Comair Rotron fans and PSU

[Matthew A.]

Recently I managed to get my hands on two 12 volt 1.8 amp, 6 inch dia. Rotron computer fans. My question concerns the amount of power using one or both of these fans with a 300 watt PSU that is running my P4. If my math is correct each fan draws 15 watts of elec. Would running both cause too much power draw on the PSU. The system in question has AGP video card and 3 pci cards consisting of: soundblaster live, ATA133 controller card, ethernet card. modded cpu HSF using the stock fan plus a 5 volt c.rota. 60mm box fan

[Patchmaster]

Those fans will pull 21.6W each. You'd really have to check what kind of amperage your PSU supplies on the 12v line and add up what all the different components use. You'll probably be okay, but you should add up all the amperages and be sure.

More important is that two of those fans is going to be severe overkill for that computer. I have a Comair/Rotron that's just a tad bigger than yours. I have it hooked up through a giant rheostat so I can tame that beast. Running at full speed the noise is quite annoying and I sometimes worry it's going to blow components right off the boards.

[dreadlord79]

Can you hook them out to a DigitalDoc 5? The new one is made to handle 120mm fans (up to 8) and if it works, you should be able to adjust the voltage to them as well. Just a thought.

[Wicked Klown]

If it`s drawing 21 watts he can not hook it up to a DigiDoc 5. "New! support for hi-performance 120mmfans. The new DigitalDoc 5 now supports 60mm to 120mm hi-performance fans. Up to 12 watts or 1000ma." Thats what it says on the back of the DigiDoc 5.

[Matthew A.]

I kind of figured that two would be overkill. I ran just one briefly just to see how much air it could move. It rips, though as previosly stated, they can create quite a bit of noise. Also, it is listed on the fan itself that it draws 1.8 amps so the Digital 5 would not be able to handle it, correct? Although, one would think that it shouldn't be very difficult to build my own speed control. I have a couple 3 amp 120 volt rheostats ones a 10K ohm and the other is a 75 ohm. Could these be of any use for building a speed controller for the fan.

[Patchmaster]

You won't be able to hook the fans directly to a DigitalDoc, but you could still use it to help control the fans. I have one on order right now that I plan to use with the big fan I have. You just have to connect the DigitalDoc to a relay or two that switch power to the fans. I plan to use a SPDT relay with one circuit going through the rheostat and the other circuit bypassing the 'stat and providing full power to the fan. So when the ambient temp is lower I can control the fan speed with the 'stat. When the temp rises the DigitalDoc will automatically switch the relay and provide full power to the fan.

I don't remember the numbers right now, but the resistance provided by the fan is very low, so adding just a bit more makes a big difference in the current flow. The rheostat I have is a 7.5 Ohm high power model. At the lowest setting (maximum resistance) the fan is quieter than the power supply. I usually run it at about 50% -- probably around 4 Ohms. I also bought a couple 25W 2 Ohm resistors that I used for a while. They'd heat up pretty good (I had them jury rigged sitting on an old heat sink to help dissipate the heat), but worked fine for bringing down the fan speed. I got all this stuff at BG Micro (http://www.bgmicro.com). They've got some pretty cool stuff in their catalog. Most of it is cheap enough you can buy it just to see if it will work and you're not out much if it doesn't. I think the rheostat was like $7 and the resistors were $1 each.

Anyway, you might be able to use the 75 Ohm rheostat, but I suspect the 10k one would be a bit too touchy to be useful.

If you get a DigitalDoc and don't hook a lot of extra fans to it, you could get a handful of the 2 Ohm resistors and a bunch of relays to build your own temperature sensitive multi-stage speed controller. When the temps are low you'd have maybe four 2 Ohm resistors in the circuit. As the temps rise the relays successively activate, bypassing one resistor at each temperature point, until all the relays are active and full power is going to the fan. Actually, that sounds better than my plan to use the big rheostat since it would be totally automatic and would always make only as much noise as was absolutely necessary.

[Matthew A.]

I like the idea of the fan being automatically controlled instead of relying on a rheostat based system that relies on a lack of human error to work well. What is the ave. cost of the DigitalDoc5 or would it be faily easy to build one. Though, writing the software to run it would most likely be more difficult to create, going on my knowledge of comp. language.

[Patchmaster]

ComputerGeeks did have the DigitalDoc 5 for $36, but it looks like they've sold out. PriceWatch (http://www.pricewatch.com) shows two different sources that each want $49. As for building your own, I wouldn't even know where to begin.

[Dagon]

What gets me about the digidoc is that for close to 40$ all you get is an overgrown fan switch. The least they could have done was implement some type of gradual voltage switch that lowered/raised DC voltage based on thermistor readings.

That limited OFF/ON controll is for the birds!

[f155mph]

I saw those fan at a computer show. They are huge!!! I wouldn't use them unless you really really need them. Those metal blades look nasty. You might want to get a bigger psu to power everything up.

[Intraveinous]

Yup, they're loud, their dangerous, and the move a TON of air... Rated at 235CFM if I remember correctly... they're also 2 inches deep and weigh a couple pounds each... but god do they move air... At 9V (using a butchered Wall Wart transformer), they still move plenty of air and are a lot quieter than at 12V.
Peace
John

[ButcherUK]

Comair fans don;t have metal blades, at least they haven't done for quite a while now. They are Al frame and polycarbonate blades. Still you could probably break your finger if you stuck it in one. ;)

[rpckvv]

re: PS problems

you can buy a "Straight-On Plug and Cord" for Rotron fans...so dont worry about connectin them to the PS...they only cost ~ $1.50 or so, so its a good deal for those with not-so-powerful PS's...

