NEW CHEAP IDEA FOR MAGNETIC STIR PLATE

[Homegrown Hops]

Absolutely the teflon virtually eliminates the friction on the bottom of the vessel, no matter how polished your ss bolt there will always be greater friction than with teflon coating.

[linuxelf]

Tekman, I notice that you're using a pulse modulator. Is this because you couldn't achieve the proper rotational speed by just limiting the current to the fan? Do you have a schematic for your control board? I'm building one now, and was planning to just limit the fan speed based on current, but if that doesn't work for me, then I'll probably be going that same route. I think I even have a 555 timer sitting on my shelf...

[Tekman]

linuxelf:

Using a 12v pulse width modulation circuit offers a true 0 - 100% speed control. The weight of the magnet mounted on the fan alters this just a bit at low speeds.

I tried the simple potentiometer route first and it sucked. Too much fiddling around to get a reliable speed.

This is the circuit I used:
http://www.nomad.ee/micros/pwm555.html

John

[nolvar]

You know a stir bar is only 1-2 dollars, but if the bolt works for you cool. I managed to scrape together the change for the good stir bar though, and that was the only money I spent. Magnet from an old HD and a fan from and old case.

[Steve]

I don't know guy's but I think I'm missing somthing here. Ok, let me review a bit, you said you cut the head off of some S/S bolts and were using those to toss into your growler. which in turn get moved around by the magnets. Am I missing something here? S/S isn't magnetic! How would they get moved around by magnets if they were real S/S?

Steve

[tnlandsailor]

I don't know guy's but I think I'm missing somthing here. Ok, let me review a bit, you said you cut the head off of some S/S bolts and were using those to toss into your growler. which in turn get moved around by the magnets. Am I missing something here? S/S isn't magnetic! How would they get moved around by magnets if they were real S/S?

Steve

Finally! I was reading this entire thread waiting for someone to mention this. You will get a tiny bit of magnetic action with SS, but not nearly enough to spin a stir bar. I would make sure of the material in your bolt before I tried to make a starter with it. If I had to guess, I'll bet you have a plain steel bolt (or maybe zinc plated or something) which will put iron into whatever you stir with it. You did such a nice job keeping the costs down on the stir plate, you should go ahead and splurge on some real stir bars. Just a thought.

Prosit!