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...84.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-piec...ets-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-ro...net-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.