Stir Plate help

[Bhamsteelerfan]

So I've been trying to construct a stir plate. Online tutorials have seemed easy enough, but man has it been frustrating. Thought I finally had everything wiried correctly. I set a filled liter flask on it and let it run. For a while, it was running like a charm, but then about an hour in, the fan slowed down to a crawl, and I couldn't get it back up to full speed. Have no ideas what is going on.

Here's how I've wired it - I purched a CPU fan controller (basically a 12-volt rheostat) and hooked it to a 12-volt computer fan. I used a 9-volt power supply. All the connections are secure. Now I did go back and read some reviews on the fan controller I purchased (it was cheap), and several people said their controller conked out soon after they got it.

If I need to replace the rheostat/potentiometer, what kind do I need exactly (I can wire things, but really know very little about electronics)? Also, do you think I may have done anything else incorrectly? Like I said, my build was pretty much the same as most of the tutorials I've seen online.

Any help is appreciated. Want to get my plate up and running!

 

[wingedcoyote]

I can't offer much help with the electronics, because I can't tell a volt from an amp from an ohm and I seem pretty unable to be taught. However! What I can tell you is that if you get tired of fiddling with it and want to start fresh, this guy here is an excellent labor saver. It's a PC fan that Thermaltake has hacked into a desk fan, so it already has a rheostat and USB power cord attached. The grills and stand come right off, and with a washer and magnets glued on it has worked perfectly for me.

 

[Bartp]

I think the problem might be that you're powering a 12v device with 9v power supply. Fan needs 1.25w. You're only giving it 0.9w

 

[charliehorse]

I think the problem might be that you're powering a 12v device with 9v power supply. Fan needs 1.25w. You're only giving it 0.9w

While this is true, when I build mine, I bought a Pulse Width Modulator (otherwise known as a PWM). Since DC runs in very quick pulses, this will space them apart or contract them, slowing or speeding up your motor.
http://www.eachbuyer.com/pulse-widt...]America(EN)&gclid=CN-d9-r1kL8CFWQQ7Aodq3AA4w

 

[Smellyglove]

You need a 12v adapter which is capable of delivering the required amps for your fan. If the fan requires 750mA and the adapter only delivers 500mA (just example numbers) the fan will not run at full speed and you can burn out the adapter since it will work at the limit of (if not over) it's capabilities to supply the fan with the amps it want to pull.

Also, you need a powerful enough fan. There are some fans out there (like Fractal design) which are designed with very low resistance ball bearings (so the fan runs easy using little effect), efficient blades and low RPMs to keep them quiet. These fans will not pull a big enough starter as they don't have enough juice. It might run fine in water, but when the yeast starts to multiplythe starter also gets more dense, creating more resistance.

I'm using this fancontroller in both my stir plates, they get a little hot, but haven't caused a fire (yet?). Cheap and easy:
http://www.ebay.com/itm/Computer-CP...51783233?pt=AU_Components&hash=item3371c0a741

You should be safe with a 1000mA 12V adapter. The fan only pulls what amps it wants, so it doesn't matter if the adapter is rated with higher amps.

 

[Bhamsteelerfan]

I replaced the CPU fan controller with a 25K ohm 3W rheostat and replaced the 9v supply with a 6v supply (the 12v supply was spinning the fan ridiculously fast even with the rheostat cranked all the way down). Now it works perfectly. Even added a rocker switch.