I could have just been riding an exercise bike, or jogging, or lifting weights. Instead, I generated and stored POWER, and I am using it right now to write this article. How totally appropriate.

Pedal Powered Generator

David Butcher

Pedal Powered Generator
I could have just been riding an exercise bike, or jogging, or lifting weights. Instead, I generated and stored POWER, and I am using it right now to write this article. How totally appropriate.
Pedal Powered Generator
by David Butcher

Every morning, I pedal to generate electricity. The Pedal Generator charges batteries, that run an inverter, that produces 110v AC, that powers LED lights, the monitor on my computer, and many other small battery-powered things. It is the most inspiring workout you can imagine.

0 Watt-hours

The workout begins. It's 5:30 AM, and I am dressed in shorts, a T-shirt and a hooded sweatshirt. It's 57 degrees F. I am not really awake yet... I mount the pedal generator from the right side, swinging my left leg over the seat. The pedal generator is tall, due to the height of the 36 inch flywheel. I begin to pedal slowly. Battery voltage is 12.78 volts.

1 Watt-hours

I am pedaling at about 50 RPM, which would be a leisurely ride on a bicycle. I am giving my legs a chance to warm up. While the pedal generator does the work of converting motion into electricity, I am responsible for creating the motion. My legs need a chance to "wake up" before I push too hard. The Watts-up meter which acts like an electronic "speedometer" for the pedal generator, reads 15 watts of power output. The polyurethane drive roller (in reality an automotive suspension bushing) is as cold as I am and it is noisy. I increase my cadence to 60 RPM.

2 Watt-hours

I am warming up. The drive roller is warming up. The air is warming up - a little. I increase my power output to 50 watts. Pedaling a permanent magnet generator (actually a motor from a Razor 200 electric scooter) is not like riding a bike. The generator output flows through a low-loss Schottky diode into a 12 volt battery bank. Until the generator begins to produce more than 12 volts (in other words, until power begins to flow into the battery bank) there is almost no pedaling resistance. There are only a few moving parts on the pedal generator: pedals, crankset, generator rotor. There are four ball bearings in the pedals (two each), two in the crankset, and two in the generator. The flywheel is smooth and solid, creating almost zero wind resistance as it spins. It's an extremely efficient machine.

3 Watt-hours

I increase my cadence a bit more, and the Watts-up reads 60 watts. My legs feel odd - it's the beginning of lactic acid buildup. My circulatory system has not "caught up" with the activity yet, so I don't have enough blood circulating to my legs to keep them properly "fueled." The other part of my "engine" that is still warming up is my breathing. I begin to take deeper, more regular breaths, timed with my left leg. Every two revolutions, inhale. Every two, exhale. Battery voltage has climbed to 13.24 volts.

4 Watt-hours

It's time to speed up to the cadence I will use for the main part of the workout. I press a little harder, spin a little faster, and I am at 70 watts of output. Pedaling is more complex than it seems. You don't just stab each leg downward and then do nothing with it until the next stroke. The more muscles you involve in the activity, the more the work is spread out between them, and the more work you can do. One way to increase power output it to actively lift the "up" leg (which uses different muscles than pressing it down) instead of using the "down" leg to do all the work. It's easy to see on the Watts-up meter - at least 10 watts of output can be gained simply by lifting the "up" leg as you pedal. I focus on this. Pedaling smoothly is also helpful. The Watts-up is fast enough to show peaks and valleys in power output. I try to keep a steady output. Another technique cyclists are familiar with is "ankling" - essentially pointing your toe at the bottom of the down stroke, and lifting it (moving it the opposite way) at the top of the stroke. This brings calf muscles into play. It's hard to do all of this when you are not warmed up, but I am definitely getting warmed up.

5 Watt-hours

I am up to speed at 70 watts of output. I am generating a Watt-hour of power roughly every 51 seconds. The drive roller is fully warmed up, and it has quieted down. I can hear the generator humming from the speed. The odd feeling in my legs is gone, as my heart rate and circulatory system are "switched on" and keeping pace with the workload. My breathing is pacing itself naturally now, no need to consciously control it. I am too warm now for the sweatshirt, so I take it off. I glance down at the edge of the flywheel, spinning at about 70 RPM between my legs. I can almost imagine it is a road surface flying by. This pace is about the same as pedaling a bicycle at 15-18 miles per hour. Battery voltage has climbed to 13.45.

