Backup Power for USB device -- does it exist?

[Deozaan]

I have a USB device that I need to keep powered. It is connected to a Raspberry Pi type device that itself is connected to a UPS, but it seems when the RPi reboots, it shuts off power to the USB ports momentarily, which resets the USB device.

I need something that will keep a steady supply of power to the USB device, but still allow a data connection to the RPi.

Does such a thing exist? Would an ordinary USB Y-cable (such as for external hard drives) do this? Or is there some kind of special Y-cable (or anything) that will provide power but still allow data to be sent/received to/from another device?

[Ath]

Some USB devices with the requirement of stable power have an extra powerplug mounted, I assume yours doesn't?

Maybe you can 'sabotage' a Y-cable, by cutting the + power wire on the RPi side, and providing stable power on the other end, besides the data wires, common ground is also a requirement.

[Shades]

You could also consider adding a power plug to the device and use an external power supply with it.

From your description I gather that (at least) the power lines on each USB port are interrupted during reboot. Splitting up cables might not be as stable as a separate power supply. If you can stomach the extra power cable that is.

If you know how long the power interruption lasts, you could also add an extra condensator (parallel) between the power lines of the USB connection in the USB device. That should add a tiny buffer that should be able to cope with short power interruptions. This requires more knowledge about electronics and the innards of your USB device, though. Something like this would be visually the "cleanest" option. And perhaps there are already existing USB power buffer devices available on Amazon, Ebay, NewEgg, etc.

Even a powered USB hub might be sufficient to help you out.

[KodeZwerg]

Maybe you can 'sabotage' a Y-cable, by cutting the + power wire on the RPi side, and providing stable power on the other end, besides the data wires, common ground is also a requirement.

-Ath (September 25, 2018, 03:23 PM)

You even could consider to buy such, like shown here
What i meant to say, sabotage works.

Ps: To get buyable results near your place, use google and type "usb data and power splitter" as search term.
PPs: YouTube offers DYI tutorials with that search term.



Regards,

KodeZwerg

[mwb1100]

Would a powered hub do the trick?

    - RPi <--> powered hub <--> device

[Edvard]

Would a powered hub do the trick?

    - RPi <--> powered hub <--> device

-mwb1100 (September 25, 2018, 07:24 PM)

Aw man, I wish I had thought of that...

There you go, problem solved.  Good one, mwb1100! 

[4wd]

The Y-cable would have also done the trick, plug the power-only lead into another USB charger/outlet or a power bank.

I know the RPi is already plugged into an UPS but if the power bank has two USB outlets and pass-through charging, could have plugged the RPi into the power bank also for a "mini UPS".

USB Host ports are usually protected against input voltage.

eg.

Backup Power for USB device -- does it exist?

But yes, a powered USB hub is cheaper/simpler, nice one mwb1100 

[Deozaan]

Some USB devices with the requirement of stable power have an extra powerplug mounted, I assume yours doesn't?

-Ath (September 25, 2018, 03:23 PM)

This device doesn't require stable/constant power. But for my uses I'd like it to remain constantly powered.

It's a multi-purpose device which can run various applications. If it loses power momentarily then it will reset to the "application select screen" and require physical interaction to select and launch the correct app. Even if there's only one app installed. So even though I can program the RPi to automatically start up and resume operations after a reboot, the fact that the USB device loses power means I need to be physically at the device to get everything running properly again. But ideally I'd like to have this all tucked away in a dark corner somewhere I'll never have to physically access and just manage everything about it remotely.

And this issue seems to be specific to the RPi. If I have the USB device connected to a (Windows) laptop and reboot the laptop, the USB device remains powered.

Or alternatively to my Y-cable idea, maybe someone knows a setting I can tweak in Linux so that it keeps power flowing to the USB ports during a reboot. That would also be an acceptable solution for this issue.

Would a powered hub do the trick?

    - RPi <--> powered hub <--> device

-mwb1100 (September 25, 2018, 07:24 PM)

I hadn't considered that. It just may work!

Though I'd hate to spend the money buying one only to find out it didn't do what I wanted. . . If I can find one cheap enough then I may give it a go.

The Y-cable would have also done the trick, plug the power-only lead into another USB charger/outlet or a power bank.

-4wd (September 25, 2018, 10:03 PM)

That's another good idea. Thanks! I do have a Y-cable and a USB charger/power bank I can try out. Actually the Y-cables I have are for mini-USB connections and this device uses a micro-USB connection, so I don't have a usable cable after all.

I guess I need to look into getting a new Y-cable or a powered hub.

Thanks to everyone for their suggestions and help!

[Deozaan]

I found this Y-cable which looks like it would do the trick for $7.58. But that would require me to give up my power bank (yikes!) or a USB "wall wart" adapter (not too bad).

Or for $2.37 more ($9.95) I can get this powered USB hub which will keep everything self contained and could perhaps be re-purposed in the future if I am ever in need of more (powered) USB ports on a given device. (I already have a USB hub but no AC adapter for it, and buying just an adapter is almost as expensive as buying a new hub with an adapter. )

Choices, choices. . .

[Ath]

If it loses power momentarily then it will reset to the "application select screen" and require physical interaction to select and launch the correct app.

-Deozaan (September 25, 2018, 10:40 PM)

Are you sure that power is disconnected during boot of the RPi? Could it be that the device is reset via USB initialization commands? In that case, all your 'keep power applied' actions will be in vane...

[4wd]

Are you sure that power is disconnected during boot of the RPi?

-Ath (September 26, 2018, 01:05 AM)

It shuts off power to the USB ports according to my USB V/A meter, for about 2 seconds ... of course that doesn't exclude a USB initialisation from also being sent.

[Deozaan]

Choices, choices. . .

-Deozaan (September 25, 2018, 11:06 PM)

Someone very generously donated the money (thank you!) for the powered hub, so that made the choice easy. I'll report back with the results in a few days.

[Deozaan]

I went to order that powered USB hub and then noticed the reviews were not favorable. So, thanks (again) to the generous donation I decided to spend a little more and get this one instead. It has the added benefit of having USB 3.0 ports.

Backup Power for USB device -- does it exist?
https://www.amazon.com/gp/product/B00TPMEOYM/

[Deozaan]

It works! 

Thanks for the idea, mwb1100! And thanks once again to the person who donated!

[mwb1100]

Glad it worked - to be honest I wasn't sure if when the computer booted up it would perform some initialization that would reset the USB hub and drop power on the ports for a moment.