making a stir plate - what potentiometer do I get?

Discussion in 'Homebrewing' started by corbmoster, Apr 2, 2015.

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  1. corbmoster

    corbmoster Pundit (848) Dec 15, 2014 Texas
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    After doing some reading, I've learned about the benefits of doing a yeast starter before brew day. And being the DIY handyman that I am, I want to DIY it. I was going to use a DV plug (12 volts if I can get one, but I could live with 7), a wooden box from Hobby Lobby, a PC fan, some type of toggle switch, magnets from old hard drive, and a potentiometer. But what type of potentiometer should I use? I see several at Radio Shack, and they have different ratings 50k - Ohm, 100k-Ohm
     
    #1 corbmoster, Apr 2, 2015
  2. PortLargo

    PortLargo Pooh-Bah (1,831) Oct 19, 2012 Florida
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    #2 PortLargo, Apr 2, 2015
  3. corbmoster

    corbmoster Pundit (848) Dec 15, 2014 Texas
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    I thought about that, cheaper at radioshack.
     
    #3 corbmoster, Apr 2, 2015
  4. stealth

    stealth Pooh-Bah (2,023) Dec 16, 2011 Minnesota
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    #4 stealth, Apr 2, 2015
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  5. wspscott

    wspscott Pooh-Bah (1,958) May 25, 2006 Kentucky
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    I just used an old cell phone charger directly wired to the computer fan. One speed, plug in to turn on, unplug to turn off. Works fine up to 2L although for a small starter (.5L) it wants to throw the stirbar.
     
    #5 wspscott, Apr 2, 2015
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  6. fishtremble

    fishtremble Initiate (0) Jan 18, 2010 Michigan

    Radio Shack by me had a terrible selection ended up getting a fan speed controller at my local computer store for under $8. Gutted an old pc and used it's case, power supply and fan for my stir plate. Took the old hard drive out of it and got the rare earth magnets from it. So at the end of the day my total costs for a stir plate was under $10. Finally my pack rat habits saved me some cash.
     
    #6 fishtremble, Apr 2, 2015
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  7. corbmoster

    corbmoster Pundit (848) Dec 15, 2014 Texas
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    That's why I wanted to use some type of potentiometer.
     
    #7 corbmoster, Apr 2, 2015
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  8. michaeltrego

    michaeltrego Crusader (447) May 21, 2004 New Hampshire

    #8 michaeltrego, Apr 2, 2015
  9. corbmoster

    corbmoster Pundit (848) Dec 15, 2014 Texas
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    #9 corbmoster, Apr 2, 2015
  10. michaeltrego

    michaeltrego Crusader (447) May 21, 2004 New Hampshire

    Maybe, but a fun learning project.
     
    #10 michaeltrego, Apr 2, 2015
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  11. KeyWestGator

    KeyWestGator Savant (1,159) Jan 21, 2013 Florida
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    How hard is it to make? I have an old laptop laying around. I'm somewhat handy but I've never messed with electronics before.
     
    #11 KeyWestGator, Apr 2, 2015
  12. corbmoster

    corbmoster Pundit (848) Dec 15, 2014 Texas
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    I'm usually not gung-ho for soldering, but I think that would be the best way to do this. You would need to solder some DC power, to a switch, to potentiometer (basically a dimmer), and to a fan. There are a lot of write ups on how to do this.
     
    #12 corbmoster, Apr 2, 2015
  13. inchrisin

    inchrisin Pooh-Bah (2,013) Sep 25, 2008 Indiana
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    I recently put a few sheets of paper (10?) in between my flask and stir plate. I've noticed that this changes how the bar stirs. Mine wants to throw the bar more often, but I wonder if this would help slow things down a little for you.

    Edit: Originally, I just wanted it to become quiter and use it as a napkin if anything got unruly.
     
    #13 inchrisin, Apr 2, 2015
    Last edited: Apr 2, 2015
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  14. GUNSLINGER

    GUNSLINGER Initiate (0) Nov 18, 2013 Colorado

    #14 GUNSLINGER, Apr 3, 2015
    Last edited: Apr 3, 2015
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  15. corbmoster

    corbmoster Pundit (848) Dec 15, 2014 Texas
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    Does it also function as a switch?
     
    #15 corbmoster, Apr 3, 2015
  16. MarkGP

    MarkGP Initiate (0) Jan 28, 2015 Rhode Island

    A 25 ohm potentiometer from radio shack and a multi volt DC adapter will give you unlimited control.
     
    #16 MarkGP, Apr 4, 2015
  17. wspscott

    wspscott Pooh-Bah (1,958) May 25, 2006 Kentucky
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    Have you used one of those before? What did you do for a power supply? The ebay page says "Input Voltage: AC 3-24V/DC 3-40V
     
    #17 wspscott, Apr 4, 2015
  18. corbmoster

    corbmoster Pundit (848) Dec 15, 2014 Texas
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    If you follow the links in this post, what the take home message is the optimal set up is using a 9 volt DC power supply, connecting to a switch, then to a 25 Ohm, 3 watt rheostat. I've done some chatting on an electronics forum and there is of course more than one way to skin this rabbit. You could use a PWM motor controller like this, or this. If you google PWM stir plate you should get a few results. You could use a computer fan controller, and I think someone above suggested that. And a PC fan controller pretty much is a DC PWM. And if those were not enough, you could use an Arduino Uno with a PWM output to drive it. If you wanted to be fancy with it you could wire an LCD screen to it. All of that is beyond my understanding, and I don't have interest to learn how to do that right now. As for me, I've gone with the first option. I am waiting for some of the parts to come in the mail, and I'm staining the wooden box I got at Hobby Lobby to house it.
     
    #18 corbmoster, Apr 4, 2015
  19. tngolfer

    tngolfer Initiate (0) Feb 16, 2012 Tennessee

    BYO addressed this in the March/April 2014 issue. It took me a while to find it so if you haven't already bought a potentiometer maybe this will help.

    1. Determine the fan and power supply
    2. Determine Resistance = Volts / Amps
    Voltage = measured value of the power adapter
    3. Determine Wattage = Volts x Amps
    4. Select linear potentiometer with a max resistance somewhat near the resistance you have calculated and a watt rating higher than the wattage you calculated.

    For example,
    Resistance = 16 V / 0.07 A = 228 Ohms
    Wattage = 16 V x 0.07 A = 1.12 Watts
    Select 250 Ohm, 2 watt potentiometer.
     
    #19 tngolfer, Apr 4, 2015
  20. stealth

    stealth Pooh-Bah (2,023) Dec 16, 2011 Minnesota
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    I use some badass rare earth magnets - can spin the hell of that bar and it will never throw.
     
    #20 stealth, Apr 4, 2015
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