Gerald Schwartz
New Member
Hello
I am in the process of building a VERY simple DC motor controller for a 1/3hp, 4a, 90 volt dc motor...I will be using a variable AC switch on the input side, a 5010 full-wave rectifying diode, and would like to add a smoothing capacitor in the output curcuit. My lack of understanding arises in computing the uf rating of the smoothing capacitor. In my searching I have found various formulae which indicate that, at 120V ac input voltage at 60 cycles, with a four amp current draw of the motor, the uf requirement would be in the neighborhood of 2778uf.... My use of capacitors has been limited to repairing motors and building various static and rotary 3ph converters. I have never seen a run-type capacitor anywhere near the rating required in the formulae...I assume that an oil-filled capacitor would be required. What am I missing? In this simple circuit, what capacitor (uf and voltage) would suffice. Jerry
I am in the process of building a VERY simple DC motor controller for a 1/3hp, 4a, 90 volt dc motor...I will be using a variable AC switch on the input side, a 5010 full-wave rectifying diode, and would like to add a smoothing capacitor in the output curcuit. My lack of understanding arises in computing the uf rating of the smoothing capacitor. In my searching I have found various formulae which indicate that, at 120V ac input voltage at 60 cycles, with a four amp current draw of the motor, the uf requirement would be in the neighborhood of 2778uf.... My use of capacitors has been limited to repairing motors and building various static and rotary 3ph converters. I have never seen a run-type capacitor anywhere near the rating required in the formulae...I assume that an oil-filled capacitor would be required. What am I missing? In this simple circuit, what capacitor (uf and voltage) would suffice. Jerry