Quiet PC

This PC was built with the following objectives in mind:
-PC workstation with entry level performance
-without expensive components and high priced cooling solutions
-low noise
-low power consumption
-good reliability

In our project, we have considered a motherboard and a power supply that are supposed to run without fan (cooling by free air convection). We chose Intel D510MO embedded fanless mainboard. Analyzing the power consumption (including one 3.5" hard disk and an additional PCI network adapter), we found that a 110 W rated power supply is enough for this computer.

Figure 1
Motherboard
Figure 2
Power supply
Figure 3
120 mm fan
Figure 4
60 mm fan

Motherboard - Intel Desktop Board D510MO (embedded):
- integrated (soldered onboard) 1.66 GHz Intel Atom D510 processor (2 cores, 4 threads) with a passive heat sink
- Intel NM10 Express Chipset
- support up to 4 GB DDR2 800 MHz memory
- integrated 1Gb/s Ethernet controller - Realtek RTL8111DL
- integrated video Intel GMA 3150
- integrated audio controller - Realtek ALC662
- integrated legacy I/O controller Winbound W83627TGH-I: two serial ports, one parallel port, PS/2 keyboard and mouse ports
- other interfaces: two SATA 3Gb/s ports, seven USB 2.0 ports
- one PCI slot (in the end, we have installed on it an additional network adapter: Intel PRO/1000 GT)
- one PCI Express Full-Mini Card Slot
- small form factor: Mini-ITX
- low power consumption
- low price

Power Supply - PPQ 1003B:
- 110 W rated power
- quad output (+3.3 V, +5 V, +12 V and -12 V)
- built-in active PFC function
- CE conformity
- switching frequency: 67 kHz
- 100% full load burn-in test with quality engineering test report
- open PCB power supply (without frame)
- short circuit, overload and overvoltage protection
- does not have a built-in voltage supervisor circuit (it is not compatible with TFX12V/SFX12V/ATX12V standards and this is a big disadvantage when it is used in PC applications)

Hard disk:
- the use of a solid state disk (SSD) is recommended. As an alternative option, a SATA model can be used. Our prototype was built with a Seagate ST250DM000-1BD141 250GB hard disk.

Case:
- we have used an old slim aluminium enclosure, initially designated for other not finished project, which was lying around for many years. We have adapted this case to our purpose. There is room inside for two 3.5" hard disks. Also this case acts as a heatsink for the hard disks. You can use any case you want: mini-ITX, ATX-desktop, minitower and so on, new or second hand. You have to find a possibility to mount the power supply and the motherboard in your case. Because the power supply and the case used in this project are non-standard for PC, we have used 12 mm metal hexagonal threaded spacers to mount all the components inside. The case is vertically positioned for better air circulation.

Fans:
- there are two fans in our project, first one is used for power supply and second one is used for mainboard. According to PPQ-1003 data sheet, with natural convection cooling, we can obtain only 70 W on continuous running. To obtain 100 W, we need a forced air cooling of 17 CFM at least. For that, we have used an ultra-quiet 120 mm fan made by Akasa: AK-183-L2B, 12V DC voltage rating, with 1400 rpm fan speed and 44.8 CFM airflow (nominal values). Because is no need for the nominal airflow, we have decided to supply this fan with a reduced voltage of 5V DC, which correspond to approx. 600 rpm. The airflow obtained is enough to keep the power supply board and the heatsink at reasonable temperatures. In this way, the noise level created by this fan is also decreased significantly.

The second fan is used to create an air flow for the motherboard (the heat sink of the processor and the RAM modules). The fan we have chosen is a MagLev ME60151V2-000U-A99 from Sunon (low acoustic noise level, high reliability, auto restart, dust resistant). This is a 12 V DC rated fan, but we have used 5 V DC as power supply for it. The fan acoustic noise level is also reduced by powering it with a lower voltage. (This fan can still work even if it is powered with 3.3 V.)

The motherboard has a fan output with PWM capability. According to our tests, in this particular case, to obtain a lower acoustic noise level, it is better to use a lower than nominal voltage for the fans power supply instead of using PWM. The only condition is to test the fans at these voltages, before using them in PC, to be sure that always start to rotate at power on.

We have performed some temperature measurements (figure 5 and 6, when the ambient temperature was 26°C and without heavy CPU usage). With fans stopped, CPU temperature was around 42°C and the power supply temperature around 57°C (close to the 60°C limit for this device). With fans running, the temperatures have been decreased to around 35°C for both CPU and power supply. Figure 7 was taken with fans running and ambient temperature close to 30°C.

Figure 5
With fans
Figure 6
Without fans
Figure 7
Ambient temp 30°C

Supervisor circuit board:
- the power supply we used has no voltage supervisor circuit, so we had to build one. The schematic diagram of this circuit is in figure 11. It was designed by us. We have used a TL7705 integrated circuit to create the Power Good signal needed by motherboard. If you don't want to make the complete circuit which will test the minimum level for all the voltages (+5 V, +12 V, +3.3 V and -12 V), you can use a simplified one with only the TL7705 chip which will test for +5 V only. However, we recommend you to build the whole circuit.

Power Cables
- Figure 10 shows the schematic of the power cables between power supply, motherboard, voltage supervisor board, hard disk and other peripherals. The motherboard has a 2x12 pin connector for power supply (that requires TFX12V or SFX12V power supply), but with some workaround wiring you can use, as we did, a 2x10 pin connector (old ATX12V 1.0 or 1.3 standard). You can see the pin connections in the schematic drawing. In our design, we have used a single supply line for both +5 V and +5V SBY.

Additional network adapter
- the mainboard includes one LAN interface based on RTL8111DL chip. It will work acceptable when this PC is used as a workstation with any Linux or Windows operating system. If you want to use this PC as a server, it will be better if you will add a network adapter with higher performance (like Intel Pro 1000 MT / GT or similar, with PCI interface).

We have successfully tested on this computer several operating systems Linux CentOS 5/6/7, RedHat Enterprise 7 and Windows XP/7/8/8.1/10. Remember, this is an entry level PC, there is no room for very high performance. It was not built for gaming.

Figure 8
Figure 9
Figure 10
Power cables
Figure 11
Supervisor
Figure 12
Layout

Warning: The power supply of this computer is an open frame device. If you choose a similar model, be careful when you work with the case open. There are hazardous voltages inside and there is no barrier between hazardous voltage parts and your hands as in other ordinary computers.

Disclaimer: The information on this web site is provided "AS IS", without warranty of any kind. The author has made the best efforts to ensure the design and the information provided are reliable. Under no circumstances shall the author be liable for any direct, indirect, incidental, special or consequential loss, damage, expense or injury incurred or suffered which is claimed to resulted from use of this site, even if expressly advised of the possibility of such loss, damage, expense or injury, including, without limitation, any fault, error, omission, interruption or delay with respect thereto.

Links:
[1] - Intel page for D510MO motherboard
[2] - PPQ-1003 power supply