Intelligent Portable Power Generator Project

[alterntech]

Hello Everyone. I would like to suggest an open source project for everyone interested in renewable energy. I have a rough outline drawing designed of a hand powered generator that can be used to power err most eneltrconic devices even small netbooks, so what I am looking for is a group of like minded people that want to get involved. What do you say guys?.....

 

[Mr RB]

Hand cranking is annoying (if you have used one of the hand cranked appliances that are currently available), what about foot cranked by pressing on it with your heel or something like that? Heaps more power available and you can do it while reading the newspaper etc.

 

[Oznog]

Leg power is about 200W sustainable for a fairly long period if you've got a bicycle.

Try measuring a hand crank LED light sometime. The power is quite low- tens of mA IIRC, as the short-circuit current. It seems like more power than it is because your eyes adjust to the light as it fades, and it's running at only a few mA before you think to re-crank it, and it lasts much longer under that kind of load.

An mp3 player... well, it depends. Look at the batt. If it's a 1100mah 3.7v lithium batt, and it lasts 8 hrs, well, it needs 138mA. So even cranking constantly wouldn't be adequate, you'll need to spend much longer cranking than listening to music.

 

[tcmtech]

I seriously doubt the 200 watt output capacity can go for more than a few minutes for most people.

The Human Engine

Consider now the human engine. In 1983 Douglas Malewicki gave a landmark paper at the International Human Powered Vehicle Association Scientific Symposium, in which he presented a graph showing the maximum duration of human effort for various steady power levels. This graph has been reproduced below for convenience. Notice from the graph that an average "healthy human" can produce a steady 0.1 horsepower for a full eight hour period, while a "first class athlete" can produce 0.4 horsepower for a similar period. Note that each data point on the curves represents an exhausted human. No more power is available without some rest and recovery. Thus at 0.4 hp the "healthy human" becomes exhausted within 10 minutes! Try to decide where you fit in this curve.

Note that in the power equation the units of power is watts (W), however we can apply the conversion 0.1 hp = 75 W (approximately) in reading the graph. Once you have decided the steady power level that you can comfortably apply at the pedals, it would be of interest to know the velocity that you will achieve at steady state when all other parameters are maintained at constant values. Unfortunately the steady state power equation above cannot be solved explicitly for velocity, thus we will develop a root finding technique to solve this problem in a forthcoming exercise. This first exercise introduces modular programming using functions, and is much less ambitious:


as taken from this site. Howstuffworks

The 75 watt number is a standard referance to average human power capacity.

 

[Sceadwian]

I think the constant energy production of a human being might be massively overshadowed by the fact that humans can burst energy levels well... and I do mean WELL above average output.
As far as practicality goes I would lean towards someone using a large amount of energy over a short period of time to lift a weight or charge a spring that would give a long average power output to a generator. That's for lower power loads.

Consider it something like the difference between a class A amplifier and a class D amplifier.
Humans work better as class D amplifiers.
I think a well focused prepared and skilled individual can release more energy than those stupid leg spinning wheel tests indicate. I just don't have the means to prove it.

 

[tcmtech]

Like a power lifter Vs a good ol farm boy Vs a cyclist Vs everyone else?

The power lifters will top most everybody on the absolute peak short burst output capacity but the cyclists will out last anyone on the longer term outputs. Us good ol farm boys have the happy medium. I cant top the power lifter on shear weight but I can take a smaller load and lift more times than he can before I get tired. But the cyclist will easily beat me on steady load endurance comparisons.

In a way its like a dragster, your average pickup, and a long haul truck. Each has its specific advantage and disadvantages.

Then you can also toss in the typical persons you will find everywhere else. They are like the crappy car that sits in the driveway and leaks oils all day. Sure it can do a burn out now and then without hurting itself too much but you wouldn't put a trailer behind it and take it across country either. Most of the time its just best off being parked and doing as little as possible.
Go to work and come back. Much of anything else is out of its realistic and practical capacity's.

