July 2014- I’ve always liked generators. Unlike alternators, they will provide electrical power even if the battery is dead since generators depend on residual magnetism to provide the lines of magnetic flux needed to produce output.
Generators are tough, too: unlike alternators, they don’t need a rectifier bridge to convert the alternator’s alternating current (AC) output to useable direct current (DC) for our airplane electrical systems.
And, they’re cheap. I can buy a belt-driven replacement Delco generator for my Comanche (or for almost any airplane that uses a belt-driven generator) by shopping the internet. The last one I bought—a 50 amp Delco 1101915—cost less than $50.
That unit wasn’t ready for installation, though. (An identical but freshly overhauled generator would have set me back around $250.) I paid $50 because my great buy needed a little maintenance. I tuned it up by smoothing out the commutator, undercutting the segments, testing the armature on a growler and installing a set of brushes.
I had already bowed slightly to new charging system technology by upgrading from the original vibrating point regulator/reverse current relay to a solid-state generator voltage regulator from Zeftronics, but I just wasn’t quite ready for an alternator.
So, what did all this work refurb work get me? A weighty, current-limited DC generator that made a lot of electrical noise and didn’t come online until around 1,400 engine rpm. (This magic number varies, but is always above 1,200 rpm.) That was okay for the day VFR flying I favored, but every pilot flying a generator-powered airplane knows these old-technology units have one or two drawbacks.
Any time the engine rpm drops below the magic rpm number, the battery alone takes over the task of powering the avionics, the pitot tube heater, the landing and taxi lights, and the landing gear motor (if equipped). One wise soul once described a typical light aircraft battery as little more than a wide spot in the wires; for every minute the battery is carrying the full aircraft electrical load, the reservoir of “juice” in the battery bank is shrinking.
Let’s say you’re flying a GPS approach into the home ‘drome on a dark and gusty night at the end of a long day and you realize you’re high. Whaddya do? If the power reduction needed is slight, you’re still good; but if you have to reduce power below your airplane’s magic rpm threshold, you’re on battery power. You’ll know it because the landing lights will dim.
Or, imagine this: you’re in a departure hold waiting to launch into the clag on an IFR flight plan. Do you ride the brakes because you have to keep the rpm up to keep the generator online, or pull the power back, reduce the electrical load and taxi slowly (and dimly) until it’s your turn to take off? (Don’t forget to turn everything back on before launching!)
And then there’s the task of polarizing. After extended non-flying periods it seemed like my generator would never come online as I taxied out to launch. So I would have to I shut her down, get out, rummage in my toolbox for my jumper wire and do the polarization dance at the regulator. It takes a jumper wire and less than 15 seconds to again set things right.
That process is relatively easy on my Comanche because the cowling opens quickly. On fully-cowled airplanes, it takes longer. The nontechnical term for this is “flashing the field.” It’s not difficult to do but can be inconvenient.
Recently my $50 generator started acting up, so I started shopping around for an alternator conversion kit. It had to be FAA approved for installation on my airplane, and it had to be made by a company that’s been around and provides good customer service.
The only company I found that sells a belt-driven FAA-approved generator-to-alternator kit is Plane-Power out of Granbury, Tex. So I bought an SAL12-70 kit and took off the old generator. It was way past time to go modern.
Save weight?
One of the advantages touted by the alternator replacement vendors is a marked weight savings when old-style components such as generators and Bendix-engaged starters are replaced with modern units.I weighed everything I took off (mounting, tension arm, regulator, generator) and compared it to my new Plane-Power replacement parts. The weight savings must be on the starter conversions, because installation of the alternator only saved 4.4 pounds (17.4 pounds versus 13 pounds). Still, that’s part of a gallon of gas.
Quality components
Every component included in the Plane-Power kit appears to be very well made and well finished. The kit includes a new alternator (12 VDC and 70 amp), two mounting brackets—one for each type of Lycoming engine mounting—a tensioning arm and bolt, an alternator controller (voltage regulator), two placards (“ALT FIELD” and “ALT INOP”), an alternator inoperative light and installation instructions.
The steel mounting bracket and tensioning arm are tough and fit perfectly. As I compared the old black generator to the shiny new alternator, I knew I’d done the right thing. After all, I’d spent the last five years slowly upgrading avionics, reconfiguring the instrument panel, overhauling landing gear components, overhauling the propeller and the engine—and an alternator was almost the final step in my goal of achieving low-maintenance airworthiness.
Plane-Power versus OEM alternators
Although I don’t have a lot of experience with Chrysler series or Prestolite light airplane alternators, I have spent quite a bit of time helping association members troubleshoot single engine Cessna alternator problems.
The alternators on single engine Cessnas are derivations of the Ford automotive alternators, and the biggest problem revolves around the rectifier bridge; specifically, one or more failed diodes in the rectifier bridge. When a single diode fails, two things happen: the voltage output of the alternator drops, and increased noise is generated.
When a diode had failed, the battery would never fully charge and the pilot would report a whine in the headset. This is easy to troubleshoot. Lower the electrical load in flight and turn off the alternator. If the whine goes away, you’ve found the problem.
According to Jason Hutchison, general manager of Plane-Power, the two enemies of alternators are vibration and heat. Plane-Power takes care of the vibration by fine-tuning the balance of the rotating components. The buildup of heat is well controlled by the open configuration of the alternator body (to permit free airflow) and by dual fans—one installed on the front of the rotor to cool the rotor, and one installed on the aft end of the rotor to cool the rectifier bridge—so that no additional cooling is required. Hutchison said that he’s aware of only two rectifier failures in the three years he’s been at Plane-Power.
