SATA (Serial ATA) is a standard interface for connecting storage devices like hard disk drives and solid-state drives to a computer. SATA was designed to replace the older Parallel ATA (PATA) interface. 3.5 inch hard drives are a common type of desktop hard drive that use the SATA interface. Like all hard drives, 3.5 inch SATA drives require power in order to operate. The amount of power a SATA hard drive needs depends on factors like disk rotation speed, capacity, and if it has features like built-in encryption. Typically 3.5 inch SATA hard drives require between 10 to 30 watts of power during operation. They require 12V and 5V rails from the power supply. Understanding the power requirements for a 3.5 inch SATA drive is important when selecting an appropriate power supply for a computer system.
What is a 3.5 Inch SATA Hard Drive?
A 3.5 inch SATA hard drive refers to a 3.5 inch form factor hard disk drive that uses a Serial ATA interface to connect to a computer’s motherboard. SATA stands for Serial Advanced Technology Attachment and is the primary hard drive interface used in modern desktop computers.
The 3.5 inch form factor means the physical dimensions of the hard drive are about 3.5 inches wide or across, 5.75 inches long, and 1 inch tall. These larger drives are designed to be installed in desktop computer cases and require more power compared to smaller 2.5 inch notebook hard drives.
The SATA interface uses a single data cable to transmit data serially between the hard drive and motherboard. This provides faster data transfer speeds compared to older parallel ATA interfaces. SATA operates at speeds up to 6 Gb/s for the latest SATA III specification.
Power Connectors
3.5 inch SATA hard drives use two main types of power connectors – Molex and SATA power. Molex connectors have been around since the 1980s and were commonly used to power older PATA/IDE hard drives. They have a large 4-pin female connector that delivers both 12V and 5V power. SATA power connectors are the newer standard designed specifically for Serial ATA devices like SATA hard drives. The most common type of SATA power connector is a 15-pin L-shaped connector that delivers 12V, 5V and 3.3V power. There are also 4-pin SATA power connectors on some power supplies that only deliver the 12V power rail.
The 15-pin SATA power connector is the primary method used to power modern 3.5 inch SATA hard drives. This connector has 15 pins – 3 pins for 3.3V power, 3 pins for 5V power, 6 pins for 12V power and 3 pins for ground. The different voltage rails ensure the drive receives stable, clean power for optimal performance. While the Molex connector can still be used, the SATA power connector is preferred as it was designed specifically for SATA devices.
Voltage Requirements
3.5″ SATA hard drives require two different voltage rails to operate – 12V and 5V. The 12V rail provides power for the drive’s spindle motor and actuator, which physically spin and move the platter heads. The 5V rail powers the drive’s electronics and logic board.
According to the SATA power specification, the 12V rail should provide a minimum of 10.8V up to a maximum of 13.2V under load. The 5V rail should maintain 4.75V to 5.25V. Voltage outside these ranges could potentially damage the drive by providing too much or too little power.
Most modern SATA power supplies provide very stable 12V and 5V rails well within the specified range. However, poor quality or failing power supplies may have excessive voltage ripple or sagging rails under load that could jeopardize drive operation or lifespan.
To ensure adequate and clean power delivery, quality power supplies from reputable manufacturers are recommended, along with proper cable gauge for the SATA power connectors. Proper voltage is critical to enabling stable performance and long-term reliability.
Peak Power Draw
All SATA hard drives require more power when spinning up from an idle state versus when operating normally. This startup surge, known as spin up current, is usually the peak power draw for a drive.
According to testing by Tom’s Hardware, a typical 3.5″ SATA hard drive requires around 2 Amps for spin up current when starting from a powered off state. Once spinning, power consumption drops to around 0.7-1.5 Amps during normal operation depending on the specific drive model.
Other sources like Seagate recommend planning for up to 2 Amps for spin up current on most 3.5″ SATA drives. So when selecting a power supply, make sure it can comfortably provide at least 2 Amps per drive on the 12V rail to account for spin up requirements.
While operating, power draw will be much lower. Power consumption during reads and writes will vary slightly, but will usually fall somewhere between 8-15 Watts on average for modern drives. So when running, a standard 3.5″ SATA hard drive will pull under 1 Amp in most cases if activity levels are moderate.
Average Power Consumption
The average power consumption of a 3.5 inch SATA hard drive depends on whether the drive is idle or under active use. When idle, a typical 3.5 inch SATA hard drive will draw around 5-6 watts of power. Under active use, when frequently reading and writing data, the power draw increases to around 6-9 watts on average.
