The vast majority of the GA fleet is still flying behind ancient generators, or at best legacy alternators and voltage regulators designed in the 1960s or earlier. Most common legacy aircraft alternators are three-phase designs that generate alternating current (AC) power using windings spaced 120 degrees apart within the stator, which is then rectified using diodes into direct current (DC) power for use in the aircraft’s electrical system. These original alternators were sized to meet the amperage (current power demand) anticipated by the typical aircraft equipment from a time when most of today’s pilots were still in diapers. Oh, how times have changed…

The advent and market success of so many electron-hungry devices in today’s aircraft have shifted the demand curve substantially in a way many mechanics and aircraft owners have not kept pace with. While it’s true that every electrical equipment installation requires that mechanics perform an electrical load analysis to make sure that adequate power is available, these calculations are made using average power numbers, rather than peak demands. Consider that for a particular set of LED lights, the wingtip and tail position lights draw 0.2 amps of constant power, while the corresponding wingtip anticollision lights draw 0.56 amps average load, and 2.09 amps peak load. The tail anticollision light draws 0.72 amps average load and 3.8 amps peak load.

The average amperage draw for this setup would be calculated by adding up the averages for both position and anticollision lights for two wingtip installations and one tail light installation. In our example, this equals an average power draw of 2.44 amps. Chances are, this is equal to or less than the power draw of the old incandescent lights that this LED installation replaced. However, this calculation doesn’t tell the complete story of the power draw on the aircraft’s electrical system because at the moment that those anticollision lights are on and emitting light, the peak power draw for the entire system is much higher at 8.58 amps. That’s 3.5 times higher than the power draw the mechanic probably calculated when evaluating the capacity of the aircraft’s electrical system. To be clear, this isn’t an issue limited to LED lighting upgrades. The same math applies to radios, navigators, portable device chargers, and anything else that draws power from the aircraft.

The difference between average and instantaneous power draws can result in effects ranging from pulsing ammeters to flickering panel lights, and even uncommanded avionics reboots. I recently encountered this issue with the air conditioning system I added to my own airplane. I noticed a voltage drop and corresponding ammeter needle jump at a fairly regular interval of about every five minutes when the system was operational. At one point, the alternator even tripped offline, I suspect because of a transient voltage spike. It turns out that this correlated to the running of the condenser fan, which was controlled by pressure switches. While the power consumption of the running fan was well accounted for in the power requirements of the system, the instantaneous power draw (inrush current) to start the fan spinning was far higher, causing the spike in the voltage and amperage demands.

To meet the electrical demands of equipment added to our aircraft, we need to address both the quantity and the quality of the power available. The quantity of power available can often be addressed by upgrading the alternator to a modern, high-capacity model available for the aircraft/engine combination. The quality of the power, on the other hand, is a combination of the alternator and voltage regulator.

Voltage regulators serve a critical purpose in aircraft electrical systems by maintaining a steady-state voltage throughout the aircraft across varying engine speeds and electrical loads. They do this by monitoring the bus voltage of the aircraft and varying the field voltage of the alternator, effectively “throttling” the alternator output up or down as needed. They often include an over-voltage cutout to protect other systems on the aircraft as well. Older voltage regulators are electromechanical devices that can physically wear out over time, are subject to heat-related degradation, and do not cope well with instantaneous voltage or power demands. They can also trip for false or transient, over-voltage conditions.

Fortunately, the aviation aftermarket has produced some remarkably advanced alternators and voltage regulators to address the issues of both quantity and quality. Hartzell Engine Tech, for example, produces modern alternators under the Plane-Power brand that not only offer increased power output, but also make this power available at much lower revolutions per minute when the aircraft is at idle and do so with “cleaner” power output. Many of these alternators include a six-phase, hairpin stator design similar to that found in modern luxury cars. The result is power-on-demand capacity that is light-years ahead of the ancient alternator design that came from the factory on most aircraft.

In addition, Plane-Power voltage regulators are solid-state devices that react faster to demand changes and have built-in logic to protect your aircraft and avionics from over-voltage conditions, while coping with variations and transient conditions caused by device demands such as LEDs (and my power-hungry fan startup).

By upgrading power generation and power regulation, you can ensure that your aircraft has a steady power supply that can meet both your average and peak electrical demands without causing issues for the sensitive devices in your panel. As with all maintenance upgrades, a little planning goes a long way to avoiding unforeseen issues in the future. Until next time, I hope you and your families remain safe and healthy, and I wish you blue skies.