Low Voltage from Heat?

[Neily]

Hi,

 

Im looking to run a small set of LEDs, with voltage generated by heat (from a dmoestic radiator) which I know is a rater bizarre idea.

 

Is there anything on the market that would enable me to do this?

 

If not from heat, would it be possible to vary the output from a battery with the use of heat?

 

Any help on this would be very gratefully received!

 

Cheers,

 

Neil

 

B)

[freeztar]

That is a bizzare idea Neil. May I ask what you are planning to do this for?

[Neily]

Hi Freeztar,

 

Im hoping to design and make a childs night light that works from the heat of a household radiator.

 

Strange!

[freeztar]

Well, I suppose the best way to make use of the heat is to 'capture' its mechanical energy. You could use the rising hot air to turn a small turbine hooked to a small generator that could power your LED array.

[Erasmus00]

Hi,

 

Im looking to run a small set of LEDs, with voltage generated by heat (from a dmoestic radiator) which I know is a rater bizarre idea.

 

Is there anything on the market that would enable me to do this?

 

If not from heat, would it be possible to vary the output from a battery with the use of heat?

 

Any help on this would be very gratefully received!

 

Cheers,

 

Neil

 

B)

 

You can use a Peltier junction to generate power from a temperature difference (slap one side on the radiator, the other side will almost certainly be colder.). However, they are expensive. I'm sure someone whose electronics knowledge isn't as rusty as mine could offer more.

-Will

[DougF]

Hello Neily,

Well this may not be what your looking for but you can get Electricity from heat.

 

High Merit Thermoelectrics- Electricity from heat...

 

High Merit Thermoelectrics (HMTE) is a thermoelectric (TE) device manufacturing company who offer devices that include an innovative' date=' patent-pending material, called YMS, that out-performs competing materials, nearly quadrupling device efficiency. Our devices are long-lasting, compact, environmentally benign power sources that directly convert heat into electrical energy and can be utilized world-wide. Anywhere heat is produced, whether intentional or as a waste product of another process, our devices can be used to produce electricity.

 

We are currently seeking funding to support our final production level prototype, based on the extensive material testing that has been done. [/quote']

 

High Merit Thermoelectrics - Home

[Neily]

Thanks for your input guys - very useful!

 

Also, do you know if its possible to store that electrical energy and slowly release it over a period of say, 30mins??

[Neily]

Also, I have realised that LEDs require specific voltages: what do I need to maintain the required voltage with changes in heat input to the Peltier Junction??

[DFINITLYDISTRUBD]

A few high capacity DC capacitors and resistors would do the trick.

 

A DC cap with a resistor after it in a circuit will discharge more slowly than it will charge. I've read here and there that caps discharge roughly 5 times more slowly than they charge. An appropriatly rated resistor in the circuit slows this down even further and keeps the maximum voltage at or below what you need to power the LEDs. A potentiometer in the circuit would allow adjustment of the output.

[CraigD]

Also, do you know if its possible to store that electrical energy and slowly release it over a period of say, 30mins??

I don’t think this will be necessary.

Also, I have realised that LEDs require specific voltages: what do I need to maintain the required voltage with changes in heat input to the Peltier Junction??

I don’t think this will be, either.

 

LEDs can operate over a pretty wide range of voltages. Were this not the case, small LED flashlight wouldn’t work as their batteries discharged, nor would LEDs on computers and other electronics be able to do that cool fade in/out blinking trick.

 

As long as the temperature difference between faces of the Peltier device can be kept fairly constant, its output voltage should be, too.

 

The trick, I think, may be preventing hot air from swirling around the device to make both sides nearly the same temperature. One or a combination of features like a wide skirt, a large area heat sink on the cool side, and good conductive contact with the household radiator will hopefully do the trick. This may be less of a problem than I’m making of it – frankly, I’ve never tried measuring the temperature of a plate set on top of radiator.

 

If and when you get this gadget working, you must post pictures :confused:

[Neily]

Excellent, thanks for your help guys!

