ac vs dc power in stir plate

I'm building a stir plate. I used a hd magnet and an 80mm fan, but it just tosses my stir bar around without spinning it. I think it's because the fan spins too fast. I have it hooked up to a potentiometer, but although it's a 12v dc fan, the only power supply I have around is a 5v AC.

Am I correct that this puts out more power than a DC transformer? Any solution other than to buy a 6v dc power source?

I heard someone mention using a dimmer switch. Would that work with such low voltage?

Thanks for the advice, guys. Stir plate is turning out to be a bit of an adventure.

DC != AC power...

Seems the best would be a variable DC supply. Then you can tune the voltage
to the spin speed you want.http://www.voltage-converter-transformers.com/switching-ac-dc-supply.html

Enjoy.

If you're asking this question, just go to stirstarters and get the lifetime warrantied one from him. NO offense, just saying. AC and DC are different types of voltage. Direct Current and Alternating Current. Basicaly constantly on and on/off in a duty cycle. If you have a wall wort that out puts in AC, you need a fan that is AC or a circuit with a converter. Most wall worts put out DC. You'll want a 12Vdc one for your stir plate.

IrregularPulse said:

If you're asking this question, just go to stirstarters and get the lifetime warrantied one from him. NO offense, just saying.

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Really? This is a DIY forum where people are theoretically encouraged to ask questions...even if they're beginners. Everybody has to start somewhere.

Dgonza9 said:

I'm building a stir plate. I used a hd magnet and an 80mm fan, but it just tosses my stir bar around without spinning it. I think it's because the fan spins too fast. I have it hooked up to a potentiometer, but although it's a 12v dc fan, the only power supply I have around is a 5v AC.

Click to expand...

First thing...they make a good point. The AC power supply outputs something drastically different from the DC power supply. While the DC supply outputs a relatively constant 5V, an AC supply rated at 5V will be putting out a voltage that goes between -5V and 5V (or square root of something over something times 5 and -5 depending on how it's actually rated) 60 times per second (or more or less again depending on the supply you have). Either way, I'm really surprised that the computer fan actually worked well at all with an AC supply.

You should definitely find yourself a DC supply that outputs a voltage in the range you want. If you could post pics, a wiring diagram that you used or links to the pattern that you're following...maybe we could be of more help.

IrregularPulse said:

If you're asking this question, just go to stirstarters and get the lifetime warrantied one from him. NO offense, just saying. AC and DC are different types of voltage. Direct Current and Alternating Current. Basicaly constantly on and on/off in a duty cycle. If you have a wall wort that out puts in AC, you need a fan that is AC or a circuit with a converter. Most wall worts put out DC. You'll want a 12Vdc one for your stir plate.

Click to expand...

I'm glad you made this reply. I am an english teacher and it's pretty unfortunate for education that no one thinks making mistakes and questions are the best opportunity to learn. They are.
Check out this book... If you want to do it yourself and you are not in the field, you basically either agree to deal with any mistakes you make and learn from them, or like the rest of society you throw away anything that breaks and buy a new one. I personally enjoy figuring things out with no background in the area and with help from the community.

I encourage anyone to try the same, as long as what you are attempting is not life threatening. Here's the book. I think a lot of people on this board would like it.

http://www.google.com/imgres?imgurl=http://www.treehugger.com/made-by-hand.jpg&imgrefurl=http://www.treehugger.com/files/2010/03/made-by-hand-searching-for-meaning-in-a-throw-away-world-book-review.php&usg=__LRQQwaZDBbv7Dz4JjgEnCrc2O2o=&h=400&w=468&sz=131&hl=en&start=14&sig2=WzOmp5UhtF6lyekKLeqZQA&zoom=1&tbnid=mp1NqmEm6TdeJM:&tbnh=145&tbnw=176&ei=I1OTTIHiLM2nnQeW6oWyCA&prev=/images%3Fq%3Dmade%2Bby%2Bhand%26hl%3Den%26biw%3D1024%26bih%3D609%26gbv%3D2%26tbs%3Disch:10%2C495&itbs=1&iact=rc&dur=561&oei=HlOTTKjZG42OnwfUubTBBw&esq=2&page=2&ndsp=15&ved=1t:429,r:10,s:14&tx=101&ty=70&biw=1024&bih=609

Anyone on here use a dimmer switch. I read a post a while back suggesting this would work.

Dgonza9 said:

Anyone on here use a dimmer switch. I read a post a while back suggesting this would work.

Click to expand...

I use a dimmer switch, but the stir plate I built has a 110 v AC muffin fan. The electronic dimmers will only work when using AC.

