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I have a Lenovo laptop with a single USB 3.0 port.

I am using a four port USB 3.0 port extender.

Can I plug in another extender into one of the open ports and will it work.

  • What model USB extender are you using? Is it an extender with only 1 USB port, or a USB hub/dock with several USB ports. In theory, yes, you can daisy-chain several USB docks/hubs together granted they are of similar brand / model. Anything is possible with those things. – t a b designworks Jan 12 '17 at 20:58
  • "will it work" depends on the amount of power your USB devices require. A single USB 3 HUB can only power so many devices, even if you connect HUBs with an external power supply, your still limited by the first USB hub your connected to. – Ramhound Jan 12 '17 at 20:59
  • @Ramhound Are you sure about it? hub without power supply usually share restriction of parent port which is limited to 200-500mA usually, but if you using USB hub with its own external power supply then this power supply will feed slave USB devices. I have on one customer premises a raspberry pi with 24 HDD's connected to it, all of them 2.5" and powered over daizychained USB hubs (Dont tell me it crazy setup, it wasn't mine :) idea ) – Alex Jan 12 '17 at 21:41
  • I am 100% positive. I only use USB hubs and I am limited by the fact I only have two base hubs even if I have dozens of USB 3 ports. RPi is notorious for that limitation – Ramhound Jan 12 '17 at 22:30
  • Background: I use hubs to plug stuff in on my desk, I can only plug in so many devices, before Windows complains about USB resources, all hubs I use have an extrenal power supply. This is tie for USB2 and 3 – Ramhound Jan 12 '17 at 23:02
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If your "port extender" (read: "USB 3.0 hub") does not have any external AC-DC power adapter, you can use only one downstream port with full theoretical capacity. Actually, it should be less than one port, since the entire power comes from a single laptop port, and some of this power must be wasted to power the internal hub chip controller (which can be about 1 W, or about 200 mA from the 900 mA official USB 3.0 port budget). If you use another non-self-powered "extender" (with no AC-DC adapter), similar consideration would apply to it: you can use only devices with power requirements under 500 mA total (another 200 mA will be needed for powering internal IC in the second "extender").

However, if your "extenders" do have proper external power supplies, there should be no restrictions whatsoever, it should work with every USB 3.0 or 2.0 devices, including bus-powered HDD enclosures. Proper power supply for a 4-port hub must have at least 4 A capacity at 5 V.

Of course, the laptop port might be able to supply more than the official 900mA, but you should not be surprised that some ("high-powered") devices will behave erratically.

  • The question isn't specifically about power. It just asks if they will work, which is a little nebulous. There's "work" at their full capabilities, "work" at limited capabilities, and not work at all. It's limited by the bandwidth of the original connection, so obviously, "work" could be at a reduced rate. It does mention just one "extender". But theoretically, is there any limit at which the bandwidth is so divided that any type of USB device could potentially not work at all? – fixer1234 Jan 13 '17 at 7:41
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    @fixer1234, I don't know any class of USB devices where insufficient channel bandwidth will result in total denial of service, where the lack of bandwidth is critical. Of course, if you try to connect 100 high-definition webcams to a single USB root port over a tree of hubs, they all should "work", but the video will be quite choppy. But obviously the decision to reject a device on these grounds is up to software driver, where everything is possible. – Ale..chenski Jan 13 '17 at 17:59

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