Interesting thought... I'm working on a project that has a 150w led and ideally I'd like a fan on the back of the heatsink to stop it overheating but the driver is 36v and a fan would be 12...

Rather than getting a transformer, I wondered if I could put a peltier between the led and heat sink to produce power to spin the fan!

Its probably a really silly idea that's come about from being up late but what are your thoughts? Would a peltier be able to dissipate enough heat to stop the led burning up? Would I just be better getting a transformer to step down the voltage?

 

Sounds almost like an over-unity idea to me.
Heat --> electricity --> fan --> reduce heat

In any case, I think there will not be enough electric power to spin the fan.

 

the peltier would never ever produce enough power ....

transformer requires AC ...leds run on DC ... two fans in series ( they're listed as 12V but will run on 24V) ...or just put a resister in series with one fan

 

An uneducated opinion on this - - - I doubt the Peltier would sink enough heat to protect the LED. And the amount of power produced will probably not run the fan. Since you don't tell us what size the fan is other than 12 volts - it could be the fan off of a car. OK, probably not - but you hopefully get the point. To know for sure we'd need to know the fan, how much current it draws and the Peltier to know how much power it can produce. If the fan requires 500mA and the Peltier can only produce 20mA - that won't work. It all starts with knowing the specs.

 

I have doubts, because there is something called a Fireplace Fan:

 

The Peltier module costs money (unless you salvaged one from a garage sale freebie cooler), and it could make the LED run hotter, because the junction will have a temperature differential across it. I'd have to know the thermal resistance of the heat sink under passive and fan-cooled conditions to be sure.

Why not run the fan off the MC34063 switching regulator out of an old car charger: change the output feedback resistor to get 12V instead of 5V, change any electrolytic caps for higher voltage ratings, make sure there aren't any zeners or transzorbs on the input side.