#5 Projek Integrasi: Fan Power Supply Requirement

Let's continue with Projek Integrasi determination of the fan power supply requirements.  I currently have three fans which I have hoarded  acquired over the years:
1.  Seada 12V 0.28A 120mm fan
2.  Yuh Jonq Inc 12V 0.13A 80mm fan circa 1994
3.  Intel  12V 0.17A 90mm CPU fan
All three fans were characterized by supplying a variable voltage and measuring the current drain.
Wind speed is the desired variable, but I simply do not have a good way of measuring wind, so I'll base it on "feel".  I might later consider a DIY thermal mass flow meter for this purpose.

Black box is unregulated supply, grey box is variable voltage regulator based on LM317, blue DMM measures voltage,  green el cheapo DMM measures current.  Fan under test is from Intel.

Seada 12V 0.28A

Yuh Jonq 12V 0.13A

Intel 12V 0.17A

The final result is as follows:

All three fan responses are plotted on a single graph.  The point where the fan starts to spin up is marked.  Seada starts to spin at the lowest voltage, around 3V.  Overall, it also has the fastest wind speed, at the expense of current drain and noise.  It was noted that the Seada fan at 9V (200mA) produces more wind and than the other fans at 12V, and at an acceptable noise level.  This means that I can put a resistor in series with the fan to drop some voltage so that 9V is presented across the fan and 3V across the resistor.  At 200mA, this works out to be 3V/200mA = 15 ohms.  The power rating of this resistor should be 3V*0.2 = 0.6W at least.

Options:
1)  Drop 3V across a resistor - need 15ohms 0.6W resistor, fan will draw 200mA
2)  Drop 4V across a resistor - need 22 ohm 1W resistor, fan draws ~ 184mA
3)  Drop 5V across a resistor - need 30 ohm 1W resistor, fan draws ~162mA

Whatever it is, it is still possible to use a 12V supply to power the fan at full blast, at the expense of 0.27A current drain.  Based or earlier 1A requirement of the ADSL modem and wireless router, the minimum power supply requirement for everything (modem + router + fan) is thus 12V 1.3A (if no resistor is used).

And what do you know?  Just weeks earlier, I purchased this 12V 1.3A SMPS (switch mode power supply) from Tonsin for RM30.  It was intended for another project, but what an amazing coincidence!

SMPS 12V 1.3A - never been tested yet

Summary of power supply requirement:
1) Power supply requirement for fan alone is 12V 0.3A at maximum wind speed, current requirement could be lower if use a series resistor to drop off some voltage
2)  Power supply requirement for total Projek Integrasi is 12V 1.3A

In the next Projek Integrasi post, maybe I'll discuss the user interface and touch some aspects of the case design.  I foresee a struggle with "antaramuka" lingo hahhahhaa!