Things That Work: The BWC 1500 Windpower Generator Tested by Mick Sagrillo c.1992 Mick Sagrillo For about 13 years, the name Bergey has been synonymous with "state of the art" in wind generators. Needless to say, when I heard that they had replaced their 1000 Watt remote battery charger (BWC 1000) with a new and improved BWC 1500, I was enticed. Bergey Windpower has been building wind generators for about 13 years, with over 1000 turbines scattered across the U.S. and more countries around the world than I care to remember. My new 32 VDC Bergey arrived in Amherst just in time for the 1991 Midwest Renewable Energy Fair. In the crate, everything was laid out in one neat bundle: the generator, tail and fin, blades, control box, and the ever important Installation Manual. I assembled the genny and solicited a few "volunteers" to help hoist the Bergey up onto the stub tower that I had built. Later in the afternoon that I had a chance to take a good look at Bergey's latest design. Three Moving Parts This wind generator is the height of simplicity. Mike Bergey explains his design philosophy by quoting Antoine de St. Exupery: "Perfection is achieved not when there is nothing more to add, but when there is nothing more to take away." The BWC 1500 reaches this goal by having just three moving parts: the rotor, the yaw, and the tail. Most alternators have the current-producing windings attached to the outer frame. This is known as the stator. The field rotates within the stator, and is known as the rotor. Slip rings are used to carry current to the spinning rotor to excite the field, and thereby generate power. The BWC 1500 generator is permanent magnet in design. This unit produces 3 phase wild (i.e. variable frequency) AC. The stator is attached directly to the mainframe of the wind generator and doesn't move. The permanent magnets, which produce the field, are mounted in the outer housing, called the magnet can. This magnet can rotates around the fixed stator. Since permanent magnets are employed, there are no brushes to wear out. Attached to the front of the magnet can are the three blades. So far, we're generating electricity with only one moving part; the magnet can. The second moving part is the yaw bearing which allows the mainframe/alternator, with the help of the tail, to follow the shifting wind. The entire mainframe assembly is offset slightly to the side of the yaw bearing. Strong winds try to push the rotor around the tower. Since the machine is offset, not directly in line with the center of the tower, it can do this. This "self-furling" protects the genny from excessive winds. Bergey controls the furling with the free floating tail, the third moving part. The tail is hinged at the rear of the mainframe, but the hinge is canted several degrees from true vertical. As the wind blows harder on the rotor and furls it around the tower, the tail continues to track the wind. Because the tail is mounted onto what is in effect a cocked hinge, it moves slightly upward as it furls, just a few inches. In the fully furled position, which is achieved when the wind is blowing its hardest, the blades are nearly parallel with the tail. See Fig. 1. When the wind diminishes, the pressure on the rotor decreases. Since the tail has moved "uphill", gravity pulls it back down to its original position. The rotor faces the wind head on again. The Rotor Bergey flies three blades rather than two. A three-blade rotor will yaw with the shifting wind much smoother than a two-blade rotor. When the blades of a two blade rotor are lined up vertically, they offer little resistance to yawing motion. However, when the blades move one quarter of a turn and are in a horizontal position, they exert maximum resistance to yawing. This continuous shifting of resistance to yaw jerks the wind generator as it hunts the wind. These vibrations eventually degrade the entire system. The inherent imbalance of a two blade rotor is totally eliminated by adding a third blade. The blades are made of extruded fiberglass with pitch weights mounted about three quarters of the way out the blade. The blades are mounted on the magnet can at a greater angle of attack than what is ideal for operating speed. Greater angle of attack means that the blades develop more torque to get the rotor started from stand-still. As the rotor spins up, the weights flatten the pitch of the blade out by 4 or 5 degrees at the tip of the rotor. This improves upper end performance at higher rpms, where performance is really needed. The best part of this design is no moving parts! As the blades are very flexible, Bergey offers an extra-stiff blade option for very turbulent areas. The Manual The BWC 1500 Owner's Manual covers the basics in 20 pages. However, Bergey does provide the 90 page Installation Manual for the BWC 1000, which is one of the most thorough documents on small wind generators and tower installation I have ever read. Beside the usual topics of assembly and installation, Bergey also covers legal restrictions, site considerations, tower selections for a variety of towers, a