6 Watt-hours

I am "in the zone" now, generating 70 watts, fully warmed up, and my mind begins to wander. I glance at the battery pack. 13 Optima Yellow-top batteries, all in parallel. They are a used/recycled electric vehicle battery pack taken from my Sparrow three-wheel electric car. When electric car batteries reach the point that range is too short for the car, that must be replaced. They may still have over half their capacity, however, so they can be used for other things until they are completely exhausted. This pack is absorbing 6 amps from the pedal generator, and gradually climbing in voltage as the power flows in.

7 Watt-hours

The batteries are hooked to a 12 volt inverter, and the power from the inverter, now 120 Volts AC, flows through an underground cable to my home office. I have a number of items plugged into that power source, including the monitor of the computer I am using to write this story. Yes, the pedaling I did for this workout is being used to write this article.

8 Watt-hours

As the generator sings, I think back to the first pedal generator I built, almost 25 years ago. It was a similar design, but it was chain driven. I had wrapped a 10 foot chain all the way around the 36 inch flywheel, and then over the sprocket on the motor. It worked, but it was noisy. I was hoping this model would be quieter, with the roller drive, and it is.

9 Watt-hours

Now I am really warmed up. I am beginning to break a sweat. I think about the web page I have put together to tell the pedal generator story, and sell plans: http://www.los-gatos.ca.us/davidbu/pedgen.html I can see the search terms people use to find that page by reading the web logs. I am amazed how many times the search seems to be for "permanent magnet power generator" or something similar. It's clear many people believe that simply placing a permanent magnet near a wire will generate electricity, and they are looking for plans to build such a system. I smile as I imagine them perched on the pedal generator, gradually learning that you have to move the magnet (or the wire, or even both) to generator power, and that takes work. Exactly the work I am doing. There is no "free energy" in the sense that a generator will just produce power from thin air. If I stop pedaling to provide the power, the generator stops generating electricity - it's as simple as that.

10 Watt-hours

It always feels good to reach 10 Watt-hours. What could 10 Watt-hours do? It could power the little 4 inch LCD Color TV we have for an hour and a half. It could run the monitor on my computer for 12 minutes. My laptop, 20 minutes. The 12 volt radio I listen to while I am pedaling, 10 hours. The LED lights over my head that light the pedal generator while I am working out, 500 hours. Wow. However, it could only run our 27 inch television for 8 minutes. The 120 watt halogen lights over the dining room table, 5 minutes. The toaster, 29 seconds. The whole house, less than 5 seconds.

11 Watt-hours

The sun is starting to rise. On the roof the garage, which is serving as my "gym" for now, there is a photovoltaic panel about four feet square. I assembled it from separate smaller panels, so it does not have a formal power rating. I think it's about 100 watts. Here I am, pedaling along at 70 watts, and the panel on the roof can beat me. Of course, I can pedal any time, even when it is raining, so I am a pretty good backup for that panel. The panel is wired into the same battery bank. Since the panel generates nothing at night, my morning workout is the first thing the battery bank sees. After a long evening of reading Email and working on web pages, the battery bank can be low in the morning. That's good! That means all my pedaling energy goes into the batteries.

12 Watt-hours

It's going to be a sunny day. That solar panel will probably generate something like 500 Watt-hours today. I'm aiming for 25 in this workout. It does not seem like much. It's something, however, and it's not just the power I am producing that is doing me good. I'm getting in better shape! I am thinking about taking my first bicycle ride of the season, and I'm ready! I used to dread getting on the bicycle after winter (in Northern California that means the "rainy season") but not any more. In a way, the pedal generator has contributed to by enthusiasm for bicycling, and that means fewer trips in the car. That's energy saved. A single trip in the car would use more power than the solar panel puts out in a week, so cutting a trip or two with the bicycle is significant. That got me thinking - I am also not using power to light my workout area - that's a savings, and I have noticed I take cooler showers after the workout... Every little bit helps.

