Troubleshooting “Little Jake”

One of the three wind turbines at the Midwest Renewable Energy Association (MREA) in Custer, Wisconsin, is a vintage machine that has its roots in the days before rural electrification. Made in 1946 by Jacobs Wind Electric, the 3.6 kW turbine was originally marketed to homes and farms that had no access to the electrical grid, and was used to charge batteries to run low-voltage DC lights and appliances.

In the 1980s, wind energy expert and MREA founding member Mick Sagrillo brought this turbine to his renewable energy shop in Wisconsin, where he remanufactured nearly every component. He donated the machine, top tower section, and controller to the MREA and led an installation workshop in July 2000 to erect and commission the system. Here at the MREA, it’s affectionately called the “Little Jake,” so we don’t confuse it with the 20 kW Wind Turbine Industries Corp. (WTIC) wind turbine (also an original Jacobs design) on site, which was recently modified into a 17.5 kW machine.

Little Jake is a 600-pound, upwind machine (meaning that the blades face the wind ahead of the generator) with a 14-foot-rotor diameter and a swept area of 154 square feet. The three blades are made of robust Sitka spruce, and finished with high-quality automotive paint and leading-edge tape, used on helicopter blades for durability. In a 24 mph wind, the rotor rpm is 325, and the system produces 3,600 watts. Little Jake will cut in at 6 mph and start to govern at 27 mph. In high winds, the pitch-control governing system automatically allows the blades to twist from their optimum aerodynamic orientation, “shedding” wind to protect the machine. For user/technician shutdown, the manual furling mechanism folds the tail, which pulls the blades parallel to the wind. It is activated at ground level via a chain that runs from the tail, down the tower, through a pulley, and to a hand crank.

This Jake is a DC generator, quite unlike a modern three-phase permanent-magnet alternator. The field poles and windings contain a residual magnetic field within their iron cores. When the turbine blades are driven by the wind and the armature rotates within the magnetic field, current is induced into the armature, and brushes that ride on the commutator deliver that power through a slip-ring assembly (so the turbine can freely yaw without twisting wires) and down the tower to the balance of system components. This machine is battery-based, so the controller delivers the DC voltage from the generator to a battery bank and diversion loads. If the batteries are full, the power is routed to a load center and to the electrical grid through an OutBack inverter to provide utility-intertied and backup energy for the MREA.

After almost 11 years in service, MREA staff noticed that although Little Jake was spinning, no voltage or current was displayed on the controller—the system wasn’t delivering power. Initial investigations showed no signs of open or shorted wires, failed diodes, blown fuses, nor tripped breakers. Little Jake needed a more thorough inspection and, fortunately, the organization’s July wind turbine maintenance and repair course was only a few weeks away. MREA small wind instructor Cris Folk and I were excited to have the opportunity to teach troubleshooting techniques on an installed machine with a real-world problem.

Troubleshooting Little Jake

The key to successful troubleshooting is to isolate and test individual system components and understand the order in which they operate. Cris and I would rely on this rather than “swaptronics”—the replacing of components until the system eventually worked again. Swaptronics is a sorry excuse for troubleshooting—plus we didn’t have spare parts to swap. We would have shared with the students the manual and/or schematics for the system—if we had any such documentation. But other than Mick’s drawings and descriptions, we had nothing.

Any component or portion of the system tested and deemed “good” would be scratched off our list of possible causes. This process of elimination would point us toward the problem and its solution. We broke the system down into three areas:

Balance of System (BOS)

• Controller voltage checks
• Inverter voltage checks
• Battery bank voltage checks
• Verify correct setpoints in the inverter and diversion loads