Intel SE440BX-3 mobo -- Max amps from CPU fan header?

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RIVERST0NE

Please, can someone confidently tell me, what is the highest amount of
Amps that can be safely supplied by the CPU fan header on my
motherboard model?

(BTW, I already tried contacting the motherboard manufacturer, but they
no longer provide support for my motherboard model.)

Also, exactly what parts could the high current damage and how could
one tell the damage is being done (ex. PC would just completely shut
down one day)?

The reason I ask is because I need to know if my motherboard can safely
power the new high current CPU fan I purchased.

Here are my specs:
old '99 Dell Dimension XPS T500
Intel Pentium III 500Mhz
Motherboard Model: SE440BX-3
Motherboard Version: AA722396-108
BIOS: 4S4EB2X0.10A.0017.P05 04/22/1999
Online mobo manual:
ftp://download.intel.com/design/motherbd/oem/72698401.pdf


Alternatives...
-- I looked into plugging the fan into the power supply instead of the
motherboard, but one tech that has had experience working on my type of
motherboard found that it would *not* be possible to do.
-- Getting another fan with less amps to lower the current may be
possible, but it will be quite a hassle (for me). I can't buy another
proprietary fan from Dell since the only replacement available from
them is this high current fan. So I would be left having to buy a
non-Dell fan and *rewire* it to the Dell proprietary connector.

I really don't want to have to go through the hassle of rewiring if my
motherboard will be fine with this high current fan. Please help.


Thank you... :)
 
RIVERST0NE said:
Please, can someone confidently tell me, what is the highest amount of
Amps that can be safely supplied by the CPU fan header on my
motherboard model?

(BTW, I already tried contacting the motherboard manufacturer, but they
no longer provide support for my motherboard model.)

Also, exactly what parts could the high current damage and how could
one tell the damage is being done (ex. PC would just completely shut
down one day)?

The reason I ask is because I need to know if my motherboard can safely
power the new high current CPU fan I purchased.

Here are my specs:
old '99 Dell Dimension XPS T500
Intel Pentium III 500Mhz
Motherboard Model: SE440BX-3
Motherboard Version: AA722396-108
BIOS: 4S4EB2X0.10A.0017.P05 04/22/1999
Online mobo manual:
ftp://download.intel.com/design/motherbd/oem/72698401.pdf


Alternatives...
-- I looked into plugging the fan into the power supply instead of the
motherboard, but one tech that has had experience working on my type of
motherboard found that it would *not* be possible to do.
-- Getting another fan with less amps to lower the current may be
possible, but it will be quite a hassle (for me). I can't buy another
proprietary fan from Dell since the only replacement available from
them is this high current fan. So I would be left having to buy a
non-Dell fan and *rewire* it to the Dell proprietary connector.

I really don't want to have to go through the hassle of rewiring if my
motherboard will be fine with this high current fan. Please help.


Thank you... :)
Click to expand...

The exact number should only come from the manufacturer of
the motherboard. It could be 350mA or it could be 800mA.
The limit can be set by the FET next to the fan header
(if one is present) or the limit can be set by the width
of copper track used to join the fan headers to the +12V
supply.

If you get a fan like this:

http://www.antec.com/productImage.php?ProdID=75009

it has a Molex disk drive connector for a power source, and
it has a three pin connector with a single wire connected
to it. The single wire carries the RPM signal, so that if
the motherboard is equipped to monitor RPMs, the single wire
provided the pulsing signal.

You can also get adapter cables, that go from a 4 pin Molex
disk drive connector, to providing power to a 3 pin fan
connector. Then, a standard case fan plugs into the adapter
and you don't use the motherboard header at all. You cannot
monitor the fan speed with that option.

I would be curious why your tech doesn't think a fan can be
powered directly from the power supply. Sometimes, motherboards
rely on seeing an RPM signal (like the CPU_Fan header, for example)
as proof that a cooling solution is connected to the
system. But a fan like the Antec above, has that possibility
covered, by providing a three pin connector that has the RPM
signal on it.

HTH,
Paul
 
Please, can someone confidently tell me, what is the highest amount of
Amps that can be safely supplied by the CPU fan header on my
motherboard model?
Click to expand...

It's generally about 6W total, 500mA per header. A few
might've been lower, only 350mA but that is rare. Even
rarer is any need to run a fan using 350mA, let alone more
current.


(BTW, I already tried contacting the motherboard manufacturer, but they
no longer provide support for my motherboard model.)

