weak power supply for stir plate?

So I just finished making a diy stir plate and everything seems to work great other than the speed of the fan is very weak. The power supply specs are:

Input 100-240V, 0.2A Max
Output 12V, 500mA

I thought in all the research I read that 12V would have been plenty but I don't know that much about electronics. Could this be the cause of the slow speed?

Only thing set up between the supply and the fan is a 25ohm reostat and a rocker switch.

Thanks!

I bought one of these motor controls from ebay and a used 12V DC Wallwort power supply from Goodwill. IMO, it's a perfect speed control for <$15. 12V will result in a higher fan speed than needed for a starter.

http://www.ebay.com/itm/12V-40V-10A...988?pt=LH_DefaultDomain_2&hash=item4614549bf4

My questions was about my current power supply being too weak, not too strong. With my current set up it barely spins my fan at all and I'm not sure why because it says on the adapter that it is 12v.

Neat looking setup BTW!

STL_Lucas said:

....Only thing set up between the supply and the fan is a 25ohm reostat and a rocker switch.

Thanks!

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What voltage are you applying to the fan?

STL_Lucas said:

My questions was about my current power supply being too weak, not too strong. With my current set up it barely spins my fan at all and I'm not sure why because it says on the adapter that it is 12v.

Neat looking setup BTW!

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Do you have a meter to measure the voltage to the fan with and without the pot inline?

Are there multiple output wires on the power supply?

I tested the fan with the power supply directly before I hooked it up to the pot and it was the same speed. I don't have a meter to gauge the voltage. The Power supply has two wires and the fan has three. I belive the middle wire on the fan is not hooked up to anything and was not needed.

I just noticed the power supply says AC Adapter on it. Is this the problem? Should it say DC Adapter?

Depending on the fan .2A could be the problem. 12V is plenty, but that current rating may not be sufficient for the fan. Can you post a picture of the sticker that is over the motor housing of the fan?

Also, AC adapter is normal. It is an AC to DC converter. It converts 120V AC to 12V DC

Thats what I thought. I'll post a link for the fan.

12V AC Adapter


Primarily used to power up fans. Each adapter can power up to 4 of our fans.
&#8226;Input Voltage (nominal): 100-240VAC
&#8226;Input Current (max): 0.2A
&#8226;Output Power Rating: 6W
&#8226;Output Voltage: 12V
&#8226;Output Current: 500mA
&#8226;DC Output Connector: 2.5mm Barrel Plug
&#8226;DC Output Cord Length: ~5 feet
&#8226;1 year warranty


Link for the fan is:
http://www.microcenter.com/product/321891/80mm_Advance_Series_Case_Fan

That fan is rated for .24A. So that power supply isn't capable of fully powering that fan. Do you have an old wireless router or any other 12 volt power supplies laying around? That is what I use for mine. It provides 12V at 1.2A and works great. To test and see what the fan can really do you can hook it up to a computer. It will get the full voltage and amperage it wants then and you can compare that to what you get out of your little power supply.

I have another little power supply with all of the same specs but it's .3A. I assume this will work? I'd test it now but I'm at work I'll have to wait until I get home.

Yes, that should do it.

DC power supply, AC fan

Setesh said:

That fan is rated for .24A. So that power supply isn't capable of fully powering that fan. Do you have an old wireless router or any other 12 volt power supplies laying around? That is what I use for mine. It provides 12V at 1.2A and works great. To test and see what the fan can really do you can hook it up to a computer. It will get the full voltage and amperage it wants then and you can compare that to what you get out of your little power supply.

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Sorry for the ignorance, I'm trying to learn more about this stuff, but I'm pretty much a total noob.

How do you know the fan is rated for .24A? I don't see the amps listed in the link for the fan?

Also, can you breify explain which value you compare the fan's amps to on the power supply? I suppose it's the DC output current of the power supply, but I'm not 100% sure.

Pie_Man said:

Sorry for the ignorance, I'm trying to learn more about this stuff, but I'm pretty much a total noob.

How do you know the fan is rated for .24A? I don't see the amps listed in the link for the fan?

Also, can you breify explain which value you compare the fan's amps to on the power supply? I suppose it's the DC output current of the power supply, but I'm not 100% sure.

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No need to apologize. We are all ignorant in some areas and knowledgeable in others. That's why this and other forums are so effective.

The picture in your link shows the sticker off the back of the motor housing that I referenced earlier. It states the input voltage (12) and amperage (.24). Your power supply should be rated with the same number of volts and at least the same number of amps as your load. Your fan wants 12 volts to run, but it needs .24amps to get that voltage. Your power supply isn't capable of dishing that out. If you replace your current power supply with a 12v 1amp power supply your fan will take the 12 volts it wants at .24 amps. It will only take as many amps as it needs to get it's voltage. It's kind of hard to explain, but basically amperage is the force that pushes voltage through a load. You can have a power supply that is capable of more amps than necessary and it will not cause any problems. However this is NOT true of volts. Push too many volts through a load that isn't rated for it and the magic blue smoke will escape. Electrical devices run on magic blue smoke. Once the magic blue smoke escapes the device will never work again.