13 Watt-hours

Halfway there! In the standard riding position, I can look straight down. I see the crank, the pedals, the flywheel spinning by, and the frame of the pedal generator. This frame is a prototype, built from water pipe, hose clamps, and electrical strut. It's not as sturdy as I would like, and it rocks back and forth slightly as I pedal. I have already designed a better frame, and I have it 90% finished. I have been riding this frame for about six months, and I am looking forward to the new model. Everything else has works well. Of course, the bicycle parts were designed for this kind of use, so the pedals and cranks are working fine. The urethane roller was a challenge. I tried a number of different designs using other materials, and all were failures. This roller has lasted through three months of workouts so far, and it's holding up well. I have recently added a small computer fan to the handlebars in preparation for Summer, but it's not yet operational. I know I will need it once the weather warms up.

14 Watt-hours

As I pedal, I can see the battery charging progress two ways. The Watts-up meter reads voltage (now up to 13.92) and I can also look at the Trace C-10 photovoltaic controller. The pedal generator goes straight to the batteries, which is ok if the battery bank is large (as mine is) and the voltage is monitored. The solar panel needs to be controlled, however, so the power it generates flows to the battery bank through the Trace. If the voltage rises too high, the Trace cuts the panel off from the battery bank to protect it from overcharge. If I am the reason the voltage is too high, I just slow down or stop. The trace has an indicator on it - a single LED that flashes out codes indicating the state of charge on the battery bank. The LED blinks to signal how full the batteries are. When I started pedaling, it was blinking singly. At around 14.2 volts, it begins to blink in sets of two. Then three blinks, etc, up to five blinks to signal that the battery is full. By the end of this ride, I expect to see more than one blink....

15 Watt-hours

14.0 volts, and slowly climbing. I'm pedaling rapidly, but comfortably. The batteries are being charged now at about 5-6 amps. With 13 batteries connected in parallel, that means each battery only sees roughly 1/13th of the charge. Batteries are not identical, however, so some of the batteries in the pack are probably absorbing more of the energy than others. This is one of the drawbacks of parallel battery strings. Fortunately, the solar panel will take over for me in an hour or so, and bring the entire pack to full charge (on a sunny day). That will equalize any differences between individual batteries in the pack. Optima Yellow-tops are good batteries for this use. They are sealed, so they are absolutely maintenance free. They are also quite efficient at absorbing and retaining charge. In fact, lead-acid batteries such as these are just about the best technology available for charge efficiency (percentage of charge returned vs. charge input to the battery) and long-term charge retention. With such small amounts of power available for charging the batteries, these characteristics are critical. I have considered replacing the batteries with NiMH (nickel metal hydride) but they are expensive and they can loose tens of percents of charge in a month. I would have to pedal that all back in the winter - like Alice, I would be running just to stay in the same place.

16 Watt-hours

Nice ride so far. This weekend I will hook up a small (4 inch) black-and-white television so I can watch the morning news. I tested it, and it draws about 6 watts. The rest will continue to go into the battery bank. Today is Thursday, and my weekday goal is 23 Watt-hours. On Friday, Saturday and Sunday, I pedal 35 Watt-hours, giving a weekly total of 197 Watt-hours. I generally cool off at the end of the ride by pedaling a bit further than the goal, so call it 200 Watt-hours per week. That would run that little black and white TV for over 33 hours, if I had that much time for watching TV.

17 Watt-hours

While I ride, the house is still "asleep." Even so, there is no way I could be powering the house with my output. Even with all the lights off, and all the appliances unused, our house uses more than 150 watts of power. How can that be true? Well, here is the list of devices that are "on" while the house is "off:" 110v smoke detectors (battery types are not code around here), heating system (thermostat), light dimmers (they each draw some power when off, due to their "touch switch" design), GFI outlets (yes, they draw several watts EACH even with nothing plugged into them!), anything with a clock (the Microwave, the oven, dishwashers), anything with a remote control (TV's, ceiling fans, garage door openers), anything with a plug-in transformer (cell phone chargers, battery chargers, cordless phones) ... You get the idea. "Modern" lifestyles use vast amounts of energy, even when it seems like nothing is in use. If all the engineers designing these devices had to pedal long enough to run them for 24 hours, I'll bet there would be some efficiency improvements in the new models....

