## interesting Idea - Looking for info!

imphill
Posts: 15
Joined: Fri Jan 06, 2012 4:24 pm

### Re: interesting Idea - Looking for info!

Hello,

I was just reading up on these - TEG's - (http://en.wikipedia.org/wiki/T....._generator)

Now if anyone has any clue how much these can produce, and if they do know, could they tell us if it would be enough to run the Rasberry PI?

I have got some very interesting Ideas if this turns out to be enough. If not, would the output of the TEG be enough to charge...say....4 AA batteries?

Thanks,

IMPhill

gimliflea
Posts: 76
Joined: Fri Nov 18, 2011 4:14 pm

### Re: interesting Idea - Looking for info!

Maybe if I used one as a heat sink on my intel desktop I could power my Rpi off the waste?

Edit for typos

JustinN
Posts: 6
Joined: Tue Jan 24, 2012 11:57 am

### Re: interesting Idea - Looking for info!

TEGs come in all sizes, so really it all depends on what you plan on hooking it up to for it's energy (heat) source, and from that you could determine the size of TEG required to make best use of the excess energy (heat) and then in turn calculate the Volts and Amps (or mA)...

So your quest is a bit broad. The short answer, is yes, it can do what you want, however there are a number of additional factors that need to be taken into account to calculate if it's a worthwhile investment or not.

Caliber Mengsk
Posts: 16
Joined: Fri Jan 13, 2012 6:08 pm
Contact: Website

### Re: interesting Idea - Looking for info!

Not only is the size important, but on these devices, the difference in temperature also makes for how much power it generates. For example, cold side is room temperature, and the device you have to generate heat is 20 degrees (f, as I'm from the US, and don't feel like doing the calculations) hotter then room temperature (for example, using body heat) will be a lot less inefficient, and generate a lot less power then something that's 40 degrees above room temperature.

Size and difference in temperature change the amount of energy output by these things.

Personally, I think it'd be pretty cool to have a few of these in, say, a shirt, power the rPi all total.

I don't think that there is enough temperature difference between the body and the average room temperature to really power anything more then a few LED's though.

imphill
Posts: 15
Joined: Fri Jan 06, 2012 4:24 pm

### Re: interesting Idea - Looking for info!

Okies. Well the info is kewl. And yes, I"m plan into use body heat. More specifically – the heat on your fore arm. And if you got a really cold other side, would that help? Size of the grid could be roughly the size of the rpi itself as I was planning to mount a teg under it and change a small bank of batteries when the device isn"t in use…

I"ll be honest… Anyone for a actual working pipboy? they never see, to run outta power… And I had to think of ways that could be done… This seems like a viable idea at first…

Edit- spellchecker

ofrxnz
Posts: 5
Joined: Sat Jan 21, 2012 2:59 am

### Re: interesting Idea - Looking for info!

imphill said:

Okies. Well the info is kewl. And yes, I"m plan into use body heat. More specifically – the heat on your fore arm. And if you got a really cold other side, would that help? Size of the grid could be roughly the size of the rpi itself as I was planning to mount a teg under it and change a small bank of batteries when the device isn"t in use…

I"ll be honest… Anyone for a actual working pipboy? they never see, to run outta power… And I had to think of ways that could be done… This seems like a viable idea at first…

Edit- spellchecker

I looked into TEG in college and from what I remember about TEG, it generates its power by the flow of entropy between a hot bath to a cold bath. If I also remember correctly, it generally requires a high delta T.  I think the base threshold to begin to produce useable wattage is around 40c or 100f.

I dont think the difference between body temperature and room temperature is enough....Though, 300mw for a RPi model A is far below anything i would have looked into.

It would be Awesome if you could pull it off though.

kme
Posts: 448
Joined: Sun Sep 04, 2011 9:37 am

### Re: interesting Idea - Looking for info!

There is no way this will work with the temperature difference between body and ambient.

The efficiency of those devices is around 5% and you'll need 3-4 W, so ...

Science classes do matter.

imphill
Posts: 15
Joined: Fri Jan 06, 2012 4:24 pm

### Re: interesting Idea - Looking for info!

@kme - Well, I will admit, I didnt do Science to any higher level, but not through choice, I just had other proities. I was always top of my class in primary and secondary school, but I chose not to persue that line of learning. But hey, no worries.

I thanks you all for the info, and for info purposes, let just assume that it goes from body temp to COLDER then room temp (ambient temp), I plan of cooling down the 'Cold' side of the TEG. Would this improve the performance, up to the point where trickle charging a small battery would be, at least, do-able?

