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Old 07-21-2010, 02:30 PM   #311
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For knowledge sake what is the raw equation to calculate the resistance needed. Just want to prove to myself i can do the actual math i use to do in high school


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Old 07-21-2010, 02:36 PM   #312
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Assuming the LED is wanting 20 ma (typical max), yeah, the 470 1/2W should work fine. Really, a 1/4W should do the trick.

The power draw of the LED/resistor combo is going to be virtually negligible in this case, so size the power supply based on the fan, figuring in some overhead for the control circuit.

Edit: the calculation is just Ohm's law. V=IR. We need the resistance, so R= V/I. The LED is going to drop 4 volts, so the resistor needs to drop 8. R=8/.020=400 ohm.



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Old 07-21-2010, 05:26 PM   #313
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As stated above "go larger for control current demands", by this I would use the larger power supply should you add other future loads your golden.
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Old 08-19-2010, 11:27 PM   #314
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I have a 9v power supply that i would like to use. This would be with the LM317T controller and a 80mm 12V fan. many people talk about the stir plate throwing bars at top speeds. Would a 9V power supply still give me a wicked vortex or is a 12V necessary?
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Old 08-20-2010, 02:09 PM   #315
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Quote:
Originally Posted by ekjohns View Post
I have a 9v power supply that i would like to use. This would be with the LM317T controller and a 80mm 12V fan. many people talk about the stir plate throwing bars at top speeds. Would a 9V power supply still give me a wicked vortex or is a 12V necessary?
The answer to that question (as most things in life) is -- it depends.

Not all 80mm 12V fans have the same top RPM, some are slower at full speed than others.

for example this fan has a speed of 2500 RPM while this one tops out at 1700 RPM. Both are 12v 80mm computer case fans.

Mine will pull a vortex to the bottom of a 1L flask at 9v, but I generally run at 4.5v because you don't need to pull a "wicked vortex" all you really need is to keep the starter moving.
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Old 08-20-2010, 08:18 PM   #316
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Yeah that was my thought that most fans to get a nice vortex will only be running at 9V max so the extra 3 volts is just a bonus. it would be cool to find a 11V power supply so i could say "but this goes to 11"
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Old 08-20-2010, 09:10 PM   #317
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Quote:
Originally Posted by ekjohns View Post
Yeah that was my thought that most fans to get a nice vortex will only be running at 9V max so the extra 3 volts is just a bonus. it would be cool to find a 11V power supply so i could say "but this goes to 11"
oblig: http://xkcd.com/670/
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Old 02-24-2011, 07:26 PM   #318
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Just ordered the following from Jameco:
Part # Description
15270 @ CAP,CERM,DISC,.1uF,50V,20%
23579 IC,LM317T,TO-220,
29082 POT,LINEAR TAPER,1/2W,10K OHM
162481 KNOB,1/4"SHAFT,METAL,RND,SLVR,
330772 @ CAP,RADIAL,1uF,50V,
577221 SWITCH,ROCKER,RRA22H3BBBNN,
609545 @CAP,RADIAL,0.1uF,50V,
637183 LED,PANEL MOUNT,GREEN,T13/4,
690865 @ RES,CF,1K OHM,1/4 WATT,5%,
696722 HEAT SINK,TO-220,1 HOLE,2 PINS

Going to Radio Shack for the enclosure, the power supply jack, and board.
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Old 03-04-2011, 03:31 PM   #319
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I just harvested 6 magnets from some hard drives on the way to be destroyed at work and it got me thinking when I was stripping these down to the bare chassis - is anyone using the motor from the drive that spins the platter?
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Old 03-07-2011, 03:58 AM   #320
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Finished everything but a bit of glue and positioning the magnets tonight. I'm hoping to be finished tomorrow. I wired the LED to the board and jumped to the leads to the fan so I'll know if the circuit is intact rather than just knowing if I'm getting power. I have a 12V and 9.4V power source thar both have M-sized jacks.

I used a set of instructions online for the circuit, but rather than just pile up the solder when putting the wire leads in, I ran them through the board and jumped with solder rather than wiring the underside of the board.


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