[PLUG-TALK] RPI4B and power bank requirements

[Tomas Kuchta]

For start - your current draw numbers are only average low activity
numbers. If you do not want your Pi crashing at random peak loads, I would
make sure that your power supply (battery bank) is capable of supplying the
recommended current 3A or close to it. Minimal 900mA limit assumption
probably guarantees unstable operation.

As about mAh - beside being able to drive the required current - the choice
of battery capacity (mAh) depends on how long would you like the battery to
last.

Example: average current draw 900mA will use 900mAh for every hour of
operation from your 10000mAh battery. Assuming that battery bank will not
let you discharge the last 10% of the battery - your Pi will stop operating
in 10 hours after drawing 10*900mAh.

I hope it makes sense.
Tomas


On Fri, Aug 7, 2020, 16:32 Rich Shepard <rshepard at appl-ecosys.com> wrote:

> A Raspberry Pi 4 model B requires 5V and draws about 900mA; the RPI specs
> recommend a 3A power supply. The 7" RPI touch screen draws about 400mA.
> That's 1.3A and 6.5W. I want to calculate these requirements in mAh. Many
> decades ago I could do so but no longer can, and I haven't found a web site
> to do this.
>
> For example, there are two RAVPower portable charging units supplying 5.5V.
> One provides 16800mAh the other 26800mAh. Both describe capacity in
> charging
> time for a few mobile phones. I want to know A) whether these have more
> capacity than the RPI and touch screen need and B) for how long each might
> power the portable tablet. If a lower capacity battery would be sufficient
> I'll go for a lower cost.
>
> TIA,
>
> Rich
>
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