My homebrew stirplate

[stevescott123]

I'm happy to have found this thread but it's been running so long maybe it's too late to join in.

I've been making yeast starters for a while but not really doing it right. I haven't stirred mine at all because John Palmer's "How to Brew" doesn't mention it. I also use a regular S bubbler airlock but that doesn't let oxygen in. I just let my Trader Joe's apple juice bottle sit for 24 hrs - who needs to spend money on a flask? (that's rhetorical folks!)

So I'm going to build a stir plate because I'm better at building things than I am at parting with money. As I read through this thread a couple of things come up that I'm not so clear on. I see the need for speed control but not sure why anybody (particularly the inexperienced) would opt to build a control circuit with several components if an appropriately rated rhesotat/potentiometer would do the trick.

I'm planning on using a spare 12v 1000mA adaptor from a damaged ext hard drive (which I threw away long before I got in to yeast starters otherwise I'd also have magnets) I saw this on eBay http://www.ebay.com/itm/251224703150?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2648 and I'm going to see if my local Fry's has one when I'm in there looking for the fan, case, hardware etc. Or I'll just get that one on eBay.

Since I don't have access to a hard drive I'm going to get these magnets: http://www.harborfreight.com/10-piece-rare-earth-magnets-67488.html which brings me to the next point. The hub of the fan will spin in a circular fashion. Why are some people putting two or more magnets spaced apart? The resultant magnetic field pattern is going to be circular and rotating however the magnet(s) are laid out - isn't it? For that matter one could get a circular magnet: http://www.harborfreight.com/40mm-round-magnet-96649.html

On the same topic, where people have used more than one magnet why are they installed with opposite poles up? But like I say experimentation will probably be the key.

Anyway, thanks for the great and inspiring thread. If anybody can shed a little light on the above I'll appreciate.

 

[MrSaLTy]

Sorry I don't always catch when this thread pops back up.

As to why go with a circuit vs. a rheostat or a pot I covered that in this post. Rheostats or pots will work but I think this is a better option and at the time I had the parts to make one already.

https://www.homebrewtalk.com/f11/my-homebrew-stirplate-8850/index3.html#post88059

As for the magnets, I used 2 magnets because a larger magnetic field seems to keep the stir bar more stable. You may be able to go with 1 centered magnet but if its off center any the stir bar will go off kilter and get thrown. This can happen even with 2 magnets if the speed is too high. As you will see if you ever try to build one of these the magnets need to have the poles opposite on the 2 magnets or the stir bar will not center. It will be obvious when you try it what happens. The more powerful magnets the better for keeping the stir bar centered. You will see that you may be able to keep it going just fine in water but as soon as you add a more viscous liquid (your starter) you may find the bar tends to get thrown more. Hope that helped.

 

[doublehaul]

Is there anywhere that shows how to solder up the actual circuit?

 

[MrSaLTy]

The site i had linked has moved around... it can be found here now....

http://sash.bgplus.com/lm_317/tutorial-full.html

 

[doublehaul]

I see the link recommends a 10K OHM 1/4 Watt Pentiometer/Rheostat. I used - I think - a 100K OHM 1/2 Watt rheostat from radio shack (says "A100K"). It throws the 11/2" stir bar really easy, could this be the cause? The closest thing I can get is a 10K 1/2 watt, - would that work? I also have a 1" stir bar with ring and one w/out ring in the mail to try, and I'm going to try 2 hard drive magnets instead of one in the center...