I subscribe to a mailing list relating to Raspberry Pi for Ham Radio. I
read a message regarding power supply issues with the Pi. I hope you find
this of interest. Here is his message:

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I ran into a hardware problem that I thought was an over-sensitivity on the part of Raspbian 9-stretch. It wasnÆt, but it got me looking into power consumption and voltage sensitivity on the part of the Raspberry PI.

The Raspberry PI wants > 4.65v all the time, no exceptions. It draws
almost an amp intermittently with no daughter cards and no USB peripherals. More current if you have peripherals. Some of the USB sources which can
power a battery device like a cellphone are not adequate to run a Raspberry
PI. The Raspberry PI doesnÆt have a battery to fall back on during high current moments.

The easiest thing to work at for your Raspberry PIÆs power situation is
cables. USB cables are not all made the same, and the longer the USB cable between the supply and the Raspberry PI the more voltage drop you will get across the wire. USB cables are commonly specified with power conductors having 24 gauge 26 gauge, or 28 gauge wire, i.e 24AWG, 26AWG and 28AWG. (American Wire Gauge) 28 gauge is really really thin. I suspect that
some of the USB cables have even thinner wire but those donÆt come with specifications. A 28 gauge wire USB cable at 2 meters long is available.
If you try to run a Raspberry PI on one of these it will go badly.
According to http://www.calculator.net/voltage-drop-calculator.html
1amp load, 5 volts, DC, copper, single set of conductors. Here is the
volts at the Raspberry PI end of the wire.
24AWG is 4.69v at 6 feet 4.85v at 3 feet
26AWG is 4.51v at 6 feet 4.76v at 3 feet
28AWG is 4.22v at 6 feet 4.61v at 3 feet
30AWG is 3.76v at 6 feet 4.38v at 3 feet

Raspberry PIs can complain if the voltage goes to 4.65v or lower. They
will put a graphic icon in the upper right of the screen. Modern firmware, after late 2016, will show a lightning bolt. Earlier firmware will show a colored square. If you get a colored square, upgrade your Raspberry PIÆs firmware. The danger is that your SDcard will be corrupted during
operation or you can corrupt internal FLASH during a firmware update or
maybe during a pin remapping.
To update your firmware do these commands
DonÆt do this if your power source isnÆt great! A power glitch or below-
volts operation can brick your raspberry pi.
sudo apt-get install rpi-update
sudo rpi-update

Since most of the 3Æ wires are 28AWG (i expect), there is your source of low-voltage warnings!

You can buy a 6inch USB A to USB-micro-B cable having 26AWG (gauge) wire
for $3. thatÆs the ticket. https://www.amazon.com/s/ref=nb_sb_noss?field-keywords=B00D0XUKIQ This
is 5 cables for $10 or so.

Power Supplies
For ham radio purposes, I use a "KIS3r33s usb moduleö. They can be had for
$3 (including shipping) on ebay. This is a 3 amp USB supply that you can
run off of 12 to 13.8v. It actually has a very wide voltage-range input. Please read up on this.

While you are at it, get your self a "USB safety power monitorö for about
$4. This will display the voltage and current passing through. I would suggest getting one with a single USB A female socket. Any unit with more
than one socket must have a bridge chip and you donÆt need another of those plugged into your devices. On Amazon you can get one of those for about
$11 in 2 days so donÆt spend that on an eBay unit.

https://www.amazon.com/s/ref=nb_sb_noss?field-keywords=B01D9Y6ZFW

Use your power monitor to measure the voltage on the Raspberry PIÆs USB-A sockets. ThatÆll give you an idea of the voltage actually at the Raspberry
PI. You can also use a voltmeter on the GPIO expansion header between pins
2 and 6. See https://i.stack.imgur.com/sVvsB.jpg for pin-out of the
header. DonÆt short the header! Shorting 5v to a 3.3v pin or signal pin
will kill your Raspberry PI!

Tadd / KA2DEW
EMAIL ADDRESS REDACTED
Raleigh NC FM05pv

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If the right side of the brain controls the left side of the body,
then only left handed people are in their right minds.

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, |[][]|
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,__/__]|| ________ | D8 |
|__!___!!`--'L_______\ |__________|() ___________
"(_)[___]====(_)(_)=| \_(___________)_/__/=(_)===(_)~'

73 de Ray Quinn W6RAY
GMRS WQTX645
Visalia, CA USA DM06ii
When all else fails, ham radio works!