Energy from Cooling

[MikeRD03]

Hi!

Everyone wants to have / build the brightest flashlight around. But there are some technical problems that limits the use of real high power leds like the 15-20W OSTAR for example. The major problem is the cooling of the great heat dissipation of this typ of emitter.

Normaly one would build a passive (or active) cooler around that led to get rid of the heat. But thinking about it - primary heat is energy and why not trying to recycle that energy with two positive effects: Get rid of the heat and try produce some energy that can power the led for a longer burntime?
There is already to technic - the peltier-element - to do that and I wonder if something like that would do a good job in a flashlight?

A peltier-element can produce power if the two sides have a temperature difference. That is our problem in every led flashlight. And the more you use the power generated by a peltier-element the more it cools on one side.
That would not recycle all waste energy of course, but perhabs it would offer the possibility of building much brighter lights in smaller form factors.

Is there anybody out there with experiences with this elements? What cooling power can be expected? Want kind of electronic would be necessarily for power recycling?

cheers,
MikeRD03

 

[Lyndon]

It's a nice idea, but Peltier devices have an efficiency of around 5%. Thermopiles will also generate electricity from heat (used in some remote spacecraft with plutonium heaters) , but if memory serves, they are even less efficient than Peltiers.

 

[MikeRD03]

Well I know that these elements have a poor efficiency but the primary goal is the cooling of a high power LED. The production of energy would be a nice side effect and is always welcome since by now we don´t have a 300lumen/watt device.. ;-)

cheers,
MikeRD03

 

[Robban]

Well I know that these elements have a poor efficiency but the primary goal is the cooling of a high power LED. The production of energy would be a nice side effect and is always welcome since by now we don´t have a 300lumen/watt device.. ;-)

cheers,
MikeRD03

You say that the primary goal is cooling the LED but how are you going to do that without powering the peltier? You can't cool the LED with the peltier and at the same time get energy out of it.

 

[nerdgineer]

You get energy from the temperature gradient by tapping (i.e. slowing down) the cooling which would have occured in your cooling path before you inserted the Peltier or whatever into your cooling path.

It would work if you had TOO MUCH cooling in your flashlight and wanted to reduce the cooling rate while generating a (very) little energy at the same time.

 

[Illum]

You say that the primary goal is cooling the LED but how are you going to do that without powering the peltier? You can't cool the LED with the peltier and at the same time get energy out of it.

it isn't entirely impossible but there wont be much energy thats recoverable to fill even a fraction of the expenditure.

this thread might be of use [Peltier cooled high power LED]

its known that peltier's can be stacked to create greater temperature difference but using only one layer and to generate power requires one side to be cooled while the other heated, while the LEDs doing the heating your going to have to figure out a way to cool the other side.

NASA's satellite that was launched years ago on a trip to Pluto carried a Radioisotope thermoelectric generator that uses the active decay of Plutonium and Peltier junctions to supply energy where solar radiation cannot reach.

http://everything2.com/index.pl?node_id=1320174] [/SIZE]Crucial to the operation of an RTG is the Seebeck effect, the physical counterpart to the better-known Peltier effect. In a Peltier setup current is passed through two sheets of different metals or semiconductors pressed against each other, causing one side to become warmer and the other cooler. A Seebeck setup instead relies on the temperature gradient between Plutonium -- which gets pretty hot, +700 degrees K during its radioactive decay -- and an external heat sink. Between the Pu and the heat sink are two plates as in the Peltier setup, and current is thus generated as the heat moves through the them.

out in space its cold enough on the outside to create sufficient temperature difference to boost its efficiency, but how do you suppose you can find a mobile [and cheap] method to cool the other side of the LED mounted peltier below room temperature?

 

[Robban]

Looks like I got my *** handed to me Oh well, at least I learned something today

 

[Oznog]

It'd work if the LED operated just as well at much high temps (200F-300F).
Not only do we not have enough temp differential to generate a useful power output, but the LED will lose a huge chunk of its efficiency (and lifespan) with even mild temp differentials between the hot and cold sides.

 

[MikeRD03]

Thanx for your thoughts, guys! At least I think it was worth trying it . ;-)

cheers,
MikeRD03