Vehicles in the avionics class have come to rely heavily on autonomous power supply units which give way to total control without the assistance of, or the need for, an external source. A flight control system can be charged and operate on its own through a 24V auxiliary power unit, a DC amp and volt that filters bus power by way of an APU receptacle.
Voltage and current information placed on the panel meters can be viewed by any experienced operator. Current limits are generally placed on the electrical output level, so the unit is able to withstand the starting load from a cold state. For safety purposes, the voltage is restricted in order to prevent overcharging, which is more damaging to systems than most realize.
A main switch in the cockpit activates the 24V auxiliary power unit. It is recommended that operators carefully examine AC requirements shown on the charger identification tag. Also, the unit works best, and without hazard, when it is used on a circuit featuring 20 amp branch circuit protection. Some units require grounding and some do not. If grounding is necessary, the necessary plug will come standard. For these types of auxiliary power units, the use of a 60 hz circuit is optimal.
Unit functions should be compatible with the flight control system of the aircraft. Integration is usually not a key function of this type of device, and operators should be careful not to attempt to rig or adjust the device or any APU receptacle parts any way.
