flyweed, make sure that the 2 magnets are lying on the fan in oposite polarities. one + and one - up, and you'll have to play with the spacing to get it to work for your stir bar (especially if you plan on using multiple stir bars).
so you guys are saying I need two smaller magnets on opposite sides of my fan, rather than one long one? I'll give that a shot if so. it's pretty funny to actually watch the stir bar stand up on end vertical and spin that way. but I'll give a couple of smaller magnets a try to see if I can get my stir bar to lay flat and spin properly.
Dan
I've built a few stir plates with 3 HD magnets stacked to get a 1/2" bar to spin full speed in a 4L flask. Click on my gallery to see higher res versions of these pics if they don't come out right.
I was always a little disappointed that my 2" would always get thrown. Then I built another strirplate with small round disk magnets. These magnets are about 1/2" across and maybe 1/8" thick (looks like a large watch battery).
I make 2 stacks, with 3 of them in each stack. The stacks must have opposite polarity for this to work!. The distance between the stacks is about 1.5" (I think). I can now spin that 2" bar. I hotglued a piece of tin (cut from a peanut can) to the fan so I had a place to glue the magnets down.
BTW, the magnets in this second picture below are held by electrical tape. I took this pic during testing and didn't take one after the final glue assembly.
so you guys are saying I need two smaller magnets on opposite sides of my fan, rather than one long one? I'll give that a shot if so. it's pretty funny to actually watch the stir bar stand up on end vertical and spin that way. but I'll give a couple of smaller magnets a try to see if I can get my stir bar to lay flat and spin properly.
Dan
K&J sells single magnets with both polarities along their center axis. I haven't used them, however I'd bet they would work as well...
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I'd rather have a bottle in front of me, than a frontal lobotomy.
--Tom Waits
You can't be a real country unless you have a beer and an airline - it helps if you have some kind of a football team, or some nuclear weapons, but at the very least you need a beer.
--Frank Zappa
You can use two button magnets or one single bar magnet, both will work OK.
Just make sure that your button mags are arranged with north pole up one side and north pole down on the other.
I think the reason your stir stood straight up is the fact that your drive magnet is magnetized through the short axis instead of the long axis. With a bar magnet you want the poles to be on the "ends" of the bar and not the "sides" if you get my drift.
I happen to have most of the Radio Shack components for this build already (leftover from an EE class I took years ago). I have one Pot, but it says 500 Ω (500 Ohms) on it. Will this work? I expect not, but I'd like to hear opinions on this.
im sorry if someone already asked this question, but I was building this today and when I finished, the potentiometer wouldnt turn it completely off. is that correct? it seems to be spinning very fast even at its lowest speed.
I happen to have most of the Radio Shack components for this build already (leftover from an EE class I took years ago). I have one Pot, but it says 500 Ω (500 Ohms) on it. Will this work? I expect not, but I'd like to hear opinions on this.
im sorry if someone already asked this question, but I was building this today and when I finished, the potentiometer wouldnt turn it completely off. is that correct? it seems to be spinning very fast even at its lowest speed.
The potentiometer doesn't work as an on/off switch. It will only vary the voltage from the DC power supply going to the fan.
__________________
I'd rather have a bottle in front of me, than a frontal lobotomy.
--Tom Waits
You can't be a real country unless you have a beer and an airline - it helps if you have some kind of a football team, or some nuclear weapons, but at the very least you need a beer.
--Frank Zappa
If anyone has a Harbor Freight Tools near by they have some real inexpensive magnets that are pretty strong. $2 for a pack of 10 vs the $2 for a pack of two smaller ones at radio shack.
Also I just ended up buying a 120mm case fan for $9 at the local computer store down the street. It JUST fits in the radio shack 5x7x3 project box width wise. In fact it snaps into the lid it's so tight. I'll get a bar or two ordered soon to check out what size I want to use.
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Going through life is hard.
Going through life stupid is harder.
The potentiometer doesn't work as an on/off switch. It will only vary the voltage from the DC power supply going to the fan.
And also, if you're just hooking up the pot directly to the power supply and the output (in other words, without using the LM317 circuit as shown), then you might risk burning it up if you try to put it at the fan's lowest setting. Essentially, it's trying to resist a lot, and it will get "hot!"
Linear Mode
