DIY power solution for case fans

[Muse]

I bought a pair of Cooler Master MegaFlow 200 - Sleeve Bearing 200mm Silent Fans in order to cool down my small (~80 square feet) bedroom in warm weather (evenings it's typically 10-12 degrees warmer in the bedroom than the outside temperature when I go to bed, in general in the low to mid-70's, sometimes higher). I made a screen for the window and a fiberboard panel that fits over the screen with cutouts for the two fans. I have the fans mounted so they draw cooler outside-air into the room. I think it's possible that it will be more efficient if I have one of those fans exhausting, don't know, but at least initially they will both draw air in. I'll have a switch next to my bed to turn them on/off.

I'm planning how I power these fans. They come with molex plugs and a molex to hook up to a PSU. I plan to have the fans in parallel and probably powered by one or two wall warts I have. Both of these wall warts are rated 12vdc, 500ma output.

The fans are rated 12vdc, current 0.16A, (Max 0.28 A), power consumption 3.36 W. I figure that one of these wall warts should do the job, but I know it's getting close to the spec, so I'm not sure and I don't know if it's a fire hazard or at least a strain on the wall wart.

I get different readings when I measure output with a digital multimeter:

wall wart 1 (on unit says input 12w): 17.13 vdc reading with multimeter, no load
wall wart 2 (on unit says input 12w, 0.1A): 19.40 vdc reading with multimeter, no load

Should I use wall wart 2? Is it probably "stronger" than wall wart 1? Or should I use one for each fan (more complex hookup), or get another power supply entirely?

I suppose it's possible to have the wall warts hooked up in parallel in the same way that the fans are so the supply would be 12vdc but the current draw would be across both wall warts giving a combined DC draw capacity of 500ma + 500ma = 1A. The total electricity usage would, I figure, be about the same. What do you think?

 

[dma0991]

If the wall wart doesn't provide a voltage similar or close to the fan's specs, it will shorten its lifespan or may cause the fan to just blow up when hooked together. If you're adamant of going with this method, get a cheap PSU that can supply its rated voltage.

As for the setup as a whole, its offers little improvement while being overly complex. I'd rather have this. It consumes more total power but it should perform better as well.

The fan orientation I would recommend is to place it as an exhaust. If you intake air into the room, it would only mix with the hot room air to normalize to a warm temperature. If its placed as exhaust, the hot room air gets extracted out. Cool air will be drawn in naturally due to the pressure difference cause by the exhaust. The opening for the air to be drawn in should be wherever the air would be the coolest(outside air).

 

[Muse]

If the wall wart doesn't provide a voltage similar or close to the fan's specs...

I'm thinking that the actual supplied voltage will be a lot less than what I'm seeing unloaded with the multimeter, probably close to the 12vdc spec of the wall warts.

Don't know about your ideas about exhaust/intake. Right now, I don't have a provision to draw in air from the outside other than what's provided by the fans blowing in, I'd have to really change the setup I've already constructed. Of course, any air drawn in will mix with the hot air inside, there's no way around that. The real problem in bringing down the inside temperature isn't so much the air temps as the warmth of the objects in the room's interior, along with the ceiling, which is adjacent to the attic, which has been warmed by a day's worth of summer sunshine. However, a steady stream of cooler air coming in from those 2 fans should keep the air temperature of the room significantly lower than the temperature of all those things that have a _ballast_ of warmth from a warm day.

The problem with the twin window fans you linked (and this is true with all the similar units they sell, I checked them out before), is that the width of the units is more than the max width I have to give a fan unit in that window. I have a window air conditioner in there already (and the remaining width to give to a fan unit is 18 7/8 inches). The AC is just not useful for cooling the room while I'm sleeping... too darn loud, and not granular in terms of when the compressor's on or not. In addition, when the AC is fan-only it draws in air from the room interior, not the exterior, which is pretty silly in my situation.

 

[Muse]

Looking around I noticed that I have a variable voltage wall wart that maxes out at 12v. It's rating is 600ma, so maybe I'll use it for that headroom. Measuring its no load voltage I get 17.4dcv. I have to think now that all these wall warts come up over spec by ~50% when not under load.

 

[Red Squirrel]

I think I recall reading somewhere that wall warts tend to supply a higher voltage but it will drop to spec with a load on it that matches spec, so I think you should be fine.

I have run 12v fans on 24 volts before (for short period like a few minutes) with zero issues. A couple extra volts wont really hurt much.

Even a "cheap" psu is going to cost you close to 100 bucks, so I say go for it, if you blow a cheap wall wart then you know to buy a slightly more expensive one. You can also look at a small battery trickle charger for lead acid batteries, it should run at 13.5 volts and provide much more amps.

