Which potentiometer do I need for a stir plate?

I want to make $10 stir plate featured on the HomeBrewTalk home, but I would like to add a potentiometer to adjust speed. Mostly just because I think it would be cool. Ebay has several different types with different resistances. I was planning on using a 12-volt cell phone charger for the power source as outlined in the HBT project. Could someone tell me which potentiometer and knob I need? Any ideas how to combine these two projects? Would a child's pencil box work in place of the plastic sheeting or cigar box?

http://mad-science.wonderhowto.com/...ally-controlled-cigar-box-stir-plate-0134284/

https://www.homebrewtalk.com/entries/diy-stir-plate-under-ten-dollars.html

Hey,

Best thing you can get for your box is an old cigar box. You should be able to call/visit a local cigar shop and they usually give those away for free. I got like 5, one for stirplate and the rest for storing things.

As for the potentiometer and knob, you don't really need a nob it's really just convenient and cosmetic. But the potentiometer I'm not positive about what their ratings or whatever should be. I have one that I got from a local electronics store that has 3 prongs on it and it doesn't have an on/off function. If it's plugged in, it's on. Id say take the charger to a local electronics store and ask them for what one would work for that power source.

I don't know that this is relevant to your question or not but in of the builds I saw he specified a 25 ohm one. Is that what you were asking for? I can try to find a link if that would help.

I didnt bother with one, never could get it to start properly with one.

I just get my stir bar centered in my flask, put the flask on the stir plate and plug it in.

if theres too many rattles i move the flask around until its quite (thus centered).

eharris8310 said:

I don't know that this is relevant to your question or not but in of the builds I saw he specified a 25 ohm one. Is that what you were asking for? I can try to find a link if that would help.

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If you could find it that would be great. I'm a bit worried about what to use with a 12 volt plug.

I would just use a 6V power supply and the pot specified in the DIY stir plate build thread. I did and it works great.

You want a pot that can handle several watts, and you only want some resistance, so 25k or 50k would be good. Anything more than that and it will just work like an off/on switch. Personally when I built mine I found a 5.5v 300ma power supply to provide the perfect amount of spin for a 1" stir bar, even in a 2L starter. I had played around with using some old guitar pots (think they were 500k, 1/4 watt) I had but I burnt one of them up pretty quickly b/c I had to use a 9v power supply with it for the fan to even spin.

Just remember that you just want a dimple in the top of the wort, not some huge vortex of death. You just want the yeast to stay in suspension and help oxygenate it.

I can't post a link but look at stirstarters.com


He has a DIY page that shows the proper way to use a potentiometer to control the fan speed...I've heard people complain that it can catch fire potentially if used to dissipate too much current for too long...with that being said I didn't do it the "right" way myself, I use the potentiometer when getting things started so it doesn't throw the stir bar off, and then ALWAYS turn it up all the way after its going so the pot isn't having to work so hard.

Hope that helps!!

There's zero chance that mine won't throw the bar unless I have it all the way down.

I think the fan inside helps keep the components cool.

LovesIPA said:

There's zero chance that mine won't throw the bar unless I have it all the way down.

I think the fan inside helps keep the components cool.

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I feel like I went through ten revisions of my stir plate before I got it all set correctly. Are you using hard drive magnets?? It is a million times easier to center a stir bar on a couple of disc magnets (that stir starter site has the type he was using, which I'm not affiliated with in any way). I bought mine from amazon and weren't too expensive at all. I can crank my 12v supply all the way up and it won't throw the bar...

It also helped to use a pencil to draw on the magnet while its spinning to find the center.

I used 2 small rare earth magnets, each about the size of an aspirin tablet. They work well, but the critical part was getting the spacing right between the two. Too close together, and the stir bar gets thrown easily. Too far apart and not enough field strength to hold on to the ends of the bar (the bar just latches on to one of them and swings wildly). Also, make sure they are both the same radial distance from the center of the fan, and one is N-pole side up and the other S-pole side up.

I did a couple trial-and-error placements before I epoxied them in place. It works just fine.

I actually ordered 3/4" rare earth discs accidentally, and when flipped one side up N and the other up S the sides of the discs attract and hold together, so I guess that would have helped making sure they are the right distance apart from center. Anyway, it works for both my 1" and 2" bar, albeit much better with the 1"...

Wacki said:

I feel like I went through ten revisions of my stir plate before I got it all set correctly. Are you using hard drive magnets??

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Yes, I'm using hard drive magnets. Yesterday I ordered some rare earth magnets that are 1.5" x 0.5" x 0.25" from amazon. Hopefully they'll work a little better.

I tried three different hard drive magnets. First one was WAY too strong. The second one wasn't strong enough. The one I have works but needs to be stronger. Hopefully the ones I ordered will do the trick.

I'm starting to think I should have just bought a stirplate.

LovesIPA said:

I'm starting to think I should have just bought a stirplate.

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I'd hate to see you give up on the project, but if you do decide to go with a commercial unit, I haven't seen a better price for a stir plate than this one.

MaxStout said:

I'd hate to see you give up on the project, but if you do decide to go with a commercial unit, I haven't seen a better price for a stir plate than this one.

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I saw that one. That sucker is tempting me.

That link is for the final product from the stirstarters.com website I referenced earlier in the thread...that dude used to just sell them through his site, looks like he's selling through distributors now!!

The link to his site is actually in the details on that distributors page...

So I am planning on building this DIY stir plate and have an old Blackberry charger I'm using. Problem is both wires are black coming off the charger. How do I know which one to splice with the red wire from the fan?

I'm pretty sure it only works one way, so just guess and check...or maybe use a voltmeter if you have one.

I don't think you will hurt anything plugging it in briefly to check.

It's DC, so the fan will just spin backwards. Get a voltmeter, they're like $5 on amazon.

donshizzles said:

So I am planning on building this DIY stir plate and have an old Blackberry charger I'm using. Problem is both wires are black coming off the charger. How do I know which one to splice with the red wire from the fan?

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One of the two wires will have some form of white (or colored) lines, ribs or something to indicate the difference.


Also from my experience building a few stir plates (for me and others). 25k ohm is great when using a 6v-9v power supply. A 50k would be good for a 9v to 12 v power supply. But, you still may want to pick up a resister to add more resistance (ie slow the fan).

I have done this in the past, but now I am going to upgrade mine by using a voltage regulator to lower the voltage rather than using just resistors, it will allow me more control over the speed that will be more stable.

What I'd do is forget the phone charger and get a universal DC power adapter. You can get one for about $12. Mine can step up in 1.5v increments all the way up to 12 volts.

Try this variable-speed controller for 12V fans.

Or this one.

I didn't bother with a potentiometer. I just used a lower voltage supply (6v maybe?) that I had lying around. Seems to spin at the right speed and works great for me..

Here's the one I used:
http://www.amazon.com/gp/product/B003L4KKF2/?tag=skimlinks_replacement-20

There are many ways to make this work.....it all comes down to cost and features you want to have on your stir plate.

For me, I love building things.
I also wanted the ability to control the speed, increased longevity/versatility, I have also installed a simple on/off switch as well and I am able to keep my total cost with all of this under $10.

I would say most if not all of these suggestions will work for you.... Brewing is suppose to be fun....do what ever makes it the most fun for you.