Negative Pressure Cases...No Way!

Post by **Rusty075** » Tue Jan 20, 2004 4:21 pm

einolu wrote:anybody think that magnets on motors could have something to do with dust?

~EO

Only if your dust is made of metal filings.

If your PC is in a automobile repair shop where they grind rotors, then I think a filter would be in order. (I have actually worked on PC that have spent time in mechanics' shops, they tend to have short lifespans)

Katana Man · Post by **Katana Man** » Tue Jan 20, 2004 4:27 pm

Positive air pressure allows the dust capture and cleanup to be more controlled. That is because the air and dust is coming in from one major location (usually the lower front bezel area). With negative air pressure, air comes in from multiple areas. Positive air pressure helps to keep it focused in one area. Because the majority of air is passing through the air filter, this makes the filter more effective. It also helps with cleanup because the majority of dust gets collected in the air filter.

Another major benefit of positive air pressure is, it helps today's quiet PSU's instead of fighting against them.

Trip · Post by **Trip** » Tue Jan 20, 2004 4:35 pm

Rusty, an intake fan should reduce the negative pressure somewhat and pull in less dust through the cracks - in theory.

It seems like it would still be between less dust vs. less noise.

Katana man's point that the exhaust fans (including PSU fan) should run slighly easier, and thus quieter, with an intake means that the noise will not quite be doubled by the addition of an intake fan.

einolu · Post by **einolu** » Tue Jan 20, 2004 4:46 pm

Rusty075 wrote:
einolu wrote:anybody think that magnets on motors could have something to do with dust?

~EO
Only if your dust is made of metal filings.

If your PC is in a automobile repair shop where they grind rotors, then I think a filter would be in order. (I have actually worked on PC that have spent time in mechanics' shops, they tend to have short lifespans)

But dust is ionized, at least to some degree. For example, my MD screen gets filled with dust mainly because (I believe) that the MD has a magnetic head, wouldnt this apply to magnets too? Just wondering...

~EO

GamingGod · Post by **GamingGod** » Tue Jan 20, 2004 4:47 pm

Well in my case the front fan did nothing for temps except kept my harddrive noticeably cooler. And the case is MUCH quieter without the 5v antec 120mm I had as intake.

mpteach · Post by **mpteach** » Tue Jan 20, 2004 4:59 pm

no, magnets having nothing to do with dust. Everything in your house eventually gets covered with dust, its in the air. Computers suck so much air through them in a long period of time so dust accuumates in them quickly.

Bluefront · Post by **Bluefront** » Tue Jan 20, 2004 5:22 pm

Well it's pretty obvious to me that Ralf's experience with positive pressure had one problem.....the air he was blowing into his computer was not filtered well enough. Either the material wasn't able to filter out fine dust particles, the filter was leaking air around the edges somehow, or the surface area of the filter was too small.....allowing the filter to clog quickly with the dust then being sucked through.

Look dust doesn't generate by itself.....it has to be carried into the computer, usually by airflow. Filter the air well enough, blow it in using positive pressure, and your computer will be cleaner than any other method.

Ralf's solution using reduced airflow with less restricted intake openings, just delays the dust build-up. It's still getting in, with maybe less being sucked through the drives. As to dust not hurting anything...crap. At the very least it makes your expensive, time-consuming fancy computer, look like a pile of dirt on the inside after a while.....depending on how dirty the air is in your home. At the worst it distroys your optical drives withdust, clogs your cpu heatsink fins, and puts a fine layer of insulation over your mother-board and related parts, making it run hotter.

The really bad part of all this is...you just cannot go out and buy a case designed with good air filtration. None exist that I've ever seen. You have to design the filtration yourself....with some sort of DIY setup similar to the many I've posted pictures of. But positive pressure helps things along, IMHO.

