Stir Plate Magnet Problems

[Stevorino]

I just did my initial run at building a Stir Plate this past weekend. I have the fan running on a rheostat and can adjust the speed. However, I bought really small fans and they don't seem to have enough torque to start spinning w/ the magnet's weight unless I give it a push w/ my finger.

I also mounted the fan upside down on the ceiling of the fan and it doesn't seem to be strong enough to make the magnet in the stir plate move. Even so, when I hold up a fan to the bottom of the flask w/ a stir rod, the rod just bounces around-- any ideas on how I can get it to connect and start spinning?

 

[bradsul]

How much power are you using? I built mine using a 12VDC 500mA input, an 80MM 12VDC fan and an LM317 circuit (as per the stir plate thread on this forum). I even added a large (2.5") metal fender washer to act as a sort of flywheel and also to space the magnet away from the fan hub.

Your stir bar is most likely kicking either because the fan is moving too fast (you need to start it slow and ramp up the speed) or because you're not getting enough connection between the magnet and the stir bar.

My guess is your fan is too small and/or you're not using enough power.

 

[BeerCanuck]

I also mounted the fan upside down on the ceiling of the fan and it doesn't seem to be strong enough to make the magnet in the stir plate move. Even so, when I hold up a fan to the bottom of the flask w/ a stir rod, the rod just bounces around-- any ideas on how I can get it to connect and start spinning?

Im having a hard time visualizing this...got a picture?

Bradsul a washer as flywheel? Its probably one of those washer that can be only purchased in Canada...happy Canada Day by the way

Cheers
BeerCanuck

 

[bradsul]

...Bradsul a washer as flywheel? Its probably one of those washer that can be only purchased in Canada...happy Canada Day by the way

Same to you! Just got back from the city celebration and fireworks, lots of fun but no beer.

Flywheel probably isn't the correct term but it gives the fan lots of inertia and it seems to work better with the extra weight (though this may simply be because the magnet is up away from the coils in the fan hub).

 

[Stevorino]

I'm using a 5 v charger-- I'll take pictures and post them tomorrow night.

 

[mykayel]

It sounds like you are starting the fan and then putting the flask with stirbar on after its running; this won't work. You have to have the flask and stir bar there before you start the fan.

Instead of bulding a riohstat to control the speed of the fan, I just bought (had on hand) one of the multi-volatge power sources that you can get from walmart. I have to turn it on 3 clicks (up to 5 volts I think) before it will start spinning and then I can back down the speed.