Build an Odometer Steve Willey copyright 1991 Steve Willey Selecting a site for a windmill can be risky. While the sun shines upon the just and the unjust, the wind only blows on SOME windmills. It is important to know how well a windmill is going to work on your site BEFORE you buy one and risk your life installing it. Unfortunately, a good meter to measure the wind available on a site and report the average speed each day cost as much as buying a small windmill. A few states (notably Oregon) had meters to loan available at state universities, but there was a three year waiting list to get one. So I designed a VERY low cost wind speed meter that can be made from hardware store parts, costing under $30. It even calculates the average wind speed for the period since you last read the meter. The Meter's Design I made a three cup anemometer with much larger diameter than the little commercial ones. This results in slower turning and easier data collection. When tested on a mast above a vehicle driving on the highway, it seemed to rotate about 233 turns per mile whether the speed was 15 mph or 35 mph, so giving a reliable count of miles of wind passing. To count these rotations automatically, I attached a magnet to the rotating part, and a magnetic reed switch just below it so that the switch would activate once each time the magnet came around. I installed the anemometer on a pole above the house and ran 2 wires from the magnetic switch to a pocket calculator in the house. Once the wires were connected to the calculator, it counted 1, 2, 3, 4... on up to 999,999, as the anemometer turned in the wind, one count for each rotation of the anemometer. I let it count wind passing for 6 hours. Then I went to the calculator and divided (directly on the keys of the calculator!) the displayed count by 233 turns per mile. This showed MILES OF WIND PASSED during the 6 hours. Next, I divided that miles-of-wind figure displayed on the calculator by the 6 hours elapsed. The answer now showing on the calculator is the average miles per hour of wind for the last 6 hours. The calculator is cleared to zero and set to start counting for the next 6 or 8 hours. Details: Anemometer Wheel The anemometer wheel is simply a 4 or 5 inch diameter ball bearing wheel with rubber tire available at hardware stores for under $10. Solid rubber tires are most desirable, but hollow ones work too. The wheel turns on a bolt double nutted to a steel shelf bracket from the same store. The cups are plastic toilet tank float balls cut in half, and mounted on the regular brass rods sold with the floats. The rods are threaded on both ends and will screw into the half float balls and the other end will thread itself into 3/16 inch holes you drill into the rubber tire. Be sure to drill all the way through the inside rim of the tire if it is a hollow one so the rod can be screwed fully into two points of support within the tire. Glue one of the cut off float ball halves over the top of the wheel bearing to keep rain out (see photo) * * * assembly drawing * * * A strong flat magnet should be glued to the underside of the rubber tire. The tire is the only place you may attach the magnet because steel will defeat the magnetic path for the reed switch. A magnetic reed switch can be purchased from Hosfelt Electronics (800) 524- 6464 part number 51-108 for 25 cents, or 51-144 for 30 cents, or 51- 145 for 50 cents. Get several in case of breakage since they are glass. Hosfelt has no minimum order amount for credit card or COD phone orders. (It is possible to use the Radio Shack door alarm magnetic switch sets, normally open #49-512 for $5.19 which includes both magnet and a switch with screw terminals, but it is oversize and bulky for this application). The reed switch mounts below the tire where the magnet will pass. Again, to avoid defeating the magnetism for the switch, the switch cannot be mounted on steel or iron. To mount the magnetic reed switch, flatten a 6 inch piece of copper pipe, screw it to the shelf bracket and bend it so that the end rides just under one edge of the tire where the magnet will pass. Temporarily hold the switch on the copper arm with a rubber band while you rotate the wheel by hand. The magnet should pass within 1/8 to 1/4 inch of the switch. Listen for the slight clicking of the switch as the magnet passes, or connect a flashlight bulb and battery to the switch to confirm operation. It should light just as the magnet passes. Slide the switch back and forth and change its direction to find a location where it is most reliably activated ONCE only when the magnet passes. Check this at high and low wheel speeds. Using silicon seal or Goop brand glue from the hardware store, attach the switch to the copper bracket you made. Finally, attach wires to the switch, long enough to reach