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There are various external USB drives, some require external power supplies, some have optional external power supplies, some have 2 USB plugs, 1 for power and 1 for power + data. If I have a device with a single USB 2.0 port, is there any way to find out if a specific USB DVD reader will receive sufficient power through that port, other than manually testing the drive by plugging it in?

Based on existing answers, comments, and close votes, some people may not be familiar with the problem: The maximum power delivered through USB ports varies by implementation. Not every USB2.0 port is the same. Many (or one be tempted to say "most") notebooks and tablets have underpowered USB ports. The same is true for USB 3 ports. Random example: http://forum.tabletpcreview.com/threads/surface-pro-3-problem-with-external-dvd-drive.63207/

But many of the Windows Tablets deliberately under-power the USB Port to conserve the battery life, the SP3 happens to be one that does this (SP2 as well)....not having the Power Connector is why I suggested the "Y" cable, it ensures that the device gets the 5 volts needed to power the device....

Background: I'm looking for a pair of a 300-400$ "Atom" laptop/tablet and a DVD drive where the DVD drive has to be connected with a single cable (not 2 USB cables, no additional power cable). I don't care about writing DVD, or about any speed beyond "fast enough to play a movie".

The only working approach that I currently know of is to search the internet for customers using a specific device, who write how they already tried a couple drives that didn't work, and then finally found one model that worked. But I really hope there's a better approach.

Peter
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  • This is hard to answer as the answer is - if you get an external DVD which only requires 1 x USB2 cable connection then the answer is yes. But you don't state the external DVD you want and as such, it's too broad as the answer is "depends on the external DVD" – Dave Feb 23 '15 at 09:10
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    Maybe you help us to help you by **enhancing your question** by adding (1) how many milliampers your USB ports can supply and (2) how many milliampers USB DVD reader demands. – miroxlav Feb 23 '15 at 09:20
  • @miroxlav I realize that if the USB port delivers more power than the device requires, then it will work, and otherwise it won't. That's trivial. So how do you find the power supplied by the USB port of the device and the power draw of the USB reader? – Peter Feb 23 '15 at 10:54
  • @Dave That is incorrect. A DVD drive which only has 1x USB cable connection is not guaranteed to work with all devices. For example the Microsoft Surface Pro is well known for not working with most USB powered DVD drives. – Peter Feb 23 '15 at 11:03
  • @Peter - just download device manual from manufacturer's web site and there it is. You typically go to **Support** section. – miroxlav Feb 23 '15 at 11:14

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The USB power specifications clearly specify that a single USB2.0 port can deliver a maximum of 500mA worth of current at 5V: that's 2.5 Watts. Any electrical device, including an external DVD drive, must list it's maximum power draw so as long as you're beneath 2.5W you will be fine.

Link to USB wiki: https://en.wikipedia.org/wiki/USB#Power

Nathilion
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  • The keywords are "can" and "maximum". So not even if I know that the DVD requires no more than 2.5 W, I don't yet know if it will work. – Peter Feb 23 '15 at 10:55
  • @Peter - I have an SP3 as well. Any luck figuring out? – Alex S Aug 22 '15 at 06:37
  • @AlexS If I remember correctly the SP3 USB 3.0 port delivers less power than the USB 3.0 spec requires, due to the small battery. The only guaranteed way to find out if it's compatible is to go to a store and try it. Remember that burning a DVD requires more power than reading, so if reading works writing may still fail. – Peter Aug 22 '15 at 15:14
  • @Peter - So its not fully USB 3 compliant? – Alex S Aug 22 '15 at 17:20
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Compare USB power drain shown in DVD drive manual with power supply specified in manual to your PC. There are standards (as seen in Wikipedia) but I'd always compare specs provided directly by manufacturers.

If values are nearly equal (there is no reserve), then be careful because device might not neccessarily work.

You should be able to download the manuals at Support section of manufacturer's sites.

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Wrap up: you are asking how to ensure – you need to obtain specification of device current from device manufacturer. (Or their confirmation the device will work with standard 500 mA USB port.) There is no other way to ensure.

miroxlav
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  • I agree that vendors should provide that information in the manual. Do you know any vendor that provides this information in the manual? I randomly checked some and didn't find it. – Peter Feb 23 '15 at 11:48
  • Yes absolutely. I can see it right now for my Dell Ultrasharp monitor or my Samsung USB portable DVD burner. Honestly, I didn't met hardware where this wasn't specified. Of course, it wasn't part of $12 RFID card USB no-name (literally) reader from China, but I wouldn't except it there. :) – miroxlav Feb 23 '15 at 13:05
  • Just tried the first Samsung drive I could find (http://downloadcenter.samsung.com/content/UM/200811/20081105100000609/SE-S084B_Eng.pdf) and I can't find anything about power. Anyway it's probably available for some models. +1. – Peter Feb 23 '15 at 13:17
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    @Peter – Looks like they are inconsistent... in case of my `SE-208AB`, I can see it printed on outside of retail package, I quote: `USB Port Current: 1.4 A or higher`. The same is in the manual. – miroxlav Feb 23 '15 at 13:27