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Running case fans on normal 110/120V AC power?

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May 26, 2006 9:55:52 PM

What is the easiest way to run this:



on this:




I want to adapt some super quiet 120mm case fans to exaust heat from an entertainment system cabinet. Any ideas? Looking for the cheapest and easiest way. Thanks.
May 27, 2006 1:30:40 AM

The easiest:

With a 120VAC to 12VDC transformer. However, the fan will run at full speed at all times.

But, why may I ask????
May 27, 2006 2:03:10 AM

Quote:


But, why may I ask????


I think you missed the last line of my post. I have a few fans lying around and I want to exhaust the heat from an enclosed A/V home theater cabinet. With all the amps and the DirecTV HD receiver in there it gets really hot.
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May 27, 2006 2:42:14 AM

First, presuming this cabinet is presently, only passively cooled, a mere one fan at low RPM will do a lot- don't go thinking that you need multiple fans or full speed because odds are good that you don't unless you room temp is quite high and then for the inhabitants, an air-conditioner is a better plan.

The easiest way is to grab some wall-wart, but therein lies the details. Suppose you grab a common 12V, 500mA unregulated wart. You most likely to not need to put 500mA into fans to cool this, so the warts are essentially going to be floating high(er voltage than 12.0V). There are formulas one can use to try and predict the exact resultant voltage once they have the other variables resolved, but some are only resolvable in use, for example the true transformer output as they are not what you'd call "high precision" devices, are subject to a few percent deviation from the labeled rating.

Anyway, the best way to go is use the largest diameter and thickest fan possible and reduce it's RPM as much as possible. Put the fan opposite the exhaust path and control the exhaust such that it passes by all components.

Then the strategy is to control current, not voltage, because a voltage control (and therefore only indirect current control) can cause pulsating as each winding on the fan motor is energized in turn and the sudden current surge causes a sudden torque increase, which is also bad for the bearings over the long-term.

Since we can't yet know just how slow the fan(s) can run and remain sufficient to cool this, I can only give you a ballpark estimate, or an example if you will...

If you had a 12V 500mA DC wall wart, and a 0.12A fan (as labeled, actual amperage used can vary from the label depending on methodology to attain the rating), you might want to put about 68 Ohm 2W (for more heat margin than 1W) power resistor in series with the positive fan lead. An LM317 or similar IC regulator in current-limiting mode would also work, but need a limited output filter cap size and frankly the additional 30 cents cost and even the trivial additional complexity is entirely unnecessary, only makes sense if one had a drawer full of regulators but no power resistors on hand.

You could just try a lower voltge wall wart instead, possibly a 5V wart would be a good match (keeping in mind that it too, if rated at higher current than the fan's rating (give or take) will be at a higher voltage. You could use a regulated switching wart instead, but unless your only goal were to run the fan at as close to 12.0V as reasonably possible, the detractions outweigh the benefits... unless as above, you happened to have them on hand already but nothing else. Then again, a 12V 500mA unregulated wall wart can be had online for about $3.

Keep in mind that the supply should be kept away from the other audio/data cables.
May 27, 2006 2:50:58 AM

Also, throw away the junk Masscool fan and use a decent make and model. For the cost of a fan on a device(s) meant to last several years or even decades, it's just not worth it to use a crap fan then have to replace it again every few years.
a b K Overclocking
May 27, 2006 4:23:51 AM

get a kit like this... just to take the power supply :) 


No joke....then if ure amp has a switched outlet u can plug it in and boom...good to go...
December 30, 2012 10:45:51 PM

I found it funny someone said use a 120VAC to 12VDC transformer. It's funny for me because there is no such thing. That would be a power suppler or DV converter. An inverter transforms DC into AC. A transformer could turn 120VAC into 12VAC but not DC. I got a good laugh out of this.

What you would need is a 12VDC wall wart power supply that is rated for 0.5A. You can get a little adapter to convert the plug on the power supply to fit into a computer 12V fan. A 120mm fan would be quiter than an 80 or 92mm one. You can also use a speed controller as well to quiet things down.
May 21, 2013 8:30:46 AM

I know this is an old thread, but I found it in my search to repair an old slide projector whose fan would no longer turn and it might help another DIYer solve a problem with cooling. I could find no replacement parts for my old projector, an Argus 300 from the 50's. The available fans were too big and too expensive, so AC fans were not the answer. After researching computer case fans I felt this might be the answer if I could find a way to run it off the household AC of the projector. Aha, found info on bridge rectifiers, this seemed like an answer. Straight to ebay and there were oodles of AC to DC converters available at many different outputs, 5, 12, 24 volts. The vendor even posted wiring photos of these bare-bones circuit board items, for under $10. I have purchased a couple of these, and some 60mm fans, so I will tear into the old projector when they arrive (May 2013). They are quite small 50mm x 30mm. If you care to hear of the results, send an email to albuquerque49@yahoo.com.
dwalden said:
What is the easiest way to run this:



on this:




I want to adapt some super quiet 120mm case fans to exaust heat from an entertainment system cabinet. Any ideas? Looking for the cheapest and easiest way. Thanks.


December 6, 2013 10:52:38 AM

gondo said:
I found it funny someone said use a 120VAC to 12VDC transformer. It's funny for me because there is no such thing. That would be a power suppler or DV converter. An inverter transforms DC into AC. A transformer could turn 120VAC into 12VAC but not DC. I got a good laugh out of this.

What you would need is a 12VDC wall wart power supply that is rated for 0.5A. You can get a little adapter to convert the plug on the power supply to fit into a computer 12V fan. A 120mm fan would be quiter than an 80 or 92mm one. You can also use a speed controller as well to quiet things down.


I'm looking to use this fan: http://www.newark.com/multicomp/mc33868/axial-fan-120-m...|pcrid|33270855741|plid|&CMP=KNC-BPLA

With some way of adjusting the speed AND hook it up to 120v...

I'm building a fume cabinet and I want to use this fan to suck the fumes and particles out of the cabinet.....The adjustable speed would allow me to adjust the fan as needed for the hood in case it affects the results inside the cabinet....

Can you point me to the "speed adjuster" ?? Is that just a potentiometer? Is it something else?

Thanks!!
!