Pedal Power John W. Hill You too can be a human power plant. A lot of folks have expressed interest in pedal power setups as backup or primary power sources. Here is a general perspective on the utility of this approach to greater independence. Power Output If you hook up a bicycle to a generator how much power can you generate? How practical is it as a home power resource? The answer depends largely on your use and expectations. The first consideration is how much power can you generate. A fit olympic class athlete may be able to generate as much as half of one horsepower for a brief time. At 746 watts per horsepower that translates into approximately 370 watts peak. A modestly fit person can expect to generate about one tenth horsepower (roughly 70 watts) for a brief period. For normal regular use a generator capable of producing 50 watts or more is quite adequate. If you are a cyclist interested in serious training, a generator capable of 100 watts or more is desirable, PM generators ranging in size from 60 watts to 200 watts are readily available and can be obtained with the bike generator options described below. Compare this to the output from a 50 watt solar panel that runs 6 hours per day. If you could sustain a 50 watt rate for 6 hours, you could match the power generated by one solar panel, provided that you had nothing better to do with your days and nights. Clearly, a bicycle generator is not a competitor for solar panels, wind generators, or microhydro as a home power source. For What Now look at it from another point of view. A high efficiency PL light will draw from 5 to 13 watts of power and a small DC television will draw from 15 to 60 watts of power depending on it's size and type. One hour of serious pedaling would provide enough power to supply a PL light for 3 to 10 hours depending on the size of the light. Or, it could power the TV set for 1 to 3 hours depending on it's size. So for such essentials as lighting, communications, or entertainment, a bicycle power system can provide adequate and useful power. Can Do The next question is, "Can you pedal at a stiff clip for an hour?" The same question is, "Can you ride a bicycle for an hour?". If you ride a bicycle for transportation or regular recreation, the bicycle generator will prove to be a natural part of your lifestyle. If you can't ride a bicycle for an hour, perhaps you should add the bike generator to your lifestyle as a physical fitness and training aid. How So "How do you use it?" To obtain the maximum efficiency possible, the generator needs to be a permanent magnet DC type. The PM generators produce a voltage output that is directly proportional to the shaft speed. Of the several generators readily available, output voltages can reach 40 to 100 volts or more if you set the bicycle into a high gear and pedal at a very fast clip. These voltages can burn up a 12 volt appliance in short order. There are two ways to handle the problem. First, you can use a storage battery to regulate the voltage that reaches the appliances. If you connect a generator that is spinning at a 40 volt rate to a 12 volt battery, the generator output voltage will drop to match the battery terminal voltage. This occurs because the current flowing from the generator has to flow through its own internal resistance and in doing so produces a voltage drop that is equal to the difference between the open circuit generator voltage and the battery's terminal voltage. If you are charging batteries, you will need a few additional system components. These include a voltmeter to monitor the state of battery charge, a blocking diode, and preferably a charge controller. You have to be a bit careful with charge controllers though. If you use a charge controller that was designed for solar panels, it may not tolerate the excessive voltages that the PM generators can produce. Some additional circuitry to protect the charge controller is desirable. Batteries A battery for use with a pedal power set up should not be too large. After all, you wouldn't want to have to pedal for two days solid just to charge the rascal back up, would you? Industrial pocket plate nickel cadmium batteries are ideal for this application because they have a relatively flat discharge curve and don't mind being deeply discharged and operated in a partial state of charge. This applies only to the pocket plate type of NiCad cell which has no memory characteristic. Unless several people are contributing regularly to the charging process, 20-40 ampere hours of capacity is very adequate. Larger capacities will work of course, or you can simply pipe the current generated into the larger battery bank of a complete home power system. Voltage Regulator The alternative to using a battery is to use a voltage regulator to buffer the variable output from the generator down to a constant 12.6 volts. With this arrangement, the lights and other appliances are on while you crank but go off when you quit. This offers a real education in the amount of power we drain from the system. Cranking a color TV and VCR is hard work while powering a reading light or two is so easy of a load that you hardly feel it. The advantage of having a regulator available is that you can get full use from the system even if your battery is flat dead. It also doesn't take up the space required by the batteries and it provides some discipline in the use of certain appliances. Some folks, for example, connect the TV set to their bike generator with a regulator and require the kids to carry their own weight when watching television. Bike Type The next consideration is the type of bicycle setup to use. Most standard bicycle trainers can be fitted with an appropriate PM generator. Daniel Millton of THE POWER COMPANY offers a relatively inexpensive conversion kit for converting your bicycle or exercise stand into a pedal power unit. He also makes a complete converted exercise stand, a recumbent pedal powered generator setup, and offers complete pedal powered systems with all electronics and system components. The recumbent is a real pleasure to use. First, it is comfortable, and the recumbent design allows maximum use of leg strength. The seat is adjustable for any size person from 6 years old on up and it comes with a book holder for reading while pedaling. You can even sit in the padded seat and lean forward and turn the pedals with your arms. After tossing a log on the fire, and leisurely cranking away while the PL reading lights ignited and flickered to life, I realized that pedal power does indeed have a rightful place in the lives of people who defy slavery to the 60 Hz. umbilicals and all the economic, environmental, and resource waste that they represent. This reminded me of an old Amish farmer's comment on electrical power and telephones. He said, "It isn't that we believe that these things are bad particularly, it is just that we don't want to have wires binding us to the Englishman's world." Security During the winter storms a few months back, when the power lines were down, the wind generator was iced up, the solar panels were covered with snow, and the main battery bank was gasping up its last amp, the pedal power unit made a very nice addition to the home environment. In summary, pedal power is valuable as a reliable emergency power source, as an auxiliary power source for driving small tools or appliances, and as a fitness aid. If you are considering pedal power, be realistic and don't expect it to compete with solar panels and other alternative power sources. Happy pedaling! Access John W. Hill, 17036 Holly St., Yelm, WA 98597 The POWER COMPANY, POB 178, Rainier, WA 98576