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I just bought a powerbank for intending of using it to power a Rasberry Pi4b

But, it seems i did not do enough research regarding the requirements of the Pi model i have.

The powerbank is listed as "2X 5V / 2.1 A" (it's got two usb outputs). (while the Pi in question appears to need recommended ~3A)

5V DC via USB-C connector (minimum 3A*)

So, i'm thinking, rather than try to return it; I could either fashion a custom USB cable, out of- or similar to, the dual-(power)cords powering certain (older) external harddrives, having the Pi plugged into both of the USB outlets. Or, mod the powerbanks output, in the same way (removing one of the outputs)

But, i am a bit puzzled if i'm even reading "2X 5V / 2.1 A" correctly, as to mean those are two ports able of 2.1A each ? ..Or, if that is commonly the total given in such spec. listings ?

below is the powerbank specs from (Norwegian) manual if anyone's curious.

enter image description here

DhP
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  • Questions on the *usage* of products are not on topic, as they depend on details which are not typically knowable from the limited information sellers are willing to provide. Running a pi from a USB powerbank might or might not work, but even if it does, it would only work for a short period of time. There exist boards designed to provide battery backup to a mains powered pi; in the grander scheme of things the pi SoC's creation as a platform for TV set top boxes means it lacks the sort of dynamic power management and sleep modes found in tablet etc SoC's actually intended for battery use. – Chris Stratton Nov 16 '20 at 19:40
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    @ChrisStratton I would think my question would be more in the 'modification' and/or 'reading of specs.' category. – DhP Nov 16 '20 at 19:43
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    If not explicitly indicated otherwise, I would assume 2.1A total. If it could do 2 x 2.1A they would have said so, because marketing. – ocrdu Nov 16 '20 at 19:44
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    Unrelated to your question, but I'm wondering why your power bank lists 'Color Temperature' (Fargetemperatur) as one of its specs ... I would hope that it doesn't get hot enough to glow ... – brhans Nov 16 '20 at 19:48
  • @brhans It's got an LED lamp built-in , that's all :) https://www.biltema.no/en-no/office---technology/mobile-phone-accessories/powerbanks/power-bank-with-led-lamp-20000-mah-2000044434 – DhP Nov 16 '20 at 19:49
  • @ChrisStratton Ok. I'll await it to be listed as off-topic then. – DhP Nov 16 '20 at 20:08
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    Basic assumption is you can use both ports at the same time, and that the ports are likely not current limited by the powerbank and are probably directly connected together. The 2.1A is set by resistors on the data lines for the phone to know that it can pull 2.1. The old Apple standard for signaling charger capability. Now, can the batteries and step up regulator supply 5v 3A or 15W? Likely. Without a schematic and or board pictures we can't tell – Passerby Nov 16 '20 at 21:07
  • @Passerby I'll cobblefabricate together a cable and see what happens. Thanks! :D – DhP Nov 16 '20 at 21:25
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    I agree with Passerby here, 2.1A limit is by protocol and likely due to connector contact rating. Two ports in parallel should do the job. However, there might be a problem. The Rpi likely has a variable consumption, and in sleep state might consume faily low current. Power banks usually will stop supplying power if the load drops below 20-100mA, so the Rpi will need to restart. I am sure this is not what you want. – Ale..chenski Nov 17 '20 at 20:42
  • @Ale..chenski Yeah, and it appears i mistook what was meant by '3A Recommeded' regarding my Pi4B .. Since that req. apparently takes into account quite a few potentially plugged in devices drawing _from_ the Pi https://i.imgur.com/4cP7XtP.png / https://www.raspberrypi.org/documentation/faqs/#powerReqs – DhP Nov 18 '20 at 22:45
  • All in all, if the Pi4B itself, under 'stress' takes _~1.25A_ , I can all but suspect it'll do quite fine with _2.1A_ supply from the powerbank, even with an external wifi adapter attached. I'll update my question if it does not, once i've braught myself to try it one of these days. – DhP Nov 18 '20 at 23:02

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