According to testing data from BuildComputers.net, a typical 3.5 inch 7200 RPM SATA hard drive draws around 6.6 watts when idle. When randomly seeking data, simulating an active workload, the average power draw increases to 8.9 watts [1].
Compared to SSDs, hard drives tend to be more consistent in their power draw between idle and load states. SSDs can vary between around 2-3 watts at idle up to 7-8 watts under heavy load [2].
So in summary, expect around 6 watts idle and 9 watts active power draw for a typical 3.5 inch SATA HDD.
Power Supply Selection
When selecting a power supply for 3.5-inch SATA hard drives, the most important factors to consider are the minimum wattage and number of SATA power connectors.
Most 3.5-inch SATA hard drives require between 10-30 watts during typical operation. However, the initial power-on surge or peak load can be much higher, often over 150 watts per drive. Therefore, the power supply needs sufficient wattage to handle all drives at peak load. As a general guideline, a power supply should have at least 150 watts per drive to allow safe parallel start-up.
In addition to wattage, the power supply must have enough SATA power connectors for all the drives. Most power supplies have 4-8 SATA connectors. If more are needed, SATA power splitter cables can be used. However, too many drives on one cable can overload the cable. Best practice is to limit 2-3 drives per SATA cable. So the power supply should have sufficient SATA connectors and cabling for the desired number of drives.
For example, a system with 8 hard drives would require at least a 1200 watt power supply with 8 SATA power connectors. The connectors could be split across multiple cables to provide dedicated power for each drive.
Selecting an appropriately sized power supply ensures all the SATA drives receive stable, clean power for optimum performance and reliability. Underpowered supplies lead to system crashes, data corruption, and drive failures.
References:
https://www.truenas.com/community/threads/choosing-a-psu-for-large-number-of-drives-not-asking-which-but-how.98427/
Power Saving Features
3.5 inch SATA hard drives implement various power saving features to reduce electricity consumption when not in active use. The main power saving states are:
- Spin Down – The hard drive platters stop spinning when not in use. This can save around 20-30% power compared to idle mode. Spin down is triggered after a period of inactivity, which is configurable in the operating system power settings.
- Sleep Mode – In this mode, the drive electronics enter a low power state, with the platters still spinning slowly. According to the SATA-IO, sleep mode consumes around 30-60% less power than idle mode [1].
- Standby/Powered Off – This is the lowest power state where the drive is completely powered down, with no disk spin. It can reduce power by 90% or more compared to idle [1].
The power saving modes are enabled by default in modern operating systems. The timing of when drives enter low power states can be configured in the OS power settings. Frequent spin up/down cycles may increase wear, so it’s recommended not to set overly aggressive power savings [2].
External Power
External 3.5 inch SATA hard drives can connect to a computer through USB or eSATA connections. These interfaces provide both data transfer and power to the drive.
For USB connections, the USB port must supply at least 500mA at 5V to power the drive. This is the standard amount of power provided by USB 2.0 ports. If the drive has a peak power draw higher than this, it may need a supplemental external power source connected to provide enough power. USB 3.0 ports provide up to 900mA at 5V which gives more headroom.
eSATA does not supply power over the cable. An external SATA drive interfacing over eSATA will need a separate power cord connected to supply 12V and 5V power rails. eSATA enables faster data transfer speeds than USB so an externally powered eSATA drive avoids the power limitations of USB.
In summary, 3.5 inch SATA external hard drives generally need to draw power either from a USB port on the computer or from a separate external power brick. Higher capacity drives with more platters and heads may require supplemental external power even when connecting via USB.
Conclusion
In summary, a 3.5 inch SATA hard drive requires both power and data connections in order to operate properly. The power connector supplies different voltage lines including +12V, +5V, and +3.3V, which provide power for the drive’s motor, controller circuitry, and I/O interfaces. Most 3.5″ SATA drives draw an average of 6-10W during normal operation, but can peak at up to 15W during spin up or heavy disk access. This means a power supply should be rated to deliver at least 15W per SATA drive connector. Some drives also support partial power-down states or other power saving features that can reduce energy use when the drive is idle. For most usage scenarios, a standard SATA power cable and connector from the power supply is sufficient to power a 3.5″ SATA hard drive. Using an external power adapter may be necessary for larger capacity drives or other specialty applications that require supplementary power beyond typical SATA power specifications.