Lawnmower filter

Xterra cabin filter

Auto air filter

Vacuum cleaner filter

Home air purifier filter

Front case fan filter

Misc filters....some of these are worthless, some are sold as computer filters, most are too small to work well.

dddp · Post by **dddp** » Tue Jan 20, 2004 5:39 pm

negative pressure = dust getting sucked in
positive pressure = dust getting blown in

the solution is having less dust in the environment

and as i do with my sonata case which can be done with all other cases too, the holes at the top of the side covers (if you don't have them, drill some) only need to have aircon type dust filters stuck on the inside of the case, that way much more air will be sucked into the side cover holes than is likely to get sucked in through any little holes in drives etc

the front door can be sealed with draft tape, like what you use on house door frames to stop drafts

the filters are easily removed and washed then re stuck to the side case after drying, i use duct tape to keep them in place, very low tech

lenny · Post by **lenny** » Tue Jan 20, 2004 9:38 pm

einolu wrote:anybody think that magnets on motors could have something to do with dust?

Static electricity is probably more to blame.

Trip · Post by **Trip** » Tue Jan 20, 2004 9:55 pm

einolu wrote:anybody think that magnets on motors could have something to do with dust?

~EO

http://www.sharperimage.com/us/en/catal ... u=SI637SNX

After reading how this filter ionises air and traps it, I would say yes I think magnets may have something to do with dust accumulation. Not saying it does, but saying it may well.

"9. How do the Ionic Breeze GP and Quadra clean the air?
They clean by trapping airborne particles as they circulate past an array of electrically charged stainless steel blades. Contaminated air from the room is drawn in through the vents at the back of the unit. As the particles enter, they are electrically charged and are attracted to the oppositely charged collection blades inside. These charged particles will stick to the blades until wiped off by the user.

10. How do the Ionic Breeze GP and Quadra move air without a motor or fan?
A regular fan works by rotating and physically pushing air with its blades. In a typical HEPA air filter, a noisy motor will power a rotating fan that makes noise as it spins. In contrast, Ionic Breeze works by using electrostatic forces to move air molecules — think of the power of same-pole magnets to push away from each other; the process is proprietary and patented (Zenion Effect Technology U.S. Patent No. 4,789,801). This solid-state technology uses an electrical charge to create air that is densely packed with positively charged ions and negatively charged electrons. (An ion is an atom with a positive or negative charge.) This "electronic linear propulsion" is absolutely silent."

I wouldn't be suprised if a magnet attracts some oppositely charged ions as well. Heh, esp. iron filings.

Trip · Post by **Trip** » Tue Jan 20, 2004 10:22 pm

We need an experiment:

1. 12cm exhaust (negative)
2. 12cm intake (positive)
3. 12cm intake and slower exhaust (slightly positive)
4. 12cm intake and faster exhaust (slightly negative)
5. 12cm exhaust with open intake vents (slightly negative)
6. A big magnet to see if dust is drawn to it.
7. open case setup (no case)

The MV being which setup, the 2 RV being noise and dust and a CV being the temperatures. What size filters to use? I dunno, perhaps make that 12# with big and small filters used for each of the first 5 above (for a total of 10).

oldabelincoln · Post by **oldabelincoln** » Wed Jan 21, 2004 1:31 am

Rusty075 wrote:... Dust doesn't damage anything anyway. ...

Optical drives.

At the very least, dust on the lens can produce read and write errors. Opticals are not sealed like hard drives, and it's possible that dust might also have some mechanical effect.

I had a series of CD-RW drives that gradually got worse just sitting there in a negative pressure case. On the third one, I happenned to notice that dust was accumulating around the bezel, and the light went on above my head - the earlier failures were probably caused by dust on the lens, and probably could have been cured with a lens cleaner. Too late for the now long gone drives.

My 16x DVD player seems unaffected by dust, but 48x and 52x CD burners seem to be much more sensitive.

This is in a relatively low airflow 4 year old Dell, with a 500 MHz PIII with just a PS and a single exhaust fan, semi-ducted (standard Dell design - plastic duct covers the Slot 1 CPU card). pretty quiet as is, but no more than 25W from the CPU to handle.

