Most of us NEED this site because we aren't in the electronics field and have no idea how this stuff works or is even figured out. That's why the DIY's posts are SOOOOO helpful. I never would have been able to build the stirplate without an exact step by step process. I have no idea how the ohms on a pot are figured. I will help out everywhere I can, but I need someone like you guys to help me with the electronics stuff and just tell me where to solder and to what. I had to do it just as the build suggested because I have no idea how much of a difference a 25 ohm pot is vs a 25K ohm pot or where you would use the two. Fact is, I really don't care. I just want a stirplate that works. It saved me $40. Got a little education along the way as well. Bonus!
P.S. My fan is 12v - not sure if that matters or not
Thanks for all the help guys, and thanks for dealing with the ignorant one (mirror
)
Sure thing!
And I got no gripes about any of that. I hope that post didn't come off as impatient; I just kept seeing all these different people with different problems, nobody was posting enough detail to help them, and the only thing in common seemed to be that everyone had a 1-25ohm pot.
Your 6V charger isn't working because it's not giving your fan enough juice. Computer fans are typically built on motors that will spin at a fixed RPM for a fixed voltage. If you bump the voltage up, it will spin faster, and if you bump the voltage down, it will spin slower. It's not so simple, though, that you can say 0V = zero speed, 6V = 50% speed, and 12V = 100% speed. All fans have an operating voltage range, and will only spin at all if given power above a certain threshold. A potentiometer works by introducing variable resistance to the circuit, which causes a voltage drop, which in turn causes the fan to spin slower than its maximum speed.
The problem is that you know how much of a voltage drop you want, but you can't know how much of a voltage drop you're going to get from any particular resistor without knowing how much current your fan draws. This should be listed on the label...something in the ballpark of 0.5A (or 500mA). So a 1-24ohm pot will cause one range of voltage drops for a 0.5A fan, and another range for a 1A fan, and yet another range for a 0.25A fan.
There are a couple solutions, but first you want to make sure that your device is wired properly. You say that it's much too high, even at the lowest setting. This probably just means that you've got a relatively powerful fan, and that even 25ohms of resistance isn't enough to get you down to a workable range. Just to make sure you're wired right, though: does the speed of the fan change at all when you adjust your potentiometer?
So solutions:
1) go to radioshack and buy a relatively large range potentiometer (say, 0-200ohms, rated for 10W) and know that this will work for 95% of fans. The down side to this is that you'll have a very narrow "sweet spot" of useful range on your potentiometer, so you'd have to be gentle with it to find a useable setting.
2) build something more like this:
https://www.homebrewtalk.com/f11/my-homebrew-stirplate-8850/ It looks more complicated than it is, but this design has the added benefit that it will work with pretty much any 12V fan.
3) post more detailed specs of your fan (particularly current draw in amps or nominal power usage in watts) or a part number and we can speculate about what kind of pot would work better for you. It would be only speculation, though, because the addition of those magnets means that your fan isn't behaving as described in its datasheet anymore.
...and let us know how it goes.
@dzlater - if you are happy with your speed range, you could get the same 1-25ohm pot but just make sure it has a higher rating than 3W. 6W or 10W should be fine.