Consolidating wall wart power supplies - Page 1
Forum section: electronics / beginners

author: HairOfTheDog
author_rank: Newbie
timestamp: November 26, 2012, 09:55:10 pm
content: I built a wooden rack to hold twelve external USB hard drives for my Mac. Though it works great one issue is that I now have to contend with twelve identical wall wart power adapters. All twelve adapters are 12 volt, 1.5 amps. I'd like to consolidate them all into one single power supply with one 110 V (AC) plug. I read in another thread that this could be done by getting a 12 volt, 18 amp (1.5 amp X 12) power supply. Shopping around for such a PSU I see that in addition to being rated by volts and amps they are also rated by watts.So, my two questions...is 12 volts, 18 amps correct?how many watts should it supply?

author: tom66
author_rank: Super Contributor
timestamp: November 26, 2012, 10:46:30 pm
content: It should supply at least 18A at 12V, and 12V*18A = 216W.As a side note, old Xbox 360 PSUs are great for this. I think they provide around 250W at 12V.

author: mariush
author_rank: Super Contributor
timestamp: November 26, 2012, 11:05:37 pm
content: The new Seasonic G-Series ATX power supplies would be excellent for your needs:http://www.newegg.com/Product/Product.aspx?Item=N82E16817151117Relatively cheap at 60$, high quality, gold efficiency, does 360 watts on 12v so you have a full 30A on 12v.It derives the other voltages from 12v so you don't have to care about them or be concerned that the 12v won't be regulated if you don't put any load on those.

author: T4P
author_rank: Super Contributor
timestamp: November 27, 2012, 05:47:54 am
content: Quote from: tom66 on November 26, 2012, 10:46:30 pmNot 250W definitely notQuote

author: peter.mitchell
author_rank: Super Contributor
timestamp: November 27, 2012, 06:01:18 am
content: I still think that would be an OK power supply to use, its size, housing ect is the kind you would need. External hard drives only need that much power when they spin up and are running, I'm nearly certain you wouldn't be using them all at the same time. Additionally, the wall warts provided are pretty overkill, most hard drives only use 8-9W when in use, 7-3W at idle and ~1W when asleep, add a USB-> Sata board, lets say 1W, that's still only 10W, or 0.85A@12V

author: mariush
author_rank: Super Contributor
timestamp: November 27, 2012, 08:47:34 am
content: The hard drive motors may actually pull more than 1A of power when they start spinning, so 1.5A may not be unrealistic, it's quite possible that much is pulled when they first start.Also keep in mind the cases probably have a linear regulator or a poor efficiency switching regulator to create the 5v and/or 3.3v required for the electronic side of the hard drives, so that will also pull a few hundred mA for each drive.An Xbox 360 power adapter is compact and can deliver let's say 150w at least, but I'm not sure it can handle being loaded with about 0.7-1A x 12 = 120w continuously. It may work but it may also be constantly hot, which just dries out the capacitors inside and eventually the adapter goes bad.Regular power supplies make more sense because they're in just a bit larger format but have fan for keeping them cool and you have the added bonus that the cables are already attached - you can take out the yellow and black wires from various power supply connectors and there's your ground and +12v, readily available.Cheap power supplies however have less power on 12v than the total wattage on the label, for example a Corsair cx 430w will have like most cheap power supplies 150w reserved for 3.3v and 5v and the rest, about 250-300w is reserved for 12v. So a 430w may still only give you about 20A of power on 12v.That Seasonic G-Series I linked to above is a special case, it uses an internal design that's more often used on high wattage power supplies or high efficiency supplies ... all the power is generated on 12v and then there are two small converters that generate the other voltages from the 12v output. This way, that power supply can actually output 360w on 12v (30A), unlike other cheap power supplies.So being able to do 30A, you know it's going to have a reserve of power even when you have all 12 hard drives booting up at the same time, pulling 18-20A of power, and you also have some room in case you're going to add more drives to the pack. Also, since the power supply won't be constantly near its maximum designed power output, it won't spin the fan a lot making terrible noise and will be relatively cool.

author: rr100
author_rank: Frequent Contributor
timestamp: November 27, 2012, 08:57:56 am
content: The specs on the xbox power supply (those were the ones that weren't designed to be put on the carpet?) are indeed somewhere around 15A (14? 16? 18?) on the 12V output if I remember correctly. Probably it will work.You have to keep in mind these are drives+enclosures, including the controller and more importantly each one includes some 5V power supply (and some capacitors for sure).Big question here is if these are designed to be powered by hand one by one or just plug in the big power supply and here you go. Because the surge current can be considerable when powering on everything at once; the enclosures that are designed to take many drives have usually some kind of "staggered powered on". Speaking of that I think this configuration with 12 USB drive is one hell of a kludge with way too many points of failure and a high probability of future headaches. Plus I assume the USBs are put together in one or a couple of hubs bringing the speed to a crawl. Any large transfer would take forever, backup would be days or even weeks (depending how large the drives are and where you backup). In short: if you already have the hardware show us some pictures, whole setup is bound to be visually impressive. If you don't have the hardware just don't do it.

author: peter.mitchell
author_rank: Super Contributor
timestamp: November 27, 2012, 12:03:08 pm
content: Quote from: mariush on November 27, 2012, 08:47:34 amIndeed, they may, but the only time they would all spin up at the same time would be when you turn them of/on at the wall socket, or if you have a power failure, I think the xbox power supply would be able to handle this adequately, they are quite powerful units.QuoteThey almost never use linear because hard drives require a reasonable amount of current on the 5v line (500-600ma)QuoteActually, they are designed to run for very extended periods of time under heavy load, they have internal cooling fans, but more importantly, why would they need to constantly provide 120w? Harddrives sleep very quickly and consume less than 1-2w in this mode?Worst comes to worst, just get two of them, put half on one, half on the other, PC power supplies, are big and ugly, you're going to have to mod them to put DC jacks and extra cables on it anyway.

author: ptricks
author_rank: Frequent Contributor
timestamp: November 27, 2012, 12:45:14 pm
content: You can get 12V switching supplies cheap all the way up to 30A. Make sure you connect each item being powered through a fuse in case something goes wrong.http://www.ebay.com/itm/New-12V-DC-30A-360W-Regulated-Switching-Power-Supply-for-LED-Strip-Light-/180852147612?pt=LH_DefaultDomain_0&hash=item2a1ba0c59c

author: G7PSK
author_rank: Super Contributor
timestamp: November 27, 2012, 03:46:58 pm
content: This power supply should do what you need 12 Volts at 33 amps.http://www.ebay.co.uk/itm/12V-33-Amp-switch-mode-power-supply-module-110-240V-AC-Very-high-quality/190760213588?ssPageName=WDVW&rd=1&ih=009&category=58288&cmd=ViewItem