Over time, a number of questions have asked about the information on the page. Here are some Frequently Asked Questions and answers/opinions:
- Do you have plans available?
- YES! Follow the link below to order plans.
- Do you have assembled PPPMs available?
- NO! It is not cost-effective OR energy-effective to build the units and ship them. The best way to obtain a PPPM is to assemble it yourself, or find a local resource to assemble it, such as a Bicycle Shop.
- Is there a recumbent version of the PPPM?
- It is theoretically possible to convert the PPPM to a recumbent Pedal Generator. The image at the top of the page shows an early, working prototype of a recumbent version. In fact, the PPPM could be assembled for both upright AND recumbent use, and the riders could simply choose the riding position they prefer. The current plans do NOT contain instructions for this conversion, but a version of the plans is being written that will provide the details.
- If I build the Generator, how to I power things with it?
- Take a look at this Power Board I built for an Energy Fair for ideas. It shows how to wire 12 Volts DC through a junction box into an inverter with capacitors to smooth out the power, and both cigar lighters for 12 Volt DC appliances, and a power Strip for 110 Volt AC devices. A 12 Volt DC Laptop Power supply enabled me to run an IBM Thinkpad directly, drawing only 20 watts. The Watt's Up meter shows how much power is flowing out to both the cigar lighter outlets and the inverter, in real time. You can power anything within reason with the setup shown. It's a great visual learning tool for educators to use in a classroom, too!
- Do you offer parts in a pedal power kit I could build myself?
- No. All of the parts needed to build your own Pedal Powered Prime Mover are likely to be available locally. All you need are plans.
- Would a car alternator work better for generating power?
- No. Most automotive alternators have one ball/one sleeve bearing, a built-in power-robbing cooling fan, and they require external power to excite them at low-to moderate RPMs. They have never been designed with efficiency in mind, since they were attached to monstrous motors capable of producing orders of magnitude more power than the alternator required. They actually produce AC power, which subsequently must be rectified to DC to charge batteries. This step causes significant power loss in the diodes (around 5%). As I noted above, I ran power output around the diode and directly into the battery to avoid this loss. In addition, alternators are designed to run at extremely high RPMs (alternator pulleys are smaller than the driving pulley on the engine, meaning the alternator turns FASTER than the car engine. Look at your tachometer reading and double it. Whew!), and do not produce usable power until they are rotating quite rapidly, requiring high ratios of step-up from your pedals. A well-designed permanent-magnet ball-bearing motor, preferable one designed to squeeze every last bit of power out of a set of batteries, will easily beat an automotive alternator in efficiency, yielding 20-50% more electricity for the same effort.
- Wouldn't gears help generate more power? And what about belts instead of chains?
- Maybe. Humans can only pedal through a small speed range, about 40-120 RPMs. Below that you can strain your joints, and above that efficiency falls off. There is a "magic" speed (different for every Human Being) at which they can generate maximum power. The proper gear ratio enables the Human to pedal at that speed. You may have noticed, though, that a Human's maximum power output can change quickly from fatigue, and slowly from changes in conditioning and age. The magic speed is always changing, so having a few closely-spaced "gears" or ratios may enable a better match of Human to generator. No matter what, though, gears don't create energy, they waste energy, so having fewer of them is always better. The same goes for bearings, even ball bearings. The pedal-power generator described on this page has very few of both, so it is very efficient.
Regarding belts, the transfer efficiency of most belts is less than chains. This is mostly due to flexing energy loss within the belt material and friction losses at the engagement points between the belt and the pulleys. Belts also work best when transferring low torque at high speed (the opposite of what a pair of legs produce!) which is why you do not see them on bicycles, for example. There may be some exotic, thin, high strength belts that could approach the efficiency of chains with the right design. For example, the "serpentine" belts used in modern automobile engines are much more efficient than the old "V-belts" from the past. Belts rely on friction to transfer power. Friction is bad. The best feature of belts is that they are quiet, so I can't say to avoid them completely. If you decide to use a belt to transfer power, use the thinnest, strongest belt you can find, and place only enough tension on it to keep it from slipping during use. I do not know whether equivalent "toothed" and "grooved" belts are equally efficient, but I believe the toothed belt has slightly lower friction losses. If I can ever find some real research data on the web I will link it in here.
- I would rather use my bicycle in a stand and rig up a generator connected to the rear wheel, or convert an exercise machine by attaching a generator to it. Will you help?
