Over the past five months we have been working our way through a 96-inch Evo motor build project. As with any motor build, there are various stages of assembly. For this project we have chosen to give our readers an in-depth look at all of the steps involved in assembling a high-performance powerplant. While some may think this project has been drawn out, there is a reason for this. We want to show all the steps, procedures, and tips that go into a complete motor build. We could have built the entire motor in one shot and run accompanying text and photos over one or two issues, but that just wouldn’t cut it. There would be no way we would be able to give you a detailed view of exactly what was going on and how all the different components work in conjunction with one another. This month we will tackle the charging system.

Charging systems are necessary on most contemporary American V-twins; without them you would not be able to start the bike, keep it running, or be able to operate any of the electrical systems on the bike, including lighting, battery charging, and accessories.

The majority of today’s charging systems consist of three basic components: a stator, rotor, and regulator. A stator is a stationary piece, made up of a lamination stack wrapped with copper wire. The configuration of the stator is such that its core is designed in a circular fashion measuring approximately 5-1/4 inches in diameter with a hole in its center allowing it to be slid over the crankshaft’s sprocket shaft. Once in position, it is bolted to the left case half. With the stator installed, the rotor, a steel shell larger in diameter than the stator, with magnets affixed to its interior circumference, is slipped over the output shaft and secured to the shaft. The system’s final component is the regulator, which takes the electrical current produced by the action of the magnets passing over the copper-wrapped lamination stack and changes the voltage from the stator from AC to DC. Then, through a series of circuits, the voltage regulator supplies 14.2 volts to the battery.

The particular system we have chosen to install on our 96-inch Evo is Compu-Fire’s latest offering, the 40-amp three-phase charging system (MSRP: $399.95). What differentiates this system from others is the fact that it operates on a principle of three-phase wiring, as opposed to most other charging systems, which operate on a single-phase theory. The new system allows for more current to be available at lower rpm. Typical systems produced in the past were unable to supply electrical power at or below 1,500-1,800 rpm. This can become a problem in a couple of different scenarios, such as when the bike idles or runs at low rpm for long periods of time (when sitting in traffic or cruising Main Street at Daytona, for instance). The second and less apparent reason has to do with the proliferation of six-speed transmissions. Lots of guys get out on the highway, hit 65 mph, and drop the bike into overdrive. Depending on a variety of factors, including primary and final gearing, as well as tire size, it is very easy to have the motor operate in an rpm range that will not provide an adequate charge for the battery. The 40-amp three-phase charging system is designed to provide 25 amps at idle and 40 amps continuously above 2,800 rpm.

Other features built into the Compu-fire system include a vented rotor, which allows for cooler operation, translating into a constant current output. In addition, the regulator operates on a series-circuit principle as compared to a shunt-type regulator, which is common with many OEM systems. What this does in principle is turn the output of the stator on and off as opposed to running the excess current to ground, which tends to create more heat in the stator.

While the charging system can be installed easily with the motor in the bike, we decided that since the motor was still sitting on the bench, we would work there to make the photography that much easier. Once we have the bike back in the shop, we will mount and wire the regulator.