That power supply should be enough--the output rating at 12V is 500mA (0.5A). The fan requires 0.24A at 12V. But, as DaleHair asked, is the fan AC? If so, no amount of DC current is going to work. You'll need an AC power supply.

MaxStout said:

That power supply should be enough--the output rating at 12V is 500mA (0.5A). The fan requires 0.24A at 12V. But, as another poster asked, is the fan AC? If so, no amount of DC current is going to work. You'll need an AC power supply.

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:smack:
MaxStout is correct. I missread your initial post. I thought .2amps was your power supplies output. The fan wants 240ma (.24amp) which is < the 500ma (.50amp) that the power supply should put out so it should work just fine.
The fan he linked is a cooler master 80mm computer case fan and runs off of DC voltage. It should spin at ~1700 RPM which shouldn't feel anemic to you. They are not powerful fans by any means, but running free air they certainly spin fast.

Thank you both, I still learned something. I'm not the OP, just someone trying to learn from their misfortune

OK, looks like the fan is DC (I looked at the linked spec). Try bypassing that rheostat so that you're connected at full voltage. Does it spin OK? The spec stated the fan's voltage range of 10.8-13.3V. That's a pretty narrow range (most 12V computer fans I've seen work well down to 5 or 6V), but maybe that particular fan doesn't work well below 10.8V

The fan manufacturer spec's indicate 12vdc & 0.96w which calculates out to an 80mA current draw and about 150ohms of dc resistance. Not sure where the 240mA came from. A 500mA 12vdc power supply should spin it fine.

Do you have a multimeter to measure the voltage being applied to the fan? The rheostat may be wired incorrectly. Is it in series or parallel to the fan? It should be in series.

Theoretically, with the rheostat in series, you should have 10v to 12v to the fan for the 25 to 0 ohm swing of the rheostat. 10v may not produce a noticeable reduction of the rpm as compared to the 12v rpm.

Does turning the pot do anything to the speed? Are you sure you have hooked up the correct terminals on the pot?

your potentiometer (pot) should be wired as shown... using one side and center terminal on pot. (The on/off power switch can break either leg)

Components MUST match - both Fan and transformer output (Direct Current)

if AC, start over, get a light switch dimmer...

good luck!

Everything is hooked up correctly. I know this because the fan works the exact same through the pot and switch as it does straight to the power supply. I've tried two power supplies now both say output is 12V - 500mA and on was .2A and the other was .3A. The second power supply was actually purchased from an LED site (rapidled.com) that actually sells these to run pc fans as cooling units in light fixtures. I've had it hooked up to 2 smaller fans before that worked great. I think the issue must be the fan. For whatever reason the fan just isn't work. Any more ideas would be greatly appreciated but I just can't figure this out.

DaleHair said:

DC power supply, AC fan

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How can I tell if a fan is ac or dc? I'm guessing this is the problem since both power supplies aren't working strong enough and I know the 2nd one ran two other fans I've had.

STL_Lucas said:

How can I tell if a fan is ac or dc? I'm guessing this is the problem since both power supplies aren't working strong enough and I know the 2nd one ran two other fans I've had.

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It is DC.

1. It's a computer case fan, and they are all DC since everything in a PC except for the power supply itself runs on DC. AC fans are common for all types of enclosures and other uses, but never for PC use.

2. It should tell you on the fan itself on the sticker on the back of the motor housing.

3. If it was an AC fan it would not run at all when hooked up to your DC power supply.

Do you have any other fans in a computer you could borrow for a test? Are you anywhere near Edmond OK?

STL_Lucas said:

How can I tell if a fan is ac or dc? I'm guessing this is the problem since both power supplies aren't working strong enough and I know the 2nd one ran two other fans I've had.

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It should have a label on it, stating something like 12VDC. Most computer fans are DC, just because the power supplies include taps at that voltage. But low-voltage AC fans are not unheard of.

Find another fan. They are dirt cheap. You can even get them for around $5 on Amazon.

I don't have another fan on hand I can try but I'll pick another one up just to be sure. Also I've read ten times that the middle wire on the fan is useless and not needed. Is leaving this out of the equation part of the problem? Should it be added to either end of the power supply?

STL_Lucas said:

Also I've read ten times that the middle wire on the fan is useless and not needed. Is leaving this out of the equation part of the problem? Should it be added to either end of the power supply?

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On a 3 pin fan you have:

Red = 12V power
Black = Ground
Yellow = Tachometer lead

The Red is the positive power lead, the Black is ground and connected to the negative pole, the yellow is not connected as it is merely for sensing the speed of the motor. sometimes you will have a white wire it serves the same purpose. A 4 pin fan has a different layout and a 4th wire for PWM, but yours is a 3 pin so that doesn't apply.