 

[Muse]

I think I recall reading somewhere that wall warts tend to supply a higher voltage but it will drop to spec with a load on it that matches spec, so I think you should be fine.

I have run 12v fans on 24 volts before (for short period like a few minutes) with zero issues. A couple extra volts wont really hurt much.

Even a "cheap" psu is going to cost you close to 100 bucks, so I say go for it, if you blow a cheap wall wart then you know to buy a slightly more expensive one. You can also look at a small battery trickle charger for lead acid batteries, it should run at 13.5 volts and provide much more amps.

I noticed today that the wall wart that came with my Maha C204F 4-cell Nicad and NiMH charger (which I no longer use) has the same spec, 12vdc and 500ma.

I found another universal multi-voltage wall wart I acquired many years ago. It was in my box of wall warts that I have accumulated here and there. Its rated at 1A, so there's lots of headroom there. The no load voltage at the 12 volt setting is a shade over 14vdc. I may use that, I certainly don't need it for anything else.

There's a 12vdc Schumaker power supply for sale at Amazon for around $23, but I figure I don't need it. My Schumaker 3A car battery charger won't work for this because it doesn't supply current until it senses it's connected to a battery!

 

[Muse]

Got the installation done last night. I could hardly be happier with the results. They justify all the grinding, the uncertainty, the work I did researching the alternatives, the thinking, the final decisions. I'm going to post a picture of the result in a few minutes.

Last night, after a day that was just like the previous, the temperature in the room after about 5 hours with the fans running (drawing air in) was about 6 F degrees lower than the previous night. IOW, the room was much cooler, very tolerable for sleep (i.e. 64 F). I went downstairs and for the first time ever it was warmer downstairs than in my bedroom (by 3 degrees), and I've been living here many years. I actually turned the fans off at that point and I was fine.

Equally spectacular is the fact that the white noise factor is perfect. The "silent" fans give off some noise, and the sum of the two fans amounts to a white noise factor about equivalent to that supplied by my urban environment, what with highways, city traffic, airplanes and whatever other random sounds contribute. So, the sum total of all that with the fans' noise are a pretty optimal buffer to the annoyance of my immediate neighbors. I think I can stop wearing my silicone ear plugs as long as I have the fans going. In cooler weather, when the fans aren't needed to cool the room, I figure to attach circular panels over the fans both to block transfer of air and sounds.

This totally rocks, if I had to choose between the AC and the fans, it would be the fans, but I have both (!!!):

Note the 1/8" screening in the custom made screen that fits in the space not filled by the air conditioner. The panel holding the fans is screwed to the thin wooden slats on the perimeter of the screen. You can see a little light between the AC and the fan system. I'm going to stuff any spaces with pieces pulled from cotton balls for added thermal insulation.

The two 200mm Cooler Master fans draw in combination 6-7 watts. I have them powered by a variable voltage wall wart I've had for many years, sitting unused. It's capacity is 13 watts, so the 6 watts shown by my Kill-a-Watt should be no problem. I have a switch by my bed to turn them off with ease (switched extension cord).

 

[easp]

Nice. I've been considering doing something similar.

If your Kill-a-Watt is showing 6 Watts then chances are you'd be fine with one of the 500mA supplies, since the fans are certainly drawing less than 6W on their own.

 

[Muse]

Nice. I've been considering doing something similar.

If your Kill-a-Watt is showing 6 Watts then chances are you'd be fine with one of the 500mA supplies, since the fans are certainly drawing less than 6W on their own.

Thanks for the feedback.

Yeah, I figure one of the 500mA wall warts would work. I may stick with this multi-choice unit though, reason being that one of the connectors that it supports is a male 1/8" miniplug. So, I'm using that to connect it to the fans. In order to do that I had to solder an accommodating female plug ( ) to the joined plus-and-minus leads from the fans. I bought the young female plug at an independent electronics store that's been in my town for decades. The young girl behind the counter seemed rather put out that she wasn't with her friends having summer fun, going to movies and such. After I'd ordered up an assortment of plugs (I was short some stuff I like to have on hand), she admonished me "I don't recommend using plugs like that for other than audio." She said if there was a short it was apt to be real trouble. I told her "I'm quite experienced in soldering and messing around with electronics." She left me with a smile and I left her with a big thank you.

Well, I was careful in that soldering job. If I use one of the 500mA wall warts I'll have to do an additional soldering job to attach an accommodating male plug to it. I may do so anyway, because I have a feeling that what I'm using is running the fans a little fast. The unloaded voltage was over 17vdc. I don't know how I can figure out the loaded voltage, maybe it's easily done. The fans do give off a pretty optimal white noise effect, however there's some whirring that I don't like at a lower frequency than the basic white noise, don't know why.