Direct Current (DC)

Parallel DC Circuits

Has two or more electrical resistances or loads, connected across the same voltage source. If one component fails, no effect on the other components. Differs from series circuit in that more than one path is provided for current flow- the more paths added in parallel, the less opposition to flow of electrons from the source. When applied to batteries, amperage is added, voltage is constant in the circuit.

Parallel Circuit Requirements

1) Power source 2) Conductors 3) A resistance or load for each current path 4) Two or more paths for current flow

Direct Current

Electricity non-varying in nature. Obtained from battery or power supply. Amplitude of voltage and current remain steady. Referred to as Pure DC- No alternating current, noise, etc.

Series DC Circuits

Only on path for electrons to flow. When there is a break in the circuit complete circuit failure. Example- cheap Christmas lights. When applied to batteries, amperage is constant, voltage is cumulative (added) for each battery in circuit. Example- Beechcraft Baron- Two 12 volt, 18 amp, connected in series = 24VDC and 18Ah

DC Terms and Values

Polarity is determined by establishing a reference point and measuring a voltage in reference to that point. Typical battery 12 VDC positive polarity in small general aviation aircraft or 28 VDC in transport type aircraft.

Transformer Rectifier Unit (TRU)

TRU's are utilized to convert 115VAC, 400HZ into 28VDC. A transformer is used to reduce the voltage from 115 volts to 28 volts. At this point the 28 volts is still AC current. To change the current from AC to DC, a rectifier is used. Each aircraft AC bus feeds a TRU which feeds a DC bus. AC to DC is transformed by a TRU. DC to AC is used by the inverter.