...It's there way to calculate the RPM's of a undervolted fan? It's safe to say that my 7000RPM@12v fan will be a 3500RPM fan at 6v? In an ideal DC motor world it's not far off, but several fans I've disembowelled have a safety diode in series with the supply (losing maybe 750mV) and the electronic...

If enlarging the case aperture is a no-no, I'd be very tempted to make up a duct (as long as possible) with cardboard & duct tape (what else?) to try the fan.

The lower revs should be more peaceful, at worst you'll not get the rated flow.

THAT DEAD SPOT DOES NOT MATTER :wink: The heat will spread on the heatsink It's one of the reasons swapping a 60mm for an 80mm fan may give higher temperatures even when the rated flow is similar. A bigger motor diameter, a bigger dead spot. I picked up CoolerMaster's 60-80 adaptor SFC-P68 today, h...

The Antec fans on my 1030B are (IIRC) about 34cfm and were fairly noisy at the full 12v. At 7v they're quieter than 12v Panaflo L1's and push adequate air for a cool case. I did remove the waffle-iron grilles, which also helps reduce the wind noise. Panaflo L1 are nothing special, they're just a low...

You can certainly reduce the extra noise produced at lower revs by PWM controllers, by blunting the pulse attack with a small capacitor between base & ground on the switching transistor. Telcom produced an Application Note (AN58) to go with their PWM chips, but I've used the method with various home...

Many fans (including Panaflo L1) have a protection diode in the power line, dropping about 0.75v, and the Hall switch drops 250-300mV, so there's not much left of the 1.5v to get through to the motor coils.

Maplin, in their wisdom, discontinued the 3.5W wire-wound pots ("loudspeaker volume controls") that were ideal for fan rheos, they came in a range 20R-200R. The 100R cermets are 2W rating, and should be OK for fan loads up to 175mA, though a 150mA limit would be safer. An alternative source for a 3W...

The resistor must go in the red wire if you're using speed monitoring. Otherwise fan negative is above ground potential and could damage the mobo.

... But since the wires inside the fan stay the same size as you lower the voltage, the resistance to power flowing through the fan increases. I suggest you check Ohms Law :wink: Reasons for the non-linearity are the non-ohmic voltage losses across the protection diode (if fitted) and hall-switch o...

There's yet another complexity I've not allowed for (ie forgot :oops: ) in the above formula. Many fans have an internal protection diode on the supply line, so the 12v fan is actually running at around 11.25v, and at 6v is down at 5.25. This will account for some non-linearity. :? edit: to add a fu...

Running fans at 5v is dodgy (some will not start every time) and is probably best implemented by a switch with 12v/5v options rather than the permanency of a molex conversion. For 7-volting a pass-through molex pair, you can remove both the fan negative black wire and the red wire at both ends and s...

...According to reviews I've read the small heatsinks on the Zalman get painfully hot to touch pretty quickly. Reviewers do like to overload controllers. :roll: With typical single case fans a small (25-30C/W) sink is fine. In fact, doing the maths, a 200mA fan running at 6v 100mA will produce 0.6W...

...AFAIK the calculation would be (12V-7V) / I (fan current) = R (resistor value) It's a tad more complex, Resistor value = (12-V) x 12 / (V x I) Where V is the voltage you want the fan to run at, I the fan current at 12v. (steps on the way shown here. ) So to 7-volt a 0.2A fan, R = (5 x 12) / (7 x...

They have a CFM-to-dB graph in the review, but isn't dB based on a log scale? True, but the noise/flow does follow a fairly linear pattern for fans from similar model ranges. http://www.cpemma.co.uk/graphics/noise_flow.gif The Papst fans all hug the "best" line, and YS-Tech the "worst". :roll: Delt...