into the house. First tie or otherwise clamp the wire to the mounting bracket so it cannot pull on the connections at the reed switch. Then solder the wires to each terminal of the switch. The glass Hosfelt switches work best, but you must carefully hold the terminal between the soldering iron and the glass with needle nose pliers, and solder quickly to avoid breaking the glass with the heat. Get help if you are not experienced in soldering. The Calculator Calculators use several different keyboard input processes. This meter requires one that will count upward 1, 2, 3, 4, ... when you enter something like 1 + = = = = = = , one count for each push of the = key. This is the most common type calculator, but a few will not do this. Try it before buying. Experiment with the + and 1 and = sequences, but it must be able to count upward with repetition of a single key after you start it with a simple sequence. Calculators that use gray (liquid crystal display) have much longer battery life than those that have red or green lighted numbers (LED display). But if you can find one that uses a 6 volt battery (4 AA cells) you can connect a lantern cell or even a golf cart battery for months of continuous service on one battery. Finally, a larger calculator like an older one, or a desktop Sharp or Casio model will be easier to open and attach the switch wires into. Don't even try it with the very thin ultra-miniature or credit card types. A desktop printing calculator on which the printing function can be turned off has some advantages, since you can switch on the printer to record your wind speed readings on the paper tape, and switch it off to count again. Some Sharp brand I have used will print subtotals even when printing is switched off. This has a potential for automatic hourly total printing for those who want to experiment further. Connecting Magnetic Switch Wires to the Calculator Carefully open your calculator. With luck you have spent only $8 or so for this unit, but be very careful and gentle with this process. The wires connecting the keyboard to the rest of the unit are usually all at one edge of the keyboard. Low and behold! There are fewer wires than there are keys. This is because combinations of wires are used, one for each horizontal row of keys, another for each vertical column of keys. Often these wires are bare, easy to connect to, but if a ribbon type cable is used, you need to make your connections on the soldered side of the circuit board where the keyboard wires connect. Presuming that your calculator counts up with each press of the plus or the equal key, as explained above, you need to connect the wires from your magnetic switch to the wires from that particular key. Once done, the magnetic switch on the anemometer will do exactly the same thing as pressing the key does. These correct wires will be the one from the row and the one from the column in which the = key is located. In case the wires cannot be visually traced from the key, you will have to turn on the calculator and experiment. Set up the sequence 1 + = = and see that it is counting ok as you press the = key. Then take a short piece of wire, and use it to connect from the first keyboard wire to the second and see the result. Then connect the first to the third and see. Then to the fourth. When the first wire has been tried to each of the other wires, repeat, this time connecting the second to the third, the second to the fourth, the second to the fifth etc. Then the third to the fourth and to the fifth etc. Somewhere in those combinations you will find the same effect as pressing the = key, and those are the locations to connect your magnetic switch wires in. Of course most of those attempts to find the = key wires will cause entry of some other keystroke and you will have to clear and restart your 1 + = = setup between each new wire tried. In my experience, there is no combination that will damage the calculator, so long as you are careful not to slip and accidentally connect your test wire to some other part of the calculator circuit board. Physically connecting your wind meter wires to the = key connections require careful and tiny soldering. Get help from a person well experienced in soldering if you are unsure, and use solder made for radio/TV work. Smaller solid wire, like the type used to wire telephones in the home is suitable to this miniature work. Make a small notch in the edge of the calculator to bring the wire out, and tie a knot in the wire that will support it inside that notch against pulling out. These smaller gauge wires can be spliced to the larger wire from the anemometer a foot or two outside the calculator. At this point you need a switch to disconnect the anemometer when you use the calculator to figure average wind speed. Hosfelt part # 51-148 or