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Powering an SSD from the mobo USB header? EDIT: It works!

post #1 of 8
Thread Starter 
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It seems kinda silly to run 5 high-gauge power wires to an SSD that probably pulls less than 5 watts peak. Has anyone made a connection to the motherboards usb or other 5v headers? Doing so would allow power to be snaked along with the SATA data cables, making a really clean build with the possibility of as little as 2 cables from the PSU.

And yes, I'm aware the sata power cable also provides 12v and 3v3. I highly doubt an SSD would use those as laptops don't always supply 12v and molex->sata adapters don't have 3v3.

EDIT: It works!

I decided to test this with my Force GT 120GB / MSI x58M and it is working perfectly.

On a Fluke 115 idle voltage is 5.116 and full load is 4.963. This is within atx spec.

On the same meter idle current is 0.070A and load is 0.656A. Well within USB spec for a pair of ports. Since the header provides 2 ports, it has to be able to source 1A by design and electrically should be capable of at least thrice that.

The x58M has no PTCs that I can see on the board, and obviously the Force GT only requires 5V. YMMV, A capacitor and/or using more than one header may be needed in other setups, but mine does not.

Going forward, I plan to run a single pair of thin-gauge wire heatshrunk along with the SATA data cable, to a sata blade-tap power plug. This will allow for a much cleaner build as there's no need for a heavy-gauge 5 conductor cable with 3 plugs coming off the PSU.

Pictures of my test setup:





Edited by Dyson Poindexter - 1/20/13 at 9:39am
post #2 of 8
Do it! It sounds like it would work. X-D
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post #3 of 8
I think one of those USB-only 2.5" HDD enclosures would be a great source for parts. You'd get a USB to SATA+SATAPOWER adapter completely ready, just cut off the data part.
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post #4 of 8
Thread Starter 
I'm thinking about chopping apart some molex adapters and soldering female pin headers to it. Sadly my main system is down for RMA but at the same time this gives me the opportunity to test on my backup system.
post #5 of 8
Your idea is basically sound, but has one potential problem.

All consumer/client SSDs only use power from the 5V rail. Yes, they have connections for the 3.3V and 12V supplies on a SATA power connector, but they are connected to nothing inside the SSD. I have a technical document for an Intel SSD, that describes all the power and data connections on its input. It clearly states that the 12V and 3.3V power connections are not connected to anything on the SSDs' circuit board. I'm sure all SSDs are the same.

The 3.3V rail is worthless for modern HDDs too, but they use 12V power. That's why you can power a HDD or SSD from a molex to SATA power adapter, since a molex connection just has 12V and 5V rails. You could literally cut the 12V wire on that adapter and plug it into a SSD, and the SSD would work fine.

The problem is USB 2.0 is limited to 0.5 - 0.8 Amps of current. For DC circuits, power in Watts is Voltage X Current, so 5V X 0.5A = 2.5Watts. The initial power spec for USB 2.0 of 0.5A has been modified, and many mother boards can supply more than that, and may have software that enables the "quick charging" feature on USB 2.0 ports, for cell phones, etc. But not all boards have that, and the actual amount of power they will provide over the USB 2.0 connections is unknown.

While SSDs do not use much power at idle, or when reading, anywhere from less than 1W to about 2W or 3W, when writing they use more power. Given the tests I've seen, some SSDs use up to 5W or more during sequential writes. They won't use that much power for very long, but they apparently need it. SSDs are all different in their power usage, and some current models are actually using more power than earlier models. When a SSD starts up when you turn on the PC, it seems to need a short but high burst of power, and may even be checking the available power as a safety feature.

If you've ever used an external 2.5" drive case that connects to a PC via USB, you'll find that many of them have a USB cable with two USB connectors on the PC end of the cable. That extra USB plug is used to provide extra power to the drive, since the manufacture knows one USB 2.0 connector has limited power capability. You plug in both USB connectors on the PC, and the power from both is available to the drive in the enclosure.

Your best bet would be to use USB 3.0 ports as the power source, as they have at least a 1 Amp current capability, so 5V X 1 Amp = 5 Watts. You would no doubt need to create your own USB to SATA power connector, and be careful that the connections are correct. Routing the USB cables from the boards I/O panel is a little messy too, or do you have something else in mind?
post #6 of 8
Thread Starter 
I get where you're coming from, but it's very likely that the USB headers are tied directly to the 5v plane on the motherboards. If they're not, a PTC fuse would be the only safety feature between the plane and pins. I'd would have to guess that if a PTC was in place it would be for both ports on each header, and likely have enough overhead for a couple times the USB spec. current. so 500ma might be 3A before you run into trouble.

Also, the "quick charge" features on most motherboards tends to only assert the data lines in a way to signal to the devices that they are allowed to pull full current, as only 500ma is allowed when USB comms are taking place. Any mobo that allows charging 2 ipads would be capable of sourcing 4.2 A within design.

However, this is all just thought, I'll try to test it tonight!
post #7 of 8
edit: I don't know if you mean to the USB header for data but it's not a good idea.

My father bought 840 pros to use as flash drives...

I can tell you from experience, the USB3 to SATA3 stuff (have used 3 different ones) is not all it's cracked up to be. You can format the drive (and partition), but you cannot update firmware, use TRIM, and Samsung SSD Magician won't recognize the drive. It's only good for migration and storage.

Also the peak thoroughput I get on my Z77 Motherboard via USB3.0 header is 250MB/s via ATTO Bench, which is crap when 840 Pro is listed as 520MB/s write and 540MB/s read and USB is 5Gb/s (compared to 6Gb/s on internal SATA3).

Here's ATTO bench for a USB 3.0 powered 840 Pro 256GB SSD:


128GB 840Pro over USB3


It's faster than USB3.0 flash drives... but I wouldn't recommend it

The things I've plugged in before:
http://www.newegg.com/Product/Product.aspx?Item=N82E16812226046
http://www.newegg.com/Product/Product.aspx?Item=N82E16817182276
http://www.newegg.com/Product/Product.aspx?Item=N82E16817620038
Edited by AlphaC - 1/19/13 at 10:48am
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post #8 of 8
Thread Starter 
Quote:
Originally Posted by AlphaC View Post

edit: I don't know if you mean to the USB header for data but it's not a good idea.
I didn't mean that, but thanks for your insight! This is only for scavenging the power lines. In theory any 5v source on the board would work.
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