My Delco generator required a blast tube to direct a one-inch-thick column of ram air to the commutator/brush end to keep it cool but I blocked off the blast tube opening in the cowling when I removed the generator. According to Hutchison, some Plane-Power alternator installations do utilize blast tubes simply because they are approved for replacement of existing OEM units under PMA and as such, mustn’t vary much from the original installation.
My installation
Since the Plane-Power alternator is capable of 70 amps of output, I needed to do some calculations to determine if the existing wiring in my aircraft was big enough. A load analysis revealed a worst-case maximum electrical load—all lights on; pitot heat on; all avionics on; landing gear motor in action; and the assorted smaller loads, such as the LG solenoid—of just over 40 amps.
Then I measured the diameter of the existing generator output wiring and found it to be #4 AWG wiring that can handle a maximum continuous load of 60 amps. No wiring changes were needed. When I discussed this with Hutchison, he told me that there’s almost never a need to change existing wiring unless additional electrical loads are installed or anticipated in the future.
In addition to using the existing output wiring, I also used other existing wiring from the generator system to complete the installation. In fact, I only had to fabricate three short 18 gauge wires; a short jumper from the “enable” to the “aux” terminals on the regulator; and wires from the alternator inop lamp to an existing circuit breaker and to an existing wire that I connected to the “lamp” terminal of the regulator.
The regulator is set to vary the amperage to the alternator rotor slip ring as necessary to maintain 14.0 volts out. It senses the main electrical bus voltage through a field circuit breaker/switch (5 amp) to the “enable” connection that turns the alternator on and off. A jumper from the “enable” connection to the “sense” connection completes the bus voltage detection wiring. I installed a Tyco W31 switch/circuit breaker in the existing row of electrical switches in my instrument panel and installed the ALT FIELD placard above the switch.
I asked Hutchison for Plane-Power’s advice on operations. He replied that he personally starts his airplane with the alternator circuit breaker/switch in the off position for a couple of reasons. First, this procedure permits a pre-start check of the ALT INOP light operation (it should be lit with the alternator switch off) and because there can be as much as 3 amps delivered to the field of the alternator if the switch is on during the start. That 3 amps might make a difference in starting if the battery is weak.
Step four of the Part 1 Installation Instructions read: “Ensure that internal jumper #1 and internal jumper #2 of the R1224 regulator are set for 12V operation.” This step required me to remove the cover of the alternator to visually check the jumpers. Both were correct. The instructions also showed the location of the rheostat that controlled the regulator voltage set point—it is adjustable in the field.
The installation instructions are complete; however, I did have to create a mounting plate for the regulator installation since the Piper regulator mounting holes were wider than the Plane-Power regulator base plate. I mounted the regulator on the base plate of an inop Zeftronics generator regulator base plate with a couple of small screws. Very tidy.
The only other installation concern is the requirement to check to make sure the pulley on the back of the Lycoming ring gear support is 7 ½ inches wide. This caveat is detailed on the Plane-Power website under the Model Eligibility tab.
The installation instructions also direct installers to use a half-inch wide Piper belt that is approximately 33.8 inches long. The old part number for this belt is 452-541 (new number 73965-15) and the street price is around $50. I had recently installed the belt called out in the Lycoming O-360 parts manual (P/N 37B19774-325) and it was too short.
2,000 Hours!
Hutchison pointed out other advantages besides the increased cooling and precision rotor balancing when he talked about the slip rings. “We certify our alternators to 35,000 feet and during testing we found that the life span of the slip ring brush material we were using could be measured in minutes, so we made changes to the material of the brushes,” he said.
He also pointed out another feature incorporated to slow brush wear. “The slip rings in other alternators are three-quarters to one inch in diameter; ours is half an inch. That may not sound like much, but it drastically reduces something called the foot travel per revolution,” he said.
According to Hutchison, the combination of the new brush material and the smaller slip ring has extended brush life so much that Hutchison tells buyers to install a Plane-Power alternator with a new engine installation. When it’s time to send the engine in for overhaul at 2,000 hours, send the alternator back to Plane-Power for an overhaul. He’s had one user who has reported no alternator problems after 3,000 hours of use.
Plane-Power alternators and regulators all come with a two-year warranty.
Overhaul and customer service
Plane-Power overhauls its alternators for a flat fee of $295 and in almost all cases can provide same-day turnaround. According to Hutchison, overhauled Plane-Power alternators are the same as new since many parts are not reused.
There are seven employees at Plane-Power. Hutchison addressed customer service by saying, “Everyone here has a green light to do whatever it takes for our customers. It’s not unusual for one of us to swing by UPS after work to drop off a unit for next-day delivery.”
Plane-Power has incorporated its brand of new technology in a wide range of retrofit and upgrade alternator installations for both direct drive and belt driven applications. Its newest alternator is the ALT-FLX which can be used on both 12 and 24 volt applications that need up to 100 amps in 12 volt versions and 150 amps in 24 volt versions.
The concerns I’d had as a Cessna tech rep have been addressed by the new production and newer technology in Plane-Power’s alternator systems. I’m glad I finally made the switch.
Steve Ells has been an A&P/IA for 39 years and is a commercial pilot with instrument and multi-engine ratings. Ells also loves utility and bush-style airplanes and operations. He’s a former tech rep and editor for Cessna Pilots Association and served as associate editor for AOPA Pilot until 2008. Ells is the owner of Ells Aviation (EllsAviation.com) and lives in Paso Robles, Calif. with his wife Audrey. Send questions and comments to editor@www.piperflyer.com.
RESOURCES
Plane-Power Ltd.
plane-power.com
Zeftronics
zeftronics.com
