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Aircraft Maintenance TroubleShoot > Aircraft Generator Aircraft Generator parallel charging system (Delco Remy style)DescriptionAccessory loads make it necessary to use two generators in the electrical charging system of twin engine aircraft. Whenever two separate generators charge into the same battery, a paralleling generator-regulator system is necessary for proper operation of the charging system. In most instances the generators will be identical and the regulators
involved are standard three unit regulators with a "paralleling winding"
on the voltage regulator unit. These paralleling windings function in such
a manner that each generator tends to take an equal portion of the electrical
load. An external two unit paralleling relay also provides for separate
operation of either generator, should one become inoperative.
Operation of the paralleling systemThe cut-out relay, current regulator, and voltage regulator unit of paralleling regulators function in the same manner as standard regulators. The paralleling coil, located on the voltage regulator unit of each regulator, is connected into the circuit so that it either aids or opposes the voltage regulator shunt winding, depending on the direction of current flow thru the coil.When the operating voltage of one regulator tends to be at a different voltage than that of the other regulator, current will flow through the paralleling coils from the regulator with the higher setting. The paralleling coils are connected so that this current flow lowers the voltage of the regulator with the highest setting and increases the voltage of the regulator with the lowest setting. The amount of current which flows through the paralleling coils is the amount required to cause the regulators to operate at the same voltage. The two-unit paralleling relay acts as a switch to either join or separate the ends of the paralleling coils of the two regulators. Each set of contacts in the external two-unit paralleling relay close when the voltage of each respective generator reaches the value for which the relay is adjusted. These contacts close the circuit joining the ends of the paralleling windings on the voltage regulator units. If one generator should fail, the contacts of the paralleling relay unit of that charging system open, breaking the circuit between the paralleling windings. If the other generator and regulator are not defective, they will operate as a normal single generator system. Efficient and proper operation of the paralleling system depends
upon the following items: (a) The resistances of the circuit between junction
A of the generator and the "BAT" terminal on each regulator must be equal,
(b) The resistance of the lead between the "BAT" terminal of each regulator
and junction A of the generator must be .01 ohm +- 10%, and (c) The resistance
of the lead connected to the paralleling terminal of the regulator and
the relay must be kept at a minimum on each regulator (not more than .01
ohm).
Testing the regulator paralleling coilWith leads disconnected from the regulator, connect a 110 volt test lamp between the "BAT" terminal and "P" terminal of the regulator. If the lamp does not light, the paralleling winding is open. Take appropriate cautions when working with 110 voltage. Check for a ground by connecting the 110 volt test lamp between the "BAT" terminal of the regulator and the regulator base. If lamp lights, the paralleling winding is grounded.References: Delco Remy Field Service Bulletin DR-1023 dated 12/30/58. Lycoming Service Letter L104B which references DR-1023 and includes a copy of DR-1023
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