Thursday, July 09, 2015

Raspberry Pi "UPS" experiment

My daughter recently bought one of those "power bar" things to charge her mobile whilst on holiday. As these are simply a rechargeable battery with some circuitry to avoid overcharging etc, they caught my eye as both an external power supply which would allow me to use the Pi outside without access to mains power and also, more intriguingly, as a form of UPS to keep the Pi running when there is a power cut (in much the same way that I use an EeePC as my weather server because it has a battery for these occasions.

Right, the first power bar she bought was an Anker Astro E1. Very pretty, small device which claims to supply 5v and 1A output. It has a capacity of 5200mAh, which is plenty to run a Pi and its ancillaries for a while!

A quick test and I ran my Pi, with wifi and a USB stick attached to take the images recorded by the Pi camera which was also attached.
I left it running for over three hours and all was fine. I am sure it would handle a bit more, but I didn't want to push things to start with.

When daughter returned from her holiday, having taken the Anker with her, she brought me a smaller power bar to play with for my very own! This one was from a very large store in the USA and carries the brand name Dynex. It is a model DX-1122 and supplies 5v and 1A output - although below that it gives 3.7v and 2200mAh. 3.7v sounds a bit iffy for a Pi, but having tested it with the Pi setup as above, it ran and completed a two hour imaging session without any problems.

So, onto the second part of my experiment!  I have read various reports that these power bars work as UPS devices - but also read that they don't!
Each has two plug holes - one for the little micro USB sockets for charging it and a standard USB socket which takes the lead to plug into your phone/Pi.
Theoretically, if I plug a lead from a power supply into the charging socket and also plug in the power out into my Pi, it will act as the UPS I am after....

No..  Neither of the power bars will work if both leads are plugged in. I have read this is the case with many of these devices. Not that I am terribly bothered (although a UPS would be nice) as I still have the power when outside functionality.

More research needed to see which ones get a mention as being able to fulfill this purpose.

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