Bluefront · Post by **Bluefront** » Wed Jan 21, 2004 3:38 am

Trip....I'm sure those electronic filters trap dust, but they do so by attracting dust to the collection plates. I'm sure one of these would work in your home to collect dust, but I wouldn't want the technology inside my computer, in effect making the poor thing a hi-tech dust collection point. It's bad enough as it is.

And if you follow Rusty's advice about no intake fans, you're back to square one....sucking air and dust through every little opening(filtered or not) in your computer. This is the problem I'm trying to avoid in the first post of this thread.

IMHO....for maximum cleanliness inside your computer, you should strive for a balance of intake and output airflow, leaning slightly toward positive pressure, with the incoming air being filtered as well as possible. There are many things to consider here....the better the filtration, the higher the fan speeds must be to suck through it, of course leading to increased noise. I guess there is no easy fix here. But I'll keep trying.

canthearyou · Post by **canthearyou** » Wed Jan 21, 2004 9:40 am

Electrostatic dust collectors are used in industry, such as power generation. They trap dust on plates and have a clean out port. In theory, you would place the unit at the intake where a normal filter would go. It might be possible to set a small unit at the intake of a case.

Trip · Post by **Trip** » Wed Jan 21, 2004 9:47 am

Bluefront, heh, good point about not wanting the computer to attract dust. I wonder if the air would still hold charges or if charged dust could escape and affect something in the computer...

canthearyou, you don't think it could attract more dust?

mpteach · Post by **mpteach** » Wed Jan 21, 2004 10:44 am

The magnets wouldnt have any effect on dust becuause the dust is electrostatically charged not magnetically charged. The exception would be if your computer operatd in a machine shop filled with steel dust.

Trip · Post by **Trip** » Wed Jan 21, 2004 10:46 am

so electrostatic charges aren't affected by magnetic charges?

mpteach · Post by **mpteach** » Wed Jan 21, 2004 11:39 am

Im not a physics major but magnets mostly effect highty charged particles in plasma, and they effect particles like electrons(electricity). I dont think magnetic field effect non-magnetic atoms regarldless of electrostatic charge.

People wear anti static straps to prevent ESD( ElecroStaticDischarge) It is recommended to blow the dust out of a computer with compressed air becuase vacuums create dangerous static electricity.

I think puting an activly charged electrostatic filtering or ionic device in your computer is crazy.

Post by **Rusty075** » Wed Jan 21, 2004 11:48 am

Obviously YMMV, but......

Using reduntant fans soley to reduce the amount of dust inside your case seems like a waste of noise. If you want to run positive pressure, just use an intake. Using a balanced intake and exhaust is acheiving nothing but doubling your fan noise: The airflow through the case is the same, the cooling is the same, and the air pressure is higher with only intakes than with both intakes and exhausts. (If your logic is that "higher air pressure= less dust" then wouldn't you want the air pressure as high as possible?)

I would rather trade a little dust accumulation for noise. Trading 5 seconds of blowing the case out with canned air once every 6 months, for reducing the fan noise 24/7 seems like a more than fair deal.

As for dust damaging components:

Nothing that dust does cannot be undone by a bi-annual blast of air and a CD lens cleaner. Yes, dust can clog the fins of heatsinks, but even after months of use the temps will only raise a couple of degrees. If that couple of degrees if enough to push you system over the edge, you've got more serious problems than dust.

And yes, dust can get inside optical drives. But only a tiny amount of dust will get into a closed drive. Dust will follow airflow; if 99% of the air in coming in the intake, then 99% of the dust will to. I'd willing to bet that the vast majority of drives that failed "due to dust" were actually simple mechanical wear-outs, and not dust related at all. Blow a little canned air into it once and a while, and run a lens cleaner through it.

