Small, simple way to generate 500 Joules in 15 minutes

[PraAnan]

Hey everyone,

I'm looking to build a simple generator that can either produce 500 Joules and then store it in a capacitor so it can be used up over 15 minutes or something that can generate the needed 500 Joules in the span of 15 minutes so you wouldn't need to store it. The thing that needs to be powered for 15 minutes is a 5V 100mA LED

I can't use solar or wind so was thinking of either using human power or gravity power but ruled the latter out because both the mass needed and the height will be too much. If it's human power the person will need to generate that in less than 30 seconds.

How would you do it?

Advice would be appreciated.

Thanks for reading.

 

[AZFIREBALL]

Bicycle wheel driving a small DC motor to charge a large cap.

 

[phyzguy]

Competitive cyclists routinely generate hundreds of watts for hours at a time. It's pretty easy to generate 50 Watts on a bicycle. 50 Watts for 10 seconds is 500 J. So hook a generator up to a stationary bicycle and you're there. Can you elaborate on what you're trying to do? I assume you can't plug it into the wall. Note that 500J of electrical power is about 0.0001 kWh and costs much less than 1 cent.

 

[PraAnan]

Competitive cyclists routinely generate hundreds of watts for hours at a time. It's pretty easy to generate 50 Watts on a bicycle. 50 Watts for 10 seconds is 500 J. So hook a generator up to a stationary bicycle and you're there. Can you elaborate on what you're trying to do? I assume you can't plug it into the wall. Note that 500J of electrical power is about 0.0001 kWh and costs much less than 1 cent.

I'm trying to build a light (with a 5V 100mA LED) that can run for 15 minutes and can be recharged really quickly. I didn't want to use a cycle generator because I wanted the generator to be a little small.

 

[AZFIREBALL]

Why don't you list ALL the attributes needed in the system and its construction, along with any material, costs, size, time, fit, form, feel, function restraints we should be aware of, so we don't keep picking at this thing?

 

[anorlunda]

I don't know why you ruled out gravity light. Please don't hold back your requirements and make us guess. How small? How fast? What size?

 

[PraAnan]

I don't know why you ruled out gravity light. Please don't hold back your requirements and make us guess. How small? How fast? What size?

The problem with the gravity light for my case is that even a 20kg load over a height of 2m (which is already too heavy and too high) doesn't have enough energy to produce the 500J unless you 'reload' the mass.

For the size, something that can fit in a box that is 15cm x 15cm x 15cm. Cost to build should be under $50 and I guess the material / construction really depends on what the actual generator type will be right?

 

[phyzguy]

The problem with the gravity light for my case is that even a 20kg load over a height of 2m (which is already too heavy and too high) doesn't have enough energy to produce the 500J unless you 'reload' the mass.

For the size, something that can fit in a box that is 15cm x 15cm x 15cm. Cost to build should be under $50 and I guess the material / construction really depends on what the actual generator type will be right?

Can it use fuel? What do you expect the ultimate energy source to be? It sounds like the only source that is acceptable to you is muscle power. I think a hand-cranked generator would fit in that size. 500J in 30 seconds is about 17W, and you can probably do this with a hand crank. Here's one you could buy that looks like it would meet your needs.

 

[phyzguy]

Another thing to think about. If you want to store 500J in a capacitor at 5V, E = CV^2/2 gives C = 40 Farads. This is a lot of capacitance, but I guess supercapacitors like https://www.mouser.com/Passive-Components/Capacitors/Supercapacitors-Ultracapacitors/_/N-5x76s?P=1ypvpvvZ1ykkebw&Keyword=190963940&FS=True&Ntk=P_MarCom could fill the bill.

 

[tech99]

You could make a primary battery, like a pair of Daniel Cells. Then use this to charge a lead acid battery.

 

[sophiecentaur]

I wanted the generator to be a little small.

Which part of the generation system are you calling the generator? The requirement seems pretty modest but you need to provide Fuel or Mechanical Effort input. If you are considering anything at all then the mechanism will take up some room. Without some details, we are working and thinking in the dark. With that approach, most of our suggestions and answers will be totally irrelevant.

I suggest that you look at electrically powered model aircraft for some ideas. Their Lion batters charge very fast and their systems have all been designed for you. The only difference is that they use a motor and you want to use a light.

 

[phyzguy]

@PraAnan are you still there? Do any of these suggestions meet your needs?

 

[Baluncore]

The solution costs about $10. and includes the generator, capacitor and LED.
Search ebay for 'wind up hand crank LED torch'