In article ,
 Markus Robert Kessler  writes:
> Hi,
>
> yes, you're right, the voltmeter comes directly behind the power supply.
> But, the cable I use is tested to have around 0.1 .. 0.2 Ohms.
>
> B.t.w., is there an upper limit, what RPis tolerate as input voltage?
>
> At least one of my USB power supplies has an open circuit voltage of 5.5
> V. Where's the limit, where damages may occur?

5.25V is the official max, and 4.75V the official min.
The low voltage is detected by an APX803-46 chip, which trips
at 4.63V. The screen flash is latched on for 3 seconds, so it
only needs quite short and occasional dips below 4.63V to keep
the screen flash on.

A good guideline for max resistance of USB lead is probably
0.25ohm. I measured a lot for a presention I gave last week,
and very few random USB leads are within that range.

The best commercial one I had was a 1m Poundland PowerGeeks
one (UK based) which measures at 0.20ohms (and costs £2).

That was beaten by one I had made which came in at 0.12 ohm
for the same 1m, and another very short one I had.

If you want to see the presentation I gave, you can find it
here. The first 10 mins is the relevant part for this.

https://skillsmatter.com/skillscasts/13427-andrew-gabriel-with-rapberry-pi

(I'm not responsible for misspelling the URL ;-)

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

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