Pico-hydro test in La Florida in 2008
The Permanent Magnet AlternatorLast year, we established that the generator was viable as a single point power source that could be installed quickly with limited resources and could produce consistent power with modest water usage. Still unresolved were issues of cost, longevity of service and overall performance for electrical output. The generator was built using a rather expensive modified GM alternator produced in the States for the home brew wind turbine market. This modified alternator, called a permanent magnet alternator (PMA) produces energy at low RPMâ€™s and works well in small-scale hydroelectric systems. In addition to the price, (more that $300.00 U.S.), the alternator would have to be shipped to its destination country, adding additional cost. The PMA was by far the generatorâ€™s most expensive component and the only element in the system that would need to be imported, so we looked to it to reduce the generatorâ€™s overall cost.
My solution was to modify the Nippo Denso alternator produced for Toyotaâ€™s 22R engine. They key was using low-tech mods that could be cheaply and easily reproduced in a basic machine shop. The Nippo Denso alternator, found in most Toyota pickup trucks and many sedans in developing countries, might just be the most common alternator in the world. They are often shipped to developing countries to be rebuilt for the market in the US and other developed countries. Where in the States these alternators are simply replaced with rebuilt alternators when they fail, in developing countries there is extensive infrastructure to rebuild them. They are available in quantity in Guatemala and are cheap.
My design for the Toyota based PMA uses only the alternator casing and the stator (the wire coils that surround the rotor inside the alternator). For the conversion, the rotor is completely rebuilt with powerful neodymium magnets and the stator is rewound with thinner gage wire. Non-functioning Toyota alternators can be had for about $20.00 US in Guatemala if bought in bulk. The magnets are the only part of the new alternator that may need to be imported.
Toyota based permanent magnet alternator
Our new hydro test benchLast year we lacked the facilities to do extensive testing of the PMA and could only determine that, yes, it worked and that it produced energy at low RPMâ€™s. But we couldnâ€™t determine which gauge windings of the stator would produce the most power given the bucket generatorâ€™s RPM ranges. We needed more controlled study conditions, particularly as field tests were difficult to repeat (distance to test site, variability of water flow, etc.).
This past month, we set up both a hydro and a PMA test bench. The hydro test bench simulates the head and water flow rate that determine the output of a small hydroelectric system. By varying the head and flow in the test bench, we can simulate the various conditions under which the bucket generator operates and rate its performance under different loads.
Bucket generator connected to hydro test bench
PMA test bench
Currently, we are trying to determine which wind of the Toyota PMA will give us the maximum current at the RPM ranges of the bucket generator system. At our maximum available head on the test bench, about 90â€™, we were able to produce over 1,200 RPMs and 90 watts. We expect to get more than 100 watts in the field at slightly higher heads. We donâ€™t know yet what the maximum output will be.
This spring, weâ€™ll be installing at least two of the bucket generators in Haiti to power ultra violet water purification equipment. A portion of the funding for this project was generously provided by St Peterâ€™s Church in Weston. AIDGâ€™s Haiti office is partnering with local NGOs, including our good friends at SOIL, to address the lack of clean potable water in their service areas. Each ultra violet purification device draws about 30 watts. With the generator, we expect to be able to power three or more UV devices at 100â€™ of head and 50 gallons a minute of flow. Currently, sites surveys are being conducted in Haiti to determine head and flow conditions and find suitable sites that provide year round consistent water. These long term test sites will provide data on performance as well as service and maintenance needs of the system.
Sam Redfield on Pico-hydro at La Florida
Parts List for Five Gallon Bucket Hydroelectric Generator