Exercise bike that produces electricity

  • #1

Main Question or Discussion Point

Ok.
Folks, first off this is my first post, and I am looking for some answers to some questions I have. I hope someone has the time to answer them :)

First off, I'm no expert in physics. I know a billion times more than any of my friends but believe me that is not saying much. I have never really studied it in an academic atmosphere, I have only read several books for laymen, QED, Brief history of time, a couple more hawkings papers, schordingers cat (spelling) and a few others. Just enough to blow my mind.

Anyway, I have a long story that I wont bother you guys with that explains how I came up with the idea for a Exercise bike that produces electricity, and then either offers the consumer the option to plug right in to an AC outlet or to store it in a battery.

I have some questions that i need answered before I start looking on how to design it.
1. If I were to say use a normal Generator, say like the ones wind turbines use, what kind of current would that produce? AC or DC?

2. A motion specific physics question. http://askalexia.com/2009/02/06/cylec-exercise-bike-generates-electricity-to-charge-your-gadgets/" [Broken]
This is the only working prototype that is currently even close to being production value. And I notice the Electrical output is minimal. It takes 2 hours to charge a battery that will power a fan for 3 hours. What would be a system that would maximize the effort used to make the electricity. I was thinking about how a gear system works. Would there be a way to get the bike to were you peddle less and turns the generator faster?

3. What would be the right battery to use. Obviously in America all the power is AC, are standard rechargeable battery's put out AC or DC current?

Also any other things I need to look at?
I am not familiar with wiring or circuitry so any resources would be great.
 
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Answers and Replies

  • #2
mgb_phys
Science Advisor
Homework Helper
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Anyway, I have a long story that I wont bother you guys with that explains how I came up with the idea for a Exercise bike that produces electricity, and then either offers the consumer the option to plug right in to an AC outlet or to store it in a battery.
Not too difficult - has been done as a joke/toy - so you can only have the TV on if you are prepared to exercise

1. If I were to say use a normal Generator, say like the ones wind turbines use, what kind of current would that produce? AC or DC?
Generally you would use DC. A dc generator can charge a battery directly.
An AC generator can in theory run an appliance directly BUT the frequency depends on the speed, so would have to peddle at exactly the correct speed to generate 50/60Hz AC (depending on your country)
A safer way is to generate DC, charge a battery and have an inverter, like the ones used to run a laptop in your car, to generate the 110/220V AC

Connecting into the grid (ie sending power back to the electric company) is more difficult. You can do it (in most areas) but you need some fancy expensive electronics to convert your power into exaclty what the company wants (voltage, frequency, phase) - it's just an upmarket version of the inverter but costs $2000-$5000
Probably not worth it for the amount of power you can generate !

Would there be a way to get the bike to were you peddle less and turns the generator faster?
Fundamentally it all comes down to power. A good team cyclist can sustain about 1/4horse power for an hour - thats 200Watts * 1 hour = 0.2kw-hours or 1/5 of a unit of electricity.
That costs about 2c in the USA but would take around 2000calories (or 10 Snickers bars) to generate

3. What would be the right battery to use. Obviously in America all the power is AC, are standard rechargeable battery's put out AC or DC current?
Normally home power systems (solar or wind) use lead acid batteries because it is cheap easy and reliable

Search for "off-grid, wind power, solar" - there were a couple of good google tech talks on youtube also mentioned here
 
  • #3


Not too difficult - has been done as a joke/toy - so you can only have the TV on if you are prepared to exercise


Generally you would use DC. A dc generator can charge a battery directly.
An AC generator can in theory run an appliance directly BUT the frequency depends on the speed, so would have to peddle at exactly the correct speed to generate 50/60Hz AC (depending on your country)
A safer way is to generate DC, charge a battery and have an inverter, like the ones used to run a laptop in your car, to generate the 110/220V AC

Connecting into the grid (ie sending power back to the electric company) is more difficult. You can do it (in most areas) but you need some fancy expensive electronics to convert your power into exaclty what the company wants (voltage, frequency, phase) - it's just an upmarket version of the inverter but costs $2000-$5000
Probably not worth it for the amount of power you can generate !


Fundamentally it all comes down to power. A good team cyclist can sustain about 1/4horse power for an hour - thats 200Watts * 1 hour = 0.2kw-hours or 1/5 of a unit of electricity.
That costs about 2c in the USA but would take around 2000calories (or 10 Snickers bars) to generate


Normally home power systems (solar or wind) use lead acid batteries because it is cheap easy and reliable

Search for "off-grid, wind power, solar" - there were a couple of good google tech talks on youtube also mentioned here
Ok.
So increasing say the wheel size to spin the turbine more times around than if normal, or is there a way with momentum to increase the output?

I was also thinking about those really old workout bikes that turned fans and the handlebars moved too. the fan gets going way faster than the rider id pedaling. Could this help me at all?
 
  • #4
mgb_phys
Science Advisor
Homework Helper
7,774
12


No you can't get more energy out than you put in.
You can spin a generator/fan faster, but with less force - it all cancels out (except that you lose energy in the gears)
 

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