Homemade magnetic stirrer power source question

Homebrew Talk - Beer, Wine, Mead, & Cider Brewing Discussion Forum

Help Support Homebrew Talk - Beer, Wine, Mead, & Cider Brewing Discussion Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

GreenDragon

Well-Known Member
Joined
Dec 27, 2010
Messages
430
Reaction score
5
Location
Wichita
So I have everything I need for my hand made magnetic stirrer except a way to power it. So far I've made everything from spare parts:

Magnets from some old hard drives (I have a ton of old drives)
Fan speed controller from an old zalman heatsink I used before switching to water cooling.
80mm and 120mm fans (I'm a computer geek if you couldn't tell).
Cigar box
Leftover Plexiglas from some window case mods I've done

So my question is, how do I power this thing? Someone mentioned using a phone charger? I have several old ones laying in my spare parts bin, how did you do rig it up?

Option 2: I have a few spare computer power supplies and I know how to short them on. I could just plug it into that using the default 4-pin molex connector the fans came with.

Anyone know of a method 3 I'm not aware of?

I'd prefer not to do #2 because I'm not sure its safe to run a power supply for 3 days by completing the circuit like that.

Thanks in advance!
 
Update: Looks as if I can get a 12 or 6v power supply from radio shack for $7. As cool as it would be to make it from all spare parts, I may buy the power supply to cut down on the fire haphazardness of this project :)
 
Cool, I'll see if my store can order me one too.

I can't get the hard drive magnets off their base plates. I used a really old 6gb quantum fireball drive thinking the magnet would be bigger. They are huge but really well glued to the base. Gonna soak them overnight in the wife's nail polish remover, lol.
 
Ha, the IT guy at work gave me a Samsung hard drive today that looked like it was fairly new. I got the magnets off of it pretty easily. Just make sure that Radio Shack power supply is compatible with the fan you are using. Seems like a heck of a deal to me, not to pass it up. The one I need that they have in stock at the store is $15 so I might as well let them order the cheaper one for this project.
 
I had a multi select power adaptor hanging around so I used it. It goes from 4v to 12v. It worked out great for me because my stir plate throws the bar at 12v even with the rheostat on the lowest setting. I run it between 6v and 9v depending on the size of the starter. 9v with full rheostat setting is like a washing machine. 10v throws the bar.
 
My solution may be too easy for you guys, but I've had excellent results powering my 12v 120mm case fan using an ordinary cheap rotary type light dimmer and a 12vdc wall wart. I mounted the dimmer switch in a surface mount electrical handy box alongside a standard duplex outlet. The dimmer controls the duplex outlet. I simply plug the wall wart into the receptacle and dial in the speed with the dimmer knob. Works like a champ with very good dynamic range control on the speed. Essentially, the dimmer is a PWM device. Here's a demo video so you can see it in action:

 
Last edited by a moderator:
Great video, thanks for the tips. I like the dimmer switch control, good idea. I was also looking at this since you can select the voltage you want but can't justify the price:

http://www.bestbuy.com/site/Hosa+Technology+-+Universal+Power+Adapter/8897027.p?id=1213399791824&skuId=8897027&st=power%20adapter&cp=2&lp=21

The dimmer works better as it has infinitely variable adjustment and it regulates the current instead of the voltage through a PWM arrangement. IME, the dimmer provides much more dynamic range in the speed control. That video was made using a 2" stir bar in a 2 liter flask. It will run fast, slow or anywhere in between.
 
Yeah, now I am thinking this might be the route I want to take for speed control. Thanks!

I predict that very soon, many others will follow suit. It's a very cheap solution with commonly available components and best of all, it works extremely well. Be sure to post back your results if you go this way. I think you will like it a lot.
 
My solution may be too easy for you guys, but I've had excellent results powering my 12v 120mm case fan using an ordinary cheap rotary type light dimmer and a 12vdc wall wart. I mounted the dimmer switch in a surface mount electrical handy box alongside a standard duplex outlet. The dimmer controls the duplex outlet. I simply plug the wall wart into the receptacle and dial in the speed with the dimmer knob. Works like a champ with very good dynamic range control on the speed. Essentially, the dimmer is a PWM device. Here's a demo video so you can see it in action:

http://www.youtube.com/watch?v=SmnPHQNwuFM

I do like that idea, got a pic of the wiring?
 
I do like that idea, got a pic of the wiring?

There really isn't much to the wiring. Here's a pic of the surface mount handy box. The dimmer is wired to control the duplex receptacle. The wall wart simply plugs into the receptacle. The fan is a 12v DC three wire version. The yellow wire is not used, so then it's just a matter of hooking up the other two wires to the wall wart. Hook it up and if the fan won't run, reverse the two wires to the wall wart. It's important that a 12v DC wall wort is used as the 12VAC versions won't work with the DC fan motor.

5499553570_7ab31bb282_z.jpg


5499553518_0764b179c0_z.jpg
 
If it were me, I would check out the voltages on your various cell phone chargers you have lying around and give those a whirl. I used a router power supply on mine.

Yeah I checked the ones I have and they are AC not DC. Most of the fans are DC unless you buy an AC fan.

