable the start capacitor because the centrifugal switch that disconnects the start capacitor doesn't engage till about 75% of rated speed (from what I've read anyway).
Goals right now are to just have a low, medium, and high option. Future plans include a temp sensor to automatically start the fan. I'm open to other ways of controlling the speed, but PWM is the best I've found so far. And resistors would waste way to much energy with this motor. I'll worry about what PIC to use after I've settled on the speed control issue.
Thanks in advance, Jerry
I am looking to make a whole house fan. I have a 1.5hp 115V single phase motor. Nominal rpm is 3600. I have fan blades for it from a 220v 1/10hp that is 800 rpm. I would like to control the 1.5hp motor to a max of 1000rpm, but also be able to have a low speed (maybe 300rpm).
I would like to do this using a PIC controlling a relay that would open and close as necessary for the PWM. I don't have any experience using any of this, so opinions on the setup would be appreciated.
It seems as if a PIC would have no problem switching power on and off to the relay quick enough, but would the relay respond fast enough? I will have to test, but I think it will have to cycle maybe 5 to 10 times a second to control the speed properly. Is a solid state relay the best choice or is there another type that I'm not aware of that would work better?
Other issues I have to work through is that this motor has start and run capacitors. Obviously I have to remove the run capacitor, but I worry about amp draw when the relay switches on. Shouldn't be too much with the shaft free spinning already. Since I'm slowing the motor down, I may have to have another relay disable the start capacitor because the centrifugal switch that disconnects the start capacitor doesn't engage till about 75% of rated speed (from what I've read anyway).
Goals right now are to just have a low, medium, and high option. Future plans include a temp sensor to automatically start the fan. I'm open to other ways of controlling the speed, but PWM is the best I've found so far. And resistors would waste way to much energy with this motor. I'll worry about what PIC to use after I've settled on the speed control issue.
Thanks in advance, Jerry