Home Brew Forums > Home Brewing Beer > DIY Projects > Chillers and Stir Plates > Stir plate - Potentiometer and fan questions...
Reply
 
Thread Tools
Old 04-26-2013, 04:06 AM   #1
kontrol
Feedback Score: 0 reviews
Recipes 
 
Join Date: Jan 2013
Posts: 198
Liked 1 Times on 1 Posts
Likes Given: 9

Default Stir plate - Potentiometer and fan questions...

Planning to build myself a homemade stir plate. I've read couple of tutorials and I'm left with some questions lol.

I'd like to wire the fan to a potentiometer so I can control the speed.

1. I intend to use a pc fan (80mm) or something. I've read against using brushless fan as you can't control the speed. How do you see if it's brushless?

2. What is the potentiometer I need. I see people say 25 ohm (http://www.homebrewtalk.com/f51/diy-...easier-225340/)
and other people say 1k ohm (http://seanterrill.com/2010/04/26/bu...ter-stirplate/)

Does it make much of a difference? Why does it work with both.
How do I calculate the required ohm? Because I will go the my electronic shop tomorow and see what fans then have in stock. If the ohm is important I should know how to calculate it.

3. I see that I should get a 2W rated potentiometer to avoid it melting because of the dissipated heat. In the second link I provided up there I know the guy says the best method is with the LM317T and yada yada, but fact is I'm a real amateur in this domain so I'd like to keep it simple for now. Maybe one day I'll do something like he said (His instruction are not simple enough for a noob like me).

So if I get a 2w rated one, I should be fine right?


kontrol is offline
 
Reply With Quote
Old 04-26-2013, 04:19 AM   #2
kontrol
Feedback Score: 0 reviews
Recipes 
 
Join Date: Jan 2013
Posts: 198
Liked 1 Times on 1 Posts
Likes Given: 9

Default

More info: Scavenged a fan from an old power supply. This is a DC12V 0.17A fan. Not written Brushless like the other one I had (which made me worry). I know it could be brushless too, let's just hope its not?

So what potentiometer should I get if I have a 12V AD/DC Adapter (I guess it must support at least 500mA right?)


kontrol is offline
 
Reply With Quote
Old 04-26-2013, 04:46 AM   #3
uxo
Feedback Score: 0 reviews
Recipes 
 
Join Date: Feb 2013
Location: San Diego, CA
Posts: 125
Liked 11 Times on 10 Posts
Likes Given: 12

Default

http://www.radioshack.com/product/in...Potentiometers


If that doesn't work take it back.

I used a rheostat from the 1970's for my stir plate build. 12v DC power supply also.
uxo is offline
 
Reply With Quote
Old 04-26-2013, 02:46 PM   #4
kontrol
Feedback Score: 0 reviews
Recipes 
 
Join Date: Jan 2013
Posts: 198
Liked 1 Times on 1 Posts
Likes Given: 9

Default

But why 25ohm? And not 2k like the other article I read? Will it change anything?
kontrol is offline
 
Reply With Quote
Old 04-26-2013, 02:56 PM   #5
a10t2
Feedback Score: 0 reviews
Recipes 
 
Join Date: May 2010
Location: Leadville, CO
Posts: 557
Liked 14 Times on 13 Posts
Likes Given: 1

Default

V = IR
12 = 0.17*R
R = 12/0.17 = 71 ohm

The closest common value would be 100 ohm: http://www.parts-express.com/pe/show...number=023-604

A 25 ohm would only allow you to reduce the speed by 25/71 = 35%.
__________________
http://seanterrill.com/category/brewing/
Quote:
Originally Posted by monty3777 View Post
squeeze your sack like it owes you money.
a10t2 is offline
 
Reply With Quote
Old 04-26-2013, 03:09 PM   #6
kontrol
Feedback Score: 0 reviews
Recipes 
 
Join Date: Jan 2013
Posts: 198
Liked 1 Times on 1 Posts
Likes Given: 9

Default

a 100ohm will allow me to reduce by 100%

Why the other guy in his article use a 2k then? Sorry for all these questions, I'm trying to understand.
kontrol is offline
 
Reply With Quote
Old 04-26-2013, 03:27 PM   #7
a10t2
Feedback Score: 0 reviews
Recipes 
 
Join Date: May 2010
Location: Leadville, CO
Posts: 557
Liked 14 Times on 13 Posts
Likes Given: 1

Default

Quote:
Originally Posted by kontrol View Post
Why the other guy in his article use a 2k then?
Because with an LM317 it isn't the value of either resistor that sets the voltage, it's the ratio between them. I was using a 220 ohm fixed resistor, so a 2.5 kohm pot allowed for a range of ~11 V.

With a potentiometer wired in series, all you're doing is sinking some of the current into the pot and dissipating it as heat. Whatever is "left over" powers the motor.


__________________
http://seanterrill.com/category/brewing/
Quote:
Originally Posted by monty3777 View Post
squeeze your sack like it owes you money.
a10t2 is offline
 
Reply With Quote
Reply


Thread Tools


Similar Threads
Thread Thread Starter Forum Replies Last Post
Do i need a potentiometer on my stir plate? JayWeezie Chillers and Stir Plates 5 03-07-2013 05:39 PM
stir plate questions. Jeepaholic Fermentation & Yeast 5 08-15-2012 04:07 AM
DIY Stir Plate Potentiometer Specs TravelingBrewer22 Chillers and Stir Plates 4 12-12-2011 11:55 PM
Stir Plate Potentiometer Question.No go. Anubis Chillers and Stir Plates 3 11-15-2010 07:43 PM
Homebrew Stir Plate Potentiometer Issues: Assistance Appreciated! mew Equipment/Sanitation 16 04-06-2010 03:55 PM


Forum Jump

Newest Threads

LATEST SPONSOR DEALS