Stir plate Help

Hello all, and Thank you in advance for your input, Now I know one does not need a large Vortex but I want to be able to achieve one and have been unable too, I am using a 120mm 12 Volt 0.36 amp fan and a 12 volt 1 amp power supply hooked directly too the fan. I am using a 2" magnetic stirbar and Four (4) 1/2" x 1/16" rare earth magnets double stacked in a row two sets North two sets South. No problem turning the bar But I hardly make a dimple in my 2000 ML Flask weather its filled half way or Full to the 2000 ML line. Id like to be able to create a larger vortex, Do I need Larger more powerful magnets or a fan with higher amperage etc. Awaiting your Kind replys. Thanks again.

it should work based on your set up. Make sure the fan is spinning and your getting the proper voltage to the fan. You may need to look at the speed control and make sure you have it set up properly as well. You can check it measuring the output voltage from the control to the fan. Marry Christmas And Happy New Year, Castermmt

Í will check the voltage as I am not using any speed control device.

The 120mm fans spin MUCH slower than the 80mm that most people use for making stir plates. If you decide to add speed control go with a 100 ohm potientometer, a lot of folks are using 25s and 50s but its my opinion with a 12 v power supply you may need the 100 ohm.

Wow, I went with 120mm Fan because of the Higher amperage , thought it would be better to spin the magnets, never thought they would have less RPM's, makes sense, as far as the potientometer for speed control I will look into your sugestion, although as far as my memory serves me Ohms should compare to the draw of Amperage not the voltage. I know a lot of folks go wrong with potientometer's by picking up 25K ohm or 50K ohm, which is a whole different animal then 25 ohm and 50 ohm. I thank you for your response and will experiment with it.

A .36 amp 120mm fan is probably spinning in the 2000-2500 RPM neighborhood, which I would think would be enough but who knows.

Let's say you buy this fan or a simular one:
http://www.newegg.com/Product/Product.aspx?Item=N82E16835119136

It draws .6 amps.

First let's find the resistance of the fan by using ohm's law R = V/I
12/.6 = 20 ohms.

Now let's assume you went with the 100 ohm potentiometer like this one:
http://www.amazon.com/dp/B002IABL6C/?tag=skimlinks_replacement-20

Now we can find the total resistance of the circuit with the potentiometer maxed out.
Total Resistnace = R1 + R2
In our case
100 ohms + 20 ohms = 120 ohms
So the total current for the circuit would be figured
I = V/R
12/120 = .1 amps
Now we can find the voltage drop across the 2, we need to make sure we can turn the voltage way down if you needed to in order to manage the speed of the fan. Using's Ohm's Law again.
V=IR
. 1 x 100 = 10 volts
.1 x 20 = 2 volts
I think 2 volts is plenty low enough.

A lot of guys use 6 volt power supply with a 25 ohm resistor.
Using the same fan
6/.6 = 10 ohms
25 ohms + 10 ohms = 35 ohms (our total resistance)
Total current
6/35 = .171 amps
Voltage Across the reistors
.171 x 25 ohms = 4.29 volts
.171 x 10 ohms = 1.71 volts (at the fan)

Actually now that I think about it here is a high speed 120mm fan that uses 4.8 amps:
http://www.newegg.com/Product/Product.aspx?Item=N82E16835706015

You'd still be able to get the voltage down to .3 volts with it.

Hopefully I did all that correctly, if I didn't maybe one of the egineers could please correct me.

Now thats what I call a Response, Thank you, You brought back fond memories of my late Father who was an Electrical egineer, I wish I had him to still go to, Many years ago I would have dreaded his response to such a question which would have been very similar to yours, Now I more then appreciate it. Thank you so much.

Upon checking the voltage today I get 11.79 volts with the meter, so power (voltage ) is there, The MFG. spec's on the fan state approx. 2000 RPM's so I will assume since I am running the fan direct to power sorce that it may not produce enough RPM's to create the Vortex I am looking to achieve so I will purchase another fan.

Thank you again.

estricklin said:

The 120mm fans spin MUCH slower than the 80mm that most people use for making stir plates.

Click to expand...

Some fans get slower w/ the magnets glued on as well. I have a similar setup and I can barley pull the vortex to the bottom of my 2L e-flask. Lucky me, I just got a 5L e-flask for x-mas so I need to rebuild mine...

Udate, I have purchased a fan with higher RPM's now waiting delivery, however I switched out the fan for an Identical one I had, I now get a vortex 3/4 the way down my 2000 ML Flask, still want a little more but it is acceptable, cant waite to see what the new fan I ordered will do.

To Zamial, whish i had a 5L Flask but I had to settle for a Gallon Wide mouth Glass Jar,

Good deal!

Purchased fan with following spec's: (Fan Diameter: 120 mm Bearing Type: Ball )
Max. Air Flow Volume: 120 CFM Brand: Adda
Max. Fan Speed: 3200 RPM Model: AD1212UB-F51
Power Connection: 2-Pin MPN: AD1212UB-F51
Size: 120mm x 25mm
12V 6.2V Minimum
0.70 Amp

its way too powerfull, I have to give it a good 7 volts for it too even start, Then when I crank it up past 8 volts it throughs the two inch stirbar, the 50 Ohmpotientometer I am am using only allows about 1/4" of travel from the halfway mark where it allows the fan to start to turn to where it throughs the stirbar. ( I have ordered a 100 ohm potientometer and am waiting on delevery) as For the magnets I am using two stacks of 1/2" x 1/16" round disc Rare earth magnets four high in each stack, whats the input too keep the stirbar in place, smaller stirbar? More magnets?
Thanks in advance.