18 Watt-hours

Many people have asked me if groups of pedal generators could be configured to power larger things. Of course! DC electricity is very easy to "add together" if it is all the same voltage. I could imaging a gym full of pedal generators, all hooked to the same equipment. Some of the power could run lighting, and some could run ventilation (although I would recommend an outdoor design for the gym if at all possible for this very reason - to avoid having to ventilate it, heat it, or light it, at least some of the time...). The remaining electricity could power a large flat-screen TV for example, or a sound system. Everyone on the same channel or station of course. That would probably use ALL the power a gym full of pedalers could create. A more efficient alternative would be little TV's like the one I have (color versions draw roughly the same amount of power), iPOD's for music, LED lighting for each pedal generator powered by that person alone, and personal fans. The result would be that instead of ALL of the power from each pedal generator going to lighting, ventilation and entertainment, maybe only 10% would be needed, and the rest could be used for something else.... Efficient use of power is absolutely critical when you don't have much to start with.

19 Watt-hours

14 volts! The batteries are filling. Why do I even use batteries? Couldn't I just hook the TV right up the pedal generator, and run it that way? Yes, I could. If the device needed anywhere from 0-70 watts to run, I could probably run it directly, with no battery. That would be more efficient, as even the most efficient batteries "lose" 10-15 percent of the power they receive. No process is 100% efficient, and charging and discharging batteries is no exception. That "lost" power would be available for the device being powered if no batteries were used. However, batteries solve two problems. The obvious one is that they let the device keep running after you stop pedaling. Not so obvious is that they "level" the power by charging when you are generating more power than your device needs, and discharging when you are producing less. Devices do not always need constant power either. Our 27 inch television draws 45 watts when the screen is showing a dark picture, and 90 watts when the scene is brightly lit, according to my "Watts-up?" 120 volt AC power meter (same name as the meter on the pedal generator, but it measures AC instead of DC). I'll bet you never thought of that, but yes, it takes more power to show brightly lit scenes on a television than is does to show dark. If you were pedaling the TV directly, you would have to constantly be adjusting your pedaling speed as the picture changed to keep the voltage at a safe level for the TV. The battery takes care of this for you.

20 Watt-hours

14.15 volts, and climbing. I can feel sweat on my forehead. I could be outside in 40 F degree weather and I would still be warm. No need to turn the heat on in the house yet! Electricity is not the only output I can make with the pedal generator. The garage is my "laboratory" and I have other experiments in progress. I have tried disconnecting the generator and powering water pumps with great success - directly from the flywheel. Theoretically, anything that spins fast (powered by the edge of the flywheel) or slowly (powered by the chainwheel on the crankset) could be powered by the pedal generator. Once the new frame is stable, I will try as many different devices as I can. I like the idea that very nearly 100% of the power I would be creating would go straight into the device.

21 Watt-hours

14.31 volts - the Trace is blinking twice! I have another idea I want to try. I have an eGO electric scooter. I wonder how efficient it would be to charge the scooter with my morning workout? I could do all the work needed to travel in the morning, store it in the eGO batteries, and then be able to travel effortlessly later in the day. A bicycle would be more efficient of course, but you can't go very far or very fast before you need shower. It's not the kind of thing you do in a suit. The eGO would absorb my morning workout and give it back as "civilized" transportation. Interesting...

22 Watt-hours

14.40 volts - and I begin my sprint. I like to speed up a bit at the end to push myself. I pedal a bit faster, and the watts-up shows 80 watts. I have to focus on breathing again. This is work. The urethane drive roller is held against the flywheel by a spring, and the tension is set as light as possible to extend the life of the roller and increase efficiency. Pressing harder would deflect the contact point on the roller more, generating heat, and wasting power. However, with light tension, the roller will begin to slip at high power levels. I have the roller tension set to handle around 110 watts. To minimize slippage, I try to pedal smoothly, and to "ankle," and I try to lift the "up" led as much as possible. I don't have toe clips or shoe clips on the pedal generator, so there is still room for improvement.

23 Watt-hours

14.54 volts! Three blinks! 90 watts! Breathe! I feel POWERFUL!

24 Watt-hours

Whew! I ease off slowly. During exercise, your heart is aided by the contractions of the muscles doing the work - veins have little "one way valves" in them that help "squeeze" blood back to your heart - so coming to a dead stop would create stress I don't need. I taper off gradually - 50 watts, 40, 30, 10 - it's almost impossible to pedal lightly enough to generate 10 watts right after generating 90 - and finally, I stop. I could have just been riding an exercise bike, or jogging, or lifting weights. Instead, I generated and stored POWER, and I am using it right now to write this article. How totally appropriate.


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