For crying out loud-why wont my damn stirplate work right

[Test_Engineer]

I'm not using the rheostats from radioshack like everyone seems to suggest. I think they are only 25 or 50 ohms. That is not very variable.

I am using a 1000 ohm linear potentiometer in a LM317T circuit.

Here is the schematic I am using.




It works a lot better for two reasons:
1) You can control the speed very precisely, mine is 10 turns for 0 volts to 12 volts

2) the LM317T is converting the resistance to heat and cooled by a heat sink. When using a rheostat, the fan and the rheostat are loaded and produce heat causing them to either fail or act strange.

When the circuit is done, it should look something like this:

[Push Eject]

So after spending nearly $70 going through the same thing you are I realized my folly and bought one of these for about the same price.

Cheers,
Push E.

[BDawg]

The thing that did it for me was the unbelievably strong magnets I got.
They look like little watch batteries, only thicker. They only sold them in lots of 5 or more, so I bought 5. They came stuck together. It took all the strength I could muster to separate them barehanded (not as hard with pliers). That and 2 potientiometers so that I can control the speed a little more accurately.

HTH-

[Crut]

I'm not using the rheostats from radioshack like everyone seems to suggest. I think they are only 25 or 50 ohms. That is not very variable.

I am using a 1000 ohm linear potentiometer in a LM317T circuit.

Here is the schematic I am using.




It works a lot better for two reasons:
1) You can control the speed very precisely, mine is 10 turns for 0 volts to 12 volts

2) the LM317T is converting the resistance to heat and cooled by a heat sink. When using a rheostat, the fan and the rheostat are loaded and produce heat causing them to either fail or act strange.

When the circuit is done, it should look something like this:

HUH? you lost me with the diagram. whats c2 and all that other stuff in the middle. Remember, I'm on the BN short bus.

Push, im building this with only the 4 dollars i spent on the stir bars, and the 2 dollars on the second rheo. Everything else i can build, but the wiring is a pain. Oh and apparently our radioshacks around here are retarded more than I am because they only carry the same 25 ohm rheo. I already burned out one of those.

I did a little test run with it last night. Made up a DME mix tossed in the stirbar, let it stir for an hour or so, then threw some leftoer coopers dry brew yeast in and waited til this morning. Ooh la la, would ya look at that, nice little swirlling actiong going on with some nice frothy foam on top. I might fidget with it later on if i can find a better rheo thats a little more adjustable, but for now it seems to be set on its sweet spot.

[linuxelf]

I ended up wiring a very small resistor in parallel with my potentiometer. It's just enough resistance that, once the fan is spinning, there's no point on the potentiometer where the fan will stop. Then I wired in a momentary contact switch to give the fan full voltage to kick start it. Now I set my potentiometer where I want it, and never have to touch it again. Hit the button for just a second to get the fan started, and it settles down right to the right speed.

[Test_Engineer]

I'm not using the rheostats from radioshack like everyone seems to suggest. I think they are only 25 or 50 ohms. That is not very variable.

I am using a 1000 ohm linear potentiometer in a LM317T circuit.

Here is the schematic I am using.




It works a lot better for two reasons:
1) You can control the speed very precisely, mine is 10 turns for 0 volts to 12 volts

2) the LM317T is converting the resistance to heat and cooled by a heat sink. When using a rheostat, the fan and the rheostat are loaded and produce heat causing them to either fail or act strange.

When the circuit is done, it should look something like this:

HUH? you lost me with the diagram. whats c2 and all that other stuff in the middle. Remember, I'm on the BN short bus.

Push, im building this with only the 4 dollars i spent on the stir bars, and the 2 dollars on the second rheo. Everything else i can build, but the wiring is a pain. Oh and apparently our radioshacks around here are retarded more than I am because they only carry the same 25 ohm rheo. I already burned out one of those.

I did a little test run with it last night. Made up a DME mix tossed in the stirbar, let it stir for an hour or so, then threw some leftoer coopers dry brew yeast in and waited til this morning. Ooh la la, would ya look at that, nice little swirlling actiong going on with some nice frothy foam on top. I might fidget with it later on if i can find a better rheo thats a little more adjustable, but for now it seems to be set on its sweet spot.

C is capacitor.
R is resistor
the r with the arrow is the potentiometer.

Just google LM317T voltage reulator or something similar and you should find a lot of examples.

here is where I took the pics from. It is the second example on the page:
http://www.cpemma.co.uk/reg.html

[linuxelf]

I was playing with the idea of building a pulse width modulator, but ditched it after experiments showed that I could get enough control over the fan with just a pot.

[Test_Engineer]

I was playing with the idea of building a pulse width modulator, but ditched it after experiments showed that I could get enough control over the fan with just a pot.

PWM's are sort of strange to work with. I have found that using them to lift the ground usually works, but if you use it on the power side, it doesn't. An easy supply of PWM generators is the dimmer switches for the meter cluster in most new cars. My original intention was to use the dimmer/PWM on a stirplate, but when I gave up using it to power it and built the circuit I posted. I came back to it a few days later and realized I can just lift the ground with it, and then it worked like a charm.

I put mine in a radio shack project box with some sticky rubber feet to damping some of the vibrations.

shitty cell phone pic, and the stirbar is at full blast in this pic: