My New PWM (4-wire) Fans



JMC 1225-12HBHA-PWM with control circuit visible in the background.


Manufacturer's specifications:

120x25mm PWM fan
3600rpm
40 – 135CFM
0.55a


Overview:
4-wire fans are gaining in popularity and offer several significant advantages over the more common 3-wire variety. With typical 3-wire fans running with a PWM fan controller, the operating voltage is switched off and on to control speed. This presents a problem as power is not on long enough to complete an entire tach cycle. The PWM drive in effect chops the tach signal output an may produce incorrect readings. To obtain an accurate measurement it is necessary to occasionally provide a longer pulse. This technique is known as pulse stretching and can contribute to commutator noise.

In contrast, 4-wire fans provide constant power to the fan. Electronics continue to function at full power even as the drive coils are pulsed resulting in acoustics almost as good as linear (constant dc) power. The component count in circuits used to drive and monitor 4-wire fans is substantially reduced. Driving the coils at rates greater than 20 kHz moves the noise outside of the audible range, so typical PWM fan-drive signals use a rather high frequency (>20 kHz). My circuit consists of a low voltage power supply, a thermistor with an input to a microprocessor's analog to digital converter (ADC) and a built in PWM generator. A “C” program burned into the microprocessor runs continuously sampling the thermistor voltage and setting the PWM duty cycle accordingly. For testing the PWM duty cycle can be varied with a potentiometer. The circuit is very simple and the use of a microprocessor makes changes easy without circuit modifications.



Control methods.



JMC 7015-HBA-PWM with 4-pin connector.


Manufacturer's specifications:

70x15mm PWM fan
4200rpm
32.3CFM
0.35a


Pin connections:

Black = GND
Yellow = 12V
Green = Tach
Blue = PWM




4-wire fan control circuit.


Tests:
I connected a Nexus 120 with a fan-mate to a molex connector. I compared the two fans by running the Nexus at 11.65V ~ 1000rpm, and adjusting the potentiometer of the PWM controller to drive the JMC at roughly the same CFM as the Nexus. I haven't been able to monitor rpm so far and the voltage at the fan is a constant 12V.

I then set the Nexus 120 voltage to 5.00V and adjusted the JMC accordingly. At both settings the noise seemed equal. I noticed small variations in whirl pooling between the relatively flat JMC blades and the curved blades of the Nexus. This is impressive as the JMC PWM fan is rated at 3600rpm, yet weighs no more than a 1600rpm low speed model. PWM fans seem to be offered in only high speed models as they can easily function at low speed with a 10% duty cycle.

Whirl pooling:
This is a broadband noise source generated by air separation from the blade surface and trailing edge. It can be partially controlled by good blade profile design, proper pitch angle and notched or serrated trailing blade edges

Conclusions:
The JMC produces noise levels comparable to the Nexus at both 5.00v and 11.65V when creating approximately the same air flow. I attribute this performance to the use of high frequency PWM. Noise is slightly lower that my 3-wire JMC 1225-12L low speed driven through a T-Balancer. The JMC 3-wire fans in my experience do not exhibit PWM howling. It is also worth noting that this fan has a nominal speed of 3600rpm and a current draw of .55a. So far, it does seem that this fan is capable of very low noise levels at low to moderate speeds. Of course anything over 1500rpm will be noisy for a quiet fan. - FG

References:
1. Application of PWM Fan Control by Michael Huang
http://www.coolingzone.com/Guest/News/N ... _2003.html
2. Analog Devices Analog Dialog by Mary Burke Vol. 38, Feb. 2004
http://www.analog.com/library/analogDia ... speed.html

I remember seeing these long ago and trying them out (the 3 pin, not 4), and then seeing the new 4 pin PWMs pop up @ FrozenCPU. My initial impression after hearing their noise was a mere 'meh'. Your findings proved to be insightful ;P.

Nice work frankgehry, good to see you still posting up SPCR goodness.

A rig with this setup would be a killer OCer setup while with spcr quiet on demand. Tempting...

Hi Frank,

nice post. I have never tested these 4-pin fans, so nice to get an opinion about them. Thanks.

Interesting. I guess that the fans PWM input can also be used with voltage regulation, if one does not desire PWM.

This makes it so much easier to make a colsed circuit fan controller, where the controller actually measures the speed of the fan, in order to control it, and not just assume that 50% PWM duty cycle is equal to 50% speed.

S,

Without a PWM signal the fan will run at a default duty cycle - around 10% of full speed. I guess you could set the duty cycle to 100% and then vary the voltage.

You are right about closed loop control. Many controllers are designed to work like an automobile cruise control. You set the default rpm, and if the voltage drops, load increases, or the fan is out of spec, the controller will step up the duty cycle. - FG

Oh, I overlooked that fact. Thanks for correcting.

Were can you get the 3pin 70mm versions of these fans in the uk?
I could do with one to replace my 70mm tmd /92mm fan with ghetto fan duct on my vantec aeroflow.

You can go to www.jmcproducts.com > distributors. There's only one in the US but email Charles and he may be able to help you. - FG

You can also check www.dorothybradbury.co.uk to see what's available in a panaflo model. I have an 80x15mm panaflo that's very quiet.

Frank,

It seems pretty obvious that you like those JMC fans, and from this post (and others) you're convinced they are very quiet. How much do the 3-pin low-speed fans cost, and can they be ordered with the tail already attached?

G,

I get them from Skyline Graphics in Dallas, TX. They are the only distributor listed on the www.jmcproducts.com website and you can contact Charles Boyd at enilyks1@msn.com for current prices and availabiltiy. I believe the 3 pin 120x25's are ~ $12 maybe $14 and the 80 and 92's are $8. The PWM fans are more expensive at $12 - $20. They all come with connectors and tach wires. I have seen a few at www.directron.com at low prices, but I'm not sure if they are 3 wire. - FG

We also carry a 92mm PWM fan in a 92 x 38mm dimension.

http://www.adpmods.com/case-modding/pro ... uctid=1705

Probably best suited for "power" cooling.

These fans are from ARX who are the originators of the ceramic bearing design.