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  #1 (permalink)  
Old 22nd January, 2002, 10:43 AM
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FAN Controlers

whats the difference between this one and this one
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Old 22nd January, 2002, 06:28 PM
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The only real difference between the two is, one is made to be placed inside of the case and the other is made to mount in a free 5.25 bay.

The will both serve the same purpose.
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Old 22nd January, 2002, 07:42 PM
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There's not too much difference between the two of them. One uses a voltage regulator (the first link) to control fan speed, the other uses a pair of transistors.

Both are pretty inefficent when they're not running at full power, which is why they need heatsinks.

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Old 27th January, 2002, 02:05 AM
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what about Reostats how Efficient are they ?
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Old 27th January, 2002, 10:09 AM
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Just as inefficent! The problem with most of them is that they generate heat due to the way they control the fan speed by restricting the flow of electricity.

If you're ok with the extra heat, it's not so much of a problem.

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Old 27th January, 2002, 04:38 PM
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A swiching controller is better as it works by turing the current on and off. This disent reduce the voltege to the fan.

A rheostat will just drop the voltage to the fan.

if the voltage is too low the fan wont spin up as you turn on. This is less likely to happen with a swiching controller.

The disadvantage of a swiching method is that you might produce a slight yet irritating hum as the fan "pulses"

Macroman details how to make a simple fan controller at www.bit-tech.net

(sorry mods I cant do links like jesters hidden ones)
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Old 27th January, 2002, 06:29 PM
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The switching controllers have the advantage that they provide higher torque in the motor than linear (rheobus) controllers.

This just means they can start the fan from standstill to a much lower speed.

The "hum" shouldn't happen in a properly designed switching controller, as it should either be filtered, or out of your hearing range.

The disadvantage to most switching controllers is that you don't get the fan speed if you have a 3 wire fan.

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Old 27th January, 2002, 11:51 PM
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any ideas how it is filtered
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Old 17th February, 2002, 01:40 AM
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Quote:
Originally posted by AidanII
[B

The disadvantage to most switching controllers is that you don't get the fan speed if you have a 3 wire fan.

AidanII [/B]
You could make an adaptor with 2 plugs. One for the switching controller and the other for the MB to monitor the rpm.
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Old 17th February, 2002, 03:09 AM
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Quote:
Originally posted by RudyNg


You could make an adaptor with 2 plugs. One for the switching controller and the other for the MB to monitor the rpm.
You will probably get innacurate readings as the RMP monitoring measures "pulses" from the motor..with a swiching controll you might get the "swiches" registering as the fan rotating too.
It might work..but i dont think it would.
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Old 17th February, 2002, 04:13 AM
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The reading will definetly be accurate. It is taken direct from the RPM sensor wire of the fan and pluged onto the MB molex riser, just like plugging the fan direct to the riser.

Take a look at the adaptor here.
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Old 17th February, 2002, 01:38 PM
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Quote:
Originally posted by RudyNg
The reading will definetly be accurate. It is taken direct from the RPM sensor wire of the fan and pluged onto the MB molex riser, just like plugging the fan direct to the riser.
The reading will be wildly inaccurate. The reason is simple.

The switching controller works by sending out a chain of pulses. These pulses power the fan, AND the RPM sensor. As the power to the RPM sensor is being turned off and on thousands of times a second, there's a good chance that the RPM sensor will produce the pulse chain from the switching controller as well as the correct RPM reading. The result will be that the motherboard will either read values that are too high (>20,000RPM) or close to 0.
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Old 17th February, 2002, 01:39 PM
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Quote:
Originally posted by kplonk
any ideas how it is filtered
Either using an inductor and capacitor, or just by moving the switching frequency above 20Khz.

AidanII
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Old 17th February, 2002, 03:12 PM
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Quote:
Originally posted by AidanII


The reading will be wildly inaccurate. The reason is simple.

The switching controller works by sending out a chain of pulses. These pulses power the fan, AND the RPM sensor. As the power to the RPM sensor is being turned off and on thousands of times a second, there's a good chance that the RPM sensor will produce the pulse chain from the switching controller as well as the correct RPM reading. The result will be that the motherboard will either read values that are too high (>20,000RPM) or close to 0.
I cannot understand what you are trying to explain. I have tried sucessfully even by running the fan supply from another PSU and by just tapping the RPM sensor wire from the fan to the MB. The reading as detected from MBM is constantly accurate. The rpm signal from the fan is a single wire and not related to the positive or negative wire of the fan supply. The adaptor that I made is the same as the one that is sold HERE.

I believe you may have not tried this method before or did not know how it is done. Give me some time I write up an article to share my experience in doing this.
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Old 17th February, 2002, 10:19 PM
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Quote:
Originally posted by RudyNg
I cannot understand what you are trying to explain. I have tried sucessfully even by running the fan supply from another PSU and by just tapping the RPM sensor wire from the fan to the MB. The reading as detected from MBM is constantly accurate. The rpm signal from the fan is a single wire and not related to the positive or negative wire of the fan supply.

Ok.. Lets try this:

A switching regulator works by turning the power to the fan on and off at high speed. High speed means thousands of times a second up to tens of thousands of times a second.

The RPM sensor is powered by the power supply to the fan. "The non-isolated techometer(sic) output fan has three leadwires. The power for the tachometer circuit is derived internally from the motor circuit"(Source: Comair Rotron)

As the switching regulator is turning the power to the fan on and off rapidly, the power to the RPM sensor is also being turned on and off rapidly. If the power to the RPM sensor is being turned on and off rapidly, the output from the RPM sensor will also carry this rapid on/off pulse chain.

If your tachometer is based on a counter, then this counter is going to end up incrementing at the same rate as the switching regulator's output - IE, a very large count.

If your tachometer is based on window sampling (some LM series), then the resulting figure will be very small - IE a very small count.

This is a particular problem with switching regulators. If you're NOT using a switching regulator then you won't see this problem. Most "rheobus" bay devices don't use switching regulation, either using a crude voltage divider (rheostat) or an almost as crude transistor operating as a current limit.

AidanII
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Old 18th February, 2002, 01:41 AM
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Quote:
Originally posted by AidanII


Either using an inductor and capacitor, or just by moving the switching frequency above 20Khz.
Or some combination of those things. I'd go with a high switching frequency and an inductor coil myself.
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Old 7th March, 2002, 10:41 AM
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This is my simplistic understanding of the RPM wire is that for every revolution of the fan it contacts the black negative wire. If the black negative wire is not negative then it would unsafe to connect the RPM wire to the MB. This is only what I have read and I haven't checked this out.

Doesn't this mean that with a pulsing or switching supply if the ground wire stays ground then the rpm wire should work?



My further deduction is that these 7v/12volt switch fan control systems would not allow rpm monitoring because the negative ground wire is now 5 volts. Can someone confirm this?
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Old 7th March, 2002, 10:11 PM
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Some further investigation into a couple of fans with Tach wires reveals the following....

The switch is a magnetically operated hall effect switch between the tacho wire and the ground wire. As this is a semiconductor switch, it requires power to operate. No power, no switching.

On one of the fans, the back emf from the motor coils is enough to power the hall effect switch. The RPM sensor will operate as long as the fan blades are turning fast enough (IE, faster than a few hundred RPM)

On the other fan, the back emf from the motor coils doesn't seem to get a chance to power anything. If no power is present then the RPM sensor fails to operate, no matter how fast the fan is spinning.

As you suggest, it should mean that a fan running across the 12V and 5V lines won't permit RPM monitoring.

AidanII
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