Radio Shack part # 275-1533 or 275- 1537 will do it. The switch will also provide a place to connect lightning protection. Test the meter now by starting the count sequence and manually spinning the wheel if there is no wind. Lightning, or sometimes even thinking of lightning, seems to instantly fry the calculators. You won't want to unplug the wind meter in a storm just when the best wind is coming in. But it can be partially protected with lightning arresting Metal Oxide Varistors (MOV) by connecting one between the wires just outside the calculator, and then resting the calculator on a wooden table far from metal or other wires. Connect two more MOVs from each wire to a grounded metal water pipe or ground rod. (See drawing) These are available from Hosfelt Electronics, part number V8ZA25 for 50 cents each or V08Z2A3 for 35 cents each. Of course using a low cost calculator and having a spare wired ready to go is the best insurance. Test the counting again with the MOVs connected. Calibration Before installing at the test site, you will need to find how many counts per mile your meter gets. My 233 counts per mile is probably close, but it will depend on the size of the wheel, arms and cups and other factors. Run it down the road mounted on a vehicle to test it. Be sure to mount it horizontal, on a pipe mast preferably 6 feet tall off the front bumper so it will be above and in front of the vehicle to avoid air disturbed by the vehicle. It should give the same number of counts per mile from 8 to 30 miles per hour, when you drive one mile by the car's odometer or by highway mileposts. Installation Attach the mounting bracket to a mast with U bolt brackets or hose clamps. For wind measurement, the anemometer should be mounted at the same height recommended for a windmill. That would be generally 15 feet higher than all trees and roofs for 500 feet around it. If it is lower, you will miss some of the wind that a windmill will receive. Start up the calculator with CLEAR, 1, +, = . When you want to read the meter, note the time elapsed since starting the count. You cannot use the calculator to divide the count while the anemometer switch continues its child-like pressing of the equal key several times each second, so turn off the anemometer switch first thing. Then with the count still displayed on the calculator, press divide by, and (your count number per mile), divide by, (your hours of elapsed time since last reading). The wind speed average should be on the calculator readout. Write it down and restart: clear, 1 + = and then reconnect the anemometer. If you understand these calculations, try something that is even more fun. Instead of pressing 1 + = to set up a count, press 1 divided by 233 + = (but using your own count per mile in place of my 233. You might need to omit the + in that sequence too) It should then count in decimals of a mile, .001, .002, .003, .004 etc reaching 1.00 after about 233 counts. You should set the calculator to use as many decimal places as possible, if it is a financial desktop type with a selector switch, to avoid rounding off the data to two figures. The count reading now comes up on the calculator directly in miles of wind passed! Measurements Needed to Evaluate Your Site A measurement of how many miles of wind passing is the best primary data. Miles of wind movement divided by the hours it has been blowing, gives the average miles per hour wind speed during that period (miles divided by hours = miles/hour). Measurement periods between checking the meter should be short, perhaps 4 to 12 hours, based on your typical duration of more or less constant wind speeds. A meter that is checked only once a day may tell you that the average wind in the last 24 hours was 8 miles per hour. You need to know if that was 8 mph all day or if it really was 16 mph for 12 hours and 0 for the remaining 12 hours. Both give the same 24 hour average speed, but the former generates nearly no power at all while the latter gives quite good generation of power for 12 hours. Taking the average wind speed reading twice a day would show that difference; reading every 6 hours would give even more accuracy. This method of recording wind speed is a lot easier to live with than a direct SPEED meter that requires close watching all day to mentally average the speed each hour. Once you have a good account of the wind speed distribution over preferably a full year, you can go to the charts in wind generator literature and figure just how much power each model would have produced had it been installed where the wind readings were taken. You then know exactly which wind machines, if any, would meet your needs, and which would not. Access Author: Steve Willey, Backwoods Solar Electric Systems, 8530 Rapid Lightning Creek Rd., Sandpoint, ID 83864 ¥ 208-263-4290