Very Simple DIY Stirplate - Is My Speed OK?

[BigFloyd]

I'm trying to get geared up to do liquid yeast in what I'm hoping is the correct fashion. One of the things I figured I'd need is a stir plate.

Here's one I cobbled together 100% from pieces and parts I had on hand. Total cost = $0

The 12V motor is a fan I took out of a really old power supply. It had a broken blade, so I broke/ground the others off to match. The magnets are pieces of one broken in two trying to get it off the innards of an old hard drive. They're epoxied to a piece of plastic pipe that's glued to the fan hub. The fan is direct wired into a 5.5V wall charger (from a Motorola cell phone) I found buried in a drawer. It's all mounted into the box that my wife's laptop replacement charger came in.

Question - The DIY stir plates I've seen online (that gave me the idea to do this) all use a higher voltage DC power source that is then wired through a rheostat, sometimes using a resistor. Should I add those things or is my plate currently spinning at the correct speed for stirring yeast starter?

Here is link to the video of it in operation with 1.8L of water in the flask.




Thanks!

 

[stpug]

Looks good to me, but you'll have a better idea once you put in some wort and yeast and let it rip for 24 hours. I find that I really like the ability to adjust speed. I will start off low, ramp up to the highest to whip in some air for a few minutes, and settle on a med-slow speed. Of course, all of this is probably not needed.

 

[BigFloyd]

Looks good to me, but you'll have a better idea once you put in some wort and yeast and let it rip for 24 hours. I find that I really like the ability to adjust speed. I will start off low, ramp up to the highest to whip in some air for a few minutes, and settle on a med-slow speed. Of course, all of this is probably not needed.

Thanks. I'd, of course, like to be able to vary the speed, but first I'm trying to see of I can get a workable stirplate that costs little (or nothing) and is so simple that folks who don't wire and solder can still easily build one.

So, here's the update to the El Cheapo DIY Stirplate project after further testing.

5.5V straight into the 12V fan motor is fine for 1.8L, but too fast for 1L (or less) in a 2L flask. The vortex reaches down to the stirbar and the action is just vigorous enough to throw it off to the side. Original design = partial fail.

Back to the drawing board. While hunting through my garage tool closet in hopes of finding something to reduce/control the voltage, I discovered a 4.8V wall charger. Might as well try that for grins to see if the lower voltage slows the motor rpm the right amount to make this work.

I ran it with 1.8L and got a 1/2" to 1" dimple at the surface----nice. Tested it with 1 liter --- still good. Reduced the level down to 600ml -- the vortex drops down onto the stirbar, but it's not spinning fast enough to fling it off to the side. I believe this will get the job done.

OK. A very simple, yet effective, DIY stirplate can be built without including a variable voltage control (rheostat). A 4.8 volt wall charger wired directly into a 12V computer fan motor provides the rpm needed to stir a 1.8 liter starter, yet won't toss the stirbar off to the side when you are stirring as little as 600ml in a 2 liter flask.

Of course, there is no arguing that it would be nice to be able to adjust the speed. If I later run across something that is going to get tossed, but contains a usable rheostat, I'll scavenge it for this project.

 

[kluge9]

Water doesn't equal yeast laden wort. The yeast starter will be thicker and harder to replicate the same conditions as you had with just water. You may see that you'll have to switch back to the 5.5v to get the right action

 

[BigFloyd]

Water doesn't equal yeast laden wort. The yeast starter will be thicker and harder to replicate the same conditions as you had with just water. You may see that you'll have to switch back to the 5.5v to get the right action

Good point. Thanks.

I'd been giving some thought to that. I think it will do a 1 liter starter just fine on 4.8V. If I ever have the need for a 2 liter volume, I can always switch over to the 5.5V source pretty easily.

 

[Hang Glider]

Water doesn't equal yeast laden wort. The yeast starter will be thicker and harder to replicate the same conditions as you had with just water. You may see that you'll have to switch back to the 5.5v to get the right action

I agree with this - even in a smaller 1L volume instead of 2L - the viscosity difference will matter. I can spin water all day with my stir plate, but when making a starter, I have to start slow to get the stir bar engaged, then ramp up the speed slowly to prevent it from throwing. Hence the importance of a speed control.