Power Supplies and Connectors


Servers based on the ATX or microATX form factors generally use an ATX power supply, while pedestal servers based on one of the SSI form factors generally use an EPS12V power supply. Servers that use proprietary form factors, as well as many slimline 1U and 2U servers, use various form factors. The following sections deal with standard types of power supplies and connectors, including ATX, ATX12, and EPS12V, among others.

ATX Power Supply Standards

ATX power supplies were originally designed for use in desktop computers, and they are also widely used in entry-level tower and slimline servers. ATX power supply standards include the following:

  • ATX version 2.03 Older entry-level tower servers

  • ATX12V More recent entry-level tower servers

  • ATX1U 1U slimline servers

  • ATX2U 2U slimline servers

The following sections provide information on these power supply standards.

ATX/ATX12V Power Supplies and Connectors

Motherboards that support the ATX version 2.03 power supply use a 20-pin main power connector, as shown in Figure 4.15.

Figure 4.15. The ATX version 2.03 power supply connector uses a positive-locking plug to secure the power supply cable.


Some servers may also feature a 6-pin auxiliary power connector, as shown in Figure 4.16. This additional connector provides additional 3.3V and 5V power to the motherboard. ATX power supplies with ratings of 250 watts or more feature this connector, but if your motherboard does not feature this connector, you can just leave the auxiliary power connector unconnected.

Figure 4.16. ATX auxiliary power connector.


Most recent servers that use ATX power supplies also feature a 4-pin connector called the ATX12V connector, shown in Figure 4.17. This connector provides additional 12V power to meet the requirements of newer processors, such as the Pentium 4.

Figure 4.17. An ATX12V power connector.


Power supplies that feature the ATX12V connector shown in Figure 4.17 are known as ATX12V power supplies. Most ATX power supplies on the market today, particularly those with 300w or higher ratings, meet ATX12V standards. ATX12V version 1.x power supplies also include the 6-pin auxiliary connector, although most recent servers do not use it.

Figure 4.18 illustrates a typical ATX12V v1.x power supply. Note the 4-pin floppy and hard disk power cables shown above the 20-pin main power supply cable.

Figure 4.18. An ATX12V v1.x power supply.


The ATX12V version 2.0 power supply standard was introduced in 2003. The 6-pin auxiliary connector was discontinued, and the main power connector was enlarged from 20 pins to 24 pins, using the Molex 39-01-2240 connector. ATX12V version 2.0 and newer connectors also feature integrated power supply connectors for SATA drives, which are increasingly common today. Figure 4.19 compares the 20-pin ATX and 24-pin ATX12V version 2.x power supply connectors to each other. The 24-pin ATX12V version 2.x connector uses the same physical connectors as the ATX-GES and EPX12V power supply connectors used in multiple-processor servers.

Figure 4.19. The ATX 2.03 power supply connector (left) and ATX12V 2.x power supply connector (right).


Figure 4.20 compares the motherboard connectors and pinouts used by these power supplies.

Figure 4.20. Pinouts for the ATX2.03/ATX12V v1.x (top) and ATX12V 2.x (bottom) power supplies.


Tip

If your server uses the 20-pin ATX power supply connector, you can use the newer ATX12V v2.x power supply by using a 20-pinto24-pin adapter. Many power supply vendors ship such an adapter with their ATX12V v2.x power supplies, or you can purchase it separately.


ATX1U/2U Rack-Mounted Power Supplies

Rack-mounted servers use a variety of power supply standards. Although most 1U and 2U servers use the power supply standards developed by the SSI Forum, some use the ATX1U and ATX2U power supply standards discussed in this section.

See "SSI Rack-Mounted Power Supply Standards," p. 253.


The ATX1U and ATX2U power supply standards use the same 20-pin ATX power supply, floppy, and hard disk power connectors used by the ATX 2.03 and ATX12V v1.x power supply standards (refer to Figure 4.14). Some 200w and larger ATX1U power supplies also feature the 4-pin ATX12V power supply connector (refer to Figure 4.17), while ATX2U power supplies feature the 6-pin auxiliary power supply connector shown in Figure 4.15.

Figure 4.21 illustrates typical ATX1U and ATX2U power supplies.

Figure 4.21. Typical ATX1U (top) and ATX2U (bottom) power supplies.


Typical ATX1U power supplies use two 40mm fans for cooling, one at the front and one at the back. Typical ATX2U power supplies use a 60mm fan for cooling.

SSI Power Supply Standards

The SSI Forum has developed a series of power supply and connector form factors designed for use in various types of servers. These include the following:

  • EPS12V Nonredundant power supply for pedestal-mounted servers

  • ERP12V Redundant power supply for pedestal-mounted servers

  • EPS1U Nonredundant power supply for 1U rack-mounted servers

  • EPS2U Nonredundant power supply for 2U rack-mounted servers

  • ERP2U Redundant power supply for 2U rack-mounted servers

  • PSMI Power Supply Management Interface

The following sections provide details of these power supplies and connectors.

SSI Pedestal Power Supply and Connector Standards

The ATX12V v2.x power supply standard discussed earlier in this chapter is actually based on the SSI Forum's EPS12V standard, one of the power supply standards developed by the SSI Forum for use in servers.

See "SSI Form Factor Specifications," p. 234.


Because both standards are sponsored in part by Intel, it should not be surprising that features from the SSI EPS power supply standard should eventually find their way into the ATX standard. The EPS12V and ATX12V v2.x power supplies use the same 24-pin connector and the same pinout (refer to Figures 4.18 and 4.19). However, the EPS12V power supply differs from the ATX12V v2.x power supply by providing an 8-pin 12V connector rather than the 4-pin 12V connector shown in Figure 4.17. The additional 12V lines provide sufficient 12V power for multiple-processor motherboards. (Recent and current processors use voltage regulators powered by 12V lines rather than 5V lines as with older processors.)

