Correct way to control fan speed in diy stir plate

Hello all,

First off I apologize if this has been brought up before but I could not find it in my search.

I have read previously (either here or else ware) that using a potentiometer alone is not a good way control fan speed in a diy stir plate. Apparently the reason for this is that the potentiometer will heat up and eventually fail while controlling the fan at low speeds.

While I have read that lots of people on here have used a pot alone to control speed to great success, I would like to wire mine the way it should be done in a commercial product.

I have read that different resistors should be used with the pot to resolve this problem. Anyone on here an electrical engineer or guru that could help me out?

Thanks all!

-Zac

I would opt for a PWM circuit.

Or just buy this, take off the fan cage and speed control mount (to be remounted later on your plate), and adapt it to your setup. Plenty of people including myself have done this with great results. And best of all -- it's got a retracting USB cable, and of course can plug into any cell phone charger USB port.

I use a plugin dimmer switch. It works fine, but I wish I could get it a little slower.

Thanks for the info all. Nick I noticed that that fan you mentioned does not have an on/off switch, do you just unplug it when you are done? Also does that fan seem to have enough power?

zvanaernum said:

Thanks for the info all. Nick I noticed that that fan you mentioned does not have an on/off switch, do you just unplug it when you are done? Also does that fan seem to have enough power?

Click to expand...

1. Nope, there's no on/off switch, so yeah I just unplug it when done. However, the hard drive magnet will most likely keep it from spinning up when in it's lowest power setting. At least mine does, esp when you've got the flask on.

Check out mine here and here.

2. Yeah, the fan has plenty of power, enough to throw my stir bar off. I typically make 2.5L starters and have never had a problem. I recommend a longer stir bar (1-1.5inches) to make the most of it.

Remember, the idea behind a stir plate is not to get that super-cool looking tornado vortex going. Most of that stuff you see is a full-on whirlpool eddy. You just want to see that there's at the very least, a dimple in the middle. Usually you want a little more.

See this guy's video -- he's easily got more than enough power going on there, and could probably turn it down just a little bit. The idea is to simply keep the yeast moving for optimal reproduction, and that in turn helps off-gas and keep foam-overs from happening (a common occurrence in hand-shaken starters).

The 8A LED dimmers (like this one) are awesome for this.

I built a circuit very similar to this, and it works like a charm:

Dial-a-Speed