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sort of free energy (again)

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large_ghostman

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Hi
Ages ago I posted a thread on the weurth elektronika energy harvesting kit. The kit basically had a energy micro ultra low power micro controller board (ARM CORTEX M3), a energy harvesting kit from Linear technology and some energy sources like a mini solar panel. The kist also had a peltier cell (works really well, much better than the solar panel in the kit).

The kit could take but didnt come with a piezo device by a company called (phi?), there was some discussion on wether the ultra flexible and 6cm piezo strip could produce enough power to charge say a phone by walking. I eventually got hold of one of the phi piezo strips and tried it on the kit etc, they work really well!!

I rigged two up in each shoe and wired to the scope, I then walked in small circles around the scope lol. They kick out around 46V each without flexing anywhere near there 25mm deflection limit, I didnt measure current but using them with the kit above they must be very low current wise.

Using the LT energy harvesting low drop out regs etc they can however produce more than enough power to charge a phone, I tried this with a dead phone batter and wired in the strips from my shoes.

The odd thing is it does slowly charge the phone, BUT if the battery is dead and your using just the strips and the LT regs etc, then you can receive a call while walking no problem, however if you try to make a call it fails. I am not sure why this is the case but interesting.

Anyway I have now managed to get two more donated (really expensive!), I have put them on a garden windmill thing and they are flexed as the blades go around (I should take some pics). So a kind of neat windmill!! Not exactly cheap but with the LT boards I can charge a leisure battery slowly (good old windy Scotland) so finally I got the answer!! Yes they can power a phone (sort of), and if you discount what they cost then its free energy as long as someone else pays for your food of course (then again no such thing as a free lunch, maybe a free breakfast?).

I will do a write up and post some pics, I am also going to fully flex the piezo's and see what voltage they can deliver.
 
The harvesting circuits I've run across are intended to be used for applications with very low duty...............i.e a remote thermometer that transmits an RF signal for a couple of seconds, then shuts off for 5 minutes or so.

In this case, what you really need to calculate, in addition to the power that Nigel mentioned, is the actual available energy. Remember, energy = Power * Time
 
yeah the stuff I played with like the Gecko micro controller boards are ULTRA low power, way way lower consumption than pics etc. The main advantage with LT energy harvesting regulators is the low drop out point etc. You can do some pretty reasonable things with the right equipment.

Nigel is right in what he says, the pettier is lower voltage but you get more power, how much I dont know yet as I havnt measured it. I can run my master controller for the polly tunnel (Giant Gecko board) for 3 months on a watch cell! So energy harvesting for that is reasonable to do.

The post was really to finish off something I was doing a long time ago
 
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