Ideal fan size?

andrew · Post by **andrew** » Sun Mar 16, 2003 10:12 pm

Well, I am finally decided on air cooling (as opposed to water cooling), and so I need to buy some fans. My question is whether fans that are greater than 80mm typically produce more airflow for the noise level. I am probably going to buy two panaflos for the exhaust, one for the CPU HSF, and two for the intake to my case, all at 5-6V, but if I can run a 120mm or even bigger at a low voltage and get better airflow for the noise, I will... I have room for basically anything (i'm going to mod the case..)

So, is my panaflo setup good, or is a bigger fan a good idea?

(BTW, I will probably be getting a 400W SilenX PSU when they are available)

Also, I read the article about undervolting fans, and I have a question: the article mentioned that to get 6V, two fans can be run at 12V in parallel. If this is the case, why doesn't splitting the voltages of all three lines with molex Y-splitters halve the volatge to all lines as well?

Last question (I think): I have stamped grills in the front and back of my antec, which I plan on cutting out and replacing with real grills. On the front though, a bezel covers the grills. Would it be ok to not install a metal grill at all in this case? I am guessing that this is the case (pun unintended), but am just confirming...

Oh, last question (sorry :\ ): Is decoupling Panaflos running at such low voltages at 5V and 6V going to make a significant difference, (>3-4dBA,) or is it not worth it.

Thanks

Post by **MikeC** » Sun Mar 16, 2003 10:46 pm

So, is my panaflo setup good, or is a bigger fan a good idea?

(BTW, I will probably be getting a 400W SilenX PSU when they are available)

Also, I read the article about undervolting fans, and I have a question: the article mentioned that to get 6V, two fans can be run at 12V in parallel. If this is the case, why doesn't splitting the voltages of all three lines with molex Y-splitters halve the volatge to all lines as well?

Last question (I think): I have stamped grills in the front and back of my antec, which I plan on cutting out and replacing with real grills. On the front though, a bezel covers the grills. Would it be ok to not install a metal grill at all in this case? I am guessing that this is the case (pun unintended), but am just confirming...

Oh, last question (sorry :\ ): Is decoupling Panaflos running at such low voltages at 5V and 6V going to make a significant difference, (>3-4dBA,) or is it not worth it.

1. There are few 120mm fans than can make as little noise as a Panaflo (or other quiet 80mm fans) at 5-7V. None I know of. The mass seems to dictate a certain level of residual noise that is just higher than a smaller fan. Others may have more experience with 120s...

2. Not parallel, SERIES!

3. No grill needed anywhere, really. Only for safety -- fingers, electric wires, pets, kids.

4. At <7V decoupling 80mm fans provides very subtle improvements. May not be worth it. But as you start to plumb the depths of quiet obsession

, every little bit starts to count.

andrew · Post by **andrew** » Mon Mar 17, 2003 8:06 am

I'm not an electrician: could you explain in detail how a DIY setup can be made to run two fans at 6V then?

I.E. what does "In series," mean?

Post by **MikeC** » Mon Mar 17, 2003 10:01 am

Parallel wiring means putting the 2 wires from XX number of devices across the same voltage terminals simultaneously. When you use a Y-adapter for a 4-pin IDE power connector from the PSU to run 2 HDD, this is called parallel wiring. Ditto a power bar or any mutiple AC adapter. All devices in parallel wiring receive the same voltage. A big bonus in most apps is that if one device fails, the rest carry on -- the electricity runs "in parallel" to all the devices independently. This is why xmas tree lights use parallel wiring.

In series wiring, the multiple devices are daisy chained. The voltage drops across each device; so unless all the devices are the same, they will not get the same voltage. Also if one device fails and blocks the current, all the devices stop working.

Hmmmm....

OK, here is an image that will explain it simply:

http://sailawayto.com/series-parallel%20cct.JPG

In this drawing, Z2 and Z3 are wired in parallel with each other, while they are both in series with Z1 as well as the voltage source.

If you eliminate Z1, Z2 and Z3 will be in parallel with each other and the voltage source -- this is the way all the electrical wiring in your PC is configured.

If you eliminate Z3, then Z1 and Z2 are wired in series with the voltage source. This is how you can get 6V to each of two identical fans wired in series to a 12V source.

One more thing to note: the drawing shows arrows marked "i" -- that is the current and its direction of flow. In DC circuits, the current is directional, and you have to observe polarity. The red (+) wire from one fan must go to the +12V (red) wire from the PSU; the black (-) wire from that fan must connect to the red (+) wire from the other fan. Finally the black (-) wire from the second fan must connect the the black or ground wire of the power supply.

If you don't get it, just get some fan voltage controllers.