Using a bike to charge batteries etc

[billyb]

Is it possible to rig up a bike to a) charge something e.g. mobile phone run something e.g. radio/telly c) get some exercise while doing so.

 

I saw one rigged up to what looked like some sort of generator at Eden Camp, this was during the war so I presume technology has improved somewhat since then?

[Machpoint005]

Is it possible to rig up a bike to a) charge something e.g. mobile phone run something e.g. radio/telly c) get some exercise while doing so.

 

I saw one rigged up to what looked like some sort of generator at Eden Camp, this was during the war so I presume technology has improved somewhat since then?

click here

Something like this, you mean?

[Nightwatch]

Get a dog and a treadmill.

[twocvbloke]

Simple answer:

 

Yes, you can...

 

Complex answer, er, ask someone else...

[KenK]

Saw a narrowboat on the K&A once with a waterwheel, made from an old washing machine drum, hung over the side on a frame. It was driving an alternator, enormous pulley ratio, so probably a reasonable amount of free energy given that the river flows fairly quickly where he was moored.

 

Ken

[Sir Nibble]

If you rig a car alternator to a bike frame, you will I promise you be absolutely astonished at the amount of effort needed to pedal the thing. It will only work briefly because even the most determined meathead will not be willing to pedal it for long.

[Guest]

Saw on once where a person had made a permanent magnet genny similar to that found on a wind genny, mounted it on an exercise bike and claimed a reasonable output. Forgotten where I saw it now.

[Machpoint005]

If you rig a car alternator to a bike frame, you will I promise you be absolutely astonished at the amount of effort needed to pedal the thing. It will only work briefly because even the most determined meathead will not be willing to pedal it for long.

That's a problem with inappropriate gear ratios, then?

[Guest]

http://www.stewardwood.org/resources/DIYcyclepower.htm

 

http://www.anotherpower.com/gallery/exercise-bike-generator

Edited February 26, 2009 by Guest

[alan_fincher]

That's a problem with inappropriate gear ratios, then?

I suspect almost certainly not.

 

If you provided a gear ratio where anyone other than superman could turn it continuously, then it would probably be turning too slowly to generate anything useful.

 

What's wrong with a bike with it's wheel supported off the ground, and a good old fashioned (bike) dynamo, please ? You could arrange a frame to fit as many as you felt able to power, if you weren't actually planning to go anywhere.

[David Schweizer]

Is it possible to rig up a bike to a) charge something e.g. mobile phone run something e.g. radio/telly c) get some exercise while doing so.

 

I saw one rigged up to what looked like some sort of generator at Eden Camp, this was during the war so I presume technology has improved somewhat since then?

There was an item on the One Show this evening about green energy, and one of the things they mentioned was a Gym rigging up their excercise bikes so that would generate electricity to power the Gym's lighting. So the answer is undoubtably yes, but where you get the kit is another question.

[chris w]

The problem to which Sir Nibble alludes is one of the maths of turning an alternator.

 

Suppose you wanted to generate say 20A for charging your batteries. 20 amps @ 14 volts is 280W. Unfortunately alternators and dynamos are only 50% efficient so you actually have to put in 560W (0.75 horsepower). The alternator will need to be turning at around 2000rpm to generate this current.

 

A person pedalling is at their most efficient at around a cadence rate of 60-80 rpm. Thus to be able to turn the alternator at 2000rpm would need a gearing ratio of around 25:1.

 

That means that the power required to be input by YOU would be 0.75 x 25 HP = 19 Horsepower!!!!! ie: impossible.

 

That's why, as Sir Nibble said, you will be surprised just what a huge effort is needed to turn an alternator by pedalling. You won't get it generating any level of current that would be remotely useful in charging your batteries.

 

Chris

[alan_fincher]

Although to be fair the OP only wanted to recharge his mobile, or run a radio or TV, not put 20 amps into his battery bank.

 

Whilst the TV might need a bit of work, the mobile phone should be a doddle.

 

If the radio can't be solved any other way, buy one of those Freeplay wind-up models, and attach it's crank to the bike with suitable gearing!

