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Radiovoltaic Generator

by Jargon, published

Radiovoltaic Generator by Jargon Apr 16, 2016
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Blender

License

GNU - GPL
Radiovoltaic Generator by Jargon is licensed under the GNU - GPL license.

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3554Views 191Downloads Found in Engineering

Summary

DISCLAIMER: This is a work in progress. Models and instructions may change significantly over time. The device itself is not meant as anything else than an exercise in countertop particle physics, and will not generate any significant amount of energy. It's also designed to contain a small sample of radioactive material, which is not to be trifled with. Read the health & safety section before you even consider building this. It's largely safe, but there are minor risks associated with the tritium gas.

I'm currently waiting for the electronic components - namely, the solar panels and the tritium. Files uploaded so far are basic prototypes, and I don't have any proper math up yet. It'll come :D

Item Description

This model is a small, printable, tritium-powered radiovoltaic generator.

Small enough to fit in a pocket, this device will provide a stable source of minor power for up to 20 years if handled correctly, and (provided nothing breaks) poses no noticeable risk to your health.

The basic principle is simple - contain a sample of a beta-active radioemissive element and use it to generate electricity. This design exploits the radioluminescent traits of tritium when encased in a flourescent tube, and is easily constructed with off-the-shelf items.

Currently, the design requires the following parts other than the files provided above:

  • Six (6) photovoltaic cells, measuring no more than 53mm by 18mm by 2.5mm
  • One (1) luminescent photon source. In this case, a 3mm by 25mm tritium vial is used.

In my prototype, I've used these solar panels and a tritium vial from MixGlo. You should take note of the orientation you print the pieces in, as the layer alignment may simplify some of the assembly steps.

The parts show in the images were printed on a Prusa i3 clone from China at a .2mm resolution with a .4mm nozzle size. No supports were used for any of the items, nor any brims. All items were printed on blue painter's tape.

Math & Physics

With the design description and source materials out of the way, we can get to the fun part - nucular sience! The dream of any kid who's ever watched one too many physics shows on Discovery or BBC is, of course, a nuclear reactor (or something akin to one), and while this little generator isn't a fission reactor, it certainly is a nuclear one.

So, what's the principle behind this? In essence, we're building a small array of solar cells that are powered by the glow of some tritium, encapsulated in a glass vial. It's a lot like a tiny fluorescent light bulb, but it doesn't need any power other than its own and lasts for like 20 years. Cool shit!

The electrons emitted by the tritium (beta emissions) come flying out of the material in all directions. In most cases, these just go off and bounce off their surroundings, depositing their energy into whatever they hit. It's a terrible waste!

Ordinarily, the electrons are completely invisible to the naked eye. Not only that, but they're not photons, so we can't capture them with our solar panels. However, in this case, we block that path with a thin layer of phosphorous. When one of the electrons hit an atom of the phosphorous, it deposits its energy into it and excites an electron in that atom. That atom needs to get rid of this energy, so an electron in it accepts the energy, "jumps" to a higher energy state (which uses up some of the energy), and release the rest of it as a light quanta (a photon). This photon comes out with a specific wavelength (colour), dependent on the material and initial energy.

This photon is then emitted from the vial, flies through the generator, hits one of the solar cells and generates electricity.

Now, tritium vials come in a variety of colours, and the amount of energy we generate from our solar panels varies quite a bit depending on the wavelength. A red light, for instance, will not generate as much electricity as a blue light. The higher the wavelength, the more energy we get.

In order to demonstrate this, I bought a number of colours from the supplier and ran the generator using each one of them. If you like math, the next part should be fun.

The base decay energy of one of the vials is [BASE ENERGY]. Now, we won't get all of this energy out as electricity. Some of it is lost in the conversion to photons, and some is lost in the photovoltaic cells, due to issues with their efficiency. Some similar designs have achieved a total energy effieciency of about 4% - that means out of 100% nuclear energy in, we get 4% electric energy out.

