Ciao,
durante le ricerche è saltato fuori quest'altro indirizzo:
http://www.instructables.com/ex/i/EC...E506/?ALLSTEPS
Lui propone questo alimentatore
A 25 volt, 2 amp transformer
ma qualcuno ha risposto in questo modo (riporto tutto così vi risparmio la fatica di andare a cercare il testo):
Here is an alternative method which I think is easier & cheaper:
A couple of years ago I made one that used a hacksaw frame (maybe $10 or less at a hardware store) and nichrome wire
The trick is that the nichrome wire should be creating 1 watt of heat per cm of wire length and this is a balancing act between the resistance of the wire, the length and the voltage of your power supply. The wire will glow a dull red and stretch a little (a resonably strong spring will keep the wire taut). I used terminal strips with the plastic removed to attach the nichrome wire to the power wires.
so a (say) 30cm length of nichrome wire (13.4 ohms/metre) will have a total resistance of 4 ohms.
V=IR or I=V/R
so with a 12V power supply: I = 12/4 = 3 amps
P=VI (power (watts) = voltage (volts) x current (amps))
so P = 12x3 = 36 watts.
That's close enough to 1w/cm and so that's what I chose.
It's a balancing act because if you shorten the length you decrease the resistance, which increases the current and power so it becomes too hot.
The power supply was a computer power supply which can produce high power at 5 or 12V and is cheaply available secondhand ($5-$10 - look at ebay, secondhand computer stores, computer recyclers or maybe markets or garage sales). Last weekend I saw whole pentium 100 computers for $5 at a school garage sale...). You just use the yellow and black wires in the power connectors (black is ground, red is 5V, yellow is 12V). Some power supplies may need a small load on the 5V rail for them to work. In that case you'd need to connect some resistors between the red & black wires so that it draws maybe 1-5W - do the calculations and buy a few 1watt resistors from an electronics shop (okay 5V at 1 amp is 5W so 5 ohms of resistance would do that - more of the nichrome wire could be used. For 1W, you want 25ohms).
Qualcuno riesce a spiegarmi quali sono le indicazioni che dà sull'utilizzo dell'alimentatore per pc? Vuol dire che se è poco bisogna attaccare tra di loro il 5v e il 12v con una resistenza? La dimensione del cavo che ha usato è di soli 30 cm? quindi non si riuscirebbe ad ottenere di più (a me basterebbero 45 cm per fare una semi-ala).
Ciao
Angelo