Question about 250mm fan dimensions

psiu · Post by **psiu** » Sat May 26, 2007 10:41 am

Question for those who have one (or more of these fans):

I'm looking at either the FrozenCPU or PerformancePCs fan (appears to be exact same fan by Power Works) and the dimensions are listed as 250x250x30. Are those accurate dimensions?

Also in the H portion of the dimensions, is there 5mm worth of excess that could be shaved off the frame, while still giving the blade room to spin?

I just realized the slot I had carved into the inner edges of the case and build I'm putting together is wrong....2.54cm...I think I was thinking of the 250mm dimension or something appropriately brain damaged at the time. And the saw is now a few hundred miles away.

http://www.performance-pcs.com/catalog/ ... s_id=21357
http://www.frozencpu.com/products/5451/ ... g36c15s566

McBanjo · Post by **McBanjo** » Sat May 26, 2007 11:11 am

The fan itself is only 220x30mm, by some odd reason they measure those fans sideways like an old monitor.
With that measurmernt a 120mm fan would be ~140mm

Felger Carbon · Post by **Felger Carbon** » Sat May 26, 2007 2:53 pm

If you inscribe a circle 250mm in diameter on a (large enough) piece of paper, a "250mm" fan will (just) fit entirely inside the circle, with the outsides of the four mounting ears just making it. The mounting ears are on a 170mm square, so a 240.42mm circle will pass thru the center of each mounting hole.

What I think happened is this: a computer case company realized that a large side fan was a good idea for the newly-hot gaming computers. That company studied the problem, and realized the smallest computer with the problem would be a mid-tower, with space for a full ATX mobo and a standard PSU above the mobo. So, the space for putting a fan in the case is limited by 1) the PSU on top 2) the optical drives up front, and 3) leaving enough sheet metal around the edges of the side panel so the side panel maintained physical integrity. The company decided that if the fan would fit into a 250mm circle, that requirement would be met by a standard mid-tower case.

So a request for proposal was issued to the standard fan makers, specifying that the fan had to fit the 250mm circle requirement. Thus, the fans became known in the industry as "250mm" fans.

Now, history has repeated itself, as it usually does. The same computer case company has discovered that the presence of the 250mm fan inside the standard 200mm-wide case limits the computer to small HSFs, or at least low HSFs - less than ~130mm. It also decided that if the fan were to be moved to the outside of the case, then the PSU and the optical drives no longer limited the size of the fan. If the fan were outside the standard mid-tower case, they decided any fan that would fit inside a 360mm circle would work...

psiu · Post by **psiu** » Sat May 26, 2007 5:50 pm

I'm tired. I think my eyes rolled back up into my forehead by the time I was trying to read your last paragraph Felger.

Okay....after a lot of rereading....the basic square dimensions of one of these puppies would be 170x30?

So it would fit completely within a square of 180mm? (180x180)?

I'm gonna just have to order one methinks. Might even end up with 2 120mm fans, but I hope not. Maybe I'll get bored this weekend and throw some preliminary pics up.

Ugh. Bedtime

Felger Carbon · Post by **Felger Carbon** » Sat May 26, 2007 7:11 pm

psiu wrote:Okay....after a lot of rereading....the basic square dimensions of one of these puppies would be 170x30?

No no no! I said the mounting holes are centered on the corners of a 170mm square. The round fan casing measures 220mm diameter, which is why I've been calling them a 220mm fan. The casing is 30mm deep for the "250mm" fan; I'm not sure about the "360mm" fan.

Consider your basic 120mm fan: the mounting holes are at the corners of a 105mm square! The casing itself is basically a 120mm square with slightly rounded corners. So, the fan blades are wider than the mounting hole spacing. This is also true of the "250mm" fan. Nothing new here. Get some sleep!

Jeff Cutsinger · Post by **Jeff Cutsinger** » Tue Aug 28, 2007 12:10 pm

Felger Carbon wrote:they decided any fan that would fit inside a 360mm circle would work...

So a 360mm fan is actually about 317mm?

Felger Carbon · Post by **Felger Carbon** » Tue Aug 28, 2007 2:33 pm

Jeff Cutsinger wrote:So a 360mm fan is actually about 317mm?]

I haven't bought one, and I don't know of anyone who has. Seems like a reasonable horseback guess.

ronrem · Post by **ronrem** » Tue Aug 28, 2007 8:02 pm

These fans come with a bezel or frame,a rond mounting ring with a max diameter of 250 mm. The inside of the frame-the blades are about 220 mm.

Thus it's a bit like cutting a hole to match a 12" woofer,you need to assume the hole must be LESS than 250 mm...more than 220 mm.

The big Antec is outter 200 mm and inner closer to 180 mm.,but the frame is flattened on the sides to make it a possible floor or blowhole mount.

I think it's Xclio that has a case with a 360 mm but so far these have not shown up as a seperate fan. As Felger has found and posted,,,the 13 blade 250's can run at a mere 4v or a bit less...very low RPM. Very quiet.

Enermax cases often have a version(250mm) that is reversable. Usually these fans get used as an intake with a tabletop type HS like a Dominator or the classic Thermalrights. I'd wonder how it would do in exhaust mode with a Ninja that has an inlet duct to the HS.

Aside from moving a lot of air at low RPM- the big fans also cover area...so help cool vid cards,HDDs. They DO in a standard setup- leave a big hole where sound gets out. Bluefront did his INTERNAL-fed through a filter.

I've sketched up a case where there's a wooden louvered laver outside the fan mount to deflect sound/air. I did another with a horizontal mobo and horizontal mount fan (fan + Zen PSU in a hinged top chamber) A real unconventional setup,as its a rather tall (wood mostly) case with the HDDs below the mobo and the inlets all down low. It would mean no short/direct noise path from the few moving parts-so an X2 could be VERY quiet.

The plan optimizes a fanless PSU and yet gives great access to the mobo.
I guess I have to load sketches to photobucket and then get it to link...it's a pretty odd design to describe.

ronrem · Post by **ronrem** » Tue Aug 28, 2007 8:05 pm

Felger Carbon wrote:
Jeff Cutsinger wrote:So a 360mm fan is actually about 317mm?]
I haven't bought one, and I don't know of anyone who has. Seems like a reasonable horseback guess.

The outter ring is probably about the same as the 250's....about 30 mm diff....so I'd guess at 330 inside diameter.