Now, for some actual, real-life tests:

Red Vial (W = [RED VIAL BASE ENERGY]
Voltage: [RED VIAL VOLTAGE]
Amperage: [RED VIAL AMPERAGE]

Green Vial (W = [GREEN VIAL BASE ENERGY]
Voltage: [GREEN VIAL VOLTAGE]
Amperage: [GREEN VIAL AMPERAGE]

Blue Vial (W = [BLUE VIAL BASE ENERGY]
Voltage: [BLUE VIAL VOLTAGE]
Amperage: [BLUE VIAL AMPERAGE]

White Vial (W = [WHITE VIAL BASE ENERGY]
Voltage: [WHITE VIAL VOLTAGE]
Amperage: [WHITE VIAL AMPERAGE]

As you can see, the colour of the vial produces very different results. All in all, the [COLOUR] vial seems to be doing best.

Health & Safety

I'm not going to beat around the bush. This design uses radioactive material, and if you build one, it should be treated with the same respect you'd give a small bomb. While it is not capable of exploding, and is not a source of anything other than minor and contained beta emissions, you should still be aware of the dangers.

When the device has been assembled, it should not be moved excessively, exposed to high temperatures, high G-forces or blunt force. Anything that may damage the vial inside the generator should be avoided wherever possible, unless you absolutely know what you are doing. Don't have a degree in engineering or nuclear physics? Be careful.

Beta emissions are dangerous, and may cause cell damage if you are directly exposed to them. Fortunately, they are easily stopped by other matter, and a few millimeters of matter will easily stop them. Beta emissions will not penetrate skin very deeply, nor will they escape this design under normal circumstances.

The type of tritium vials this generator is made to hold are not very dangerous, and are commonly sold as keychains and fobs - usually in the form of a metal cage around the vial. They're also often used in iron sights, watch faces and emergency lighting. In all of these cases, the vial is in some form of hard enclosure.

However, this generator is made out of plastic, and has a number of loose-ish parts. The main power source of this generator may be made out of glass, and contains a non-negligible amount of tritium gas. If the vial shatters or cracks, the gas will escape and you may breathe it in. If you do, the tritium can replace normal hydrogen in your body and cause some damage over a long period of time. Should you damage the vial, leave the area and wait for the gas to disperse - a few minutes should suffice in a well-ventilated area.

If you should breathe some in, it won't be worse than your average CT scan (depending on the quantity). Still, if it worries you to be slightly radioactive on the inside - Tritum tends to bind to water in your body. If you up your water intake over the next week or so, you should increase the rate at which you flush it out. All in all, you shouldn't have to do much beyond being careful.

Before building this design and purchasing the parts necessary, check with your local law to see if you can import and make use of the amounts of tritium you'll be dealing with. Where I live, tritium lights are unregulated up to an activity of 15 Gbq, but you may live under different laws. I accept no responsibility for any repercussions you may face if you do not follow the law (from the government, your workplace, parents or otherwise).

Print Settings

Printer Brand:

RepRap

Printer:

Sunhokey Prusa i3

Rafts:

No

Supports:

No

Resolution:

0.2mm

Infill:

20%

Post-Printing

Depending on your setup, minor filing or cutting may be required for a perfect fit between the parts.

Assembly is best done with some glue for the end caps, and a rubber mallet. If you decide to use a mallet, place something in between the part and the mallet to avoid damaging it. DO NOT USE A MALLET WHEN MOUNTING THE TRITIUM.

How I Designed This

The design itself springs from different science fiction generators, such as the thermonuclear devices from Mass Effect, and the Naquadah generator from stargate (the real early versions). However, it is at its core a very functional design with little eye candy.

I may add some viewing ports so that the glowing tritium will be visible from the outside, but it may adversely affect performance.

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Any new updates to this project? It seems so interesting!

Nothing yet, I'm afraid - it's been put on ice. Didn't buy any tritium, and then life got in the way. The design is still sound :)

May 29, 2016 - Modified May 29, 2016

If you are still working on this I would like to trade some knowledge. By chance I am working on the exact same project, and my current design only outputs 1.5 milivolts. Obviously this is terrible - the only ways to make it usable I can think of so far are manually flipping a switch with an inductor, or manually charging capacitors and using them to charge up other smaller capacitors.

