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Post by calorchis on Feb 18, 2008 22:53:52 GMT -5
Hey Lloyd! Went to active surplus - that is an AWESOME place! Got a fan, adaptor and a tool to cut acrylic...Last night, I finally wired a fan to an adaptor ... they had 12V ones and the guy said that I can hook up 6 fans to one adaptor, so I got that one instead of the adjustable one (he said I can only hook one fan to each adaptor)....big mistake! The fan runs really loud...I don't know whether all fans run at 12V are like this, or whether it's just the fan...ideas ?
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Post by lloyd on Feb 19, 2008 10:07:12 GMT -5
Calorchis: WARNING!!
You're going to blow the fans! My first post goes over this.
1) When the wallwart (adapter) says 12V it means more or less that the output voltage will be probably somewhat greater than 12V at the rated current of the wallwart. Say the rated current is 750 ma. and the fan's rated current is 125 ma. The voltage at the fan could be something like 18V! So the fan's specifications are exceeded and it will fail much sooner than usual.
2)The number of 12V fans a 12V adapter can power depends on the current the fans are drawing. So if in the previous example of a 750 ma. wallwart and 125 ma. fans, you could run 750/125=6. The sum of the currents should not exceed the wallwarts current rating or the wallwart will fail much earlier than usual.
3)You want to use some form of current limiting or voltage regulating. Resistors waste power. Diodes can drop the voltage if you are aiming for really cheap. Far better, but somewhat more expensive is to use an active voltage regulator like the 7812 and a couple of capacitors. A somewhat bulky solution is to take an old computer power supply from an old computer for a few bucks and use the 5V & 12V regulated outputs
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Post by calorchis on Feb 19, 2008 11:44:50 GMT -5
Okay so my wireless keyboard batteries died before I finished typing that post (What kind of stupid keyboard uses triple A batteries...I hate wireless keyboards). Luckily I stopped running the fan after I discovered it was so load otherwise I may have already blown up a fan by now! I completely missed that in your first post but I just read it again....that's what you get for not reading things carefully. So is it possible to get an adjustable wall wart that has enough current to power several fans? I will look around for one. Otherwise I may just buy two of the adjustable power ones (they're like 9 bucks each). I think that's still cheaper than getting a computer power unit Thanks for all your help - I really appreciate it!
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Post by lloyd on Feb 19, 2008 19:33:02 GMT -5
Actually computer power supplies are dirt cheap but they are bulky. Just go to any Goodwill, Salvation Army, surplus computer place or computer recycling depot and buy any junky old computer for $5 and take out the power supply. If you want to go the adjustable wallwart route, make sure the rated amperage is greater than the current requirement of all the fans you want to use. If you ever want a tutorial on how to wire voltage regulators, let me know.
Adjustable wallwarts are available at the stores I mentioned in this thread.
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Post by hal on Feb 15, 2009 15:59:30 GMT -5
I have access to all sorts of wallwarts from 4V DC up to 12V at various amperages from 3A to 500mA. I assume they be suitable to power a fan?
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Post by lloyd on Feb 15, 2009 18:59:21 GMT -5
Hal, almost certainly some will be good. Just take the fan and connect it to the wall wart. Hook up a multimeter and plug the wall wart in. If the voltage is above 12.5V for a 12V fan, you will need some sort of regulator (see above). If it's below 12V and it's moving enough air, you can use it.
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