It thinks its a dragster/work truck/heavy hauler but it wont ever take on the real ones! It would but its got a flat tire, or its low on antifreeze, or the dash is dirty, or the blinkers dont work right, or its seat hurts.

 

[Mr RB]

Powerlifters? Farmboys? Dragsters? None of it is really relevant to the OP's question.

Which is probably why he has not been back.

 

[Sceadwian]

Mr RB, perfectly on topic in context, tcm was comparing the differing type of activities a human could do to generate power with examples from real world devices.
The posters idea is sound, but for practical use it would require a relatively large battery and some pretty heavy duty gear mechanisims, those hand cranks you typically see on consumer devices break easily and from the ones I've used don't seem to be geared properly to take advantages of the amount of torque a persons arms can produce when they're really trying. The main problem would be getting people to use something like this, power is almost always only a plug away so you'd have to have a good reason to want to hand crank something. It's a good idea for developing countries but in order to market anything there you have to make it absolutely dirt cheap.

 

[tcmtech]

Exactly. Individual peak power is far different from realistic continuous power. And even that will vary greatly from person to person.
Some people can do a solid 100+ watts and hour for extended periods without any difficulty. Others couldn't do 20 Watts for more than a few minutes without exhausting themselves.

Usually its the ones who couldn't do the higher exertion work that claim they can easily do it but never show them selves actually doing it. Then there are others that do that level of exertion all day every day for years and never think twice about it.

Here is how I see it from a single application in my life.
The power pack for my laptop is rated at 19 volts 4.74 amps and when I am using it while the battery is in a high charge cycle it draws around 80 watts and stays at that draw for more than an hour.
To reproduce that equivalent output from a human power source a person would need to generate over 100 watts of physical output to get the roughly 80 watts of electrical energy needed for the laptop to work and charge at the same hour plus time frame.
Thats well beyond the realistic continuous hand cranking capacity of most everyone.
If its broken down into a easier but still reasonable effort of 20 watts per hour thats still some 5 hours of non stop cranking just to charge up a laptop and use it to any degree.

I still dont think many people would actually ever put forth that amount of effort for that time frame just to use their computer for a hour or two. I sure wouldn't.

Even if a exercise bike type of generator system was used I would like to see anyone pedal a 100 watt exertion level for an hour or more while working normally on their computer at the same time!

The OPs design would have limited applications for very low power usage applications being done by people with far more time than money. But those people usually cant afford the Ipod, cell phones, and other lower power electronic toys that are within the realistic human powered recharging range.
And I seriously doubt they could afford the charger device in the first place.

For anyone who says thats why you give them out charitably to the low income people, well someone is still paying for them at some point anyway and if its me thats expected to pay for one I would rather let a few dozen bums stand around in my shop all day with a hundred power pack chargers plugged into every outlet and power cord they can find for free first!

 

[Oznog]

I think there's a lot of room to improve hand-crank devices.

The little flashlight I had was downright annoying because it wasn't enough resistance to justify the cranking motion. I could have pushed a lot more, and slower, more comfortably. In fact it wasn't that much more resistance than I could overcome by twirling the handle with my finger. But... look here... with a more powerful motor and gearing for lower speed/higher torque, the limiting factor's not actually how much torque you can turn with your arm, but how well you can hold it with your stationary hand. The natural hold is in the palm and it's hard to grip under a lot of load. Think about that for awhile- there must be far better shapes to hold.

 

[Mr RB]

Hand cranking is just annoying, not the least annoyance is that it usually ties up both your hands which is just dumb.

I have a squeeze crank torch that is usable, in just one hand but gets tiring and it's noisy and crudely made.

I made a very nice rotary hand cranked lantern with a zero-cogging brushless generator, charging a 2.2F 4.5v supercap and using a 1W luxeon white led. It was designed for good cranking ergonomics and has MUCH better bearings and overall design than any handcranked lantern I've tried, but it is still a bit annoying to use and requires 2 hands.

What I proposed in thread 2 was to get away from the 2 hand cranked annoyance and go for something that uses NO hands, ie heel->floor cranked and generates more power. You could be charging your cellphone or blackberry with it and at the same time sending a SMS etc. Much smarter.

