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First question here. I saw some posts about powering 2 HDD's from one molex, but I want to power 3-4 drives. I want to use a single molex and use splitters for the rest of the drives.

Below is an image of the power supply I want to use for a 4 Bay NAS. 150W is more than enough power for the setup I want to do, and the size is appealing considering limited space inside the enclosure.

Power Supply Image

It has 1 SATA connector for a drive, but I will need to get power to the other 3 drives, possibly 1 more for the OS if possible.

I'm wondering if I use a molex to 4 SATA cable, if I will have enough power.

I'm just hoping I'm not going to go over the amount of current available on startup, since I know it's going to be one of the most uses of power when all of the disks start up.

Sorry if I did a duplicate question.

Edit: Question already about what power supply limitations are.... So I'll link to the specs of the power supply:

PICOPSU-150-XT

Also looking at 4TB hard drives. Probably WD Green or Blue drives. Hard drives is flexible if the option is available.

Andrew Konken
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    This might depend on your PSU and the power limits per output. What do the specs (typically on a sticker on the PSU), say and how does that compare to the total device current you want to supply from one output? – fixer1234 Jun 23 '15 at 14:23
  • Different hard drives have different power draws and power dissipations. What model hard drives are you looking at for this? – armani Jun 23 '15 at 14:31
  • Thanks for the reply, and that's a good question. I editted the original post to include the Power Supply information instead of the link to the molex to 4 Sata connector. – Andrew Konken Jun 23 '15 at 14:31
  • Gotta run, no time for maths, but here's some hints... this question (http://superuser.com/questions/565653/how-much-power-does-a-hard-drive-use) says a 3TB WD Green drive uses about 21 Watts, and (https://en.wikipedia.org/wiki/Molex_connector) shows the output of a power supply. – armani Jun 23 '15 at 14:35
  • The WD Green spec sheet I linked in my answer shows the WD Greens at far less than 21 watts, except of course at spin-up. – Jamie Hanrahan Jun 23 '15 at 14:37
  • Why use a DC-DC PSU? – Ƭᴇcʜιᴇ007 Jun 23 '15 at 14:43

2 Answers2

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Four drives should be fine.

The maximum current rating for the standard "Molex" drive power connector is 11 amps per pin. So you can get, as far as the connector is concerned, 11A at 5 volts and 11A at 12 volts. These are "returned" through the ground pins, so you don't get 11 more A through each ground pin! The current you return through the ground pins is the same current you got from the + pins.

The +5 usage of a hard drive will be well under half an amp, so we can ignore that.

Most hard drives pull from 2 to 2.5 amps on the 12 volt line for a few seconds when they spinup, so four drives could get you to 10 amps. If this was a continuous draw I would say this was too much, because that "11 amps per pin" is for a 30 degrees C rise above ambient at the connector. 30C is almost 54F. That's a lot! If ambient is 70F that means the +12 pins would be heated to 124F. Not good.

That would make me very uncomfortable if it was a continuous draw, but it isn't -- it only lasts as long as spinup takes. What's the continuous draw? For some reason both Seagate and WD have gone to rating continuous operation in watts, not amps. The typical consumer drives are 8 watts or less, which at 12 volts is less than an amp (again, we're ignoring the draw on the 5 volt line, as it is negligible). With four drives you'd still be under four amps, less than half the connector's ampacity.

So four drives should be fine. I wouldn't try for more, though.

If your motherboard or controller can be set to sequence the startup of your drives, so much the better.

Seagate desktop drive specs: http://www.seagate.com/www-content/product-content/desktop-hdd-fam/en-us/docs/desktop-hdd-ds1770-5-1409us.pdf

WD specs for their "Green" drives: http://www.wdc.com/wdproducts/library/SpecSheet/ENG/2879-800026.pdf

Jamie Hanrahan
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According to the manual for that PSU, it has a 6A max (continuous) draw on the 5V and a 8A max (continuous) on the 12V.

According to WD the 4TB Green drives (currently) pull about 1.75A max (peak). So four of them could be pulling ~7A from the 12V rail (say, during spin-up).

So you should be within the limits, as long as all other devices (including the Motherboard, RAM, CPU, etc.) pull a total of <1A of 12V.

I personally wouldn't do it, as it's way to close for my comfort, and slightly larger PSUs that can handle a bigger load are available.

Ƭᴇcʜιᴇ007
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  • Yeah after looking at the manual that looks to be not quite enough power. To order one of these with the power brick it was starting to get a bit expensive in comparison to other options. – Andrew Konken Jun 23 '15 at 16:20
  • Yeah there's no way. CPU at full load will probably be 3-5A on 12. Then again I have an OCed hex core Xeon (from when you could). ED: yeah 5A*12 is only 60W and I idle in the 200s with four HDDs and an old midrange GPU. – Arthur Kay Jun 24 '15 at 06:28