 

Surprisingly, (to me at least), the wind up LED torches I've just bought will burn bright for at least an hour with no more than a minute's hand winding. So if you are winding all the time, not just for the first minute of an hour, even the generators in these must be good enough to run the equivalent of 60 LED torches, (whatever amps that equates to. )

[robkg]

The problem to which Sir Nibble alludes is one of the maths of turning an alternator.

 

Suppose you wanted to generate say 20A for charging your batteries. 20 amps @ 14 volts is 280W. Unfortunately alternators and dynamos are only 50% efficient so you actually have to put in 560W (0.75 horsepower). The alternator will need to be turning at around 2000rpm to generate this current.

 

A person pedalling is at their most efficient at around a cadence rate of 60-80 rpm. Thus to be able to turn the alternator at 2000rpm would need a gearing ratio of around 25:1.

 

That means that the power required to be input by YOU would be 0.75 x 25 HP = 19 Horsepower!!!!! ie: impossible.

 

That's why, as Sir Nibble said, you will be surprised just what a huge effort is needed to turn an alternator by pedalling. You won't get it generating any level of current that would be remotely useful in charging your batteries.

 

Chris

Hi Chris,

I would respectfully like to challenge one element of your calculation.

 

If the alternator generates 280W and is 50% efficient, then the power input requirement is 560W - agreed.

However ignoring inefficiences in the drive train, the human energy input is 560W, not 19 horsepower.

i.e. the gear ratio of the drive train is irrelevant to the power. (just multiplies up the torque requirement)

 

I should just add that 560W is still a lot of power for a human to generate.

[alan_fincher]

If there's going to be a fight, I'll hold your coats!

 

But I am (nearly) brave enough to say I thought the same as Rob.

 

No!, I'm surely not!

[chris w]

Hi Chris,

I would respectfully like to challenge one element of your calculation.

 

If the alternator generates 280W and is 50% efficient, then the power input requirement is 560W - agreed.

However ignoring inefficiences in the drive train, the human energy input is 560W, not 19 horsepower.

i.e. the gear ratio of the drive train is irrelevant to the power. (just multiplies up the torque requirement)

 

I should just add that 560W is still a lot of power for a human to generate.

You're quite correct.. I got carried away.....or maybe should be!!

 

OK, so working out the torque... the torque required to turn the alternator above when attempting to generate 560W is about 2 ft.lbs since HP = torque x RPM/5252 (where torque is measured in ft.lbs)

 

So gearing up by a ratio of 25:1 would require you to expend a continuous torque of around 50 ft.lbs. If you think how small the gear would be to which the pedals are attached to get a 25:1 ratio, the actually pounds of effort required will be of the order of a continuous 100 lbs force!!!!!!!!!!

 

Chris

[chris w]

Surprisingly, (to me at least), the wind up LED torches I've just bought will burn bright for at least an hour with no more than a minute's hand winding. So if you are winding all the time, not just for the first minute of an hour, even the generators in these must be good enough to run the equivalent of 60 LED torches, (whatever amps that equates to. )

The "ultrabrite" LEDs used in torches only require a surprisingly small amount of current, about 5mA each to get a very bright light. So a typical wind-up 3 LED torch will require only about 15mA which is supplied usually by 2 x 1.5v NiMH batteries or a single 3.6v Lithium battery. The "generators" inside them are just simple little "toy" dc motors used in reverse. So when you turn the handle you are actually turning a little motor which generates a small amount of electricity.

 

I would be very surprised if you could get 1 hour out of your torch from just 1 minute's turning, given the batteries are absolutely dead to begin with. I would reckon more like 20 minutes max for 3 LEDs.

 

If you turn the handle at a typical 120 rpm (twice a second) you will generate just under 1 watt. So after one minute, you will have generated 1 watt minute of energy or about 0.3 ampere minutes of energy (based on a 3v battery). Let's assume the charge process is 80% efficient, so you will have around 0.25 ampere minutes of energy available after 1 minute's turning.

 

With this amount of energy available, and to last 60 minutes, the average current cannot be more than 5mA. This about a third of what is needed to run the 3 LEDs so the actual time will be closer to 20 minutes. You will only get an hour if you have just one LED lit.

 

Chris

Edited February 27, 2009 by chris w

[FadeToScarlet]

http://pedalpa.org.uk/

 

^^^ MoominPapa's Pedal Powered PA (Or at least, I think it's his. I wouldn't be surprised!)