I was planning on this -

Getting a credit-card (Rasberry PI sized ) TEG mounted on the bottom of a rasberry pi.

Trickle charge a small battery off the TEG, while the device is being worn.

I was also going (trying) to include other forms of renewable portible ways of charging a small battery.

I was going to remove any parts of the device and OS which are power hogging. I am planning on making a wearible PDA. like an iphone, but something which is easyier to use and earier to run. The OS (or primary loading programs) will be simple touch based ones, much like the Andriod or iOS at mo...

Thanks agian,

IMPhill

redman684
Posts: 48
Joined: Fri Dec 09, 2011 5:25 pm

### Re: interesting Idea - Looking for info!

To make some sort of pda you would also need to power a display

I gues it's going to be something like http://0.tqn.com/d/animatedtv/...../leela.jpg

I'd go with some system converting motion into energy, being a moving weight or fluid. At least you'll be able to generate some extra power by shaking your arm.

JustinN
Posts: 6
Joined: Tue Jan 24, 2012 11:57 am

### Re: interesting Idea - Looking for info!

@redman684 - unfortunately the return of current you get from that type of energy is very small. They've started putting it into TV remote controls so that you no longer require batteries for them, however that only generates enough power to send a single button press at a time. Not the type of power to keep a device (R-Pi) powered on for prolonged periods of time.

redman684
Posts: 48
Joined: Fri Dec 09, 2011 5:25 pm

### Re: interesting Idea - Looking for info!

That depends on how heavy you make them

I don't see it as a realy practical solution to power a wrist pda, it's just that I expect far better results from moving a weight, than from a thermoelectric device.

I think only a generator attachted to a joint, or in the sole of your shoe can generate the required power.

imphill
Posts: 15
Joined: Fri Jan 06, 2012 4:24 pm

### Re: interesting Idea - Looking for info!

Well,

It's going to be a fun time, but i'll just have to see about making this work… what about a voltage amp? would that give the boost we need to run this?

Acutally that being said, Im not planning on running a RPi off this solely, im planning on using a small battery, to run it, and have the TIG to trickle charge the battery... would the not work? Same way you can trickle charge a car battery with a solar pannel, no?

spamel
Posts: 196
Joined: Sun Jan 01, 2012 8:43 pm

### Re: interesting Idea - Looking for info!

With regards the pipboy, flat batteries from phones would be the best bet. And i don"t mean discharged, but flat in profile. I have seen people making imitation pipboys with a lit screen and a transfer sheet to give the impression of a working pipboy, but their battery choice is always a big chunky battery, the type you lick and pull that mad face! Surely a couple of nokia batteries woukd be better as their slim profile makes it easier to house in the unit.

veronicathecow
Posts: 25
Joined: Wed Oct 05, 2011 9:10 pm

### Re: interesting Idea - Looking for info!

Hi, TEGs output voltage varies with Tdiff (Difference in temp between hot and cold).

Here is a graph some people have done. Assuming a 20oC Tdiff (body to ambient ) you will be getting about 0.5 of a volt.

http://www.picotech.com/experi.....sults.html

Also assuming a 5% efficiency and you wanted to generate say 50 milli amps at 7 volts to trickle charge a pack of batteries (at 70% efficiency of charge) you would need to be drawing this many watts of heat from about 3 square inches of arm.

350mW *20 (5% efficiency of generator) * 1.4 (efficiency of charge storage) = 9.8 Watts call it 10 watts.

The human body at rest generates about 100 watts of energy. So 10% of you at rest body energy would be going through a small patch of skin.

I would guess that unless you are cooling the outside with say "Dry Ice" and are happy with a serious case of frost bite that perhaps a solar panel and/or mechanical generator might be best.

Sorry to disappoint, I love the idea, maybe the next generation Pi will use 1/10 the power of the current one and then it might be more feasible.

imphill
Posts: 15
Joined: Fri Jan 06, 2012 4:24 pm

### Re: interesting Idea - Looking for info!

For a moment there, I thought the Math was ging to save me...

Okies, no worries. Onwards! To the next idea!

maybe a trasnprent OLED screen backed by a solar cell....hmmm..

Anyway, thanks lads for the info, been fun.

IMPhil - over and out.

nyx777
Posts: 2
Joined: Tue Jan 24, 2012 7:14 pm

### Re: interesting Idea - Looking for info!

Hey, sorry I joined the conversation possibly too late, but here is my \$0.02.

