Magnus Danielson wrote: > From: "Poul-Henning Kamp" <[EMAIL PROTECTED]> > Subject: Re: [time-nuts] Fan for old HP synthesizer (was RE: time-nuts > Digest, Vol 21, Issue 20) > Date: Tue, 18 Apr 2006 21:43:18 +0200 > Message-ID: <[EMAIL PROTECTED]> > >>In message <[EMAIL PROTECTED]>, "Christopher Hoover" writes: >> >> >>>As someone else mentioned, the form factor is often quasi-standard. Poring >>>over the Digi-Key catalog may be your best bet. >>> >>> Mtg Hole Ctr Sp - English : 3.25 in >>> Thkns - English : 1.5 in >> >>This is what's called a 92mm x 92mm x 38mm fan these days. >>
>>There are many 92x92x25 mm fans available, you may be able to >>substitute one of these if 92x92x38 is impossible to find. > > > When checking the EBM-Papst site (http://www.ebmpapst.us) the 92x92x25 mm > fans did not > reach the same CFM, but those that I found (3212JN and 3214JN) was not doing > 117 VAC > (they where doing 12 VDC and 24 VDC respectively). While Papst isn't all > there is to fans > they are usually a good benchmark on what is available. You have to be careful with cfm ratings on fans. For small fans like this, the cfm rating will be in free air - i.e. no restrictions near by. For some larger fans, which must not be operating in free air, then this is obviously not so. As soon as you restrict the flow by putting obstructions in the path of the airflow, so the flow rate drops. At a particular back pressure, the flow drop becomes zero. The actual shape of the flow vs pressure curve, which you see in fan data sheets, can be changed by the design of the fan blades. I had an email from one of the fan manufacturers some time back when I was trying to replace a really odd sized fan in my Sun Ultra 80. (Sun's answer is to buy a new DC-DC converter with the fan on it, which was not too attractive.) Anyway, the fan manufacturer said that if a fan is designed for a particular customer, then it is quite common to optimise the fan blade design for there particular application. If the old fan is still working, and you can measure the air inlet and outlet temperatures, then find the difference between them. If the new fan results in a smaller difference between air input and air output temperatures, then the flow is greater so all is well. Obviously if this is in a cabinet with multiple fans, it is best to measure the difference only over the region being cooled by this fan. HP kit is usually well over-engineered, but you need to be careful as you are at high altitude, where the air is thinner and so less effective at cooling. Your safety margin will be smaller than for someone at sea level. dave _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