CATT22,

So with your set up, it would be best to have a 12v wall wort so you have the full range of speed and control vs. using a 6v wall wort with a rheostat? Also, how much is an electrical box and dimmer switch set up like that cost. I'm not having much luck locating those on Lowes Website?
 
Yeah I checked the ones I have and they are AC not DC. Most of the fans are DC unless you buy an AC fan.

CATT22,

So with your set up, it would be best to have a 12v wall wort so you have the full range of speed and control vs. using a 6v wall wort with a rheostat? Also, how much is an electrical box and dimmer switch set up like that cost. I'm not having much luck locating those on Lowes Website?

Yes, I used a 12v 500 ma wall wort. The electrical box and cover cost was about $4 and the light dimmer about $6. Roughly $10 total cost. Typically, Lowes, Home Depot etc don't bother to list miscellaneous stuff like the electrical box and cover on their web sites, but these are common items that they always stock in the stores. Most any hardware store would also have them.
 
Its generally a bad idea to use dimmers with anything other than a conventional light bulb. They are not designed to drive the inductive load of the transformer in the "wall wort" power supply. I'm almost amazed it works at all, I can only assume its because the current is so low.

A PC power supply should work fine running for years even if its jumpered on. That is all the motherboard basically does to turn it on. As long as the built in fan is running its all good.

For speed control a simple potentiometer(pot) will work. I'm not sure what size would work best off the top of my head. I'm thinking around 1k would work good. They usually have 3 terminals, one is the wiper and the other two are the ends of the resistor. The wiper slides along the resistor to get different amounts of resistance. So all you need to do is connect one end of the resistor to 12v positive power and connect the wiper to the red wire of the fan(The black wire goes to negative or ground). As you turn the knob your moving the wiper, closer to the end with 12v and the resistance drops, the current goes up and the motor speed increases. Move the wiper away from the end that has power connected and the resistance goes up, decreasing current and the motor slows down.

The best way to control speed is with pulse width modulation(PWM). Your voltage(12V) and current(150mA typically) remain constant so you get the full torque of the motor. PWM works by switching the motor on and off at a high enough frequency that it appears to be running steady. Speed is controlled by ratio of on time to off time. So to get say 75% speed each pulse would be say on for 75ms and then off for 25ms repeating continuously. The simplest way to create these signals is using a micro-controller like an Atmel Atmega(aka. arduino). It can also be done with a 555 timer but the part count goes up a little.
 
Its generally a bad idea to use dimmers with anything other than a conventional light bulb. They are not designed to drive the inductive load of the transformer in the "wall wort" power supply. I'm almost amazed it works at all, I can only assume its because the current is so low.

A PC power supply should work fine running for years even if its jumpered on. That is all the motherboard basically does to turn it on. As long as the built in fan is running its all good.

For speed control a simple potentiometer(pot) will work. I'm not sure what size would work best off the top of my head. I'm thinking around 1k would work good. They usually have 3 terminals, one is the wiper and the other two are the ends of the resistor. The wiper slides along the resistor to get different amounts of resistance. So all you need to do is connect one end of the resistor to 12v positive power and connect the wiper to the red wire of the fan(The black wire goes to negative or ground). As you turn the knob your moving the wiper, closer to the end with 12v and the resistance drops, the current goes up and the motor speed increases. Move the wiper away from the end that has power connected and the resistance goes up, decreasing current and the motor slows down.

The best way to control speed is with pulse width modulation(PWM). Your voltage(12V) and current(150mA typically) remain constant so you get the full torque of the motor. PWM works by switching the motor on and off at a high enough frequency that it appears to be running steady. Speed is controlled by ratio of on time to off time. So to get say 75% speed each pulse would be say on for 75ms and then off for 25ms repeating continuously. The simplest way to create these signals is using a micro-controller like an Atmel Atmega(aka. arduino). It can also be done with a 555 timer but the part count goes up a little.

Nonsense. The light dimmer works just fine and actually much better than anything else I have seen. While the dimmers are not specifically designed for this type of application, no damage will occur to the dimmer, the wall wart or the fan motor. There is absolutely no overheating problem or any other problem that I can detect. BTW, the light dimmer is a PWM device.
 
BTW, the light dimmer is a PWM device.

I was under the impression most standard light switch dimmers were essentially pots. There are however some called thyresistors or something like that, which work more like PWM. I guess it depends on what kinds of light switch dimmer you got.
 
I was under the impression most standard light switch dimmers were essentially pots. There are however some called thyresistors or something like that, which work more like PWM. I guess it depends on what kinds of light switch dimmer you got.

The older (much older) light dimmers were resistance based units. The modern versions are electronic devices which do work much the same as a PWM device. IOW, they switch on and off very rapidly and the frequency of the on/off cycle is infinitely adjustable with the control knob. The electronic dimmers do not heat up when in use like the older versions did. Much less energy wasted with the newer ones. I've found that the cheapest and commonly available electronic dimmers work just fine. This is the one that I've been using:

http://www.doitbest.com/Electrical+...+Co-model-DB1-700-00I-doitbest-sku-510971.dib

http://home.howstuffworks.com/dimmer-switch2.htm
 
Back
Top