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IN RESPONCE TO <p>a little design help...<p>I like playing with stuff too, but what you suggest is a fire bomb in your house. No disrespect intended. United Labratory and the uniform electrical code exists for a reason. (Go to their web sites and read their mission statements) Now let me whip an old school phrase on you. <p>FAIL SAFE<p>So you control your sprinkler with a solinode. What flavor do you choose? <p>NO (normaily open)
or
NC (normaily closed)<p>If you choose NC you'd be the winner cause when the NO failed, an uncontroled amount of water would dispursed. That might not seem too bad, but what if that sprinkler was in a field sloping to an aniaml pen, and your gone for two days?<p>
Fail safe, when it fails (all things do) do the least amount of damage.<p> Go to a store buy a new fan that is UL listed. Use the fan for it's intended use.<p>If your electrical and electronic experiments use elecricty that has enough power (watts) or has the right current / voltage to hurt or kill living things, do not leave them unattended (Like in your bathroom). (watts. Can you hold it in your hand when it's as hot as it will EVER get?)<p>The killing ability of eletricty is a vary tricky thing. If for intance your skin is broken your resistance (ohms) is incredability low at that point. <p>Get cut on a device with 12v @ 200ma relays. Your cut contacts the open terminals (not uncommon) on the relay and if that current goes through your hart, you are dead. It may not even take that much current. <p>IT IS YOUR RESPONCIBILTY TO KNOW THIS STUFF.<p>Would you build a pipe bomb for the 4th and hammer the end of the pipe?<p>My harsh tone was for those that responed, knew better, and said nothing.<p>This stuff can be fun. But if if you cook the dog, kill your baby sis, or burn down the house it won't be fun no more!<p>I will be happy to engage intelligent dialog about this subject.

I basically agree, he should spend a little money and err on the side of safety. on the other hand, your example of death by 12V is a little extreme even if you tried. (and I would not build a pipe bomb any day of the year and thus would never hammer the ends on)<p>I am not as familiar with the UL spec but the semi safety spec (SEMI S2-93) (a similar spec to UL) says the level at which circuits are considered dangerous is 30V RMS, 42.2V p-p, 240VA, 20 Joules or any RF signal (UL1950 & 1262, IEC950 & 204 and NFPA79-14.3) No danger level for DC voltage is given. (though I personally never touch any DC higher than 24V)<p>With that said, if a suitable 12V DC supply were used and that supply were housed so that it could not be touched, it could (repeat, could) be a safe design.<p>In any case, such a fan in a permanent installation probably would not pass any building inspection and you would need to remove it if you wanted to sell or remodel your house. However, if you are trying to make a window fan it should be ok, just be safe and insulate.