 

He manages a 50w continuous output, I think.

[WJM]

We did not invent engines for fun you know!

[alan_fincher]

I would be very surprised if you could get 1 hour out of your torch from just 1 minute's turning, given the batteries are absolutely dead to begin with. I would reckon more like 20 minutes max for 3 LEDs.

 

With this amount of energy available, and to last 60 minutes, the average current cannot be more than 5mA. This about a third of what is needed to run the 3 LEDs so the actual time will be closer to 20 minutes. You will only get an hour if you have just one LED lit.

 

The type we have, (4 of now), uses a fixed arrangement of 3 LEDs that can't be varied.

 

I've certainly left one unattended for an hour, that was still well illuminated by the time I got bored and turned it off.

 

The only bit of my original claim that might be open to question is whether it was actually cranked for a minute, or rather longer.

 

When I have an opportunity I'll run one down, (they always work, even if left a week or more), and try again.

 

Is there any particular suggestions you would make for a controlled test.

 

(They are sealed units, so I can't see what's inside, nor break in to measure charging or discharge currents, unfortunately).

[NB Alnwick]

So gearing up by a ratio of 25:1 would require you to expend a continuous torque of around 50 ft.lbs. If you think how small the gear would be to which the pedals are attached to get a 25:1 ratio, the actually pounds of effort required will be of the order of a continuous 100 lbs force!!!!!!!!!!

 

Clearly, it is possible but only with a generator set to provide a much lower output and then it would require many hours of very hard work to generate enough to re-charge a half-decent battery bank on a narrow boat.

 

Ten years ago, I used to cycle regularly covering the twenty miles between work and home (on a rising gradient) in an average of around 80 minutes. The journey seemed much slower after dusk, so I ditched dynamo lighting in favour of re-chargeable battery packs. The result was a time saving of around ten minutes after dusk.

[chris w]

The type we have, (4 of now), uses a fixed arrangement of 3 LEDs that can't be varied.

 

I've certainly left one unattended for an hour, that was still well illuminated by the time I got bored and turned it off.

The batteries will easily give many hours of illumination if they are fully charged. You need to differentiate between the charge in the batteries and the additional amount of charge you are putting in by cranking for 1 minute. Based on my calculations, it would take about 3 minutes continuous cranking to get 1 hour of illumination from totally dead batteries.

 

The only bit of my original claim that might be open to question is whether it was actually cranked for a minute, or rather longer.

 

When I have an opportunity I'll run one down, (they always work, even if left a week or more), and try again.

 

Is there any particular suggestions you would make for a controlled test.

 

(They are sealed units, so I can't see what's inside, nor break in to measure charging or discharge currents, unfortunately).

For a controlled test, leave the torch switched ON for a few hours until the LEDs are definitely not glowing at all. Then switch OFF and crank for 1 minute. Then switch ON again and time how long till the LEDs self extinguish.

 

Chris

Edited February 27, 2009 by chris w

[Amicus]

I think I've always "known" that a reasonable continuous output on a cycle exerciser was 80 watts, about 120 in a short burst, I have no idea how I "knew" this, if indeed I did "know" it. Funny old world, innit.

[twocvbloke]

Going back to actually charging mobile phones or mp3 players or (ugh) ipods, I think that a regular 6v bicycle dynamowould be fine for the job, you may need to do some fiddly electronics work though to make the power useful for said devices (USB devices require 5v, phones about 4.5v etc)...

 

I have a little gadget I got for 50p at the local carboot sale, it's a hand-wound dynamo charger, it's a pain to use, but with a little modification, it could be connected to a bicycle dynamo (removing the built-in motor (yes, it's a motor!!!), soldering wires from the dynamo in place, and there you go), I can't recall it's name or make, but I'm sure most cheap dynamo charger thingies are the same internally...

 

It also has the added bonus of having an LED circuit fitted, so when you're not charging, you have a light too (though swapping it for a white 4.5v LED torch might be better than the single amber LED), very handy...

[Guest]

Bilge pump anyone?

 

http://www.edc-cu.org/ppt/WheelDeal.pdf

Edited February 27, 2009 by Guest