- Yes, but I have all my attention focused on this design. I want to improve it, and make it even more efficient and easier to build. Every stand and exercise machine is different, and I can't invent a solution for each one separately. It's also impossible for me to work with equipment that I can't see, touch, or measure in any way.
If you are still interested, click on "Convert Your Bicycle" to the left.
- Could I generate more power with my bicycle in a stand and a generator connected to the rear wheel?
- No. You certainly can rig up a bicycle stand and hinge the generator against the back tire using a tension system. I don't think you will be able to generate more power than the PPPM does, and here's why:
To get an idea of how much energy is wasted in a bicycle power train, pick up the back end of a multi-gear bike, like an 18-speed mountain bike, and give the wheel a good spin - backwards. See how long that much energy input can keep the machinery moving. I would be surprised if you counted more than five complete revolutions, unless you are testing a perfectly-maintained track bike.
With the same "push" the PPPM flywheel keeps spinning more than a minute. The difference is not caused by the flywheel - it's due to the rapid loss of the energy you put into the bicycle machinery due to friction. That loss will be a constant drag on your generator. The PPPM design is simply more efficient.
- If I pedal now and store the energy in a battery, can I watch TV later?
- Of course! A Pedal Generator plus a battery is an interesting combination of technologies. Here are a number of different scenarios:
- If you pedal the TV directly, with no battery, almost all of the energy you create will go into the TV set. Very efficient.
- If you pedal the TV and have a battery attached to the system at the same time, the energy used by the TV will be used efficiently. If you pedal a bit more energy than the TV needs, the surplus will go into the battery. Due to battery inefficiency, you will only be able to get some of that surplus energy back. It could be anywhere from 70% to 90% depending on the chemistry of the batteries. If you wait a month to use the surplus stored in the battery, with some chemistries (like NiMH) you may find it has completely dissipated in battery self-discharge.
- If you pedal ONLY to the battery, with the idea that you will watch TV later, you will loose 10%-30% of ALL the energy you create in the manner of #2 above.
So - lets say it takes 60 Watt-hours to watch TV for one hour.
In scenario #1, you pedal at a 60 watt output for one hour, and watch TV for one hour.
In scenario #2, you pedal at, for example, 70 watt output, and watch TV for an hour while pedaling. The surplus (10 Wh) gets stored, but you can only draw 8 Wh back out of the battery, enabling you to watch TV for an additional 8 minutes, not 10 minutes as you might expect.
In scenario #3, you pedal at 60 watts for an hour with the TV off. Later you watch TV, and you discover the power is all consumed after watching 48 minutes of TV (80%).
In other words, if you pedal the TV directly for an hour, you need to maintain a 60 watt output. If you want to watch TV for an hour later, after pedaling, you will have to pedal at 70 watts for an hour to account for the power lost through inefficiency.
No matter what, you will be watching TV!
- How much power can one Human Being create?
- This is an opinion. I used to be a competitive swimmer, and for a number of years, I worked out 6 hours a day, swimming approximately 13 miles. Yes, 13 miles a day. If you pedaled that hard for that long you might be able to run one ordinary refrigerator for 24 hours. To make any kind of significant contribution to your energy supply, you must use the most efficient devices you possibly can. For example, a small refrigerator designed to be powered by solar power would be much more practical. For example, if you are prepared to use a slightly unconventional refrigerator there is a chance that you could power it with one good workout a day, and maybe even have some energy left over for other things. A rule of thumb: if the device was designed to be powered by batteries, even BIG batteries, you might be able to keep up with it.
If your electric bill shows KWH (kilowatt-hours), take the number, multiply by 8 (assuming you can crank out 125 watts for an hour, which is very ambitious) and that is how many hours you will have to be in the saddle to create the same amount of power. Sorry, it can be depressing. The moral of the story: Using less power is as important, if not more important, than making more.
There are numerous sources of efficient appliances on the web. One place I like to shop is Real Goods, and of course I have spent time inventing my own efficient devices. The white LED light I built shows how technology can create new solutions to increase efficiency. Pedaling for an hour at the 200 watt pace, with 80% efficiency of generation/storage/extraction, would create enough energy to run that light for 320 hours!!!
You may be interested in the details of the effort and energy required to run the 12 volt appliances. I have compiled a Pedal Generator Energy Statistics page with the details.
