Slowing down a stir plate

[JimRausch]

Hey Folks,
Did a search but didn't see the info I need.
I built a homemade stirplate from a used computer fan and cellphone charger. It works, but is way too fast- throws the stirbar.
I figure I need a rheostat, but my local radioshack is nothing but a cellphone sales store, and has no spare parts, and no one who knows anything electrical. Went to an electrician buddy who replaced my 12V charger with a 6V one, but it's still too fast. Went to a local hobby shop thinking that the model train section might have something, but no dice.
So, what now? And if I do get ideas where to go, what specifically am I looking for?
Thanks!

 

[KOamps]

If you can solder, build a variable voltage regulator like the schematic at the bottom of this page: http://www.stirstarters.com/instructions.html

Should be able to get the parts at the local radio shack. If not, tayda electronics is nice and cheap.

 

[johnnysoj]

You'll need one of these (LM317T)
http://www.radioshack.com/product/index.jsp?productId=2062601

And a 5k potentiometer:
http://www.radioshack.com/product/i...89&filterName=Type&filterValue=Potentiometers

When I built mine, I didn't use the LM317T voltage reg, and only used a potentiometer, but I don't have a fine enough control over the fan.

 

[CliffMongoloid]

can you increase the distance between the stirbar and magnet?

That might slow it down enough to catch

 

[kevinb]

If you can solder, build a variable voltage regulator like the schematic at the bottom of this page: http://www.stirstarters.com/instructions.html

Should be able to get the parts at the local radio shack. If not, tayda electronics is nice and cheap.

+1 on this. I built mine using this. It works like a champ.

 

[Mobeers]

I had the same problem that you did. I have a potentiometer inline and raised my flask above the stirplate to increase the distance and get a power reduction to no avail. Last week I added a 47 ohm resistor after the potentiometer and it now works perfect. I tried to other resistors with the 47 ohm ( I think this is what it is, it's out side) being the best. It was simple to solder and I should've done it along time ago. Good luck!

 

[neo71665]

http://m.harborfreight.com/router-speed-control-43060.html?utm_referrer=direct/not provided


I built mine using a fan switch in a rat shack project box.

 

[brawny]

I built a stir plate without the volt reg and resistor. It works OK but like others, it sometimes throws the stir bar. Tonight I decided I would take it to the next step and add the LM317 and a 330 Ohm resistor. I really do not understand the diagram listed in this thread.

Should the LM317 have the middle post going to the Rheostat, with the tab facing away, the post on the left is from the power source and the post on the right is to the fan?

What about the 2nd post on the Rheostat? Does it connect to the fan? Thats where I am lost.

Electronics are not my thing.. As I sit here and type, I am thinking I should have bought a stirplate..

Thanks,
Mike

 

[Sbarnard80]

I was on a mission to only use free stuff from the house and found that a spare Christmas light bulb draws just enough power to slow mine down. Perfect funnel now and a cool lighted stir plate as a bonus.

 

[raouliii]

I built a stir plate without the volt reg and resistor. It works OK but like others, it sometimes throws the stir bar. Tonight I decided I would take it to the next step and add the LM317 and a 330 Ohm resistor. I really do not understand the diagram listed in this thread.

Should the LM317 have the middle post going to the Rheostat, with the tab facing away, the post on the left is from the power source and the post on the right is to the fan?

What about the 2nd post on the Rheostat? Does it connect to the fan? Thats where I am lost.

Electronics are not my thing.. As I sit here and type, I am thinking I should have bought a stirplate..

Thanks,
Mike

Here is an image of the LM317 pin designations. This view is from the label side, not the tab/metallic side.

http://4.bp.blogspot.com/-LhiYdu_H0Lw/TqDdhxxNSZI/AAAAAAAAAjw/YE20_Z95tH0/s1600/LM317.jpg
The left tab is ADJ. The center tab is Vout. The right tab is Vin.

As for the diagram linked above at stirstarters.com, the entire bottom line represents ground, wherein the negative terminal of the power source, one lead of the capacitor, one lead of the potentiometer/"rheostat" and the negative wire of the fan are all connected together.