Also, exactly what parts could the high current damage and how could
one tell the damage is being done (ex. PC would just completely shut
down one day)?
Click to expand...

On old boards like that, most often it would heat the supply
trace and it would first delaminate then eventually wear
through to be an open circuit. The system will not shut
off, unless it happened to have (as some more modern ones
do) a bios or software monitor that senses fan RPM, a fan
that provides RPM feedback, and the mechanism to shut it off
when fan rpm falls below a certian very very low threshold.

Odds are, your board doesn't have any of that.

The reason I ask is because I need to know if my motherboard can safely
power the new high current CPU fan I purchased.
Click to expand...

Don't use it. There is no need for a CPU fan that uses over
350mA, not even one that uses 250mA. A P3 CPU with a
typical heatsink on it can be cooled sufficiently with a fan
using under 200mA... the rest is just higher RPM, fan wear,
and extra noise. Put simply, you have the wrong fan for the
job and if you want to use it anyway you should consider
getting an adapter and powering it from 5V via the PSU
connectors, or put a current-limiting resistor on it's power
lead (in series). Typically about 68 ohm 2W would be a good
target.
Here are my specs:
old '99 Dell Dimension XPS T500
Intel Pentium III 500Mhz
Motherboard Model: SE440BX-3
Motherboard Version: AA722396-108
BIOS: 4S4EB2X0.10A.0017.P05 04/22/1999
Online mobo manual:
ftp://download.intel.com/design/motherbd/oem/72698401.pdf


Alternatives...
-- I looked into plugging the fan into the power supply instead of the
motherboard, but one tech that has had experience working on my type of
motherboard found that it would *not* be possible to do.
Click to expand...

He's wrong, most likely. THe only issue would be what i
mentioned above, if the board bios detects lack of fan RPM
and shuts system off- if it does that, AND if there is no
way for the user to shut the feature off. It would be very
unusual on a system that age.

-- Getting another fan with less amps to lower the current may be
possible, but it will be quite a hassle (for me). I can't buy another
proprietary fan from Dell since the only replacement available from
them is this high current fan. So I would be left having to buy a
non-Dell fan and *rewire* it to the Dell proprietary connector.
Click to expand...

Maybe if we had more details, like the fan size (dimensions)
and connector the Dell system needs, we could beter advise.
It should not be a hard thing to do, odds are the fan is a
standard size and the connector either soldered or the
plastic plug (only) swapped or ??? (depends on the issues).

I really don't want to have to go through the hassle of rewiring if my
motherboard will be fine with this high current fan. Please help.
Click to expand...

Turn the system on without the fan connected- the system
will not overheat in the few dozen seconds (actually about a
dozen should be enough) to determine if the system shuts off
without a fan RPM signal. If it does not turn off in this
period of time, you can connect the fan to the PSU
instead... but again, it's overkill and you'd be better off
in the long run with a lower rpm, lower current fan.
 
To compare notes about max fan, I had OEM fan in a compaq on a 440 bx @ .36A
, 120mm Large. on a <250 watt psu.
I later monitored it myself with "speed fan" and the like. The delaminating
overheating circuits never happened to me with 440 generation boards, go for
the biggest you want, the MB is newer than some posts may think.
-Barry
 
To compare notes about max fan, I had OEM fan in a compaq on a 440 bx @ .36A
, 120mm Large. on a <250 watt psu.
Click to expand...

That's a very large fan for an old Compaq box, usually they
were no larger than 92mm. What model was it?

The key to fan amerage can be where it was and how the power
was implemented. In your case it was certainly not running
at full speed as that would be unbearably loud and wholely
unnecessary for adequate flow rate (with a 120mm fan) there
must've been a fan control circuit throttling it back.

It is extremely unlikely that any major OEM has ever
produced ANY PC that had a regular-sized fan (60mm or
larger) running at .350mA or higher. That doesn't mean it
wasn't labeled as such, only that it never ran at that full
amperage.


I later monitored it myself with "speed fan" and the like. The delaminating
overheating circuits never happened to me with 440 generation boards, go for
the biggest you want, the MB is newer than some posts may think.
-Barry
Click to expand...


Why would you want one drawing 350mA?
It's unnecessary, loud, accumulates dust faster and wears
out faster. It's just senseless except to save a buck if
that's all that was handy. Again this is speaking only of
actually drawing 350mA, not using a fan spec'd for that in a
circuit that throttles it down below that current
 
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