HELP! Magnetic stirrer

[Scoo84]

There are so many posts about building your own magnetic stirrer and it seems so easy but I am having a hard time! I'm not electronically minded and I'm trying to be with disastrous results. I need some advice/HELP!

So I have a 3W 25ohm rheostat which starts smoking after the device has been on for a while.

Fan is 12V DC, 0.32A, 3.84W
Adapter is Input 120V AC, 60 Hz, 13W, Output 12V DC, 600mA

I think it's the adapter or I need a bigger Watt Rheostat maybe, well I actually have no idea obviously.

 

[dr pepper]

Your rheostat wattage is less than your motor wattage, however your motor will only pull full wattage at full power, so you might get away with it.

Can you post a schematic or describe how its connected, I wonder if you've got a wire wrong.

It shouldnt be difficult to get that to work.

You know you might be able to get away without having a rheostat altogether, if you can rig up a means to move the rotating magnet away from the stirrer magnet then that will give you a speed control, the stirrer magnet will slow down as it gets further away from the motor magnet, then just run the motor flat out.

 

[Gobbledok]

I haven't googled what a magnetic stirrer is but from your information you need a bigger reostat.

As it is, it may be dissipating up to 4.8W depending on where it is set.

 

[Mikebits]

I haven't googled what a magnetic stirrer is but from your information you need a bigger reostat.

As it is, it may be dissipating up to 4.8W depending on where it is set.

It is just a motor that spins under a small pad, a beaker can be placed on top of the pad and a small magnet placed inside the beaker. The spinning motor in turn spins the magnet, thus stirring the contents inside the beaker. This is a device a chemist would use.

 

[Reloadron]

Given a choice I would just build a small PWM circuit. We were trashing one of those stirrers at work several years ago so I gutted it out of curiosity. Small board driving the motor using PWM, not much to it. AC in to a small full wave bridge, some filter caps, then a LM7812 regulator. They use a LM324 so I would guess PWM starting with a triangle wave and then a comparator. Finally an output transistor so not much to it. Something like that or as mentioned a higher power pot.

Ron

 

[Mikebits]

At any rate, a rheostat is not the best way to control motor speed. Something more on the lines of what Ron suggested.

 

[jbeng]

There are fans made which have a PWM input specifically for speed control. I probably wouldn't PWM the supply voltage to a normal brushless fan without a speed control input though, the fans internal electronics may behave unpredictably since they're designed to be powered by a specific DC voltage.

 

[KeepItSimpleStupid]

The unfortunate part is you said you were not electronically minded. This https://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_120539_-1 kit will do it for you. I've used it, but not for a fan. I will assume you have a 12 VDC power supply.