A potentiometer or rheostat usually has three terminals. The two side terminals simply have the fixed resistance between them while the middle is the wiper. This application of the potentiometer is as a variable resistor wherein the wiper is used with only one of the side terminals. The side terminal you choose will effect how it controls the fan speed in whether a clockwise turn of the potentiometer creates an increase or a decrease in the speed. It is common practice to directly connect the unused side terminal to the wiper terminal in this configuration like the B example of this image. http://www.nzart.org.nz/assets/exam/sg/images-sg/resistors.gif

 

[whoaru99]

There are inexpensive PWM speed controls around. That's what I use and is the ticket...

A 5A or 10A is way more than you need for a stir plate but that's about as small as they routinely come.

 

[brawny]

Here is an image of the LM317 pin designations. This view is from the label side, not the tab/metallic side.

http://4.bp.blogspot.com/-LhiYdu_H0Lw/TqDdhxxNSZI/AAAAAAAAAjw/YE20_Z95tH0/s1600/LM317.jpg
The left tab is ADJ. The center tab is Vout. The right tab is Vin.

As for the diagram linked above at stirstarters.com, the entire bottom line represents ground, wherein the negative terminal of the power source, one lead of the capacitor, one lead of the potentiometer/"rheostat" and the negative wire of the fan are all connected together.

Thanks so much! I guess I am missing the capacitor. I will stop by RS tomorrow and pick one up.. Hopefully, I will have this working.. Again, I appreciate your help on this!!!

 

[estricklin]

I made a detailed post explaining in detail the numbers behind this, it may help you, just some food for thought.

https://www.homebrewtalk.com/f51/stir-plate-help-376276/

 

[raouliii]

I made a detailed post explaining in detail the numbers behind this, it may help you, just some food for thought.

https://www.homebrewtalk.com/f51/stir-plate-help-376276/

That discussion was centered around using a voltage divider to adjust the voltage applied to the fan.

This thread has centered around building a variable voltage regulator circuit that, imo, is a better option. It doesn't have the resistor heat dissipation requirements that a voltage divider does and can be designed with more controllable parameters. In fact, the circuit can be modified fairly easily to establish a min and max voltage that works with a given stirplate to minimize the unusable portion of the potentiometer.

BTW, estricklin, your second post to that thread has some flaws in the discussion concerning the 6volt power supply use. The fan will not change its resistance when a different voltage is applied.

 

[brawny]

Thanks so much! I guess I am missing the capacitor. I will stop by RS tomorrow and pick one up.. Hopefully, I will have this working.. Again, I appreciate your help on this!!!

Added the capacitor and totally rewired. It is now working like a champ.. Thanks again for the explanation!

Mike

 

[brawny]

Added the capacitor and totally rewired. It is now working like a champ.. Thanks again for the explanation!

Mike

Also added this diagram to help those like me that have no electronics BG..

 

[fathersergius]

Also added this diagram to help those like me that have no electronics BG..

Brawny, are you sure the leads are correct on the potentiometer? I made a stir plate of the same design and I soldered the wire from the switch to the far right on the potentiometer. That is, from the Earth on the switch to the far right on the potentiometer as it's positioned in your diagram and the stir plate works.

Please let me know what you think as I don't know too much about electronics.

 

[masonsjax]

I power my fan with a cell phone charger wired through a home light dimmer switch and an old PC power cord. It works great.

 

[brawny]

Brawny, are you sure the leads are correct on the potentiometer? I made a stir plate of the same design and I soldered the wire from the switch to the far right on the potentiometer. That is, from the Earth on the switch to the far right on the potentiometer as it's positioned in your diagram and the stir plate works.

Please let me know what you think as I don't know too much about electronics.

One lead will slow it down one way and the other will slow it down the opposite way. So, if you connect to one side, it will slow it down turning the switch counter-clockwise and if you connect it to the other side, it will slow it down turning it clockwise.