12

I notice that my new Motorola Droid phone charges perfectly fine when I connect it to my computer via the USB cable, or if I connect it to a car cigarette Lighter -> USB adapter, or a wall Power -> USB adapter. It also works fine when I connect it to a powered USB hub that is connected to my computer.

However, if that same powered USB hub is not connected to my computer when I connect the phone, it does not charge. If I connect the computer to the hub, and then connect the phone to the hub, it will charge. If I then disconnect the computer from the hub, the phone will continue to charge.

Does anyone know why this is happening, or what I can do to be able to charge my phone from a powered hub, without my computer being present?

fixer1234
  • 27,064
  • 61
  • 75
  • 116
pkaeding
  • 1,470
  • 3
  • 18
  • 27
  • Wait, **what**? Your USB Hub have a big battery or something? And why so many answers without questioning this?! [Am I](http://apple.stackexchange.com/questions/9090/can-i-use-my-iphone-charger-for-charging-other-usb-based-devices/9164#9164) going insane? I get a very [similar symptom on my macbook with my iPhone](https://discussions.apple.com/thread/2321464?start=0&tstart=0), but it has a battery! Of course a unplugged usb hub wouldn't charge: it has no energy! - [nevermind](http://superuser.com/questions/3729/need-a-quality-usb-hub-that-is-able-to-power-external-hardware) :P – cregox Sep 13 '11 at 13:06
  • related: http://superuser.com/questions/96563/can-i-charge-usb-devices-from-a-powered-hub-that-isnt-connected-to-a-pc/96574#96574 – cregox Sep 13 '11 at 13:56
  • @Cawas, it is a powered usb hub (as mentioned in the question, and originally in the title before Tom Wijsman edited it). Thus, it is plugged into the wall power. – pkaeding Sep 14 '11 at 00:53
  • I should begin using drugs to have justifications in those cases... – cregox Sep 14 '11 at 00:56
  • @Cawas, I'm not really sure what you meant by that. I was hoping to be able to charge my phone by plugging it into a powered hub, that was plugged into the wall power (that is where I expected the juice to come from), but not plugged into a host computer. I now understand why that is not possible (see the accepted answer below). – pkaeding Sep 14 '11 at 00:59
  • I meant I could say I didn't know / read / noticed because I was high... Anyways, I doubt it's impossible to do what you want. Worst case scenario, the hub would need to be a switcher. No big deal. – cregox Sep 14 '11 at 01:12
  • @Cawas, Ok, thanks for the clarification. I guess it isn't impossible, but, according to the USB spec, everything is working properly (by it *not* doing what I wanted). I suppose I could make some sort of usb terminator plug to short out the two pins described below, and connect that to my hub (where the computer would go) so the phone starts drawing power, but that seems significantly more complicated than just plugging the phone into my computer. :) – pkaeding Sep 14 '11 at 17:46
  • Have you seem the related link I've posted on my second comment? – cregox Sep 14 '11 at 21:08
  • @Cawas That is an interesting link, but do you know for sure if a computer was never introduced into that setup? I was successful in charging my phone off of the usb hub as long as a computer was connected to the hub (the charging even continued after the computer was removed). Since most people probably have their USB hubs connected to computers, perhaps CNET left that detail out? Or, perhaps the Belkin hub mentioned there handles the voltage negotiation itself when a computer is not hooked up. If that is the case, then I suppose I need one! – pkaeding Sep 16 '11 at 17:56
  • 1
    (I posted the answer below about modifying a USB hub). Regarding that other answer/the CNET article it seems pretty likely that they didn't mention that the hub was attached to a computer. I've never gotten ANYTHING to charge at all from a non-modded powered hub, and I tried a bunch when I was trying to figure this out. Frankly I'm surprised nobody sells such a thing since it's so incredibly useful (hello, entrepreneurs!) but it's a pretty low-risk project and the hubs are dirt cheap if you mess it up. Been using one for over a year now and it charges everything fine. – jamietre Sep 23 '11 at 20:30

4 Answers4

19

Note that the USB Specification somewhere says that devices that are only connected but haven't "authorized" yet may only drain 100 mA instead of the usual 500 mA. It could be that your USB Hub simply does not supply the full 500 mA if it isn't connected to a PC, to be in line with the standard.