My math says that this thing should be outputting a few microwatts worth of light. Now obviously that much energy isn't going back into electricity at the end. The solar panel is very very very VERY inefficient.

Have you had any success, and if so what did you use?

Edit: Also, make sure you have a very precise multimeter. The current draw is incredibly low for my device. I used aluminum foil surrounding a solar panel.

Apr 18, 2016 - Modified Apr 18, 2016

Maybe silly question but could you encase the core in glow in the dark filament. Would the phosphorous in the filament illuminate? The filament would be in direct contact with the core eliminating distance and it might protect the core

While definitely an interesting idea, it would not work using this design. Glow in the dark filament doesn't contain phosphorous, but rather zinc sulfide or calcium sulfide which absorb photons and release them again. Additionally, the only thing that leaves the tritium vial are photons, and not the radiation itself which makes phosphorous glow.

However, it would be interesting to attempt to print a containment vial with filament containing phosphorous. Perhaps it could even be used as a short-range radiation detector, or an an early warning system.

Oh, and another thing, will you be doing tests to determine the optimal number of solar cells? I imagine if you made it pentagonal, each solar cell should get more light, and it should roughly balance out. At what point would efficiency dwindle? Should be useful to determine the most economical way to make them.

Since the photon source is round and emits an equal amount of energy in all directions, I don't think the angles of the panels will matter all that much. I can certainly try and print out a pentagonal one and try that as well. The optimal number (provided that each panel gents an equal amount of light) is basically as many as you can cram in there. The limiting factor will eventually be distance to the tritium, as the light which hits the panel will decrease with distance.

What I meant is that the more panels there are, the less light each one gets. Because the same amount of light is spread over a larger surface area.

Ah, I see what you mean now. I'll try!

If I understand correctly, the idea is that the 2 ends are supposed to hold the glass tube of tritium in by force. Therefore, if force is put on the top of the reactor, it will transmit directly through the glass tube. Have you considered using springs on either end to hold it in? The glass would sit in between the springs. This would also create a basic suspension system.

Ok this is really cool. I'll be watching your progress.

Apr 16, 2016 - Modified Apr 16, 2016

So how much electricity does this thing generate anyway? Could a few of them run a raspberry pi?

Apr 16, 2016 - Modified Apr 16, 2016
Jargon - in reply to Linkreincarnate

At the moment, that's still unknown - I'm waiting on electronics and the tritium vial, so I haven't been able to test any power output. That's why the math section is still empty.

Using them to power a raspberry pi is a very interesting idea, though, and I'll be sure to try it! The minimum power requirements for the A board is 500mA, which is probably way out of range for a single device.

EDIT: Looks like the B+ is down to about 280mA with networking. That's a lot less. Still, can't say anything solid until it actually runs.

Have you tried it out yet? My math may be wrong, but it seems like this would have a very low amount of power.
https://en.wikipedia.org/wiki/Tritium#Decay

Tritium gives off ~5.7Kev of electron when decaying, which is ~2.54e-19 watts over 12 years (the half life of tritium) per atom. There is some loss when the electrons interact with the phosphorus to become light, and most solar cells have about 15% efficiency. It's hard to tell how much tritium there is in any given vial (depends on how much gas they put in when they make it), but you may not even be able to detect a current coming from the panels with a multimeter.

I'm going to try it out too, because i'm it sounds super cool and I'd love for it to work. But unless my understanding or math is off, I doubt it'll produce anything detectable.

Which color produced the most energy? Or have you not completed that analysis yet, which is why it says "The one that produced the most electricity was [COLOR]"?

Yes, that's right. I'm still waiting on the electronics. Going off of the theory behind solar panels, the blue vial should produce the most energy. However, some testing with a single panel and an RGB LED strip gave me a greater output for green light. I suspect that the green light is simply brighter, but I haven't measured that yet. Can't use my eyes, since humans see more green light than other colours :P

It's definitely green light. Green tritium vials will give you the brightest option. I think it might have to do with green being near the center of the visible spectrum so less of the energy goes off as infrared/UV, but that could be completely wrong.

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