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Stir Plate Prototype

So I finally got around to doing some playing with my stirplate components. I tried several different types of circuits, such as an LM317 variable voltage regulator circuit, which seems to be the main one people use out there in the internet, a PICAXE 08M-driven version using PWM (pulse-width modulation) which worked well but was a horrible waste of a microcontroller, and a few other ideas I cooked up myself which were less than stellar. I ultimately settled on a different PWM circuit from this site based on a 555 oscillator chip… much cheaper and simpler to implement than a PICAXE-based one.

The circuit gives very good control and continuous control from the slowest speed up to the fastest, and seems to be a very good way of implimenting a stir plate from an old 12V computer fan. There is no dead zone, and when the control knob is all the way up, the fan runs flat out … no 1.5V drop due to a component like the LM317. Kudos to the author, and if any of you out there are thinking of doing this, I would suggest this as a more robust way to go.

My circuit currently uses a 2N4401 transistor to do the switching instead of the heavy-duty TIP31 he cites in his web page schematic, and it seems to do fine – although I have not done any extended stress tests to see if it overheats or fails. Its easy enough to add some spare pads to the PCB design… in incase I need to replace it at some point with a more robust solution. I’ve also scrounged up a 9V wall wart to power the circuit… which actually puts out 10.5V, as best as my VOM meter can tell… It’s not 12V (the fan rating), but its better than it could be, AND its free – unlike the ones they sell for $22 at Radio Shack (OUCH!). I can always swap it out if I ever happen across a cheap 12V one… but the one I’m using seems strong enough to power the fan to a speed that can throw a stirbar… so I question whether the extra power is even useable.

I’ve got all the plexiglass I need to build the case, however I unfortunately do not have any adhesive / solvent weld – the stuff that Brian gave me to build the pump skid control box has all evaporated, so until I can manage to hook up with him and get more I’m gonna have to leave this as a project pending completion.

Additional Info:

I hope to brew tomorrow – My first brewing seession in about 3 months. Plan is to make an Abbey Brown (the WLP540 Abbey IV ale yeast is on the stirplate as we speak), but I still need to get by HDYB for some Special B malt…. Probably a good idea for me to do this session tomorrow since I’m expected to teach an all-grain class at HDYB next Sunday – and if I am just coming off a 3 month hiatus, I’m bound to be a little rusty.

Categories: Tech geeks
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  1. April 4, 2011 at 6:58 am
  2. April 13, 2012 at 5:31 am

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