Wall chargers ignore that as they aren't USB devices but simply Power Bricks that output 5V/500mA on a connector that looks like a USB Port.

Edit: Copy/Pasting from Wikipedia:

Some non-standard USB devices use the 5 V power supply without participating in a proper USB network which negotiates power draws with the host interface. [...] The typical example is a USB-powered [...] battery chargers (particularly for mobile telephones), [...]. In most cases, these items contain no digital circuitry, and thus are not Standard compliant USB devices at all. This can theoretically cause problems with some computers; prior to the Battery Charging Specification, the USB specification required that devices connect in a low-power mode (100 mA maximum) and state how much current they need, before switching, with the host's permission, into high-power mode.

Michael Stum
  • 3,101
  • 6
  • 35
  • 46
4

I think the answer is simpler. The two data lines only need to be shorted to each other and not connected to any voltage. I tried this with my Droid and it works. This seems to be part of the USB specification (from http://pinouts.ru/Slots/USB_pinout.shtml):

"A simple USB charger should short the 2 data lines together. The device will then not attempt to transmit or receive data, but can draw up to 1.8A, if the supply can provide it."

I connected my Droid to a 5V power source using a USB cord that I had opened up, cut the two data lines (white and green) and shorted them to each other on the Droid side. It charged perfectly.

2

USB is a host-based protocol, relying on the PC for a lot of things. It's quite possible that the way the Droid is designed, it disables power flow to the connector unless it detects a host connection or the wall adapter.

I've also heard of certain cases for the Droid causing charging issues, but that's probably just for cases that have a passthrough connector between the one on the phone and the data cable.

I suppose it's also possible that the hub is not quite providing enough power without both the computer and the hub power connected, if it's defective.

phoebus
  • 3,921
  • 1
  • 18
  • 15
  • Hmm, that is interesting. The hub successfully charges my iPod (through a builtin dock connector) and a bluetooth headset through usb. I tried disconnecting all of that stuff, though, and connecting the droid, and it still doesn't work. So I don't think the hub is defective and not delivering enough juice. – pkaeding Dec 02 '09 at 03:47
  • 1
    I've tried this with my Blackberry before and the hub wouldn't charge my Blackberry without a computer being attached. I would assume that it won't work and that you need an actual AC adapter or a PC to charge. – mrdenny Dec 02 '09 at 06:38
  • 3
    It's due to the Droid **actually following the USB standard**. I have a phone that does the same thing (it's so bad that in fact there are options to force 500mA draw). – Broam Mar 04 '10 at 18:48
1

I used the following method to get my Motorola Droid phone to charge from a wall-powered USB hub.

1) Open the case and solder together pins 2 & 3 of each USB connector where it is soldered to the circuit board.

2) Cut the traces on the circuit board coming from these two pins only (carefully) on each port using an xacto knife to isolate those pins from the rest of the circuitry. This step may be important depending on your hub - in my case simply soldering the two pins together was not enough, and it did not work until I also cut the traces.

The hub will not, of course, work any more as a data hub connected to a computer after you do this, since you've severed the data ports.

This USB hub is a Belkin high-powered job with a 1.5 amp power supply, and after these mods the android charges fine. Works with several devices plugged in simultaneously, too.

I also have an iPad which, although it says it's not charging, does in fact charge when connected to this modified hub. The iPad claims to require 2.0 amps. After being plugged in for a couple hours it will reach full charge, despite the "not charging" indicator, so it works even for that picky device with 1.5A.

jamietre
  • 188
  • 1
  • 8
  • sounds a lot like a later hack I've read elsewhere: http://androidforums.com/motorola-droid/18667-droid-charge-through-usb.html#post2891265 – cregox Sep 13 '11 at 13:08