Utilizing waste heat convert to electrical energy

[liangchui]

I'm currently do a project as topic shown above, my idea is to uses the waste heat produce by underneath of the laptop then convert back to electrical energy to have an output of 5v (USB) , so that we can use it to recharge phone , USB fan , etc . I was looking though goggle and found that the peltier module could do it which convert heat to electricity with having different temperature on both side ...I have tested on my laptop temperature which I getting around 50 - 55Degree Celsius from underneath of my laptop and the room temperature was around 25 degree celcius .Now problem come , I wouldn't know which specification of the peltier element most suitable for project which can get the voltage of 3-5v and suitable ampere for recharging a phone.

 

[WTP Pepper]

Although a Peltier device can convert heat to electricity, the reverse ineffiency is no use for your application. They are generally used the other way where you pump amps into them to maintain a differential cooling effect across the opposite surfaces.

 

[KMoffett]

In that vain Google: "eco fan".
This uses a Peltier module to convert heat (~450°F) from wood stove tops to electricity to power a small fan motor. The fan also provides cooling on the "cold" side to improve the temperature differential. My sister-in-law had one. I couldn't figure how it kept a fairly constant speed with large changes in the stove top's temperature. I finally realized that it has a small bi-metal strip in that channel on the underside of the base. As the top's temp increases, the strip bends and lifts the front edge of the base. This reduces contact, reducing heat transfer, reducing the temperature differential, and reduces the voltage to the fan motor. Rather elegant analog electro-mechanical feedback control. But...$150...!

Ken

 

[liangchui]

I have browse thought da YouTube on thermoelectric generator , I had seen some of the people manage to light up LEDs or run a small motor by using peltier element . So , I was wonder it will work for my project or not ....

 

[KMoffett]

I doubt it. There has to be a significant temperature difference to produce much current, and you need to move the heat (like with a fan...using power) away from the cold side to the Peltier. They work great for specific applications, but are not very efficient conversion devices. I don't see much of a free lunch with the excess heat from you laptop.

Maybe a metal coffee cup attached to a metal heat absorbing plate that slides under you laptop. Would keep your coffee/tea/cocoa nice and warm.

Ken

 

[duffy]

Solid state thermoelectric generators are only 1-2% efficient at converting heat to electricity and will present a significant temperature drop in the heat flow diagram. Even if you could get 50W of heat to pass directly though it from the laptop (difficult) so that you could collect the meager half-watt or so of energy, the temperature on the laptop would have to go up quite a bit to accomplish this.

 

[liangchui]

Is there any alternative method to convert waste heat into electricity other than solar ...?

 

[jpanhalt]

Is there any alternative method to convert waste heat into electricity other than solar ...?

Don't quite know what you mean by converting waste heat to energy by using solar...

The Stirling motor has been another favorite of hobbyists to convert waste heat into mechanical power, which can then run an electrical generator. There is a group on Yahoo dedicated to "Hot Air Engines" (**broken link removed** ).

It is mostly hot air, and I have not seen much in the way of actual designs that produce a reasonable amount of work, say >400 W.

John

 

[duffy]

Yes, a Stirling's the usual alternative - but once again, it must present a temperature differential to work. In practical terms this means it is going to have to run hotter than it would otherwise.