-peter

btw...here's the site that i found the stuff on...just search for whatever fan you have and it'll come up w/ accessories, too...
http://www.newark.com

[rpckvv]

funny, that http://www.newark.com site...the comair-rotron caravel (their 550 CFM model) costs AS MUCH or less than their tarzan, their falcon and the patriot, all smaller models...the caravel costs $73 at the site, and all aforementioned fans from $73 to $100...funny, dont you think? as for me, i'm seriously considering putting one or two (you really have to put two in...if you're gonna blow 550 CFM in, you gotta blow 550 out...) in my new case (when i get it)...if theyre that cheap (relatively), i might as well get two and see what it does...

-peter

[Patchmaster]

if theyre that cheap (relatively), i might as well get two and see what it does... Not to spoil anyone's fun, but a brief sanity check might be in order here. In a push/pull arrangement, two of those fans would completely turn over the air inside a typical full tower case about 4.5 times per second . Working together, they'd make a nice whole house air circulator for a 2000 sq. ft. house. And that's not even addressing the whole noise issue.

Might I suggest something that's a little less extreme and a lot more economical? MPJA has the Comair/Rotron Major DC (http://www.mpja.com/product.asp?product=14039+FN) for $12.50. This is a 6-3/4", 235CFM fan. I have one that acts as a heatsink fan for both the CPUs in my dual celery system. (I have it attached to a giant rheostat so I can turn it down when the room is cooler and I don't need the full air flow.) I ordered two more from MPJA to use as ventilators in a couple areas around the house. The order arrived last week without any difficulty. (If you order from MPJA, be sure to check out their monthly specials. They have 2m CAT 5 patch cords for $0.50. I didn't really need any, but at that price I figured I'd pick up a few just to keep on hand.)

[rpckvv]

aww, c'mon now...:beer:

[rpckvv]

and anyway, i realized that it would be insane to have 2 caravels, considering that they're 10" in diameter and i dont have that much space on my case for two(who does?)...i'll probably get 2 major's...one on the side and one on the top for exhaust

-peter

[Intraveinous]

Not to mention the problem of "woops, the cat got within 10 feet of the computer and got sucked in" or "woops, I left some papers in the same room without a 10 pound weight on top of them, and they blew away." hehe

1100CFM in the form of two fans would probably break things inside your computer
hehe
Peace
John

[rpckvv]

more than likely what im gonna do is get 2 "major"s and put one in the bottom of the front of the case and another on top as exhaust...that'll give me around 685cfm total(im gonna get an addtronics 7896a, modded from www.coolcases.com), which should be enough...hehe...just cant wait until i can build it...

-peter

[Patchmaster]

considering that they're 10" in diameter and i dont have that much space on my case for twoCome on, where's your resourcefulness? All you need is an adapter that will go from 10" down to about 5" and you can put one on top of the case. Of course, you wouldn't be able to put any loose paper within about ten feet of the computer, but you'd sure have a lot of air flow!

[rpckvv]

which more or less means i couldnt put my LEGS near the computer, lest i wish to have the hairs ripped from my body (free tan line jobs, girls...uhh...im sorry) ...was a kinda cool idea though...WHAT in the world would you use a 10"in. fan for in the first place? i mean those arent just computer fans (for reg. cases)...you "could" put one on the side, but all that is is a freakin huge window/paper/hand/cat/meat shredder/slicer...and i could see 4 pounds of fan warping the hell outta the case without proper (see eiffel tower or local roller coaster) supports...stupid anyway, but the major's arent a bad idea considering they're 12 bucks (how much regular 120 fans are...this one is a BIT larger and provides 2x the CFM)...

-peter

[Patchmaster]

The Major DC is a real quality piece of work. I don't have enough experience with it to know if it actually will last a lot longer than a more common fan, but the construction on this thing makes the Panaflos and all the other smaller fans I have look like cheap crap. Given that list price on the Major DC is about $75, I suppose that's to be expected.

If you're interested in picking one of these up from MPJA, I suggest you jump on it as soon as possible. The last time I saw these things at a price like this they sold out in about a week. And unless you like living in a wind tunnel, plan on getting a large capacity rheostat or several 25W resistors to help tame this beast. You don't need a lot of additional resistance, but it does have to be able to handle the comparatively high wattage the fan pulls. (The rheostat I have only goes to 7.5 Ohm, but that's more than enough. I run it at about 50% most of the time.) The Radio Shack web site has 25W 2 Ohm resistors for $1. I'd suggest getting two or three so you have some flexibility.

[Matthew A.]

Rest assured that the Majors are a quality fan. The two that I have I pulled out of an old Intergraph mainframe. Who knows how many hours are on them, in the thousands I would suspect. And they just purr right along. I finally broke down and made the cutout in the sidepanel. Installed the Major along with a 15 ohm .9 amp @ 300v. rheostat which works just great just as long as I don't attempt to slow the fan down to near 0 rpms. The one problem that I did run into was having to use another power supply to run it. The 300 watt (280 actual) PSU running my P4 just couldn't quite hang and would cause the system to shut down almost immediately. I figured that if the PSU was that loaded, it would probably be a good idea to run all my fans off of the spare 300 watter I'm using to run the Major. Oh yeah, while on at full throttle, it brought my CPU temp down from 132 F. @ idle to 118 F. @ idle. It still gets rather warm though. 163 F. under heavy load down to 151 F. under heavy load. Plus the benefit that it brought down the graphic card temp another 6 degrees F.