At the end of my previous blog post, I mentioned that I was going to test the large pack to see if it was suitable as an uninterruptable power supply (UPS). Since it can be charged while being used, it seemed reasonable to see if it works for this function.
Three days testing
So I decided to put it on test for three days. Those three days ended at 9 am this morning, although I’ve still left it running. The pack has been powering the Pi, while the pack itself is connected to my 1 Amp Nokia charger. The charge indication light has been flashing, the whole time, to indicate charging in progress.
But what about interruptions?
Four times during the test period, I’ve either pulled out the charger from the mains, or pulled the micro USB charge lead from the battery pack. All four times, the Pi has remained up and running. I logged in after each time to check.
Each time I’ve done this, all three ‘charge state’ leds on the battery pack are lit, indicating fully charged.
One further test to do
I want to simulate a long power outage of, say, three hours. This will enable us to see whether the pack will be able to recharge properly whilst still powering the Pi. I expect it will, but we’ll find out tomorrow.
If it passes that test, it can be used as a UPS (see warning below).
Update: It passed. I unplugged the charger for three hours this afternoon to simulate a long power outage. Checking on it a few hours after plugging the charger back in and it’s fully recharged the pack.
That’s not a recommendation though
A warning though. Just because it works, doesn’t necessarily mean it’s a good idea. The life of the pack may be drastically reduced by doing this. Lithium batteries are delicate and don’t like being float-charged.* The device is not sold as a UPS. You do this at your own risk.
But the fact is, that, because it works, you are free to make that choice and take that risk. I don’t need a UPS on any of my Pis, so I won’t be doing it. I tested it for fun and science.
But I’m not saying don’t do it either. I’m saying know what you’re doing and make an informed choice.
* It’s been pointed out to me that technically we’re not float charging. But being on constant charge (even though it cuts off when full), we are no doubt using up cycles of the battery’s life. Also, lithium polymer batteries lose capacity with age a lot faster if kept fully charged.
Great couple of posts.
Can you do a fast test, 10min, and see if the 2200 mAh baterie back also your as UPS? Just for the fun of it.
I’m about to order them.
OK I will, but a fast test may not be a reliable one because we already know the small one can power a Pi for 3 hours without any charging input. If you’re asking whether or not it can be charged while being used, the answer is yes it can. :)
OK. I’ve just put this one on for you. I’ll check it’s stable in the morning, try a couple of “outages” including one for about an hour, and then the recharge test. I don’t think a 10 minute test will give us any useful information.
I did this and it worked OK. Took a long time to recharge though after the “hour and a bit” outage. The small one can only charge itself at 800 mA, whereas the larger one can charge itself at 1 Amp. In this application, it makes a difference. Small one would be OK for occasional short outages, but the big one would be a lot better.
Thanks for the testing.
I’m going to try setup a video conference using netcat and two pi’s and the ability to be mobile is great.
How are you going to handle the sound?
thanks for the test!
could you please tell me what happens if the battery is empty and the power supply is restored: do you have to push the power button again?
Almost certainly, but I’ll try it at some point
why not adding a relay, to stop charging when power comes up or battery is charged ?