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Guide: Power Consumption of Minor Components

post #1 of 8
Thread Starter 
This is a guide to the average typical power consumption of "minor" computer components, that is hard drives, optical drives, fans, etc, as opposed to major components like the CPU, graphics card, and mainboard.


Hard Drives

Hard drives vary a bit in terms of power consumption, but most drives spinning at the same rotational rate will have similar power consumption. However, hard drive power consumption varies widely depending on the type of load they are experiencing at any given moment.

A hard drive's platter (or disk) needs to spin in order to operate, and this is generally accomplished by the use of a rotational motor. This motor is powered by the +12V rail from the power supply.

A hard drive also has a read/write head which is moved by a voice coil. There is also ancillary circuitry for interpreting and manipulating the data from the hard drive. These components all run on the +5V rail.

The load on the +5V rail is generally pretty consistent except during read/write activity, when there are spikes as the voice coil operates to move the drive head. Generally the load on this rail is 2-5W.

The +12V operated motor generally uses a small amount of power, 5-8W for a typical 7200RPM drive, 10-15W for a 10kRPM drive. EXCEPT when the hard drive first powers up the platter has to be spun up to speed. Generally in these circumstances a hard drive motor will consume ~20W for a 7200RPM drive, or ~35W for a 10kRPM drive. Because of this large transient load at start, special consideration should be taken when building a NAS or other system with a large number of rotational hard drives to make sure that no cable is too heavily loaded with drives and that the PSU is able to take the large transient load without too much voltage drop.

One other thing must be mentioned. Many "green" hard drives (such as the Western Digital Caviar Green series) employ a technology in which the hard drive's rotation is slowed from 7200RPM down to only 5400RPM when the drive is idle, in order to conserve power. This makes these drives ideal for situations where the drive will be continuously idle for most of the time, punctuated by short periods of sustained read/write activity, such as a backup or storage drive. However, when used in a situation where drive usage varies on a second by second basis, as when running an operating system, the drive may constantly switch between 5400RPM and 7200RPM modes, meaning that the motor is constantly reving up and down. Each time the motor revs up the power supply will experience a 10-20W transient spike on the +12V, which can cause poor power supply performance and even instability.

Summary: On a typical enthusiast system with one to three hard drives the power consumption of these parts will be very low and the drives can be essentially ignored. However special care must be taken when dealing with large RAID arrays or file servers.

Numbers:
7200RPM HDD average power consumption: ~8W - 12W
7200RPM HDD spin-up power consumption: ~15W - 25W
10,000RPM HDD average power consumption: ~12W - 20W
10,000RPM HDD spin-up power consumption: ~30W - 40W



Solid State Drives

Solid state drives are becoming more and more popular among enthusiasts for their extremely high performance compared to traditional hard disk drives.

The vast majority (read: 99.999%) of modern solid state drives use what is called NAND flash memory, which is a high-speed, non-volatile memory (both SLC and MLC SSDs are NAND; just different variations). This technology is found in all modern consumer SSDs, both high-end and entry level.

NAND SSDs generally consume very little power, and this power consumption varies little over time. Most SSDs draw power from the +5V rail, though there are exceptions that draw from the +3.3V or +12V; these are rare.

Power consumption generally ranges from 0.5W to 2W.

There are also rarer DRAM SSDs, which use the same technology as system RAM. This is volatile memory and requires power at all times or data is lost. This technology is virtually never seen today except in certain enterprise applications. DRAM SSDs generally draw 8-20W depending on capacity and speed, and require power from either a battery or the PSU's standby rail when the system is off.

Summary: Typical SSD power consumption is negligible.

Numbers:
NAND SSD: 0.5W - 2.5W
DRAM SSD: 8W - 20W






More to come later.
post #2 of 8
Always a good read.

One thing I wonder though, is there a difference in power consumption between 3.5" and 2.5" drives? I have been reading up on SSDs lately, and at the listed draws it would seem that SSDs would be a clear power saver, but all the information I've come across has stated that SSDs save no battery life at all.

I suppose if you're eating 2Watts on the 5V rail that's 2/5A compared to 8W on the 12V rail which is 4/6A, over a 3 hour session that's ~1200mAh vs 2000mAh which is a fairly big deal if you're on say a 4000mAh battery.
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post #3 of 8
Very nice job, and this will be even more excellent once you have the time to add more in here. For the sake of my personal knowledge could you add a little bit about watercooling as well?
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post #4 of 8
Very nice. Now we can have a better idea how to "calculate" our needs for PSU.
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post #5 of 8
Will you be including chipset and RAM power consumption figures?
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post #6 of 8
Thread Starter 
Quote:
Originally Posted by ocpokey View Post
I suppose if you're eating 2Watts on the 5V rail that's 2/5A compared to 8W on the 12V rail which is 4/6A, over a 3 hour session that's ~1200mAh vs 2000mAh which is a fairly big deal if you're on say a 4000mAh battery.
Actually for the drain on the battery you need to divide the wattage by whatever the battery's output voltage is, not by what the device takes. There are VRMs between the battery and the other components, built into the motherboard.

And the battery output voltage is not the same as the charger voltage. You may have a situation like this.

............................Charger............... ...Battery VRM............MoboVRM
Wall outlet --> 115VAC->19VDC --> 19VDC->14VDC --> 14VDC->5VDC --> SSD
post #7 of 8
Thread Starter 
Quote:
Originally Posted by DuckieHo View Post
Will you be including chipset and RAM power consumption figures?
No. I plan on doing fans, water cooling pumps, mice, keyboards... Things like that.
post #8 of 8
Haven't been on OCN for a while. I've seriously been too busy putting together an amplifier/speakers...and god it's a royal pain the ass...and expensive. But I'm glad to see you've put this up.
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