I have a bunch of small computer case-type fans lying around, but they run at 12V and I wanted to hook one up to my router, which has a USB port (which provides 5V, but I need that for a USB drive and I don't have the $ to buy a 5V fan right now).
The power supply for the router runs at 19VDC, and I figured I could tap that to run one of the 60mm fans I have which is rated at 12V @ 0.17A--although some initial measurements with my multimeter shows that it draws about 40-50mA at ~12V (hooked up to the power supply that's integrated into my soldering iron station).
A long time ago I bought an electronics "components kit" from Microcenter on clearance for $33
http://www.elenco.com/search/searchdetails/basic_parts_kit=ODc= that includes a range of resistors, but the resistors are the the 1/4 watt size. I've hooked three 470 Ohm resistors (in parallel) and then in series with the fan [edit: sorry, I forgot to mention that the resistors are in parallel because I figured they could dissipate the heat instead of using a single 150 Ohm resistor) and it seems to be about right, but I'm worried that they will get hot and burn out if the fan stops or gets jammed up for whatever reason. There are a bunch of other components in the kit, including transistors, capacitors, etc., so I'm thinking I can throw together something simple that would be able to handle a range of currents and finally put some of these components to use. It doesn't even have to adjust the speed of the fan--I just don't want to set my house on fire, as it were.
Any thoughts would be appreciated, or point me to something I can search. The link above has the info that's better formatted, but here's the parts list:
Resistors: 1/4W - 5 each 10?, 100?, 470?, 1k?, 2.2k?, 4.7k?, 8.2k?, 10k?, 18k?, 27k?, 47k?, 82k?, 100k?, 220k?, 330k?, 470k?, 1M?
Electrolytic Capacitors: 50V Radial - 2 each 1?F, 4.7?F, 10?F, 47?F, 100?F, 470?F, 1000?F
Mylar Capacitors: 100V Radial DIP - 2 each .001?F, .0047?F, .01?F, .047?F, .1?F, .33?F
Ceramic Disc Capacitors: 500V - 2 each 2.2pF, 4.7pF, 10pF, 1pF, 22pF, 47pF, 100pF, 220pF, 470pF, 680pF
Inductors: 1 each 4.7?H, 10?H, 47?H, 100?H, 470?H, 1mH, 10mH, 33mH
Trimpots: Single turn - 1 each 500?, 1k?, 5k?, 50k?, 100k?, 500k?, 1M?
Switches: 2 each Push-button, SPDT slide, DPDT slide, 8-position DIP
LED's: Standard T 1 3/4 size - 5 each Red, Green, Yellow
Displays: 2 each 7-segment common cathode, 7-segment common anode
Integrated Circuits: 2 each 7805, 7812 regulators, LM386 audio amp, 555 timer, 741 Op-amp, 74LS00, 74LS02, 74LS08, 74LS10, 74LS47, 74LS74, 74LS86, CD4013, CD4017
Transistors: 2 each PN2222, PN2907, 2N3055, 2N3904, 2N3906, 2N5457
Diodes: 2 each 1N4148, 1N4001, 1N34, 1N4728, 1N4733, 1N4739, 1N4743, 1N4747
Miscellaneous: 25' 22AWG Hook-up wire, Alligator lead set (red and black), 5V DIP relay, Photo Cell, Microphone, Speaker, Buzzer, 9V battery snap, 4A 200V SCR
------Updated as of message 15 - Posted here because I like it when OP's update their original posts to make things easier to find.------------
https://www.eevblog.com/forum/beginners/cheap-approach-to-down-convert-19v-to-12v-to-power-a-computer-case-type-fan/msg530519/#msg530519------
Hey guys. Wow. Nice to see so many responses. To kind of answer some of the questions:
1. Router - ASUS RT-AC66U (I've read many forums that state this thing "runs like a champ" regardless of how it is. However, I figured why take the risk.
2. I connected two fans in series (the second of the fans was the same physical size as the one above, but rated at 12V and lower current 0.14A) and, as predicted in one of the replies, the voltage drop split was different. Curiously, this 0.14A rated fan had the lower voltage drop (about 4.6V, with the first fan taking the rest). I am surprised because the first fan is a new fan from a 2.5" SSD drive cooler and the second fan was from a really old PC (the kind with a third wire from a Hall sensor in the fan), and so I thought the first one would be closer to spec. However, the second one actually did draw about 150mA at 12V and the first, like I said, only drew about 50mA at the same voltage. Not having experience with computer fans other than plugging the in and leaving it at that, I'm not sure if this is something completely unexpected.
Because the second fan worked at around 5V @ 50-60mA (though not at a high CFM, I'm sure), I'm going to just hook into the USB port--though I believe I will have to implement one of the suggestions in the thread with the first fan because, ironically, the second one is actually going to be too loud at 12V.