Author Topic: What are these fan motors and what not to do ?  (Read 124 times)

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Offline lordvader88

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What are these fan motors and what not to do ?
« on: June 13, 2019, 08:02:10 am »
I want to use a 4pin intel i3/5/7 CPU cooler fan and it's.heatsink. Here's a few spec's
They have +12Vin,GND, PWM and a sense pin. I want to drive it with some basic 555 circuit. Any idea what level voltage and current is meant to be feed to these, AC or DC ? IDK if there's active circuitry in these motors, IDK for sure what type they are. They're all pretty standard tho, because all CPU coolers are motherboard driven and work on any MB.

Also they don't list zero rpm as the minimum speed, is that excluded for any real reason ? Maybe these fans are all digital, maybe I should use a common 12V fan and just PWM a driver FET or BJT

Online mariush

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Re: What are these fan motors and what not to do ?
« Reply #1 on: June 13, 2019, 08:19:40 am »
It's standard 12v DC ... ATX standard says +/- 10% tolerance, so up to 13.2v DC should be tolerated.
3rd wire is rpm sensor, two impulses for each rotation of fan
4th wire is pwm signal ... it's standardized and in specification  ... see the attached file.

pwm can't turn off fan ... it's designed to work between 30% of maximum rpm or less (but minimum guaranteed to get fan working from full stop) and 100%.

I'll quote it anyway

The following requirements are measured at the PWM (control) pin of the fan cable connector:
PWM Frequency: Target frequency 25 kHz, acceptable operational range 21 kHz to 28 kHz
Maximum voltage for logic low: VIL = 0.8 V
Absolute maximum current sourced: Imax = 5 mA (short circuit current)
Absolute maximum voltage level: VMax = 5.25 V (open circuit voltage)

Minimum Fan Speed Requirements
The vendor shall specify the minimum RPM and the corresponding PWM duty cycle. This
specified minimum RPM shall be 30% of maximum RPM or less. The fan shall be able to start
and run at this RPM. To allow a lower specified minimum RPM, it is acceptable to provide a
higher PWM duty cycle to the fan motor for a short period of time for startup conditions. This
pulse should not exceed 30% maximum RPM and should last no longer than 2 seconds. See

Fan Speed Response to PWM Control Input Signal

The PWM input shall be delivered to the fan through the control signal on Pin 4 (see Section 2.4).
Fan speed response to this signal shall be a continuous and monotonic function of the duty cycle
of the signal, from 100% to the minimum specified RPM. The fan RPM (as a percentage of
maximum RPM) should match the PWM duty cycle within ±10%. If no control signal is present
the fan shall operate at maximum RPM. See Figure 2.

« Last Edit: June 13, 2019, 08:21:19 am by mariush »
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Offline lordvader88

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Re: What are these fan motors and what not to do ?
« Reply #2 on: June 13, 2019, 08:33:01 am »
Excellent. If I had more LED displays and CD4026's, it would look really cool to have the fan RPM and loadtester temp, but that can wait for today anyways.

Assuming CD4026 can be used to display a 2 or 3 digit temperature somehow, looking into that now, perhaps if it can only count, I'll make a V2F circuit.

A loadtester should have a big temp display, or at least some LEDs driven with comparators, that would look cool, and an alarm and auto-shutdown
« Last Edit: June 13, 2019, 08:42:51 am by lordvader88 »

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