Using an electronic light dimmer to control the speed on an AC motor is not technically the proper way to do it, but it does work. I've been running my stir plate this way for several years without issues. I used two 1/4" X 3/4" rare earth magnets and a 5/16" x 2" stir bar.





The light bulb is wired in series with the dimmer and functions as a resistor to reduce the voltage supplied to the fan. This tames it down considerably and improves speed control. I've built about 20 of these for my brewing buddies.

Jesus, I didn't mean to discourage anyone from learning. Just saying stirstarters makes a quality product for $42 that has a lifetime replacement warranty. If your asking questions like that you're obviously unfamiliar with electricity and will likely burn out enough stuff to make it not cost effective in the long run. I'm all for DIY and learning as you go.
The first thing you need to do is decide if you want to replace your wall wort or your fan because they're not compatible with each other. I'd recommend the wall wort because everyone has them laying around from old cellphones ect. Just fine one with a 12-24 volt DC output. Then check out the stirstarters website. Click on the DIY tab and he shows the parts and ckt he uses. I just completed mine last week using that circuit as have many others.

Catt22 - Very Mad Scientist feel to your stir plate. I dig.

Only reason I built mine was because I had fans and hard drive magnets and wall worts and most of the electronics components laying around since I'm in the electronics and PC fields.

IP,

I second the suggestion to just buy a stir plate from one of the vendors. You cannot beat their pricing and especially so considering you get a warranty to boot. I have an inside low cost connection for the fan motors and the acrylic platform, but even with that advantage, the components for mine still cost more than what the vendors are charging for theirs. I'm not in the stir plate business and don't want to be.

IrregularPulse said:

Jesus, I didn't mean to discourage anyone from learning. Just saying stirstarters makes a quality product for $42 that has a lifetime replacement warranty. If your asking questions like that you're obviously unfamiliar with electricity and will likely burn out enough stuff to make it not cost effective in the long run. I'm all for DIY and learning as you go.
The first thing you need to do is decide if you want to replace your wall wort or your fan because they're not compatible with each other. I'd recommend the wall wort because everyone has them laying around from old cellphones ect. Just fine one with a 12-24 volt DC output. Then check out the stirstarters website. Click on the DIY tab and he shows the parts and ckt he uses. I just completed mine last week using that circuit as have many others.

Catt22 - Very Mad Scientist feel to your stir plate. I dig.

Only reason I built mine was because I had fans and hard drive magnets and wall worts and most of the electronics components laying around since I'm in the electronics and PC fields.

Click to expand...

I hear ya. Sorry I misinterpreted your reponse. I actually had all the parts laying around from an old hard drive and whatnot. I found a dc power transformer, but at 12v it seems to spin too fast throwing my stir bar around, even with the potentiometer. I'm going to play around with it and search the forums a bit more.

Anyway, thanks for the suggestions. Enjoy your weekend.

If you have a goodwill or other thrift store nearby you can probably find a old cell phone charger for a couple $ . Alternatively, the variable voltage wall wart I used for mine gives me satisfactory control without having to get into wiring anything.

Dgonza9 said:

I hear ya. Sorry I misinterpreted your reponse. I actually had all the parts laying around from an old hard drive and whatnot. I found a dc power transformer, but at 12v it seems to spin too fast throwing my stir bar around, even with the potentiometer. I'm going to play around with it and search the forums a bit more.

Anyway, thanks for the suggestions. Enjoy your weekend.

Click to expand...

What size is your pot? You can buy a smaller one, or throw a resistor across the two legs you're adjusting between to drop it to a finer adjustment. For example, stirstarters.com uses a 2000ohm, radio shack had 2500. I bought that and and used a resistor (don't recall value) to bring it down to a smoother adjusting range.

Dgonza9 said:

I'm glad you made this reply. I am an english teacher and it's pretty unfortunate for education that no one thinks making mistakes and questions are the best opportunity to learn. They are.

Click to expand...

I agree with that for a lot of things but making mistakes with electricity could have fatal consequences.

How are you wiring in the potentiometer?

I use a 15v DC transformer...

There are 3 legs on the "pot" I applied the ground (-) to one, 15v power (+) to the other and the 3rd leg transfered power to the fan.

the 2 outer legs are the positive and negative... then use the middle leg to carry the power to the fan.

Put a meter on the ground and middle leg... with power to the fan you should see your voltage vary from 0v to 15v (15v being my case).

No need for resistors or other parts... just a potentiometer, a switch, a fan and something to put it all in.



Hope this helps.

mmurray said:

How are you wiring in the potentiometer?

I use a 15v DC transformer...

