connected devices seem to be starved for milliamperes


#1

Topics About this product: 7 Port High Speed USB 2.0 Hub with 3A Power Adapter

I have this: Plugable USB2-HUB-AG7 7-port USB 2.0 Hub with 3A Power Adapter

http://plugable.com/products/usb2-hub…

(correct me if I am wrong) When a host PC is attached and this hub is properly connected to a regular AC outlet, up to 6 connected USB devices are each supplied with 500mA of power.

(correct me if I am wrong) The red LED light on this device indicates that the hub is receiving power, either 500mA from the PC (upstream USB port) or 3 amperes from the external AC adapter. So the red light does not tell me if the device is supplying full amperage to connected devices. If 7 devices are connected and this hub is not connected to an AC outlet, it is possible for the red light to be lit but each device is receiving less than 100mA.

Here is my problem: Sometimes connected devices seem to be starved for milliamperes. I suspect this problem is intermittent because sometimes the power connector becomes loose and I do not notice it (again, because I am seeing a red light all this time).

Question: Please recommend some sort of handy-dandy way that I can quickly determine how many milliamperes are being supplied (by a port on this device) to connected devices.

I found this:

http://www.amazon.com/gp/product/B005…

Question: What do you think? Can you recommend another device better suited to this purpose?


#2

Hi Steve,

Thanks for posting your question here, I’ll be happy to assist. Your thoughts about the available power per port are correct: you can expect the hub to fully power at least 5 devices and in practice it should be fine for all 7 ports.

The red light indicates that the hub is receiving power either from the AC adapter or from the upstream USB port. So, even if the AC adapter is disconnected the led will still be on but the hub will have approximately 500mA to split among the ports.

As far as current measurements go, the official USB Integrator’s Forum (usb.org) method is to use a multimeter and one of these-- http://www.elitelex.com/USBTestAdapte…

It’s more expensive than the one you pointed out, but I’ve used it extensively and it works great. It’s a passive device so there’s no effect on the USB connected device under test.

This is important if you are hoping to measure the current draw of devices that require special signaling on the data lines like Apple devices. From reading a few of the reviews of the device you linked it looks like it doesn’t work well with devices like iPads.

Here’s a good post with some details about what’s happening if you are interested:
http://blog.curioussystem.com/2010/08…

I hope this helps, let me know if there’s anything else I can help with.

Thanks,
Jerome.


#3

Ok.

Thank you.

That is good information.

Steve


#4