Perhaps my lack of understanding of this dust obsession is because none of my machines ever get that dusty. I was inside of a machine of mine yesterday that's been running continuously for nearly a year without being opened. Inside there was some dust; a few dust bunnies in the HS fins, and a bit on the trailing edges of the fan blades, but that was about it. The was only a thin film of dust on the bottom on the case, hardly enough to even write your initials in. And this case was running "negative" pressure, unfiltered, while sitting on the floor in a high-ish traffic area.

And trust me, I've never been one to worry much about keeping the house spotless either.

Now I have seen some machines that were so dust filled that it was impossible to even tell what sort of hardware was in them. My personal fav was a woman who spent years sitting next to her machine chain-smoking and petting one of her 7 cats. That entire machine was covered in cat hair that had been "tarred" to it by the cigarette smoke.

lenny · Post by **lenny** » Wed Jan 21, 2004 11:49 am

This is seriously getting off topic, but it reminded me of a discussion on slashdot about dust and computers, and of course the Sharper Image Ionic Breeze got mentioned as well, with some folks also agreeing that electrostatic filtering inside the computer is probably not the most intelligent thing to do.

But the best suggestion I came across in that thread is from someone who said, since computers attract so much dust, the obvious choice would be to add more computers and have them work as filters

mpteach · Post by **mpteach** » Wed Jan 21, 2004 11:56 am

I agree with rusty, I could have cleaned out my computer in less time than it took ro read this montrous topic.

EDIT: For the clean freeks out there, live in a clean room or watercool your pc with an external raidiator and then caulk your case to death, and hope you dont ever have to use an optical drive.

canthearyou · Post by **canthearyou** » Wed Jan 21, 2004 12:46 pm

In regard to ESD sensitivity. It might be safer to place any electrostatic collector outside the case. I think if it were grounded on the same plane as the case ground, you might avoid any potentials building up.

The main problem with blowing dust out of the case is that a charge builds up on the vacuum tool end, which if it contacts the case or any part of the computer may be an ESD hazard. How practical this may be is a matter of how careful you are.

I agree, it's pretty far out to use one of these devices on a computer and I do get a fair amount of dust into my machine. It seems to be our location. I keep the PC on the upper shelf of my desk, which _is_ noiser, but on the shelf designed to hold it the dust I see in in sic months is the same as a year or more on the upper shelf.

skwang · Post by **skwang** » Wed Jan 21, 2004 2:36 pm

mpteach wrote:Im not a physics major but magnets mostly effect highty charged particles in plasma, and they effect particles like electrons(electricity). I dont think magnetic field effect non-magnetic atoms regarldless of electrostatic charge.

This is off-topic but magntic fields affect any charged particle.

The force equation governing electromagntic (EM) fields is: F = q*E + q* v x B . Where F, E, v, and B are vector fields, x represents the cross product, F is the force the particle feels, E the electric field, v the velocity of the particle, B the magnetic field, and q the charge of the particle.

N.B. In reality particles are rarely affected by either electric or magnetic fields. Most macroscopic objects are eletrically neutral. Also, to give any significant acceleration to a macroscopic you need a large force. This is why all the examples of EM fields that we experience everyday only deal with microscopic particles, specifically electrons.

The electrons are fired from the rear of your CRT moniter and deflected to their final position on your phorphorus screen by a magnetic field. The sound coming from your speakers is a diaphram vibrated by a electromagnet. The electromagnetc vibrates due to the electrons coming from the sound card. The fans in your computer run because the DC motors rotate arms (called armatures I believe) which are electromagnets. You get the picture.

einolu · Post by **einolu** » Wed Jan 21, 2004 2:49 pm

sry for the low quality picture, but here you can see that the dust is attracted to the recording head of my MD recorder (Panasonic MR220)... The units itself isnt that dusty on the inside, the dust seems to be magnetiaclly attracked only to the recording head

...

Dont know if that proves anything...