There are 3 legs on the "pot" I applied the ground (-) to one, 15v power (+) to the other and the 3rd leg transfered power to the fan.

the 2 outer legs are the positive and negative... then use the middle leg to carry the power to the fan.

Put a meter on the ground and middle leg... with power to the fan you should see your voltage vary from 0v to 15v (15v being my case).

No need for resistors or other parts... just a potentiometer, a switch, a fan and something to put it all in.

Hope this helps.

Click to expand...

He needs a resistor if the pot he already has is too large. If it goes from nothing to full blast with the tiniest turn of the knob, it's too large.

Here's how I have mine wired.

Black wire to switch to center of the pot. Blk wire out top leg of pot to blk wire on fan.

Black and white wire of power source to red wire of fan.

Bottom leg of pot empty.

When I measure voltage I get 12v with pot turned up all the way, 10v with it turned down all the way.

Here's the potentiometer I used:

25 ohm 3 watt Rheostat (aka Potentiometer): Part number 271-265 - $3.99

I'd appreciate any advice. I didn't follow mmurray's wiring suggestion. It sounded like he suggested running both power wires to the two legs and then one wire from center to the fan. What about the second wire on the fan?

Here is how to wire this. As you can see in the picture above there are 3 legs on this pot.

the 2 outside legs are for your DC power lines... 1 ground and the other 12v power source. The positive on the fan hooks to the middle leg and then tie the fan ground into the other ground (it can tie in on the ground leg if you want as long as it is grounded)

Imagine... draw a straight line... on one end you have 0 volts on the other end you have 12v. Now imagine the middle leg moving across that line from one point (0v) to another point (12v) as that leg moves away from the 0v (you are turning the dial) the voltage increases and the fan starts turning... continue to the dial is on all the way and you will give the fan the full 12v. No need for resistors when you wire the pot correctly!

Dgonza9 said:

Here's how I have mine wired.

Black wire to switch to center of the pot. Blk wire out top leg of pot to blk wire on fan.

Black and white wire of power source to red wire of fan.

Bottom leg of pot empty.

When I measure voltage I get 12v with pot turned up all the way, 10v with it turned down all the way.

Here's the potentiometer I used:

25 ohm 3 watt Rheostat (aka Potentiometer): Part number 271-265 - $3.99

I'd appreciate any advice. I didn't follow mmurray's wiring suggestion. It sounded like he suggested running both power wires to the two legs and then one wire from center to the fan. What about the second wire on the fan?

Click to expand...

I used the same Pot from Radio Shack.

if you have little to no voltage drop on the pot then it's not wired correctly. Sorry to confuse you, but I meant to say the hot (red, usually) should be wired to the center lead on the pot and the ground (black, uaually) will be wired to the the ground (your choice... the ground on the pot, the switch, or where ever else you can find a ground)

So here is a closeup of my wiring. On the left is ground on the right is 15v hot and in the middle is the hot lead going to the fan. you will see a very small ground wire going to the left leg (the ground leg) and that is the ground for the fan.

Hope this clears things up.

Good Luck.

Sawdustguy said:

I agree with that for a lot of things but making mistakes with electricity could have fatal consequences.

Click to expand...

There is absolutely no possible way (outside of maybe tripping, falling and having the prongs gouge an artery somewhere) that a 12V wall wart is going to provide enough energy to be fatal unless he decides to open up the plastic housing (which would be really unlikely). I've taught electronics and controls labs to both high school students and undergrads and I have yet to lose a student to an accident with low-voltage DC power.

Yes, 120V and 240V power is dangerous. Even 48V DC can be dangerous. However 12V at 750mA is not dangerous, so don't try to scare him out of tinkering.

It looks like your pot is wired correctly. There are two types of pots out there in the world, audio potentiometers and the other kind. The audio pots have a different taper to them (logarithmic) which just means that if the middle pin is 0V turned all of the way down and 10V turned all of the way up, then it's not 5V in the middle. It's probably a lot better if you don't use one of the audio taper types (you want one with a linear taper...meaning that it would be 5V in the middle). If you have a log taper pot, you might be blowing through your usable range really quickly...and might not be able to fine tune the speed at all.

Many thanks for all the help. Here's the stir plate in action:


It was indeed wired incorrectly. Mmurray's diagram is 100% correct. When wired correctly you can use the potentiometer knob to completely stop the stir bar.

Looking forward to a rocking starter the next time I brew. Gotta wait for a fermenter spot to open up.

Thanks again, guys. I learned quite a bit from this little project and enjoyed it, though there was some cursing involved. Cheers!

Congrats! and Cheers! Glad I could help!