CPU/fan

  • Thread starter Thread starter bob
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bob

Anyone know what the metal slivers are above the CPU on a Dell
Optiplex? They get hot.

Also, anyone know why the fan has 3 pins? Isn't 2 enough?

Thanks.
 
The extra wire allows the fan speed to be
monitored so fan failure can be detected.


Nope, not to detect fan failure.
Click to expand...


Depends on the design, I have a PSU that does detect fan
failure by monitoring only the 2 (power/gnd) wires. Stick a
straw in to stop the fan, PSU shuts off. Liteon 300W Server
Supply, for Compaq IIRC.
 
Depends on the design, I have a PSU that does detect fan
failure by monitoring only the 2 (power/gnd) wires. Stick a
straw in to stop the fan, PSU shuts off. Liteon 300W Server
Supply, for Compaq IIRC.
Click to expand...

More reliable with 3 wires when any fan can be plugged in.
 
Rod said:
More reliable with 3 wires when any fan can be plugged in.
Click to expand...

A circuit can be used that will detected fan failure with ANY two
wire fan. Simply monitor the time between current pulses. Once the
fan stops, the circuit times out, as does whatever it was designed
to do. Simple circuit, really.
 
UCLAN said:
Rod Speed wrote
Click to expand...
A circuit can be used that will detected fan failure with ANY two wire fan.
Click to expand...

Yes, but its reliable to check the speed with a 3 wire connection.
Simply monitor the time between current pulses. Once the fan stops, the circuit times
out, as does whatever it was designed to do. Simple circuit, really.
Click to expand...

And a 3 wire connection allows you to see the speed as well.

There's more involved than just running/not running.
 
A circuit can be used that will detected fan failure with ANY two
wire fan. Simply monitor the time between current pulses. Once the
fan stops, the circuit times out, as does whatever it was designed
to do. Simple circuit, really.
Click to expand...


This particular PSU can also discriminate a very low RPM, I
think it triggers below about 200-300 RPM. I have more than
one of them and on one I have tried different fans. Some
fans work, others have a low (electrical) noise design and
the PSU won't run at all with them.
 
Anyone know what the metal slivers are above the CPU on a Dell
Optiplex? They get hot.

Also, anyone know why the fan has 3 pins? Isn't 2 enough?

Thanks.
Click to expand...

The CPU generates quite a lot of heat.
most of the energy it takes from the mains, it converts into heat.
No wonder: the thing has millions of transistors in it, all working
very hard for you. So it starts to "sweat" just like you do, when
working hard.
One of the major problems in designing a CPU is getting rid of this
heat, to avoid "melt down".
Packing too many transistors on too small a surface, would burn the
CPU...
So we have to take the heat out of the CPU. You can do that by
mounting a "heatsink" on the CPU (the metal slivers thingy)
The effect is, that the surface that can transmit the heat to the air
is greatly enlarged. That's where the fan comes in: it speeds up the
airflow over the fins of the heatsink, thereby improving the heat
dissipation.
If the fan breaks down, the heat cannot get away quick enough, and the
CPU will burn anyway... so it's a nifty idea to monitor the
functioning of the fan. Hence the 3rd wire on the fan.

(next would be to monitor the fan speed monitoring electronics ;-)

There is a heat conducting paste between CPU and heatsing, to make
heat transport between the two parts easier. (finnicky, but it shows
how important heat dissipation is)

Once you have the heat taken off the heatsink by its fan, the hot air
must be blown out of the casing too... so many have a case fan too,
like a second stage...
Of course, you must leave enough room behind the case, to let the air
out, or else...
(like you leave enogh space behind your fridge to let the thing get
rid of the heat it took out of your food. A fridge is heating
equipment, in effect.)



Heat in computers is a major point of interest... Graphics cards often
have a fan too. hard workers too, the high end things...
 
kony said:
This particular PSU can also discriminate a very low RPM, I
think it triggers below about 200-300 RPM. I have more than
one of them and on one I have tried different fans. Some
fans work, others have a low (electrical) noise design and
the PSU won't run at all with them.
Click to expand...

The above circuit does that, too. As the fan slows, the current
pulses get further apart. These pulses feed the input of a simple
comparator. The output charges a cap. If the pulses get too far
apart, the cap discharges to below an adjustable level and sounds
an alarm, shuts down the PSU, or whatever you want it to do. A pot
adjusts the RPM level for a wide assortment of fans.
 
UCLAN said:
The above circuit does that, too. As the fan slows, the current
pulses get further apart. These pulses feed the input of a simple
comparator. The output charges a cap. If the pulses get too far
apart, the cap discharges to below an adjustable level and sounds
an alarm, shuts down the PSU, or whatever you want it to do. A pot
adjusts the RPM level for a wide assortment of fans.
Click to expand...

You dont need any manual adjustment with the 3 wire system.
 
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