 

Im going to give it a bash, there maybe more questions in the future!

 

Thanks,

 

Neil

[modest]

Also, do you know if its possible to store that electrical energy and slowly release it over a period of say, 30mins??

I don’t think this will be necessary.

 

With most modern central heaters that operate once every one or 2 hours it would be necessary. If this is only intended for a continuously heated radiator then I'd agree with Craig.

 

If storing a charge is necessary you might consider a rechargeable led flashlight. It might not be hard to convert... I believe there's a flashlight that you shake to charge??? That might have all the components needed - except the Peltier of course.

 

-modest

[Neily]

Hi,

 

Ive been advised that the Peltier probably wouldnt be effective due to its low voltage output, so have been told to look into using a battery with some kind of thermal sensor connected to a 555 timer???

 

I have no idea where to look!!

 

Help!!

[modest]

Ive been advised that the Peltier probably wouldnt be effective due to its low voltage output,

 

Too low to light an LED? You never know till ya try - or watch somebody else try (I found this on youtube):

 

YouTube - Peltier Cooler Concepts of ThermoElectric Generator (TEG) http://www.youtube.com/watch?v=o1zbiPLKFu4

 

He's getting better than a volt and better than an amp.

 

so have been told to look into using a battery with some kind of thermal sensor connected to a 555 timer???

 

Doesn't a battery defeat the purpose? I thought the idea was to do it using the heat as the power supply.

 

Also, if you're just hooking up a thermal sensor, battery, and light - the 555 is completely unnecessary - unless you are building a 'dark sensor' from scratch. Have you been talking to the blokes at radio shack?

 

-modest

[Neily]

^^

 

Well to use the battery as a backup, to suppliment the output i guess. The 555 is to enable the light to fade over a few minutes. Or would a series of capacitors be easier?

[CraigD]

Ive been advised that the Peltier probably wouldnt be effective due to its low voltage output…

I’d be skeptical of this advice.

 

The typical small thermoelectric power module (AKA reverse Peltier device), generate about the same voltage (1.5 V) as a typical battery. Like batteries, they can be wired together in series to produce higher voltages as needed

Well to use the battery as a backup, to suppliment the output i guess. The 555 is to enable the light to fade over a few minutes. Or would a series of capacitors be easier?

Before bothering with more complicated solutions, I’d recommend Keeping It Simple, and just connecting some LEDs to a thermoelectric module, putting it on a heater, and seeing how it works. Because the voltage across the module in a constant resistance circuit varies roughly as the heat difference across the TE power module, it will have tendency to fade out naturally as its hot-side metal sink cools. Getting the light to glow at varying intensity as your heater goes through its usual cycle should be possible by “tuning” (that is, fiddling with) the mass of its heat sinks, and their conductive and convective insulation.

 

Lots of commercial TE modules vendors’ websites, such as this one seems to show size, cost, power, and temperature difference requirements are about right for your project.

[modest]

^^

 

Well to use the battery as a backup, to supplement the output i guess. The 555 is to enable the light to fade over a few minutes. Or would a series of capacitors be easier?

 

Well, yes - you would have to use external resistors and capacitors even with the 555. I believe the discharge time is given by the product of the resistor and capacitor... ok, it's 1.1 x R x C = time in seconds. C would be in microfarads and R in megohms I believe.

 

But I'm still not exactly sure what you're wanting to do with it. If you want the Peltier and a battery then why are you contemplating storing a charge? Is the stored charge supposed to supplement at times when the heat isn't running (i.e. for hours)? Is it supplementing the battery?

 

As I pointed out before - a capacitor system that stores a charge, works with a widely variable input voltage, lights a rather bright LED, and is cheap is already available via a shake-and-charge flashlight.

 

Something else you might consider cannibalizing are the exterior lights that store solar power all day and light all night. Substitute the Peltier for the solar power and you're in business.

 

Solar powered lights for your exterior lighting needs

 

-modest