I am an electrician doing qualification testing of a 10KW power amplifier. Internally it has a single phase 220VAC input transformer driving a full- wave bridge rectifier and then large filter capacitors on the DC line. The end-use will be 50/60Hz ballast testing. I need to set up a worst-case test for capacitor heating. Please correct me if I am mistaken, but I think that the worst case is when the output feeds a resistive load bank with a sine wave that is phase shifted 90 degrees from the AC power input. The amplifier input has a 1 MegOhm input impedence and requires a 10V peak- to-peak input to reach the rated output voltage. I also have a 25KW load bank on the output that can be set to draw whatever current I want it to. I can get a capacitor load bank if needs be but it would be a hassle. If I remember correctly from my electronics 101 class, I can use a resistor and a capacitor to generate a 10VPP (7.07VAC RMS) sine wave with close to a90 degree phase shift from my 220VAC input. I am not quite sure how to calculate the resistance and capacitance to get a 7VAC 90 degree phase shifed output from my 220VAC input. What values should I use? Does the capacitor or the resistor go from the 220VAC to the amp input? Does the capacitor or the resistor go from the the amp input to common?
I am connecting at the service entrance where 220VAC GND and 220VAC NEUTRAL are connected together, and I am seeing less than 1/20th of a volt AC between them at the amplifier AC power input. Here is what I am going to test next week unless someone tells me differently:220VAC GND -> AMPLIFIER CHASSIS 220VAC NEUTRAL -> AMPLIFIER AC POWER INPUT 1 220VAC HOT -> AMPLIFIER AC POWER INPUT 2 220VAC HOT -> 10 Microfarad 300V AC-Rated Capacitor 1 10 Microfarad 300V AC-Rated Capacitor 2 -> 3300 Ohm 25W Resistor 1 3300 Ohm 25W Resistor 2 -> 100 Ohm 10W Rheostat (Potentiometer) CW 100 Ohm 10W Rheostat (Potentiometer) CCW -> 220VAC NEUTRAL 100 Ohm 10W Rheostat (Potentiometer) WIPER -> AMPLIFIER SIGNAL INPUT HIGH 100 Ohm 10W Rheostat (Potentiometer) CCW -> AMPLIFIER SIGNAL INPUT LOW
Will this give me a 7VAC sine wave with close to a 90 degree phase shift between 220V and Amplifier input?
I also have some 12V Zener diodes (current rating unknown). Should I put two of them connected back-to-back parallele across Rheostat CW and Rheostat CCW?