So I did a 'back of the napkin' calculation with an assumed efficiency of 20% and heat transfer coefficients that mirror some of today's tech and found that with a temperature differential of human body temp to room temp (~14 K on an average day for an average human in the average room), you would need a TEG that covers ~97 cm^2. That would get you ~5W of power.(Source: engineering student enrolled in heat transfer).

After reading where someone mentioned that the efficiency is actually much lower than 20%, the area needed would be much higher. So if you are up for plastering one to your back and legs then running cords, maybe it could be done. But you would still need to account for chances in ambient temperature as well.

Best of luck with your future projects.

Benedict White
Posts: 224
Joined: Sat Dec 24, 2011 12:24 am

### Re: interesting Idea - Looking for info!

NASA use them attached to plutonium bricks to power long rage space flight, but are thinking of replacing them with Stirling engine generators with one moving part as they are twice as efficient.

I have to say it is impressive to build an engine generator set with only one moving part! (the power piston, it is a thermo acoustic Stirling engine)

imphill
Posts: 15
Joined: Fri Jan 06, 2012 4:24 pm

### Re: interesting Idea - Looking for info!

Since this is continuing - question - (and humour me here) / say you connect a teg about the size of the rpi to you skin ( assuming all averages ) how much would you generate?

I"m thinking is it enough to trickle change a battery over a period of time? If so, how much time? Assume I had 4xAA batteries rechargeables. Could anyone do the math, cause I can"t lol - well I can if someone gave the info to do so!

IMPhill

veronicathecow
Posts: 25
Joined: Wed Oct 05, 2011 9:10 pm

### Re: interesting Idea - Looking for info!

There are so many variables and the calcs I made assumed mostly no extra losses so here are some more thoughts.

Skin thermal resistance, probably quite high, perhaps best situated near a major blood vessel that is close to the surface of the skin so increases heat flow to that area.

Heat sink to cool, how big? The bigger the heatsink the lower the cold side of the TEG. Assuming passive air cooling it would depend on horizontal or vertical or whatever angle the body was at or might change to.

So I would have to quote "How long is a piece of string?"

sisk
Posts: 32
Joined: Thu Jan 12, 2012 5:04 pm

### Re: interesting Idea - Looking for info!

Ok....A raspi powered pipboy just got officially added to the 'projects for when I have too much time on my hands' list.

Now, how do I get the thing to change my clothes and store my weapons and ammo for me?

veronicathecow
Posts: 25
Joined: Wed Oct 05, 2011 9:10 pm

### Re: interesting Idea - Looking for info!

Nanites.

laszlo
Posts: 25
Joined: Thu Jan 26, 2012 6:03 pm

### Re: interesting Idea - Looking for info!

I think an iPod or iPhone with an arm band is pretty much a Pip-Boy already.. while the idea sounds cool it seems like you'd be a lot closer with a touch screen cell phone than you would with just a Raspberry board.

This is probably your best bet for powering it: http://fallout.wikia.com/wiki/Microfusion_breeder

hstubbs3
Posts: 31
Joined: Fri Nov 18, 2011 7:11 am

### Re: interesting Idea - Looking for info!

Ooooo.. Yeah, that'd work.. We just need some of them breeders...

You can't quite mod an iPod or iPhone the same way.. How can you hope to survive the wasteland if you can't even plug a proper USB device in?

imphill
Posts: 15
Joined: Fri Jan 06, 2012 4:24 pm

### Re: interesting Idea - Looking for info!

@laszlo - just on a minor point. I didn"t know you could get a wrist strap for an iPhone...?

laszlo
Posts: 25
Joined: Thu Jan 26, 2012 6:03 pm

### Re: interesting Idea - Looking for info!

I've seen people jogging with stuff like this..

http://www.amazon.com/iPhone-A.....B001IK868O

It looks quite similar to a Pip-Boy really, minus the extra casing/buttons: http://images.wikia.com/fallout/images/ ... y_3000.png

If you search the web you can find a few themes/apps that people have already made for various mobile phones, to turn them into Pip-Boys.. but I guess it would still be fun doing your own.  I guess if you went with the realistic Pip-Boy design, the case would leave you room for batteries and a screen.  I saw a geiger-counter app too, using the camera as a sensor for radiation: http://itunes.apple.com/us/app/geiger-c ... 19975?mt=8

So I guess you could get pretty close.. if you could figure out how to power it for 200+ years.. I have yet to see a reference app for that.

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