Ok so the way I have mine hooked up I have the Red to the hot wire, the yellow to the negative and the black is not hooked up. Could this be the issue with the fan running slow or should it not run at all like this? I'm going to swap out the yellow and black wire when I get home and try that.

STL_Lucas said:

Ok so the way I have mine hooked up I have the Red to the hot wire, the yellow to the negative and the black is not hooked up. Could this be the issue with the fan running slow or should it not run at all like this? I'm going to swap out the yellow and black wire when I get home and try that.

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Yes. The Red is the positive, the black is the negative, and the yellow is the sense wire, or at least it should be. I've never seen a case fan wired any other way except that sometimes you will see a white sense wire instead of yellow. One option is pealing up the sticker on the back of the motor housing until you can see the wires themselves soldered onto the board and look at the +/- symbols next to the cables. If these symbols are there it proves which wire is which.

OK, here you go:



Look at the plug you cut off your fan. Orient the connector in the same way this one is, with the little ridges pointed towards you. The wire on the left is negative, the middle wire is positive, the wire on the right is the tachometer/sense wire and should have no connection in your setup, just ignore it completely. Now you know what color is what. Hook up the wire that is the same color as the wire on the left in the plug to negative and the wire that is the same color as the wire in the middle of that plug to positive. Your fan should now function correctly.

Thanks I'll let you know as soon as I try this out tonight! I just got an email that my stir bar delivered so hopefully it works and I can test it out! Thanks again for the help.

That did the trick. The stir plate is up and running and after using the black wire and removing the yellow wire from the equation it's running much faster and holds a vortex in the flask. Last question is, is there any danger letting this thing run when I'm not home with any wires touching or anything happening. After running for a couple hours there is a white powdery like film coating the inside of the project box and the fan and I'm not sure why. It looks like some of my super glue from putting a small piece of pvc on my fan may have sprayed around the box a little but any ideas what could cause this coating in the box? I'm going to let it run overnight and check on it again in the morning just wondering what kind of risk there is with this type of a project. Thanks everyone for your help with this!

STL_Lucas said:

That did the trick. The stir plate is up and running and after using the black wire and removing the yellow wire from the equation it's running much faster and holds a vortex in the flask. Last question is, is there any danger letting this thing run when I'm not home with any wires touching or anything happening.

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Nice! I'm glad that worked out! You should be fine with the safety aspect as long as you hooked everything up correctly and in a sound manner. You are dealing with 12VDC at .5A so you don't have a lot of power to cause issues here. That said, there is always a danger of electronics melting down and causing fires. An electrician is who you should seek for answers about the safety of anything electrical you have made before trusting it with your or your families lives. Soldering connections and using wire nuts wrapped in electrical tape instead of just twisting wires together and wrapping in tape are good first steps in making sound connections. Always build strain relief into your system as well. Make sure the cable is securely attached to the project box and not just attached to the components. You want any tugs on the cable to tug on the box, not the component connections. Again, you should get an electrician's opinion on anything you have created before using it.

The white stuff is probably dried cyanoacrylate (super glue). Whenever it dries it vaporizes, then the vapor settles on things nearby. You can place the glued components in front of a fan next time and the fan will carry the vapor away instead of it being deposited locally. Rubbing alcohol can remove it. A few months ago I glued the halves of a hamster ball together as it kept falling apart (yes, I left the door portion unglued). I had forgotten about the vapor problem. My daughter brought it in to me the next day and we could see all of the finger prints left on the inside of the ball since the vapor deposits brought them out. This technique is used by forensic scientists to get finger prints off of surfaces and was pretty neat to see in action.

Setesh said:

The white stuff is probably dried cyanoacrylate (super glue). Whenever it dries it vaporizes, then the vapor settles on things nearby. You can place the glued components in front of a fan next time and the fan will carry the vapor away instead of it being deposited locally. Rubbing alcohol can remove it. A few months ago I glued the halves of a hamster ball together as it kept falling apart (yes, I left the door portion unglued). I had forgotten about the vapor problem. My daughter brought it in to me the next day and we could see all of the finger prints left on the inside of the ball since the vapor deposits brought them out. This technique is used by forensic scientists to get finger prints off of surfaces and was pretty neat to see in action.

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This is exactly what I think it is. I could see my finger prints and all. Thanks for clearing this up and thank you for all your help. I really appreciate all of the feedback and thank you all again for taking the time to respond.

STL_Lucas said:

Thanks for clearing this up and thank you for all your help. I really appreciate all of the feedback and thank you all again for taking the time to respond.

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You are more than welcome. Building/rigging things for brewing is one of the things I find most fun about it. There is a feeling of satisfaction you get from making something yourself that just can't be had any other way. It makes the beer you produce that much more 'yours' than if everything was purchased from the store. At least that's how I feel about it.