Figure 9-98.  A static inverter. Paralleling Alternators or Generators Light Multiengine Aircraft Multiengine aircraft typically fly faster, higher, and farther  than single engine aircraft. Multiengine aircraft are designed  for added safety and redundancy and, therefore, often contain  a more complex power distribution system when compared to  light single-engine aircraft. With two engines, these aircraft  can drive two alternators (or generators) that supply current  to the various loads of the aircraft. The electrical distribution  bus system is also divided into two or more systems. These  bus systems are typically connected through a series of circuit  protectors, diodes, and relays. The bus system is designed to  create a power distribution system that is extremely reliable by  supplying current to most loads through more than one source. Today’s aircraft employ solid-state control circuits to ensure  proper paralleling of the alternators. Older aircraft use  vibrating point voltage regulators or carbon-pile regulators  to monitor and control alternator output. For the most part,  all carbon-pile regulators have been replaced except on  historic aircraft. Many aircraft still maintain a vibrating point  system, although these systems are no longer being used on As can be seen in  Figure 9-100 , both left and right voltage  regulators contain a paralleling coil connected to the output  of each alternator. This paralleling coil works in conjunction  with the voltage coil of the regulator to ensure proper  alternator output. The paralleling coils are wired in series  between the output terminals of both alternators. Therefore, if  the two alternators provide equal voltages, the paralleling coil  has no effect. If one alternator has a higher voltage output,  the paralleling coils create the appropriate magnetic force to  open/close the contact points, controlling field current and  control alternator output.  Since two alternators (or generators) are used on twin engine  aircraft, it becomes vital to ensure both alternators share the  electrical load equally. This process of equalizing alternator  outputs is often called paralleling. In general, paralleling is a  simple process when dealing with DC power systems found  on light aircraft. If both alternators are connected to the  same load bus and both alternators produce the same output  voltage, the alternators share the load equally. Therefore,  the paralleling systems must ensure both power producers  maintain system voltage within a few tenths of a volt. For  most twin-engine aircraft, the voltage would be between  26.5-volt and 28-volt DC with the alternators operating. A  simple vibrating point system used for paralleling alternators  is found in  Figure 9-100 .  Figure 9-99.  Distribution circuit. .  Inverter power switch (optional) DC bus A C L O A D S Inverter Various DC loads 115 VAC (optional) AC loads Power from aircraft battery  or alternator DC AC 9-57