PDA

View Full Version : Converting Heat Energy from the Barel into Electricity


chasep255
April 18, 2011, 10:16 PM
I think it would be cool if there was a way to use the heat generated from firing the gun to charge a battery. Does anyone know of any small scale device which can take in heat and output electricity?

What I was thinking of doing with this is creating a cooling fan for my AR-15. Just a fun project, nothing serious. It would be neat if I could use the heat from the barrel to power it so that it only comes on when the barrel is hot enough to generate power.

Clark
April 19, 2011, 12:09 AM
I have a resume that looks like every year I have designed another power supply or battery charger for 30 years.

When I was a little kid I asked my father if there was a way to get the heat energy our of one area, turn it into a ski slope, and put it into another area and make it tropical.

Then he started quoting laws of thermo dynamics.
Something about the only way to get energy out of heat is to have something colder and the have the heat move.

If you look at a Stirling engine, you can see something that takes the difference in temperatures of two things and converts it to motion energy.
http://en.wikipedia.org/wiki/Stirling_engine

It has been 200 years, and lots of effort, but not working well enough yet.
You can make one work, but it generally is not worth the time, money, and effort.

FrankenMauser
April 19, 2011, 02:13 AM
It would probably be more effective to harness muzzle blast, than barrel heat.;)

mapsjanhere
April 19, 2011, 09:22 AM
Look up Peltier elements (http://en.wikipedia.org/wiki/Thermoelectric_cooling). No mechanical parts, so they are pretty shock resistant. But - as laid out above, you to dump heat to make it work, maybe start designing a quad rail with doubling as a heat sink?

brickeyee
April 19, 2011, 10:53 AM
You can convert heat directly to power using thermocouples.

Long duration space satellite (think years of interplanetary travel) use radiation thermopiles.


radioactive decay provides the heat, and a screen made of thermocouples provides the conversion.

It is generally not worth the effort if ANY other source if another is available.

Solar cells are not adequate as you get out further.

Pahoo
April 19, 2011, 11:07 AM
You can convert heat directly to power using thermocouples.
TRUE, and a cluster of thermocouples connected in the right polarity makes a thermopile. The output is limited by the size and composition. Keep in mind that each thermocouple's output, is in the MilliVolt range. Now, how you get there and efficiency would be in question and probably not cost effective. ... . :confused:


Be Safe !!!

chasep255
April 19, 2011, 02:33 PM
Well this project is way beyond me.

1911rocks
April 19, 2011, 06:19 PM
Thermocouples are in the mV range (J,K,T,E types). The output is similar to an induced current in that it doesn't support current. Subsequently, you'll need to connect them to a high impedance load. Shoot in the daylight and buy some photo voltaic cells. There aren't enough BTUs produced by the barrel to develop an appreciable Heat Rate. A good Heat Rate from a Combined Cycle Gas Turbine site is ~6900-7000btus/KWH.

brickeyee
April 20, 2011, 10:44 AM
The output is similar to an induced current in that it doesn't support current.

It supports current just fine, just not a lot.

The current tends to cool the junction though.

If you are measuring temperature you use a high impedance to not change the value, if you are using it to generate power the junction will be heated just fine by the source.

Eagle Eye
April 20, 2011, 10:39 PM
It will be complex and could get bulky or heavy IMHO. And it could be very expensive to operate given the price of ammo. A battery is cheaper, smaller and lighter. KISS

wncchester
April 27, 2011, 06:30 PM
"You can convert heat directly to power using thermocouples."

Very low voltage but some significant currents are possible.

Eagle Eye
April 27, 2011, 07:02 PM
While I agree that significant currents are possible (depending on your definition of significant), the current will also be dependent upon the resistance of the load (typically the LED in this discussion). But the current is primarily dependent upon the dissimilar metals used in the thermocouple and the amount of heat. Power as you must know is the product of voltage times current.

In the most simple example, you will need the heat source, the appropriate thermocouple, an LED for the load and some sort of regulatory circuitry which will also consume power.

I go back to my previous statement that a battery will be cheaper for a few reasons. I will state a few here, but I will not try to educate the uninitiated, for I studied electrical engineering for my BSEE, for my graduate courses, and continued throughout my career from which I semiretired many years ago and cannot hope to pass on the entire course in a blog with my tired fingers.

Reasons or issues:

LED designed for a tight range of voltage. This must be supplied by the circuit. Too much voltage and the LED will be cooked quickly. Too little and it will just not conduct any current (no light.....dark.....no workee in either case!)

Heat source needs to be fairly predictable to be practical. Your pistol light will not work until you have fired it enough to generate that heat. You likely will need the light for your first shot. Oh yes, you could back it up with a battery (or some storage circuitry), but then you would be done....you would not need the expensive and complicated circuitry.

There are others, but I will not try to design this for you...the battery is still cheaper, more simple and will likely work as intented.

Yes it can be done. Is it practical? I don't think so. For many of the same reasons that powered flight can be accomplished with photovoltaic cells -- it can and has been done but due to the complexities (cost, weight, etc.) it is just not practical.

Light your fancy dandy gun light? Can be done but it will be expensive, heavy, costly and ugly as compared to a very small and simple battery which reliably supplies the voltage as the driving force at the current you need for a fairly predictable amount of delivered power to the LED load.

Just how much ugly, complexity, reliability and cost are you willing to sacrifice? This is a hobby proposition for someone with too much time and money on their hands.

And no, I will not draw the circuit for you, but define your heat source and conversion technology and it can be done.

Pahoo
April 27, 2011, 07:18 PM
Yes it can be done. Is it practical? I don't think so. For many of the same reasons that powered flight can be accomplished with photovoltaic cells -- it can and has been done but due to the complexities (cost, weight, etc.) it is just not practical.

BINGO !!!


Be Safe !!!