very extensive section on tower anchoring for various locations and situations, another great section on wiring for all applications, tool requirements, and various schematic diagrams. They even cover such esoteric subjects as a life cycle energy cost analysis. Built to Last Bergey set out to develop and build a wind generator that would last the generations, the same approach taken with the famous Jacobs Wind Electric wind systems of the 30s and 40s. Attention to detail is what sets this machine apart. All painted surfaces are coated with DuPont Imron, probably the most indestructible, as well as the most expensive, paint available today. The mainframe and tail boom are hot-dip galvanized inside and out. The slip ring brush cover is made of clear yet unbreakable Lexan. All hardware, as well as the tail pivot pin, are stainless steel. The quality of the materials used by a wind generator manufacturer is usually reflected in the maintenance that the machine will need. Skimp on materials, and something will eventually rust off, resulting in necessary repairs if not an outright catastrophe. Installation We finally got around to installing the BWC 1500 last fall. The tower top weight of the unit is 168 pounds, not something you want to carry up the tower on your back. Up went the gin pole and cables. We assembled the BWC, with the tail, on the ground in about half an hour. The next step was to hoist the genny up the tower via the gin pole with the help of a tractor. Getting the unit on top of the tower in place took less than two hours. Attaching the blades, tail pullout cable, and electrical wiring took another hour. Back on the ground, we spent another hour installing the control panel and a fused disconnect switch. The entire operation, including wrestling the gin pole and hoisting cables up and down the tower was about a day's work. This was with an experienced crew of two: a ground person and a tower person. We weren't out to break any records. It was a nice way to spend an autumn day. The Controls It was time to throw the disconnect switch and crank the tail into the wind. The BWC came smoothly up to speed, and began pumping amps into the 32 Volt battery bank in the shop. The folks at Bergey told me that the controller tapers the charging current to maintain a constant battery voltage by cutting off a portion of the sine wave (remember, this is a three phase wild AC alternator, not a DC generator). Rather than regular rectifiers, the controller uses SCRs, that is silicon controlled rectifiers, or diodes with a gate for turning them on and off. The controller is compatible with both lead acid and nicad batteries. System Versatility The alternator stator is bolted onto the generator mainframe, making it easy to service of the stator in the field. If your system voltage requirements ever change, you need only change the stator and the regulator voltage card. This offers a certain degree of modularity to the BWC 1500. The BWC 1500 is offered with a water pumping option. This is a machine wound specifically for pumping water when connected to a three phase motor. There is a dedicated controller that allows the three phase motor to run at variable speed, depending the power output of the generator. With the addition of a battery charging controller, the water pumping unit will also charge batteries. Why a Bergey? The factory price for the 24VDC BWC 1500 is $3095, plus another $815 for the controller (other voltages cost slightly more). That comes to just over $4000 with the shipping. A lot of money for a wind generator, you say? Well, not really, especially when you consider what you're getting: quality, quality and more quality. Like the Jacobs of a bygone era, this will probably be the last wind generator you'll ever need to buy. As they say down at the complaint counter, "you get what you pay for!" The BWC 1500 was designed for village electrification projects in developing countries and remote/unattended telecommunications installations. Maintenance and repairs promise to be simple. For example, Bergey uses integrated bearing assemblies on both the rotor and the yaw. You won't be needing any fancy pullers or other such equipment. Anybody with an adjustable crescent wrench and a screwdriver can work on a BWC. I asked about allowing the wind generator to freewheel. Freewheeling means letting the blades run without a load on them. Virtually all manufacturers turn white at the mere mention of letting their machines freewheel. With no load, wind generators can reach dangerously high speeds, often self destructing. Mike Bergey's comment was "Let it go!" Thinking that he had misunderstood my question, I clarified myself. Mike's response was that I could let it freewheel in any wind speed that I wanted, that the BWC 1500 was built to survive. That's confidence in a job, (or in this case, a product) well done! Access Author: Mick Sagrillo flies a BWC 1500 at Lake Michigan Wind & Sun, E3971 Bluebird Rd., Forestville, WI 54231 ¥ 414-837-2267 Bergey Windpower Company, Inc., 2001 Priestley Ave., Norman, OK 73069 ¥ 405-364-4212