My homebrew stirplate - Page 32 - Home Brew Forums

 Home Brew Forums > My homebrew stirplate

07-21-2010, 02:30 PM   #311
ekjohns
Recipes

May 2009
IL
Posts: 1,405
Liked 22 Times on 20 Posts

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

07-21-2010, 02:36 PM   #312
Scimmia
Recipes

Oct 2007
QCA, Iowa
Posts: 959
Liked 5 Times on 5 Posts

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.

07-21-2010, 05:26 PM   #313
BrewBeemer
Recipes

Feb 2006
small island paradise, the lost atoll
Posts: 3,500
Liked 26 Times on 26 Posts

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.

08-19-2010, 11:27 PM   #314
ekjohns
Recipes

May 2009
IL
Posts: 1,405
Liked 22 Times on 20 Posts

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?

08-20-2010, 02:09 PM   #315
camiller
Recipes

Apr 2007
Omaha, NE
Posts: 1,907
Liked 33 Times on 33 Posts

Quote:
 Originally Posted by ekjohns 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.

08-20-2010, 08:18 PM   #316
ekjohns
Recipes

May 2009
IL
Posts: 1,405
Liked 22 Times on 20 Posts

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"

08-20-2010, 09:10 PM   #317
camiller
Recipes

Apr 2007
Omaha, NE
Posts: 1,907
Liked 33 Times on 33 Posts

Quote:
 Originally Posted by ekjohns 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/

02-24-2011, 07:26 PM   #318
jtkratzer
Senior Member

Recipes

Oct 2010
Lititz, Pennsylvania
Posts: 2,811
Liked 40 Times on 40 Posts

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,
577221 SWITCH,ROCKER,RRA22H3BBBNN,
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.

03-04-2011, 03:31 PM   #319
jtkratzer
Senior Member

Recipes

Oct 2010
Lititz, Pennsylvania
Posts: 2,811
Liked 40 Times on 40 Posts

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?

03-07-2011, 03:58 AM   #320
jtkratzer
Senior Member

Recipes

Oct 2010
Lititz, Pennsylvania
Posts: 2,811
Liked 40 Times on 40 Posts

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.