PARALLELING OF ALTERNATORS

• On Dual Engine Aircraft, where two alternators provide electrical power to a common bus, it is necessary to balance the output of the alternators so that both contribute approximately the same amount of power to the bus load. This balancing procedure is called "Paralleling" the alternators.

• To accomplish the load balancing or the paralleling procedure, an accurate ammeter, either of the shunt type or direct reading type should be installed in the output line of each alternator. It does not have to be a permanent installation if so desired, as the ammeters are a must only for paralleling procedure. The more accurate the ammeter the more perfect the load balancing. However, for practical purposes, + 10 to 20% load balancing between alternators is satisfactory.

• With both engines off, start one engine and allow it to stabilize. Adjust regulators to 14.5 Volts for a 12 Volt system, and 29 Volts for a 24 Volt system. Shut the engine down and repeat this procedure for the other engine. This establishes a common voltage datum.

Place a load on the system bus, roughly one-half (1/2) the operational load is ideal, lights or any applicable load is satisfactory. Start both engines and allow them to stabilize. Now the paralleling operation will be done one regulator only. It does not make any difference which one you choose to use. Do not adjust the other regulator, using one regulator makes life simple! Observe the ammeter readings of both alternators and adjust  (one) regulator until both alternators outputs are approximately the same. As you slowly adjust the regulator, you will see a rise in the current from the other alternators, and a drop in current from the other. Do not panic, adjust the regulator slowly, as it is a sensitive adjustment. Adjust the one regulator until both alternators are providing approximately the same output to the bus.