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Simple bike generator - help!

Discussion in 'General Electronics Discussion' started by bicycleman, Nov 6, 2012.

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  1. bicycleman

    bicycleman

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    Nov 6, 2012
    I am building a bike-powered generator. The output will be 1500 to 2300 watts of fairly clean AC power to run a small refrigerator and a small induction cooker during a power outage (or whenever). I can source a bicycle, bike stand/trainer, belt, alternator, rectifier, four 12v AGM or other deep-cycle batteries and wiring locally. The problem is, I do not know what kind of alternator to use (what specs are needed, how much to spend), what kind of rectifier matches the alternator, what gauge of wire to use between different parts, and do I need a charge controller and if so, what rating? I am familiar with battery-to-inverter hookups so there is no problem there. Any advice is appreciated.
     
  2. donkey

    donkey

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    Feb 26, 2011
    ok first of all find out what your fridge operates at.
    find inverter to match.
    find a battery to suit
    then look at the alternator/ dynamo
    a standard car alternator can take up to 200 rpm before it starts producing adequate voltage to restore power.
    now the battery needs to have enough charge for said 2300 watts. lets make it 2400 for easy maths. to get this you take the watts and divide by volts in this cse 2400/12=200ah... so a 200 ah battery will run the load for 1 hour. given the fact there are inefficiences in life and the fact that no lead acid battery should go below 50% for any period of time you cut that to 30 minutes... ish.
    if however you want something similiar try the camping supply store who have a 12volt stoves and fridges that need no hard work done.
    or try a generator these can be had for less than $1000 aud and produce that amount without need to recharge (just refuel)
     
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    How many people will you have pedalling? Around 10?

    At the peak of my fitness I could generate 1kW of power on a cycle operated generator for a couple of seconds. 200W felt like I could do it all day. (These days it's closer to my peak..).
     
  4. CocaCola

    CocaCola

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    Apr 7, 2012
    A 4000W generator in the US can be had for under $300...

    Only if you have some physically fit people rotating in/out every few minutes... :p

    To give the OP some perspective a generator like the above (4000W) is using a 7 HP engine to sustain that level of power, the average human can sustain about 0.1 HP... So the quick math is 70 people pedaling away to produce the equivalent sustainable power... Now of course you wouldn't need to match that fully as there are variables, but to suggest that it would take 30 or 40 isn't unreasonable... And that brings up the question of can the fridge supply enough food that is worth it for those people :)
     
  5. Laplace

    Laplace

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    Apr 4, 2010
    So how much electrical energy can a bicycle produce? Assume a 195 lb person, 175 mm crank radius, and pedal speed of 50 rpm. Also assume that the person is able to keep their full weight on the pedal for each downward stroke and no weight on the pedal for its upward stroke. So for each rotation a force of 195 pounds exerts through a distance of 700 mm thereby transferring 447.8 ft-lbs of energy. Now 1 ft-lb of energy equals 1.356 joules, so at 50 rpm the bicycle is generating:

    447.8 ft-lb/rotation X 50 rotation/min X 1 min/60 sec X 1.356 joule/ft-lb = 506 joules/second

    I would view the 506 watts as a peak value for bicycle generation. For the long term a more realistic value would be only a third of the peak, and assuming electrical efficiency of 70% yields a sustained generating capacity of 120 watts from the bicycle generator.

    Which means that a 2400 watt load would require 20 bicycle generators, or one generator would need to charge a battery for 20 hours for each hour of running a 2400 watt load.
     
  6. CocaCola

    CocaCola

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    Apr 7, 2012
    I think the short of it people are not a viable source of alternative energy, at least not at this level :)
     
    Last edited: Nov 6, 2012
  7. KJ6EAD

    KJ6EAD

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    Aug 13, 2011
    That can't be! In a movie I saw people being used as batteries to run the matrix. ;)
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    You ignore a number of important aspects:

    1) you can provide a small amount of "pull" on the upstroke if you are using cleats (see also circular pedalling).

    2) you are holding the handlebars and you can get additional force by reacting against them.

    p.s. I promise that link is not cheating.
     
  9. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    A 500lb flywheel might be a good idea. Then find a guy they call Godzilla.

    Chris
     
  10. Laplace

    Laplace

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    Apr 4, 2010
    Those are good suggestions. Now, how would you calculate that?
     
  11. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    By measurement :)

    I was just taking exception to your assertion of the absolute maximum.

    See here. Puts my 1000W for a couple of seconds (more likely some 1000W spikes over a period of a couple of seconds) into perspective.

    edit: This also looks interesting.
     
    Last edited: Nov 7, 2012
  12. wingnut

    wingnut

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    Aug 9, 2012
    I watch the Tour de France where they give the wattage of cyclists.

    A pro can put out 300W continually, about 1000W for a few seconds.

    The real question is whether you will be taking steroids or not ;)
     
  13. donkey

    donkey

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    Feb 26, 2011
    to put things simply a bike generator is a GOOD idea for renwing enrgy but not at high consumption. getting a generator is best but you need fuel and in disaster areas that is hard to get.... unless you make biodiesel which is a whole other thing.
    if its just normal blackouts for a few hours then the fuel shouldn't be too much of an issue for stoves and fridges. having said that there are alternatives to the mains powered appliances. you have 12volt fridges (small capacity) and ovens, gas burners, BBQ's, kerosine fridges..... the list goes on
     
  14. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    As has been suggested, under 250W per person if you're going to expect them to keep it up for any length of time. Even that assumes some fitness.
     
  15. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    Does this mean that in, let's say 1950, 1ft-lb did not equal 1.356 joules? :p

    Chris
     
  16. CocaCola

    CocaCola

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    Apr 7, 2012
    Ironically most people ignore the fact that in many cases natural gas supplies still function, during these disasters... Meaning you have a source of fuel pumped right to your front door... Of course many areas don't have natural gas and rely on propane tanks, but then again you 'might' have a large source of fuel right there in your front yard... Like anything circumstances are never the same, but there are other options to explore...

    If you really want to be prepared a natural gas generator can be a huge asset...

    FYI there are 'conversion' kits out there to convert standard gasoline operated generators to also work with natural gas (and propane), meaning with a little work you can have a three fuel generator in a single unit...
     
    Last edited: Nov 8, 2012
  17. CDRIVE

    CDRIVE Hauling 10' pipe on a Trek Shift3

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    May 8, 2012
    That really is a fact. Very few home owners in Florida don't have emergency generators and a sh!t load of 5 gal fuel cans. When a storm passed without loss of power we have to dump it in our vehicles before it turns to varnish. The same varnish problem applies to the generator. They should be run dry when put in storage. Natural gas and propane doesn't suffer from this, that I know of.

    Chris
     
  18. CocaCola

    CocaCola

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    Apr 7, 2012
    Propane and Natural Gas are much more stable, long term storage no problem... Another alternative is ethanol, as it has the shelf life as well and only needs a carb adjustment to be used as an alternative on 'most' small engines... The only drawback to ethanol is that it can cause corrosion to the engine/carb if left in for extended periods of time... So just like gas, the generator should be drained of fuel and properly 'fogged' before storage...
     
  19. davenn

    davenn Moderator

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    Sep 5, 2009
    now there's a term I have never seen before


    we live and learn ;)

    Dave
     
  20. CocaCola

    CocaCola

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    Apr 7, 2012
    It's amazing how many people don't know what it is, but living where I do where we get the full winter months and the full summer months most people that have recreational toys know what it is as those toys generally are in storage for 6 months each year... Or at least 'should' know what it is, many times they are oblivious to what it is and just pay someone to 'winterize' their boat prior to storage...
     
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