Stir Plate for 5L Flask

One of the things I have started doing is overbuilding my starters.  In doing this, I can harvest 100 billion yest cells from the starter itself.  This process will be detailed in another blog post.  The purpose of this post is to address the sheer size of the flask I have been using to accomplish this.  Instead of using step starters, I use a 5L Erlenmeyer Flask.

This thing is a beast.  It doesn’t sit on my single stir plate at all. When on my dual stir plate, one side and the back hangs over the side, making me nervous.  After taking inventory of what I had that could possibly be the housing for this monster, I came up with this:

A Cisco Catalyst 48-port 10/100 switch.  Given the fact that I am a network engineer, I have a few of these sitting around.  A quick search on eBay can find one for $30or less.

I had a massive 180mm fan pulled from a computer that I used in this build.  It’s a 12v .3AMP fan, so it was perfect.  I also had a 12 lamp that I used as a power indicator.

The purchases made for this stir plate were:

12V 10A Pulse Width Modulator (PWM) – $9.97

Home Depot
8-32 x 2 inch Flat Head machine screw 4-pack – $1.18
8-32 Zinc plated nut 12-pack – $1.18
1/2 in. x 2 in. Metallic Stainless Steel Fender Washer (2 per Pack) – $1.18
3/4 in. Neodymium Rare-Earth Magnet Discs (3 per Pack) – $3.98

Bringing the grand total for this build to $17.49.  On to the build!

I wanted the switch to look as normal as possible, so I kept the 110V AC plug in the back and found an AC to 12V DC adapter that fit inside the chassis.  You’ll see how I implemented this in a bit.

There are six screws on the back of the switch.  These are the only screws holding the chassis together.

Once the screws are removed, slide the top to the rear and lift up.  As you can see, there is not a lot on the inside.

Disconnect the ribbon cable connecting the console port to the system board.

Then disconnect the power harnesses.

Remove the single screw on the left side of the power supply to remove that whole assembly.

Once that is done, remove the nuts holding the cooling fan in place.  This will leave the threaded studs in place.

Until the Dremel finds them

Speaking of the Dremel, I buy cut off wheels by the gross.  One of the handiest tools in my modding arsenal.  Using this wonderful creation, I cut through the system board.  I wanted to ensure that the ports on the front look and feel like a functional switch.  I made sure there were screws holding the ports in place for the whole width of the board.  Then I started cutting.

Once the cut was complete, I removed all the screws from the board are discarded the leftover piece.  Look at all that space!  What potential.

Wanting a power switch, I snagged one from an old Cisco Router to keep the look consistent.  I used my trusty Dremel to cut the rectangular hole and snapped the switch into place.

I then measured and drilled the mounting holes for the PWM.

Once the PWM was installed, I measured and drilled the holes for the fan mounts. I snugged them down with a nut and screwed a second nut on top of that one.  I will use this nut to adjust the height of the fan.

Once the fan is installed, I measured the needed clearance from the top and cut the screws down to height.

I started wiring it up by placing the AC to DC adapter where I wanted it and connecting the DC end to the PWM.  At that connection, I also attached the 12V Lamp for use as a power indicator.  I then connected the fan to the PWM.  Red to +, Black to -.  White is unused.

I then soldered the switch to the AC Input and to the AC to DC Adapter.  Once that was done,  I drilled the hole to install the Potentiometer for the PWM.

I taped the 12V lamp to the light runner I wanted to use

Then I turned on the stir plate to test.  The light works…

…and so does the fan.

Since the chassis is made from some pretty heavy gauge metal, I had to cut a hole in the top.  I would rather to have kept it whole, but the magnets left the fan as soon as the top was close to being in place.  Note that I used a 2 inch fender washer and all three magnets on the hub of the fan.

Finished, ready for the yeast!

Here’s a view of the back.  Since the top also covers the back, I had to cut holes for the switch and PWM knob here, as well.

Full view of the back

With flask, for size

5L starter is spinning!

Notice that there is no part of the flask that overhangs at all.  A very stable stir plate for the largest of starters.  I am very happy!

With the proper salvage chassis and loose parts, I was able to build this massive stir plate for less than $18.

Brew happy, brew often!

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