 

[tcmtech]

I have felt the same way about my hand cranked LED flashlight.
They could have easily built it with a much higher input torque and designed it with a battery that can power three .1 watt LEDs for more than 3 minutes without needing to be re cranked again.

Double or triple the input torque and put ten times the battery capacity in it. That way I fell like I was doing something that was going to actually amount to anything useful and then give me a battery that backs up my efforts.

I really like the self powered LED flashlights but they can be greatly improved on for run time and practical efforts applied to get that added run time.

 

[Sceadwian]

Unfortunately there's very little consumer demand for making these kinds of products better.

 

[tcmtech]

Well I am a consumer and I demand better!
Plus everyone else that has one seems to come to the same general conclusions as well.
Whether we crank ourselves silly for 10 seconds or two minutes we still get 3 crappy minutes of quickly fading light from the most efficient battery powered light source available to date.

Make it cost $21.95 instead of $11.95 and give us a better battery and generator in it! I will happily pay $10 more to get ten times the run time out of it while feeling like I just might be actually working on charging something when I am cranking.

 

[Sceadwian]

You're _A_ consumer... The vocal minority.
They want widgets. Give them a widget and they'll flock like seagulls to a crumb of bread. But only if you have a widget that will sell. They don't care about better engineering, doesn't matter the increased cost or loss in efficnecy, they want widgets that sell. What sells, is almost never what is best,

 

[tcmtech]

So if I make it take pictures and work on the web then it will get better?

Or will it then only work in certain places where I dont really need it?

 

[Mr RB]

You're _A_ consumer... The vocal minority.
They want widgets. Give them a widget and they'll flock like seagulls to a crumb of bread. But only if you have a widget that will sell. They don't care about better engineering, doesn't matter the increased cost or loss in efficnecy, they want widgets that sell. What sells, is almost never what is best,

I agree that sums up the idiot consumer market pretty well.

But a product like this can definitely enter at the quality end of the market. Like your urban professional who goes backpack trekking on the weekend, look in the camping store junkmail there are 3kg hiking tents for $80 and 1.5kg hiking tents for $300... There are some people who will pay for top of the line performance.

A really nice human powered generator could sell for $$ if it is designed right.

Here's my take on it;
1. plugs direct into mains (has mains prongs to no wallwart needed), micro controls charging.
2. micro gives alert on low bat to protect expensive battery
3. single foot heel-cranked with good metal geared mechanism
4. plug adapters to power GPS, cell phone, charge AA/AAA battery
5. built in tiny FM radio, why not
6. as small and light as possible given the above

 

[Sceadwian]

I definitely agree Mr RB, it's difficult to find quality products even at a high cost sometimes though. The markets are there for people to exploit (just hopefully not abusively)

 

[alterntech]

Hand crank power generators are annoying for some, I agree.... But China has military hand crank generators not much bigger than a PDA that can output 60 watts of energy... I had built some generators like it myself.. one that had a detachable handle and wind blade assembly for dual use.. that unit was rated at 1.5Watts .... the idea was to throw an idea into the arena to get some people thinking about this and us maybe working on a joint project.... what say you all....

 

[Oznog]

**broken link removed**

60W, 4kg. You need a tree or whatever to support it or it'll be really awkward to crank.
I'm bettin that thing takes some major work to get 60W out of.

But I could bring along a lot of extra batteries and be under 4kg. And not need an hour of cranking during camp time, which would pretty much eat into the time I'd actually want to use said appliances.
The other thing is that unless the batts are LiFePO4, a batt like a 500mA 3.7v phone batt, 1.85Watt-hrs, couldn't be charged in two minutes even though the generator is technically capable of it. No, you'd have to crank for an hour or two (or three) to get through the lithium's normal charging cycle. That's kinda problematic- I'd much rather do 10 min of intense cranking than 2 hrs of very very light cranking. I'd be very sore after 2 hrs even if there was zero load, the arm motion alone is exhausting.