Use 4-port *hub* as *charger* for high-power (2+ Amps)? Possible with multiple devices?


#1

About http://plugable.com/products/USB3-HUB…

I want to use this product as a *charger* for my iPad2 and need to know what else would I be able to charge at the same time… like, another iPad2? For charging iPad 2 needs 2A of current. More powerful devices that use USB to charge require 2A (or more?) so I want to find a product that allows me to charge one or several of those at one time, if possible.

The 4-port Super Speed USB 3 hub - can it be used as a *charger* rather than a *hub*?

Does a USB hub have the same functionality a charger would have and then adds the hub functionality (USB *in* and data)?

Do the specs mean that 4A is full power, shared across all ports and/or 900mA per port? But 4 x 900mA = 3.6A… please clarify and specify what is the max per port and what happens if I use multiple ports.


#2

Hi - Thanks for asking ahead! Unfortunately, the iPad 1 & 2 will limit its draw to 500mA (and at that rate, it won’t charge while iPad screen is on, and charge at less than full rate when off).

What’s happening is Apple has extended USB with proprietary signalling to tell its devices when they can draw more than 500mA (see here for the interesting details: http://www.ladyada.net/make/mintyboos…) , and they try to restrict others from using that signaling.

So there’s no good way to charge and iPad with any hub, USB 2.0 or USB 3.0, regardless of what the hub is capable of in terms of amperage. The iPad just won’t pull more than 500mA. You need an Apple brand or approved charger.

There is a better way. Hopefully in the future Apple will support USB’s standard way of higher power charging: the USB Battery Charging specification.

Here’s more detail on that: http://support.plugable.com/plugable/…

So our USB 3.0 hub with 4A adapter is not the product you’re looking for, given you’re charging an iPad.

But if you did have USB Battery Charging compliant devices (like the new Amazon Kindle Fire and Kindle Touch), then our Battery Charging compliant hub would be what you want: http://plugable.com/products/usb2-hub4bc – with both BC 1.1 compliant, you can charge up to 1.5A, even without an attached computer.

Hope this background helps!

Thanks again,
Bernie


#3

Bernie, thanks for your knowledgeable and detailed replied; most interesting and appreciated.

Let’s take the proprietary iPad device aside. I am also looking for a solution for other USB devices. I have a Galaxy Nexus and iPhone in mind. Not sure what type of power they draw but the spirit of my question is if it is OK to think about a *hub* as a charger for devices that may draw higher power. My thinking is that if I get a charger that can put out 2A, I can rest assured that whatever device I plug in (excluding maybe Apple devices) will charge at fastest rate possible. Am I thinking about this the right way?

I also was thinking if I get such a hub to travel with I can use it as a charge station and a USB port multiplier. So looking for a hub that has USB 3 and has as much power as possible for the charging scenario, I came across your product. But is my reasoning valid in the first place for getting one hub/charger to rule them all?

Thanks!


#4

In short, without the new USB Battery Charging specification, USB can’t do what you’re hoping.

With “normal” USB 2.0 devices, the important aspect is that devices are required (by original USB spec) to limit themselves to 100mA until they negotiate with the host (host must be on), then they can negotiate up to a max of 500mA (900mA for USB 3.0 devices; but no phones or tablets are USB 3.0).

In terms of a standard, it’s only with USB’s new Battery Charging specification (BC 1.1+) that devices can negotiate purely at an electrical level (no PC needs to be attached and on), and get up to higher amperages (up to 1.5A per port).

Both the device and the hub/host must support BC 1.1 for this better behavior to be possible.

The Apple devices all use their own similar methods, so the iPhone will be similar to the iPad - circa 2011, none of them support USB Battery Charging spec (the only thing that’s simpler about the iPod, is it will charge at 500mA in cases where the iPad won’t).

Looking at the Galaxy Nexus, I don’t see evidence either way of whether it supports BC – given no datapoints, I’d want to be conservative and assume it predates the new standard.

Let us know if you find any mention of Battery Charging spec compliance for it, though, because we’d love to be able to mark that down as one supporting the standard.

The links in the prior reply have some good deeper background, if you’re interested.

Best wishes,
Bernie


#5

Thanks for the clarification; did not imagine it is so complex but what you are saying makes perfect sense.

Galaxy Nexus has not been released yet; hoping Verizon will make it available soon. Will post back when/if I get more info on its capabilities.


#6

Thanks, we’d love to hear more on the Samsung Galaxy Nexus once it’s out.


#7

Hi, I figured this would be a good topic to post in for my issue, because it regards the Samsung Galaxy S II (similar to the Nexus, and it was released in September 2011)…

I bought one of your four port BC1.1 hubs, because I need to be able to use my phone’s USB connection while charging at high rate. The Galaxy S II will charge at 1000mA while hooked to the AC adapter (presumably has the data pins shorted) or 100mA when connected to an actual USB port. It does not do software negotiation for extra power units.