Finally, here are some facts. Lots of people write to me and suggest that a more efficient method of capturing Human energy would result in a better power output. I am using this page for reference: Horsepower - Wikipedia. Here is the figure that matters:
1 horsepower = 33,000 ft/lbf/min = exactly 745.69987158227022 Watts
Calculating:
- A Human would have to lift 33,000 pounds one foot in a minute to generate one horsepower (746 Watts output for one minute) - or, equivalently:
- A 200 pound human would have to run to the top of a 14 story building (12 feet/floor, about 4 seconds per floor, 165 feet stright up) in one minute to generate 745 watts of output, and would have to continue that pace to keep generating one horsepower. Lighter weight people would have to get to the top even faster to generate the same amount of power.
- So - I dare you to generate 746 watts/one horsepower, even for one minute ;-)
- As you can see, even if we could capture Human output with 100% efficiency (we can't) you alone are not going to be able to run a refrigerator or airconditioner, or even a plasma screen TV directly by pedaling. No way. (Unless it is an unconventional refrigerator!!) However, if multiple generators are combined, anything is possible!
- Can I generate 110v AC? Can I run my electric meter backwards?
- I don't recommend this! If someone were to replace the permanent magnet DC motor in a Pedal Generator (such as the one on this page) with a 1/4 to 1/2 horsepower 110v AC induction motor and pedal that it would result in an amazing thing. If the motor was hooked to the power lines and it was "pedaled faster than it wanted to go", it would start generating 110v alternating current. Beautiful sine wave AC. If it was creating more energy than your clocks, refrigerator, all those little square black power supplies you have plugged in around the house, your lights, and that 300 watt stereo you are listening to while you pedal all use together, your electric meter would slowly creep backwards. However, that same motor would generate exactly 0 power if it is not plugged in to 110v AC.
For very light duty "off the grid" use of 110v AC, you can try pedaling your 12 volt DC generator into a large battery and hooking up an inverter (12v DC - 110v AC) to get some pretty decent 110v power. In general, plan on being able to pedal at the rate of about 70-150 watts for half an hour or so, if you are in good shape. WARNING: You CAN'T use an ordinary inverter to "run your meter backwards"!!!! If you are lucky enough to have a "grid tied" inverter that matches the output of the PPPM, you just might be able to send power back to the grid.
For efficiency, however, you are much better off producing 12v DC for a 12v DC TV (for example) than you are producing 12v DC to charge a battery to run an inverter to power a 110v AC TV. The UPS (uninterruptable power supply) for my website computer system can power the computer for about five minutes. The same battery (12v 1.5 AH) would power my laptop computer for about 45 minutes. Everything (efficiency-wise) works FOR you when the device being powered is designed to be efficient (12v DC) and AGAINST you when it is not (110v AC).
- How big should my batteries be?
- If you are considering building a similar system, plan on using two batteries, and a simple switch which allows you to use one while charging the other. Flip this switch right before you begin charging to ensure that you are charging the battery with the lowest charge (the one most recently used). Also be sure to use a battery that is roughly equal to ten or twenty times your power output for a charging session. For example, if you crank out ten amps for an hour each time you charge, choose a 100-200 amp hour battery. Larger batteries will simply loose charge through self-discharge faster, resulting is less efficiency for your system and more useless work for you.
- What are "rim strips" and what did they do in the original Pedal Generator?
- On the original Pedal Generator, I used rim strips on the outer edge of the particle board disk to keep the chain from slipping. They were exactly what you would use on bicycle rims to keep the spokes from poking through. The rim strips I used were for narrow 27 inch wheels. They were approximately one half inch wide. I had tried leaving the particle board groove bare, and there was no way to prevent the chain from slipping.
The particle board disk I used was too large for a single rim strip, so I used two strips end-to-end and glued together with silicone rubber. I overlapped the seam several inches. They are quite thin, so there was no noticeable "bump" going over the seams. I was also pleasantly surprised to find they prevented slipping completely, and there was no evidence of any wear on them for the life of the machine. Be careful when lubricating the chain, however. Keep the lubrication on (and inside if possible) the rollers, not on the outside of the side plates. I was very careful to not let the lubricants reach the parts of the chain contacting the rubber strips.
- Where can I learn more about Electricity?
- Learn about basic DC electricity here, and all kinds of electricity here.