# How can I power 13 External Hard Drives (requiring 12V, 3A each) using 1 or 2 Power Supply Units?

#### DayCaesar

Joined Feb 20, 2018
10
Hello

This is my first post.

As I'm dyslexic, its easier to ask my question via this video.

I don't have a background in electrical engineering, so if I've missed out any crucial information, please let me know.

Grateful for any advice / solutions

PS In the time it took for this video to upload, I found some useful posts on this forum.

So basically I have 13 devices:

1) 10 devices x 12V 3A = 360W
2) 3 devices x 12V 2A = 72W

So total power needed is 432W.

That's as far as I've got......

#### ian field

Joined Oct 27, 2012
6,536
How about a high power ATX computer supply, such this 600W unit.
Not unless the TS loads the 3.3 & 5V rails to keep the SMPSU chip interested.

#### crutschow

Joined Mar 14, 2008
32,894
Not if you don't load the outputs that are sensed for regulation.
So can't that be provided by some minimum size power resistors?

#### Dodgydave

Joined Jun 22, 2012
10,947
Not if you don't load the outputs that are sensed for regulation.
Just stick a 10 ohms resistor on the 5V rail...

#### DayCaesar

Joined Feb 20, 2018
10
Thanks for all the replies and advice.

I've decided on getting an 750W ATX as suggested by Dodgy Dave, and I've watched several youtube vidoes on converting, so I think I'll manage this up to a point, however, I'm not sure on 2 points:

1) Once I've gathered all the yellow 12V wires, how do I make this into a supply which splits 13 ways each with a
Power Supply Barrel specs of: Outside 5.5mm Inside 2.5mm (Positive Center)? Is there a tidy way anyone can advise me on?

2) Could you advise on putting a resistor on the 3.3v and/or 5v rails as Ian Field suggested above? Do I need to a resister on both rails? Can the resistor be 10 ohms in both cases? How do I actually do this...?

#### Dodgydave

Joined Jun 22, 2012
10,947
A 10 ohms 5W resistor only on the 5V rail will be enough to keep the psu on it will draw 0.5Amp, you need to join the Green wire to any Black to power up the atx,

You can join your barrel connectors to any yellow and black, or join all the Yellows together and join all the Blacks together and put them into a 30A strip connector then wire all your barrel connections to that.

#### ian field

Joined Oct 27, 2012
6,536
Just stick a 10 ohms resistor on the 5V rail...
That's only 1/2A from an output that could be rated somewhere in the general direction of 100A.

The mark space ratio is determined by the sampled rails - the 12V rail usually isn't one of them.

One PITA customer was in the habit of checking ATX PSUs by sticking a hard drive on them - most hard drives draw high current at 12V and low current on5V. Most of the PSUs ended up in my goods in and I had to play hunt the faulty item.

#### crutschow

Joined Mar 14, 2008
32,894

#### Dodgydave

Joined Jun 22, 2012
10,947
The TS reqires 36A total so that could be a little marginal.
Likely more reliable to use two supplies and split the load between them.

Since that is stated to have a single 12V rail internally, perhaps it does not require a load on the 5V output to properly regulate.
YES it would be easier to use two 450W atx psus.

#### ian field

Joined Oct 27, 2012
6,536
YES it would be easier to use two 450W atx psus.
I salvaged a HP generic form factor PSU with 2x high current 12V outputs, but I haven't really followed it up, and it may not have any 5V rails.

#### crutschow

Joined Mar 14, 2008
32,894
YES it would be easier to use two 450W atx psus.
Just make sure its 12V output current rating is a least 25% over the load current.

#### DayCaesar

Joined Feb 20, 2018
10
Thanks again for all the replies

OK so it looks like I'm looking for either a single PSU or two PSU which give me at least 45A.

If I found a single unit which was rated at 45A or above, this seems to be the easiest (and most cost effective) solution.

If such a PSU had just a single 12V rail, would that also let me of the hook with having to add a resistor?

Lastly, thanks for the suggestion about using a strip connector Dodgydave. I saw this one, which is rated at 60A, which I'm guessing will suffice (assuming I find a suitable single PSU), and as it only has 12 connectors, and I need 13, I could just buy 2, and cut to size couldn't I?

#### DayCaesar

Joined Feb 20, 2018
10
The TS reqires 36A total so that could be a little marginal.
Likely more reliable to use two supplies and split the load between them.

Since that is stated to have a single 12V rail internally, perhaps it does not require a load on the 5V output to properly regulate.
What does TS stand for here (excuse the rookie question!)

#### bertus

Joined Apr 5, 2008
22,217
Hello,
What does TS stand for here (excuse the rookie question!)
The TS is the Topic Starter or Thread Starter, the person who created the topic (thread).

Bertus

Joined Jan 15, 2015
7,218
Your numbers are a little high not that it really matters much. Here is an example of 15 Enterprise type drives starting so the start current is plainly visible. I have several drives laying around here and some include current on the labels. Some old non efficient Western Digital Raptors (10K RPM Drives) 5.0 VDC @ 0.70A and 12 VDC @ 0.75A. I also have a WEstern Digital External HDD which uses a 5.5mm Size K DC Power Plug, Powered by a 12 VDC 1,500 mA (1.5 Amp) external supply. All here nor there.

As to the connectors? I recently bought this 10 Pack from Amazon. The package includes one each male and female mating connectors. They are also AWG 18 wire which is nice. A Google of "terminal barrier strips" should get you dozens of hits, as to how to join things together.

Ron

#### crutschow

Joined Mar 14, 2008
32,894
What does TS stand for here (excuse the rookie question!)

#### MisterBill2

Joined Jan 23, 2018
15,630
Thanks for all the replies and advice.

I've decided on getting an 750W ATX as suggested by Dodgy Dave, and I've watched several youtube vidoes on converting, so I think I'll manage this up to a point, however, I'm not sure on 2 points:

1) Once I've gathered all the yellow 12V wires, how do I make this into a supply which splits 13 ways each with a
Power Supply Barrel specs of: Outside 5.5mm Inside 2.5mm (Positive Center)? Is there a tidy way anyone can advise me on?

2) Could you advise on putting a resistor on the 3.3v and/or 5v rails as Ian Field suggested above? Do I need to a resister on both rails? Can the resistor be 10 ohms in both cases? How do I actually do this...?