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Topic # 240059 18-Aug-2018 11:50
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I'd like to have a play with a powerbank UPS setup as described here, There is some local discussion here.


I'm after recommendations for locally available USB powerbanks that have passthrough *and* continuous power output. Many powerbank devices that have the passthrough capability (outputs power while the charging input is connected) will momentarily drop or disconnect the output voltage when the charging input is disconnected, causing the powered device (RPi, Arduino, etc) to reset. For example Jaycar's MB3796 and MB3797 have this issue.


The ideal device would also run some sort of UPS comms protocol over the output USB connection so the attached device could read the battery level, etc. I expect that it's highly unlikely that any of these devices will have that feature, but you never know unless you ask.


I realise that a 12V SLA and 5v regulator is probably a better solution, but that requires more components and some construction. The powerbank method is so simple and, if you are not concerned about sensing when the mains goes off, only requires USB cables.





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  Reply # 2075266 18-Aug-2018 12:40
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The cheaper powerbanks use the same DC-DC converter circuit for both charging and discharging. When it is being charged, the 5V input will be getting passed straight to the output. When the mains fails, the converter circuit has to switch modes. Hence the momentary loss of output.

You also need to consider their charging speed. Otherwise the load might be able to flatten the batteries, even while the mains is still live.


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  Reply # 2075879 19-Aug-2018 18:12
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If you want to do it properly you'd have to get a Micro UPS or UPS Pico or something similar, a repurposed power bank really isn't going to cut it.

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  Reply # 2075881 19-Aug-2018 18:30
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I tried using a cheap 5v boost converter off am 18650 with a charging chip connected at the same time, basically just 2 boards off aliexpress and the results were poor. Charger would only go to 1A which was about what the boost converter took when running the pi with nothing plugged into it, and also got very warm when doing it. Thought about a diode from the 5v in to the 5v out to give that a direct path to the pi when available but didnt have any of the schottky ones lying around, and like most projects got shelved waiting for the slow boat from china to bring me some.


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