How to build a human powered generator

  1. Hi all,

    Sorry if this is an incorrect part of the forum.

    Living a relatively sedentary lifestyle, consuming a Western diet, living in an area where drivers see pedestrians/cyclists as moving targets to run over and after packing on a few pounds, it got me thinking. I'd like to (as a side-project) make a small device that can provide power while I'm sitting and pedaling. Here are some requirements that I'd like to have:
    * Balance the load. I can plug in my computer in one end and have a connection to a live outlet at the other. The idea being that I won't lose power to my box whenever I stop pedaling. If I do pedal, then I simply use less energy from the grid.
    * I need some way to keep track of how much I'm generating in terms of watts.
    * I need to be able to sit at a regular office chair (at home) and pedal away.
    * Ideally, the amount of pedaling I do will proportionally increase the amount of juice I generate and that I can vary the resistance (and increase the amount of power production) as I build up strength and can produce even more power.

    Like I said, this is a side-project. And I'd like to say that I'm a complete n00b to electronics (some exposure at work, some things that I picked up over time), so I'd like to cover that part first. Any books or tutorials out there that some of you might know of?

    I realize that this will take me months of on and off effort before I can even have a prototype with half of the previously mentioned requirements, but I don't expect this to be easy :) .
    Last edited: Jun 17, 2010
  2. jcsd
  3. mgb_phys

    mgb_phys 8,809
    Science Advisor
    Homework Helper

    1, Bike - already has the gears, pedals, drive train.
    2, Trainer - basically a pair or rollers and a stand to hold bike wheel. used by us masochists to cycle inside in winter when it's snowing
    3, Swap the magnetic brake on the trainer for a 12V DC generator
    4, UPS - converts 12V battery power to 110V/60Hz and has a battery so your computer doesn't lose power when you do.
    5, Cheap $5 bike computer will keep track of how far/how much power (not terribly accurate but do you care?)
  4. Any model of UPS that you know of that would be a shoe-in?
  5. mgb_phys

    mgb_phys 8,809
    Science Advisor
    Homework Helper

    Shouldn't matter. You to open it up and a tiny bit of electronics knowledge and a multimeter to hook up the generator to the battery.
  6. russ_watters

    Staff: Mentor

    I'm not sure the UPS idea will work. A UPS switches between two different power supplies, it doesn't draw from both at the same time. And a bike won't power a desktop PC on its own for very long unless you're Lance Armstrong.
  7. What would recommend as a solution?
  8. mgb_phys

    mgb_phys 8,809
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    You could disconnect the 110V input and just use the battery (while it is charged by the bike) you should be able to do 250W which is enough for a small PC (at least with an LCD)
  9. Try the Microsoft way.

    Attached Files:

  10. DaveC426913

    DaveC426913 16,555
    Gold Member

    Even bikes already have a generator. There are bicycle headlights that tap the turning wheel to convert to electricity.
    Click me...
  11. russ_watters

    Staff: Mentor

    First, I'd re-evaluate your goals. If your primary goal is to get exercise, then idly peadling a bike while doing office work is a good idea. If your primary goal is to do a project to see if you can make it work, that's fine too (and mgb's idea is workable). If your primary goal is to generate a useable amount of electricity, then I'd abandon the project and look for something else to spend my time on.

    Lance Armstrong is capable of putting out 500 watts for a long period of time. A good recreational rider, 300 watts. A relatively normal adult in decent shape, 150 watts. But this is all aerobic exercise. If you want to just peadle idly while sitting at a desk for a few hours, you can't expect to generate more than about 50 watts unless you are in very good shape. And if you could generate 50 watts for 4 hours a day, 5 days a week for a year, you'd generate about $7.50 worth of electricity at residential rates.
  12. uart

    uart 2,776
    Science Advisor

    Very true. And just in case the OP's interest is environmental in nature then consider the following.

    On average we use over 10kJ of fossil fuels in production (and packaging transporting etc) per each 1kJ worth of supermarket food we consume! (and I’ve seen realistic calculations and statistics to support that figure). Now factor in the relatively low overall efficiency of a home generator and the biomechanical inefficiency and you'd probably end up with something like 50 to 100 kJ of fossil fuels used per 1kJ of energy returned to the grid. So the irony is that even a coal fired power station is far more environmentally friendly than this human power generator.
    Last edited: Jun 19, 2010
  13. Ha! Thanks, I'm good :p . I'm typing this response on my laptop running Ubuntu 9.04 ;) .

    But I have all 3 major OSes. Mac OS 10.6, Vista Ultimae 64-bit and Ubuntu 9.04 (need to upgrade, haven't gotten around to it yet.)
  14. I believe I was reasonably clear in this. My primary interests was a little hobby on the side and having some exercise. The part about making electricity was to add interest to the entire project beyond simply pedaling and then using friction to make the whole process more difficult. The extra juice generated is just gravy. I don't genuinely expect to save the planet or power some of my appliances (except maybe recharge my phone or laptop.)
  15. Interesting. Does that provide any challenge while pedaling? I realize that the newer bike light generators are supposed to be easier on you, but I'd prefer if they were more taxing...
  16. DaveC426913

    DaveC426913 16,555
    Gold Member

    I guess It's too small for your purpose. It was a marginally noticeable amount of resistance. Mostly what it did was make trying to coast coast for any distance fairly ineffective - you'd slow down too fast.

    The reason I brought it up was to begin to address the problem of how much power you'll get out of how much physical effort.
  17. mgb_phys

    mgb_phys 8,809
    Science Advisor
    Homework Helper

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