Which wire goes where?

[de5m0mike]

I'm trying to build a stir plate and can't figure out the wiring. If I touch the + & - wires from my power source (a 9v cell phone charger) to my fan (a 12v computer fan, the fan powers up, but I can't figure out the prongs on the back of the control knob.

Here is the control I have.

500K Ohm Volume Control with Push Switch - RadioShack.com

I have a voltage meter but not much knowledge on how to use it. All I know is if I set the meter to ohm and touch the top two, the dial on the meter goes up and down as I turn the knob. There are also three other prongs on the back. One on each of the three remaining sides. If looking at it from the back the one on the left is numbered 2, the bottom (opposite the two prongs) is 1 and the one on the right is 3. Touching the meter to the 1 and 3 gives a reading on the dial when it's on and no reading when it's off. Did I mention that pressing the dial like a button turns it on and off. Can anyone help me out?

 

[de5m0mike]

Here is a pic of the fan. It's attached to the bottom of the cigar box.

Here is the back of the volume control push switch I was trying to describe. I figure it might make more sense with a photo.

 

[Andrewjl]

Use the a positive lead from the power source to pin 1 and then a lead from pin 3 to the positive of the fan.

 

[Andrewjl]

that is, if you connect the multimeter to the pin 1 and pin 3 and when you turn the knob the ohm values change up and down.

EDIT: I think I read your original post wrong. hah, sorry. If the top two pins give you a up and down ohm value on the multimeter that's what you'll want to use to have one pin take the power input, (positive) and then the other pin out to your positive fan lead.

I'd just play around with it and see. That's what I'd do. Hopefully that helps.

 

[de5m0mike]

that is, if you connect the multimeter to the pin 1 and pin 3 and when you turn the knob the ohm values change up and down.

I just tried touching the multimeter to pin 1 (bottom) and 3 (right) and I get a reading but it does not change when I turn the dial.

 

[de5m0mike]

EDIT: I think I read your original post wrong. hah, sorry. If the top two pins give you a up and down ohm value on the multimeter that's what you'll want to use to have one pin take the power input, (positive) and then the other pin out to your positive fan lead.

I'd just play around with it and see. That's what I'd do. Hopefully that helps.

I see you edited your post while I was typing. Yes, touching the top two and turning the dial does adjust the ohm value on the multimeter. If I connect the two positives here, where do the negatives go?

 

[Hang Glider]

straight to the motor. You're only controlling one "leg" - like switches do.

 

[de5m0mike]

I just attached positive from power supply (black with white stripe wire) to top left pin, and the positive from the fan (red wire) to the top right pin. When touching the negative from fan directly to negative of power supply the fan kicks on. Turning the knob does not adjust the fan speed and pushing the knob does not turn it on or off. It was interesting that the knob had to be turned all the way up for the fan to go on though. Turning the knob down, even slightly, turns the fan off.

 

[de5m0mike]

With the positives still attached to the top two, if I touch the negatives to pin 1 (bottom) and pin 3 (right) the fan turns on and off when pushing the button but still does not adjust speed when turning the dial. It only works when the dial is fully on.

 

[de5m0mike]

Ok, further testing show that turning the knob does adjust speed, the only problem is it is an extremely fine adjustment, and almost unnoticeable. Imagine if you turn the knob clockwise from left to right, you can feel that there are about 30 small clicks before it stops. Only the last two clicks do anything. I have fast and slightly faster. No more range across the rest of the dial. Could this be because my power supply is 9v and the fan is 12v?

 

[Hang Glider]

more than likely the design of the knob portion of your set up. It is a potentiometer, a variable resistor. They come in many different resistances, and yours has too much resistance for the current to get through.

I am not an electrician, so I cannot make a recommendation, but you may need to hit the Radio Shack for a different size (resistance, not physical size). Perhaps a volume control knob would work better? (voltage on speakers is quite low)...

I suggest you wait for someone else more knowledgeable to chime in with a specific requirement

 

[Andrewjl]

the ohm rating is a little high for that voltage. Something around 25-50 ohm would be better

 

[de5m0mike]

Thanks for the help on this guys.

I liked this one because it had the on/off built in, and they guy at Radio Shack told me it would work. I could kind of tell they weren't staffing the same kind of expertise they use to though... Anyway, would it work better with a larger power supply, or would I still need to get a new potentiometer? Also, am I loosing any top speed on the fan by having a 9 volt power supply vs. the 12 volt?

 

[Andrewjl]

Yea you are loosing the top potential speed of the fan , but all you technically need is just a little dimple in the starter for mixing and aeration. In fact this morning I had to jack my 12 volt power supply for my home made stir plate for something else, and put in place a 9 volt power supply. I still have a 1 inch dimple in the vortex.

I guess you could put a higher voltage power supply on there but you'd risk over powering it if you start at the lower resistance setting of the pot or go too far turning it at some point.

 

[Jwood]

A 500 KOhm potentiometer is way, way, way too much for this application. You need to go down to like 25 Ohms (yes 25, not 25K) to get any sort of variability. Right now i bet you are just able to basically turn the fan on and off with a nudge of the potentiometer.

Radioshack 25 Ohm, 3 Watt Potentiometer (Rheostat) is what you need.

 

[de5m0mike]

Sounds good. I'll stick with 9 volt power supply for now and swap out the potentiometer.

 

[de5m0mike]

Picked up this one yesterday, and just installed it. Seems to work well. I still need to get a stir bar before I can actually test it out though.

25-Ohm 3-Watt Rheostat - RadioShack.com

 

[Huaco]

I am planning to build one of these... I picked up some parts from RS the other day... I hope I got the right things.