Ambient Energy LED lighting contest! / General Science and Electronics / Forums

Forums

4hv.org :: Forums :: General Science and Electronics

« Previous topic | Next topic »

Ambient Energy LED lighting contest!

first previous 5 6 7 8 next last

Move Thread

LAN_403

Bjørn

Sat Feb 17 2007, 06:27PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

I have one peltier module that is more than 10% efficient, it is more than most. It depends on how high themperature you are willing to run it at. The larger the temperature difference the larger the efficiency. So good cooling the cold side is just as important as the heating bit.

It is hard to get more than 1W from a small module but I have seen more powerful modules deliver more than 10W even with good safety margins. With the larger modules it is easier to have power left over for a fan to get higher efficiency.

Marko

Sat Feb 17 2007, 07:25PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

I was generally much of dissapointed with power I was able to get from my peltier.
The best case was a bare 1W with excessive heating of one side with open flame and massaging the other with an ice cube. (quite unlikely use in reality).

With some more realistic heatsink for the cold side I am actually happy if I light a LED to a full shine. Due to low voltage losses on the boost converter are in any way huge.

My only current peltier is pretty big 60*80mm unit from acient coolbox, considering it's age it may not be as efficint as newer ones.

To fulfil contest rules, I tried using my concave mirror to focus sunlight on one side of peltier.

To coll another side, I used some water resembling a cooling pond.

Results were pretty defeating from this one. It was impossible to evenly heat all thermocouples without losing majority of light beam.
Peltier was lifted from the bottom so some water could flow over cold side, but it didn't have much effect. I had to shake the craddle and keep water moving to actually light the led.
In overall, performance was as bad as if I heated the peltier with my hand, although the hot side was torched with 100 degrees C or so.
I could maybe improve the setup by using copper plate on hot side to disperse heat more evenly, and some kind of heatsink on cold side, but it wasn't worth.

So I don't think you are going to charge a cell phone from a single peltier of this size. Maybe with several of them in seriies, with an Odin-the-all-fragger sized heatsink and blowtorch as heat source..

I couldn't take a picture with clearly visible led.. camera was dazzled with brillance of focused sun rays and I can only asusre you that led is lit. Yes, it was so weak.. peltier was generating some 180milivolts at most.

Hot side is painted black for better absorption.

Avalanche

Sat Feb 17 2007, 10:48PM

Registered Member #103 Joined: Thu Feb 09 2006, 08:16PM
Location: Derby, UK
Posts: 845

Hmm, that's not much voltage for (what I'm guessing) is a 12v peltier. I'm trying to work out whether or not it's worth me buying one of those CPU cooler peltiers, I wonder if they would perform better than the fridge peltier? But it looks like all thermocouples are in parallel and there's no way of rewiring them. I would need at least 6v at 100mA - that would be really useful to me for charging stuff off the lamp (which can run all night from a single fill).

Anyway here's my addition - It's mostly a demonstration to show that LEDs can also work in reverse. A slightly more 1337 version of solar?
I have a PCB containing a whole array of infra-red LEDs, from when I was messing around with nightvision a couple of years ago. When placed in front of a 60watt bulb, the array generates 5 volts open circuit. The whole array just barely lights a red LED, here it's shown running from my 10 watt halogen desk lamp (all that wasted light, why not harvest it to produce some....light

)

Bjørn

Sat Feb 17 2007, 11:06PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

The voltage from a peltier will be low, usually far less than 2V but the current can be quite high. I use a step up circuit that can make 3.6V or 5V regulated.

6V at 0.1A is quite possible to get from a peltier with a step up circuit but it requires that you can keep the temperatures reasonably correct without cooking the peltier.

Marko

Sat Feb 17 2007, 11:14PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

There are 126 series couples on my peltier. And yes, it normally runs on 12V.

Realistic voltage you could get from one peltier like mine in your case would be 300...500 milivolts, so you anyway need several of them to get the voltage high enough for a stepup converter to work efficienly. (as bjorn states, current can get pretty high, I easily got over an amp with mine) so you don't need to stack peltiers for full 6V.

Heatsink size required is also likely to ruin the ting's likeness as a 'handy mobile phone charging gadget'.

If seebeck effect was efficient, it would have much more uses.

You would probably be better by boiling some water with that lamp and running a small turbine or steam engine.

Conundrum

Thu Feb 22 2007, 12:06AM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

rofl :)

-A

Myke

Thu Feb 22 2007, 02:27AM

Registered Member #540 Joined: Mon Feb 19 2007, 07:49PM
Location: MIT
Posts: 969

Bjørn

Thu Feb 22 2007, 03:29PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

This is the obvious choice for lighting a LED from waste energy. I found some spent zinc-air batteries that seems to have quite a few hours worth of LED time left in them.

ShawnLG

Thu Feb 22 2007, 04:16PM

Registered Member #286 Joined: Mon Mar 06 2006, 04:52AM
Location:
Posts: 399

"I found some spent zinc-air batteries that seems to have quite a few hours worth of LED time left in them."
This is why the joule theif was invented.

Bjørn

Thu Feb 22 2007, 06:21PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

I can sense that no one was impressed by the use of zinc-air chemistry.

This time I made a hydroelectric power plant. The bottle was free, the motor/generator was free out of an old printer. The water is unmetered and free.

first previous 5 6 7 8 next last

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob