Decouple fans and hard disks supplies

I don't think I would worry too much, unless of course the fans are
the 'carbon brush' types which could create a very noisy invironment
due to the arching, these type's could cause un wanted magnetic fields
which could cause hum in the audio department or wipe data from the
hard drive ....!

'The squirrel cage' motor type's are better in this respect but tend
to create a high magnetic field which could also cause havoc as above
due to their large magnetic field, at least these don't create arching
as they are brushless.

The type's normally used in computers are the 'brushless DC fans',
true all all motors require a magnetic field to convert power into
torque, the the filed in these are self contained within the rotor,
they tend not to generate any external field, no sparking being
brushless henve no RFI (Radio Frequency Interferance) which could get
into the logic and audio circuitry.

Modern computers fans require very little power to run, a typical fan
at the most might only draw between 80 ~ 120MA or 0.08 ~ 0.12 Amp, so
we can say VxI = P in Watts, being operated at 12V works out 1 ~ 14 W
appx. I know the logic circuitry is the main power zapper, but feel
1 amp is peanuts....!

Does seem strange stopping a fan with a finger would cause data error,
I would imagine a stalled fan isn't gonna going to do anything apart
from an increase temperature rise and doubt that a hard drive is not
that sensitive..... a cpu could be, a thought could be given to the
RAM chips in this respect, think I'd be looking elsewhere...

unless of course the hard disc are close to melting in it's normal
environmental conditions..!

Davy
 >> Stay informed about: Decouple fans and hard disks supplies 

mike RemoveThis @spamforbidden.com wrote:

> I've built myself a frame where I've put six hard disks for a RAID5
> system, and six 8x8 cm fans to cool them down (they live in a quite
> hot environment!). The PSU is a 500W one however I was concerned that
> the fans may pollute the hard disks' supply too much.. since they're
> motors after all!
> I've accidentally put a finger into a fan (what a pain!), and this
> stopped the fan for a moment and also caused hard disk errors, and
> thus convinced me even more that I need to decouple the fans' motors
> supply from the hard disks supply.
>
> But how?

> The best scheme I've thought so far is to link all 6 fans together in
> parallel, then apply power through a circuit like this:
>
> 6 fans--*-ind-*-ind-*-ind-*-ind-*-ind-*-ind---diode------*-----PSU +12V
> | | | | | | |
> cap cap cap cap cap cap 6 HDs---PSU +5V
> | | | | | | |
> Gnd ----*-----*-----*-----*-----*-----*------------------*-----Gnd

I seriously doubt you need such an elaborate L-C filter, and a single L
and C for all 6 should be enough for all but the worst motor noise.
Also the diode is unneeded.

Its possible that stalling the fan caused disk errors simply because
the +12V line was overloaded and the voltage dropped, not because the
fan created excess electrical noise.

> of course in the above scheme I don't even need them to be six,
> it's simply the more the better, I just happened to have six of
> them on my bench (more or less a coincidence).
>
> But now the big question: what's the right size of the caps, also
> to not overload the PSU at start? Will the diode really help the
> hard disks to not get some bad bad bad back EMF?
> Notice also that the wire that feeds the fans is AFTER all the wires
> that feed the hard disks (otherwise the voltage drop caused by the
> fans would have affected the hard disks). Yes, at least I know this.
>
> Is my scheme ok? What can I do to improve it? I really care about
> the hard disks and the data they contain!
>
> Thank you very much,
> Mike
 >> Stay informed about: Decouple fans and hard disks supplies 

On 15 Jun 2006 08:15:24 GMT, mike.RemoveThis@spamforbidden.com wrote:

>
>Hello respected engineers!
>I've built myself a frame where I've put six hard disks for a RAID5
>system, and six 8x8 cm fans to cool them down (they live in a quite
>hot environment!). The PSU is a 500W one however I was concerned that
>the fans may pollute the hard disks' supply too much.. since they're
>motors after all!

It would be nice to know the approximate current the fans
use, running and stalled... as well as any adjustment for
current if you will undervolt the fans to reduce noise.

Note that the current rating on the fan label is not typical
(RMS) current, they will have to be measured with at least a
filter (RC?) in front to get a reasonable reading.


>I've accidentally put a finger into a fan (what a pain!), and this
>stopped the fan for a moment and also caused hard disk errors, and
>thus convinced me even more that I need to decouple the fans' motors
>supply from the hard disks supply.

.... or put fan guards on the fans and secure all loose
wires, if not both.


>
>But how? I'm just a hobbyst when it comes to electronics, so I may
>even intuite correctly, but I won't be really sure of my thoughts.
>Right now, they are that I need some big inductors (with as low DC
>resistance as possible), some (big?) capacitors and maybe also a big
>rectifier as well.

I doubt you need inductors, nor that if you did they would
need be "as low DC resistance as possible". In the end the
key is whether the fans provide enough cooling, it is easy
to go overboard on fans, choosing faster than needed which
just accelerates wear, increases dust and noise buildup. It
is also easy to choose higher (RPM) spec fans and if they
voltage is below 12.0V, their RPM drop can be acceptible.



>
>The best scheme I've thought so far is to link all 6 fans together in
>parallel, then apply power through a circuit like this:
>
>6 fans--*-ind-*-ind-*-ind-*-ind-*-ind-*-ind---diode------*-----PSU +12V
> | | | | | | |
> cap cap cap cap cap cap 6 HDs---PSU +5V
> | | | | | | |
>Gnd ----*-----*-----*-----*-----*-----*------------------*-----Gnd
>
>of course in the above scheme I don't even need them to be six,
>it's simply the more the better, I just happened to have six of
>them on my bench (more or less a coincidence).
>
>But now the big question: what's the right size of the caps, also
>to not overload the PSU at start? Will the diode really help the
>hard disks to not get some bad bad bad back EMF?

Do you know that you have bad bad bad bck EMF?
A capacitor or two alone might suffice.
If you had the current requirements of the fans, a regulator
might do the job too, as might the typical fan bay
controller which is ready made and thus, might not only be
quicker but as inexpensive too.



>Notice also that the wire that feeds the fans is AFTER all the wires
>that feed the hard disks (otherwise the voltage drop caused by the
>fans would have affected the hard disks). Yes, at least I know this.

Something else a bit simplier is to use a different lead
off the PSU, and a cap or two if needed.


>
>Is my scheme ok? What can I do to improve it? I really care about
>the hard disks and the data they contain!

In that case, do all of the above. It's not THAT expensive
or time consuming.
 >> Stay informed about: Decouple fans and hard disks supplies 

mike.DeleteThis@spamforbidden.com wrote:

> Hello respected engineers!
> I've built myself a frame where I've put six hard disks for a RAID5
> system, and six 8x8 cm fans to cool them down (they live in a quite
> hot environment!). The PSU is a 500W one however I was concerned that
> the fans may pollute the hard disks' supply too much.. since they're
> motors after all!
> I've accidentally put a finger into a fan (what a pain!), and this
> stopped the fan for a moment and also caused hard disk errors, and
> thus convinced me even more that I need to decouple the fans' motors
> supply from the hard disks supply.
>
> But how? I'm just a hobbyst when it comes to electronics, so I may
> even intuite correctly, but I won't be really sure of my thoughts.
> Right now, they are that I need some big inductors (with as low DC
> resistance as possible), some (big?) capacitors and maybe also a big
> rectifier as well.
>
> The best scheme I've thought so far is to link all 6 fans together in
> parallel, then apply power through a circuit like this:
>
> 6 fans--*-ind-*-ind-*-ind-*-ind-*-ind-*-ind---diode------*-----PSU +12V
> | | | | | | |
> cap cap cap cap cap cap 6 HDs---PSU +5V
> | | | | | | |
> Gnd ----*-----*-----*-----*-----*-----*------------------*-----Gnd
>
> of course in the above scheme I don't even need them to be six,
> it's simply the more the better, I just happened to have six of
> them on my bench (more or less a coincidence).
>
> But now the big question: what's the right size of the caps, also
> to not overload the PSU at start? Will the diode really help the
> hard disks to not get some bad bad bad back EMF?
> Notice also that the wire that feeds the fans is AFTER all the wires
> that feed the hard disks (otherwise the voltage drop caused by the
> fans would have affected the hard disks). Yes, at least I know this.
>
> Is my scheme ok? What can I do to improve it? I really care about
> the hard disks and the data they contain!
>
> Thank you very much,
> Mike
>

Looks to me like you're trying to solve a 'problem' without knowing what
caused it. For example, when you whacked your finger in the fan blades you
might have also bumped the cabinet and that could be what caused the drive
errors rather than any electrical incident.

Even if it were electrical, you're guessing. Was it a drop in voltage
caused by over current or an inductive spike, or what?

I don't know what size fans you're using, and their current draw, but it's
hard to imagine how one going into stall could over current a 500 watt
power supply and just as hard to imagine how an inductive spike could get
past the PSU's output filter plus the drive's input filter. Not to mention
they're usually current limited with some filtering in the fan itself to
protect the internal electronic brushless motor controller.

If you want to attack this then the first thing would be to characterize
what it is you're attacking. I.E. Put it on a test bench and see what the
effect of a sudden fan stop is.

A simpler solution might be to not stick your fingers in the fan, and I
don't mean that tongue in cheek. I'd think it falls into the same category
as don't kick the case or pull out the power plug while it's running, and
numerous other 'improper operating conditions'. You don't expect fingers in
the fan to be routine, do you?
 >> Stay informed about: Decouple fans and hard disks supplies 

Well, many 8 cm fans have high rpms make lots of noise to push the air. The
problem with cooling is it is often better to bring in cooler air to heat
the the drives from outside of the case.

Heat can build up inside a case so to properly cool the drives, you need
room for air to circulate between the drives. This might require a special
case configuration that allows more drives that are spaced so air can flow
between them. Drives create a lot of heat. When they are stacked one on
top of each other, they are like a giant metal brick.

You may acutally need more than the wattage you have. Some power supplies
can not actually create their max voltage without burning up.

I think you can create more air flow with 120mm fans. They spin at slower
RPMs and move a larger volume of air per fan. You really need a case that
has a good air flow pattern that can move air unimpeded from the front to
the back.

Water cooling might help in a really hot system. Another option is using a
motherboard with a Pentium M Motherboard. There are not many, but some
companies make them. A-Open makes a few and some cube cases have
motherboards with Pentium M motherboards. They run cooler and use fewer
watts and need less cooling. They may run slightly slower but still can
handle a lot of load.

If you have heat problem it may not be the drives. The chipset or the cpu
or the video cards can all overheat as well as the memory. Often memory is
real near to the CPU so that can cause it to overheat.

Power supplies can appear to be functioning and actually be fluctuating.
They can also create more heat if they dont operate at peak efficiency.

This is why the total picture is important. Motherboards sometimes have
problems with chipset fans failing. This is a common problem, especially if
the system is exposed to high Dust conditions. One option could be to put
the computer in a booth and cool the booth. Another option could be to
build the box as a server and have a small client machine access the server
which does most of the work, which is referred to as Thin Client.

"Davy" <no DeleteThis @spam.invalid> wrote in message
news:XMakg.164812$Bk2.61473@fe05.news.easynews.com...
>I don't think I would worry too much, unless of course the fans are
> the 'carbon brush' types which could create a very noisy invironment
> due to the arching, these type's could cause un wanted magnetic fields
> which could cause hum in the audio department or wipe data from the
> hard drive ....!
>
> 'The squirrel cage' motor type's are better in this respect but tend
> to create a high magnetic field which could also cause havoc as above
> due to their large magnetic field, at least these don't create arching
> as they are brushless.
>
> The type's normally used in computers are the 'brushless DC fans',
> true all all motors require a magnetic field to convert power into
> torque, the the filed in these are self contained within the rotor,
> they tend not to generate any external field, no sparking being
> brushless henve no RFI (Radio Frequency Interferance) which could get
> into the logic and audio circuitry.
>
> Modern computers fans require very little power to run, a typical fan
> at the most might only draw between 80 ~ 120MA or 0.08 ~ 0.12 Amp, so
> we can say VxI = P in Watts, being operated at 12V works out 1 ~ 14 W
> appx. I know the logic circuitry is the main power zapper, but feel
> 1 amp is peanuts....!
>
> Does seem strange stopping a fan with a finger would cause data error,
> I would imagine a stalled fan isn't gonna going to do anything apart
> from an increase temperature rise and doubt that a hard drive is not
> that sensitive..... a cpu could be, a thought could be given to the
> RAM chips in this respect, think I'd be looking elsewhere...
>
> unless of course the hard disc are close to melting in it's normal
> environmental conditions..!
>
> Davy
>
 >> Stay informed about: Decouple fans and hard disks supplies 

One thing I just thought about and no one ever asked, including me
........ was the hard drive spinning when you stopped the fan... need
not say more..?

How about dodgy connections..... did you try the proverbial
engineering test.... try tapping around with a insulated object for
bad connectoions etc.

A good clue could be had by the above question.

Davy
 >> Stay informed about: Decouple fans and hard disks supplies 

Quite right Paul......

Just checked for curiousity... a fan I tried draws a 100mA when
stalled drew 220mA, of course all fans will be different - something
I overlooked, sorry folks, read on and you'll see why.

The reason why I did not consider the point that Paul made, a stalled
fan is not going to draw one heck of a lot of current, yes there will
be an increase that is obvious with every stalled motor.... since we
are not dealing with a 'wound' rotor with it's carbon brushes these
will draw much more current than the DC brushless types, so much so
the armateur will burn up..

If the computer is so effected by a such a minute change in current,
obviously leaves the PSU to question, but I would have imagined it
would have been able to cope with this increase..... since ~

no effect had been mentioned when booting up, ie, the hard drive
running or any problems with the added load when any disc drives are
running or how about when the CPU and RAMs are fully loaded....
that's when the PSU is stressed .............. not with a measely
fan.

Oh, and what about the 12V feed for the motor drives..?

Davy
 >> Stay informed about: Decouple fans and hard disks supplies 

On 15 Jun 2006 08:15:24 GMT, mike DeleteThis @spamforbidden.com put finger to
keyboard and composed:

>The best scheme I've thought so far is to link all 6 fans together in
>parallel, then apply power through a circuit like this:
>
>6 fans--*-ind-*-ind-*-ind-*-ind-*-ind-*-ind---diode------*-----PSU +12V
> | | | | | | |
> cap cap cap cap cap cap 6 HDs---PSU +5V
> | | | | | | |
>Gnd ----*-----*-----*-----*-----*-----*------------------*-----Gnd
>
>of course in the above scheme I don't even need them to be six,
>it's simply the more the better, I just happened to have six of
>them on my bench (more or less a coincidence).
>
>But now the big question: what's the right size of the caps, also
>to not overload the PSU at start? Will the diode really help the
>hard disks to not get some bad bad bad back EMF?

Back EMF is usually suppressed by connecting a reverse biased diode
(eg 1N4001) in parallel with the motor.

_____________ +12V
_|_ |
/ \ _|_
| M | /_\
\___/ |
|_____|______ Ground

When the supply to the motor is interrupted, the current continues to
flow in a loop through the diode until it decays.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
 >> Stay informed about: Decouple fans and hard disks supplies