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

[codewritinfool]

Lin / Log pot differences could cause the observed sensitivity issues, but if I had the problem, I think I'd consider PWM drive for the motor. The mass of the magnets would smooth out the rotation just by inertia, and I think you'd have really good control.

You could use a micro to do it or if you wanted to stay in the analog realm you could use a 555 to drive a pass transistor or even the enable on a regulator.

If you REALLY wanted to do it right you could use a hall-effect device as part of a feedback loop so that you don't lose your magnetic coupling to the stir bar.

I can whip up a schematic if someone wants to prototype it.

[Test_Engineer]

Lin / Log pot differences could cause the observed sensitivity issues, but if I had the problem, I think I'd consider PWM drive for the motor. The mass of the magnets would smooth out the rotation just by inertia, and I think you'd have really good control.

You could use a micro to do it or if you wanted to stay in the analog realm you could use a 555 to drive a pass transistor.

I can whip up a schematic if someone wants to prototype it.

I got a bunch of PWM generators here and a few PC fans, I can see if it will work. Isn't a 555 timer basically the same thing as a PWM generator?

Now that I think of it, a lot of the PC fans with 3 wires are actually PWM fans. The orange or yellow wire is the control wire.

[Crut]

Why dont I just send it out to one of you techie guys and you can finish it for me Mine is all redneckish and wire here and there in a homemade plexiglass case.

this is before the second rheo was added, but you get the idea of what im working with, or at least until i find another suitable box.

[BadRock]

Aww...the smell of nerds in the morning!

[linuxelf]

Before building mine, I breadboarded a PWM using a 555. Even without the magnets on the fan, I was able to get it to spin pretty much any speed I wanted. but I didn't have a socket for the 555, and I didn't feel like trying to solder the 555 to a board without a socket. I've burned up a 555 that way in the past.

And BadRock, if it makes you feel better, I just barely understand what we're talking about here myself.

[SphericalCamel]

I only "borrowed" mine from work, so I can't help much. I did find a site that has cheap stir plates though if you want to buy one. They look like they were used though.

http://www.biosurplus.com/cgi-bin/DisplayPage.cgi?PageToDisplay=SearchInventory&SessionID=&SelectedProductCategory=33&ProductCategoryNumber=33&SearchRequested=Y

[BrewBum]

I got confused in this thread

My stir plate is made out of cardboard box, computer fan, hard drive magnets and a car charger. I tried a rheostat, it screwed everything up so I hooked the sum bitch straight to the power supply and it turns just fine and doesn't throw the bar.

you think yours is ghetto, you should see mine. It is assembled with hot glue, nails wood and a CD case for rigidity. the cool thing, it cost me nothing but time.

Have you tried it without the rheostat all together? You may have but I don't want to read or can't read.

[SunkenBier]

I got mine on ebay for 49 bucks and another 50 for shipping. It is 4 stir plates and they all can heat up to 300 c. I do my boils on them as well.




I think the thing is about 30 years old.