Note

For motherboards equipped with a 4-pin 12V connector, you can plug the 8-pin cable into the 4-pin connector without needing an adaptor.


An EPS12V power supply closely resembles an ATX12V v2.0 power supply except that an EPS12V unit is somewhat deeper. An ATX power supply has a maximum depth of 140mm, while an EPS12V power supply can be as much as 230mm deep. Because an EPS12V power supply can be used in place of an ATX power supply if the chassis permits, some vendors refer to EPS12V power supplies as "extended ATX" power supplies. If you want to use an EPS12V power supply in a server chassis designed for ATX hardware, check the space available for the power supply and compare it to the depth of the EPS12V power supply you are considering.

ERP12V power supplies use the same connectors and form factor as EPS12V power supplies, but they contain two or, occasionally, three removable power supply modules. Generally, each module has its own AC power cord. By connecting each module to a different circuit, you have protection against AC power failure as well as against power supply module failure.

For more information about redundant power supplies, see "Redundant Power Supplies (RPSs)," p. 675.


SSI Rack-Mounted Power Supply Standards

Although the EPS12V power supply can be considered a "supersized" power supply in both features and form factors, EPS power supply standards for rack-mounted 1U and 2U servers feature much different form factors. While the EPS1U and EPS2U power supplies use the same 24-pin main power connector and other power connectors used by the EPS12V power supply, they feature slimmer form factors designed to fit in rack-mounted cabinets and provide adequate cooling.

Typical EPS1U power supply designs feature a trio of 40mm fans: one at the front of the power supply and two at the rear. Typical EPS2U power supply designs feature a 60mm fan. See Figure 4.22.

Figure 4.22. Typical EPS1U (top) and EPS2U (bottom) power supplies.


SSI has also developed the ERP2U standard for redundant 2U rack-mounted power supplies. Essentially, an ERP2U power supply contains two removable power supply modules similar in size to the ESP1U power supply shown in Figure 4.22. A folding handle can be flipped upright to enable each module to be removed. ERP2U power supplies use the same connectors as other SSI power supplies. See Figure 4.23 for a typical example.

Figure 4.23. Rear view of a typical ERP2U redundant power supply.


ATX GES and WTX Power Supply Connectors

Although all recent x86 server motherboards with 24-pin connections are designed to use either ATX12V v2.x or EPS12V power supplies, some servers use one of two other power supply standards:

  • AMD developed the ATX GES power supply standard to support its first server-class processor, the Athlon MP, when used in dual-processor (two-way) configurations.

  • Some servers based on the Intel 860 chipset used a version of the WTX power supply standard.

Caution

Because the ATX GES and WTX power supplies use different pinouts than the ATX12V and EPS12V power supplies, if you install an ATX GES or WTX-compatible power supply in a server designed to use ATX12V v2.x or EPS12V, or vice versa, you will damage the motherboard and power supply.


The WTX power supply pinout listed in Table 4.8 was used primarily by motherboards based on the Intel 860 chipset and the first-generation Xeon processor based on the Pentium 4. These motherboards include the Tyan S2608 (Thunder i860), Iwill DP400, and MSI MS-6508. These motherboards also used a 6-pin CPU power supply connector to provide additional power for the motherboard's CPU power regulator.

Table 4.8. ATX-GES, EPS12V, and WTX 24-Pin Primary Power Connector Pinouts

Pin #

ATX-GES

EPS12V ATX12V

WTX

1

+5V red

+3.3V orange

+3.3V orange

2

+5V red

+3.3V orange

+3.3V orange

3

GND black

GND black

+3.3V orange (Sense)

4

GND black

+5V red

GND black

5

PS-On green

GND black

GND black

6

GND black

+5V red

+5V red

7

+3.3V orange + orange

GND black

+5V red (AUX)

8

+3.3V orange

Pwr-OK gray

GND black

9

GND black

+5V SB purple

GND black

10

GND black

+12V yellow

GND black

11

+12V yellow

+12V yellow

PC

12

+12V yellow

+3.3V orange

FAN C

13

+5V red

+3.3V orange and brown

+3.3V orange

14

+5V red

-12V blue

+3.3V orange

15

GND black

GND black

GND black

16

+5V SB purple

PS-On green

GND black

17

-12V blue

GND black

+5V red

18

GND black

GND black

+5V red

19

+3.3V orange

GND black

+5V red

20

+3.3V orange

-5V white

-12V blue

21

+3.3V orange

+5V red

+12V yellow

22

GND black

+5V red

+12V yellow

23

GND black

+5V red

PSON

24

+12V yellow

GND black

FAN M


The ATX GES power supply standard shown in Table 4.8 was used by the Tyan Thunder K7 (S2452 series) and Tyan Thunder K7X (S2468 series) motherboards made for the AMD Athlon MP processor. Note that the Tyan Thunder K7X Pro uses an EPS12V power supply.

Table 4.8 compares the pinouts of the ATX-GES, WTX, and EPS12V/ATX12V v2.x 24-pin primary power connectors.

If you need to replace the power supply in a server, be sure to verify what standard it uses. Some power supply vendors list specific motherboards or system compatibility information on their websites to help you select the correct power supply.

Note

The ATX GES power supply also uses an 8-pin processor power connector: Pin 1 provides +5V, pin 2 is used for power good, pins 35 provides ground, and pins 68 provide +12V. The WTX power supply also uses a 6-pin processor power connector: pins 13 provide +12V, and pins 46 are signal grounds.





Upgrading and Repairing Servers
Upgrading and Repairing Servers
ISBN: 078972815X
EAN: 2147483647
Year: 2006
Pages: 240

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