More quiet 80mm fans to meet these specifications?

Mohan · Post by **Mohan** » Fri Feb 12, 2010 9:32 am

Hello,

this is not about PC parts but everything air cooled is of interest here I think and it just bugs me enough to ask: I have a video projector which is using two 80mm fans of this kind:
http://db.sanyodenki.co.jp/product_db_e ... er_id=1882

It's got "only" 29.3CFM but is rated at 23dB(A) which is why I thought... hmm... there are more silent fans for the PC world out there! However I'm not sure how far the "static pressure" value of 22.5Pa is of importance in the application.

The projector can be used in diffferent modes, an ECO and a NORMAL mode, the fan is spinning a lot more slowly in the first, and quite noticable in the latter. When turning the projector off, the fan will run a minute longer on full speed to cool things down further. So the application would require the fan to run at different voltages.

So... do you have ideas for a silent replacement or shall I just skip this as a baaaad idea?

Thanks for your help, I appreciate it!
Mohan

Darth Santa Fe · Post by **Darth Santa Fe** » Mon Feb 15, 2010 10:54 am

I would keep the stock fans. A projector makes a lot of heat, and I wouldn't want to risk over-heating the electronics inside. I could be wrong, but it's better to be safe, right?

dhanson865 · Post by **dhanson865** » Mon Feb 15, 2010 1:32 pm

http://www.jab-tech.com/Scythe-S-FLEX-S ... -4449.html might be quieter or might be the same noise or even louder.

It claims to be quieter and lower RPM but close enough to the specs you quoted so it's worth a shot if you don't mind paying $15 to $20 a fan and are willing to test it.

It might save you 1 or 2 dBA.

Mohan · Post by **Mohan** » Tue Feb 16, 2010 7:21 pm

Hmm... from the datasheets, as far as I could see, also the S-Flex 1500 might be suited... Did you actually only rate CFM?

lodestar · Post by **lodestar** » Wed Feb 17, 2010 3:36 am

As I understand it the original fan is 80x25 and runs at 2350 rpm, and in actuality maybe 2500 rpm. The Eco mode is some proportion of this. Personally I would not risk dropping down to as low as 1500 rpm or 2000 rpm because while the cost of the fans is relatively small I assume the cost of the projector is not. Claimed CFM ratings are not a reliable guide to fan performance anymore than dB figures.

So I would suggest looking for a fan of the same spec, which might be quieter (better bearings?), possibly the 80mm Panaflo M1A as here http://www.frozencpu.com/fan-09.html, but you could be spending around $25 to achieve very little.

dhanson865 · Post by **dhanson865** » Wed Feb 17, 2010 5:59 am

lodestar wrote:As I understand it the original fan is 80x25 and runs at 2350 rpm, and in actuality maybe 2500 rpm. The Eco mode is some proportion of this. Personally I would not risk dropping down to as low as 1500 rpm or 2000 rpm because while the cost of the fans is relatively small I assume the cost of the projector is not. Claimed CFM ratings are not a reliable guide to fan performance anymore than dB figures.

If you always use the device in an air conditioned space and are willing to take the risk you could push it some. I wouldn't push it down to the 1500 RPM myself (35% decrease). It really is a risk of damaging the device should it overheat.

2000 RPM doesn't scare me though it's only a ~10% decrease. It's up to you to decide if your ambient temps are low enough to afford slowing down the fan(s). Do it right and you quiet the device with little risk. Do it wrong and you'll kill the device.

Mohan · Post by **Mohan** » Wed Feb 17, 2010 9:03 am

Actually why do you see this as a matter of RPM? I'd think the CFM is more important. I'm not going to do anything with the original fan itself like hanging in some resistor or fan control. It's not *that* noisy.

Is there actually an easy way to test the Sanyo Denki fan in some external box (not in the projector) to rate its CFM compared to a fan that I could test in the same conditions? That way I would only measure relative differences between the models as I wouldn't need correct absolute values. It's enough to be better than the original at the same voltage (not exactly speed) but most probably less noisy.

However what I was worrying about is that even given they have about same CFM for the voltages used (I would also need to measure how the fan speed is regulated in the device... PWM or by voltage) that the air pressure might be also a factor.

Thanks for your input!
Mohan

dhanson865 · Post by **dhanson865** » Wed Feb 17, 2010 7:48 pm

Mohan wrote:Actually why do you see this as a matter of RPM? I'd think the CFM is more important.

Check out http://www.silentpcreview.com/Anatomy_of_the_Silent_Fan or google "fan laws" with the quotes.

RPM and CFM go hand in hand unless there is a significant variation in design of the fan.

We know the diameter is the same. The input voltage will be the same. Both fans have 7 blades.

The only minor difference other than RPM/CFM is that the Sflex has 4 struts vs the 3 struts on the Sanyo Denki which would make almost no difference.

CFM is very, very hard to measure in an apples to apples manner. I trust rated RPM more than rated CFM.

The two articles below detail how hard it is to measure CFM in a way that allows you to compare any two fans.

http://www.silentpcreview.com/article687-page1.html
http://www.silentpcreview.com/article734-page1.html

pretty much when going by manufacturers specs RPM, voltage, size, and a picture (not a drawing) is all I'd trust. Too easy to mistest or intentionally misrepresent dBA and CFM.

Mohan · Post by **Mohan** » Fri Feb 19, 2010 1:20 am

Well... thanks for the links (which should have been more obvious ressources for me earlier already). I'll have a look anyway when I'm opening the case again, how the fans are mounted, I suppose some rattling at least is coming from an undamped mounting. I'm coming to the conclusion, that the only way to really get trough with it, would be to test the different fans in the same conditions and actually just listen and somehow get some sort of comparable CFM rating, not thinking of it as absolute truth at all. Hmmm. In short: Most probably not worth the effort then. Dang.

Anyway, thanks for all your time and input, guys! Much appreciated!
Mohan