The output is controlled by means of a three position illuminated rotary switch. It has a maintained and momentary position, and a center OFF. When turned ON, a relay is energized and the internal lamp is illuminated. The contacts of the relay provide AC voltage directly to one pair of yellow binding posts, and through a full wave bridge rectifier to a pair of red and black binding posts. LED indicators next to the binding posts and near the meter indicate AC or DC mode.
A 20 kOhm load resistance is connected to the DC output along with a 12 volt zener diode and an indicator LED. This provides a 3-12 watt load for the DC output, and indicates if there is an output voltage above about 20 volts as a safety precaution.
This power supply has no filter capacitors, and is intended to be operated with no load capacitance. If a capacitive load is applied, the output voltage may increase to as much as 140% of the unfiltered output value, and the voltmeter will not read correctly. The voltmeter will read the unloaded AC voltage that will be applied to the output. The actual AC voltage will drop by as much as 11% under rated load, and the voltmeter will read the actual voltage. The calibration resistor for DC will be set so that the voltmeter reads the expected DC output at no load, but this will drop by 11% or more depending on actual load. Snubbers are connected across the output terminals to reduce noise and high voltage spikes when connected to inductive loads.
This is a small portable AC and DC power supply intended for circuit breaker charging motors and other general purpose applications. It will provide AC and DC voltage in three nominal ranges from 0 to 120, 240, and 480 volts, at 2 kVA. It is housed in a rugged enclosure approximately 21.5” x 18.5” x 11.5”, and weighs approximately 70 lb.