~EO

Trip · Post by **Trip** » Wed Jan 21, 2004 10:15 pm

Rusty, a reason for having an exhaust and an intake instead of just an intake is to try and pull heat away from the PSU. Really, if the PSU is isolated and has a duct (like everyone recommends in here) then maybe an exhaust wouldn't be needed... but the PSU would really need to be sealed off or else not at the top of the case b/c the PSU would pull a lot of warm air through itself otherwise. Heh, I'm just restating the obvious. Though like you said, redundant noise and perhaps not much of an improvement. Also like you said, perhaps dust isn't as big of a problem as it seems.

So, who else thinks dust is or isn't a problem for drives? and this magnet issue is interesting - maybe even a fanless computer would attract dust.

I tell you, I quit smoking a year or two ago and recently noticed how much cleaner my car is. Everything (prob. incl. my comp.) used to be coated in a thin film of soot. Another reason not to smoke, it's bad for your computer!

EDIT: actually, ducts seem to work well with controlling airflow, maybe a decent duct and a single, filtered intake would work pretty well, I dunno. As simple as all of this is, it gets damn confusing.

Trip · Post by **Trip** » Fri Jan 23, 2004 9:26 pm

take a look at this post by Mike C. I know the idea has been covered well in this thread, but it made me wonder if a slow 80mm fan could actually reduce airflow if used with like a medium speed 120mm exhaust. What do y'all think? I had noticed in Ralf's setup that he left some holes around his smaller intake fan.

Interesting stuff, thes are definately the most intelligent forums I've ever read! Figured I'd squeeze this last little bit out of this thread before it died.

Bluefront · Post by **Bluefront** » Sat Jan 24, 2004 3:07 am

Trip....this airflow thing is a complicated subject. As I stated above I have one 120mm exhaust(the PSU fan), and one 120mm intake fan...that's it. They both use the same Evercool motor. I have manual control over each with rpm monitoring.

Here's something to consider....when I increase the intake fan speed, the rpms of the output fan also rise (without touching the output control knob). I can gain as much as 200 rpms on one fan by adjusting the other. Go figure.....

pdf27 · Post by **pdf27** » Sat Jan 24, 2004 3:33 am

when I increase the intake fan speed, the rpms of the output fan also rise (without touching the output control knob). I can gain as much as 200 rpms on one fan by adjusting the other. Go figure.....

Presumably increasing the intake fan speed reduces the pressure drop across the PSU fan. Hence, for the same power supplied to the output fan the fan will run faster.

snutten · Post by **snutten** » Sat Jan 24, 2004 4:47 am

Rusty075 wrote:
But whatever you do, don't do both an intake and an exhaust fan. That's just doubling your noise production for the same amount of airflow. Blowing 30 CFM into your case, and sucking 30CFM out of your case does not give you 60CFM flowing through it... it gives you 30, only with twice the noise.

I basically agree, but this statement is true only if the airpath is unrestricted. A filter, for example, adds up on the negative/positive pressure. Slow radial fans, especially smaller ones, are very sensitive to backpressure. They push MUCH less air when the backpressure increases. Using both push and pull fans may therefore be a tradeoff you have to make if you want to use filters.

I remember reading a thread about this backpressure problem here on SPCR. It even stated some CFM numbers at different pressures and such, or did I read this somewhere else perhaps... either way, if any of you knows which info I´m referring to, please give us a link cause I can´t seem to find it anymore.

IsaacKuo · Post by **IsaacKuo** » Sat Jan 24, 2004 6:32 am

einolu wrote:

sry for the low quality picture, but here you can see that the dust is attracted to the recording head of my MD recorder (Panasonic MR220)... The units itself isnt that dusty on the inside, the dust seems to be magnetiaclly attracked only to the recording head ...

Dont know if that proves anything...

~EO

This doesn't prove anything, because the head could simply be acting like a broom sweeping up dust that happens to land on the discs. Also, the physical action of the head sliding across the disc likely creates something of a static charge--that will attract dust.

Negative Pressure Cases...No Way!

Some physics