Unfortunately I hit a snag. If your hub has the AC adapter connected to it (regardless of if it is connected to a computer host), the phone goes into high rate charge, but does not activate the USB connection.

If the hub is connected to a host but does NOT have the AC adapter plugged in, when I plug the phone in, the USB mode activates but it is in low rate charge. If I plug the AC adapter in at this point, it stays in low rate charge.

If I read the spec correctly, you are supposed to be able to use the USB 2.0 mode while fast charging, correct?


#8

I just re-read what I posted, and I just wanted to clarify the situation a little better…

Basically this is going to be installed with a vehicle “car-puter”. I bought it to replace the standard 4-port powered hub that I have now, which has three “non-BC” devices on it. I intended to use the 4th port to connect my new phone (Galaxy S II) into the system, as both a charger and a USB modem tether for the computer.

This particular phone, during certain operations, can actually draw more than 100mA from the battery, so the standard USB charging mode can not keep up. I was unaware that this was a problem when I bought the phone, which is why I thought I had found a solution in your BC1.1 hub…

I need the phone to charge at the higher rate (even if it’s 500mA) while also having data transfer over USB 2.0. I was under the impression that if the device could support high current charging through a USB port, that it was BC1.1 compatible.


#9

Thanks for reporting back with this result with our BC 1.1 hub (http://plugable.com/products/usb2-hub…) and the Samsung Galaxy S II - you’ve got a really interesting scenario with trying to tether+charge for the car-puter.

It’s great to know that charge-only appears to charge at the higher rate (I’m curious how is that visible on the Galaxy – and is it possible to distinguish 500mA from higher-than-500mA charging?).

Let’s try to figure out what might explain the charge+data behavior, then. Based on the behaviors you’re seeing, I’m suspicious that the Galaxy S II isn’t really doing BC 1.1 signaling, but let’s try to figure that out.

First thing to note, the hub without its AC power adapter attached doesn’t have enough power to charge anything beyond what the PC’s USB port supplies (which is only up to 500mA in theory). If you’re in a car and don’t have a way to supply power to the hub, I’m not sure if things will work out in the end.

On charging+data transfer: The BC spec supports that with a special case (that, if it was working, should be enough for the Galaxy). During HS data transfer, he BC 1.1 specification limits power draw to 900mA (down from the max of 1.5A). Here’s how it’s shown in the spec:

!](https://s3.amazonaws.com/satisfaction-production/s3_images/647429/bc1.1-hs-fs-ls-charge-rates_inline.PNG)](https://s3.amazonaws.com/satisfaction-production/s3_images/647429/bc1.1-hs-fs-ls-charge-rates.PNG)

Given that the Galaxy S II isn’t doing any data transfer when it thinks it’s connected to a charger; and only 100mA charge when it’s set up to sync – I’m suspecting that the Galaxy doesn’t support or isn’t taking advantage of these BC 1.1 features, though.

Have you seen any documentation from Samsung about whether the Galaxy II S supports BC 1.1?

Thanks again!
Bernie


#10

Thanks for the quick reply! I have not seen anything in the documentation about BC1.1 specifically, but I do know that it uses UCS (which I thought BC1.1 is built on) and it has (at least) two charging modes. In the ‘battery status’ menu, when plugged in it will read either “Charging (AC)” or “Charging (USB)”. (“Charging (AC)” shows whether plugged into the AC or DC car adapter.)

Both the AC and DC adapters have an output rating of 1000mA. I have tried using a generic USB port cigarette lighter adapter with a 700mA output, and the phone refuses to charge from it, so it wants to pull more than that.

I realize that the hub requires external power to run higher than bus current. I have a 5v 2.6A DC-DC adapter already in the vehicle for the other hub I was using. It uses the same tip and polarity, so external power isn’t a problem.

I’m just confused as to why it seems to be all or nothing as far as what the phone sees. If the phone is truly not BC1.1 compatible, shouldn’t it just go into regular USB 100mA mode if there is a host connection present?

This issue that I’m having actually makes things worse for me, because I have to use a powered hub. Two of the attached devices are 2.5" USB hard drives, which draw too much to run on bus power. With the hub I have now, the phone will only charge at 100mA, but at least the USB mode works. With your hub connected to external power, it fast charges but won’t go into USB mode. I’d have to disconnect the power, then connect the phone, then reconnect the power. That makes things harder, not easier! :slight_smile:


#11

One thing that’s non-intuitive about USB power: The USB device chooses how much power to draw. The host or hub won’t physically limit the device, until they hit the limit of total available power, or trigger overcurrent.

That’s why even with a charging only device like the cigarette lighter charger with 700mA output, a device might not choose to draw all that (or even any at all).

It’s interesting that the Galaxy says it’s UCS compliant, because the other evidence isn’t pointing to BC 1.1 compatibility. That would be interesting to untangle - we’ll search forums on the phone to see if there’s anything more definitive there.

It’s a shame that the Galaxy is fast charging but not also connecting at the same - I agree, that makes for a combination that isn’t useful for what you’re shooting for!


#12