[arm-allstar] Powering Your Pi (Lessons learned from Pi 3B+)

Sun Jan 13 23:49:57 EST 2019

I know there has been a lot of noise about Pi power today and I want the
larger group that is not experiencing any problems to know that there is
absolutely no reason to start messing with things if you are not
experiencing problems with your Pi. There are literally thousands of Pi's
being run by users of this email list and when problems occasionally crop
up like this everyone goes bananas thinking they might have a problem when
the larger audience does not.

The bottom line is if you have a wall wart supply (the most common power
source for a Pi) that is rated for the Pi you probably will not have any
problems and should not be alarmed by all this talk of different supplies
and connection schemes. FOB's draw little power and the same for USB
sticks. If you plug in anything heavy into the USB ports like hard drives
or other power hungry devices then, yes you need to be aware of the current
drawn. In that case you always have the option of using a powered USB hub.

*73 Doug*

*WA3DSP*

*http://www.crompton.com/hamradio <http://www.crompton.com/hamradio>*

On Sun, Jan 13, 2019 at 10:34 PM "Jim Kinter Jr. via ARM-allstar" <
arm-allstar at hamvoip.org> wrote:

> Since we Hams usually have 12VDC handy, I like using UBEC's to run my
> Ham Pi stuff.
>
> https://hobbyking.com/en_us/power-systems/power-distribution/vr-ube-bec-sbec.html
>
> I have had really good luck with the HobbyKing and Turnigy brands,
> and they seem to have enough amperage that a Pi never complains.
> I just scarf the microUSB off a USB-A ->uUSB cable and tie to the
> output of the UBEC.
> I did learn (the hard way) to always go in the uUSB port on the pi
> and NOT direct to a 5VDC line on the 40-pin, as the uUSB has extra
> regulation on that port.
>
> 73
> K5KTF
>
> At 02:34 PM 1/13/2019, \"Doug Crompton via ARM-allstar\" wrote:
> >I find that the wall warts designed specifically for the Pi work very well
> >in most cases. I usually buy from Microcenter and get the 5V 2.5A or 3A
> >models. They actually are 5.2 or 5.25 volt output. One of the problems is
> >people using charger type supplies not designed for running the Pi. Also
> >poor USB cables which are only designed to carry 1/2A.
> >
> >Here are some good articles on Pi 3B+ power design.
> >
> >https://www.raspberrypi.org/blog/pi-power-supply-chip/
> >
> >https://www.datenreise.de/en/raspberry-pi-power-supply-recommendation/
> >
> >
> >*73 Doug*
> >
> >*WA3DSP*
> >
> >*http://www.crompton.com/hamradio <http://www.crompton.com/hamradio>*
> >
> >
> >On Sun, Jan 13, 2019 at 2:09 PM "Jim Darrough via ARM-allstar" <
> >arm-allstar at hamvoip.org> wrote:
> >
> > > I am currently using a PiJuice HAT device to power my RPi. This device
> > > has a charge port (conveniently a micro USB) and my Pi power supply
> > > plugs into that. Since the Pi Juice acts as a UPS and provides power to
> > > the RPi, it should alleviate any voltage drops since it plugs into the
> > > expansion (IO) headers.
> > >
> > > Nice device. It will run the RPi for over 3 hours. The producers are
> > > also selling large capacity (12,000 mah) LiPo cells that can be
> > > connected to the PiJuice external power terminals and will be charged
> by
> > > the HAT.
> > >
> > > 73 Jim KI7AY
> > >
> > > On 1/13/2019 09:17, "Doug Crompton via ARM-allstar" wrote:
> > > > I am resending this as the original from Randy was blocked due to
> > > > graphics.
> > > >
> > > > Writing this email with the intent to share some knowledge I learned
> > > > this week, and with the hope that you can avoid a problem that I'm
> > > > currently experiencing at my remote repeater site - an unhappy Pi and
> > > > a repeater that's mostly off the air.
> > > >
> > > > *Key Point #1:*
> > > > *The Pi Model 3B+ is a power hungry beast. The power supply that
> > > > previously ran your Pi 2 B, or Pi 3 B hardware may be inadequate for
> a
> > > > Pi 3B+
> > > > *
> > > > *
> > > > *
> > > > *Key Point #2*
> > > > *Voltage Drop in cables and internal input circuit to the Raspberry
> Pi
> > > > is material. If you start with a 5V supply, the chips in your Pi will
> > > > have less than 5V.
> > > > *Starting with a 5V power supply, voltage drop in your power cable,
> > > > and a further voltage drop through the internal protection fuse of
> the
> > > > Pi can easily result in the 4.63V Low Voltage Signal from the
> regulator.
> > > > Micro USB cable losses can easily be 0.3V, and combined with the 0.1V
> > > > drop across the Pi's internal fuse, we're at 4.6V
> > > >
> > > > *Key Point #3*
> > > > *The Micro USB connector is rated for 1.8A, this will not support the
> > > > full power that the Pi 3 B+ and usual peripherals can draw.*
> > > > It may be time to consider powering Pi 3 B+ via the header pins,
> > > > possibly with some sort of Pi Power Hat having a 12V to 5V converter
> > > > located close to the Pi. (for those that run their Pi's at repeater
> > > > sites with DC power)
> > > > This bypasses the 1.8A limit of the Micro USB connector, and the 0.1V
> > > > drop across the input fuse. (The Pi Power Hat should have appropriate
> > > > current limiting)
> > > >
> > > > *Background Data and Reading: */*Raspberry Pi 3B+ power input and
> > > > voltage regulator system.*/
> > > > The Raspberry Pi website provides hardware documentation re power
> > > > input, however it is one version of hardware behind - It describes
> > > > power requirement for a Pi Model 3. (not 3 B+)
> > > > It would be easy to read this and assume these specs also apply to
> the
> > > > 3B+.... Hint: They don't.
> > > > There have been substantial changes to power consumption between the
> > > > Model 3 B and the Model 3 B+
> > > >
> > >
> >
> https://www.raspberrypi.org/documentation/hardware/raspberrypi/power/README.md
> > > >
> > > > *Pi 3 B+ Power Input Circuitry:*
> > > > image.png
> > > >
> > > >
> > > > *Micro USB Connector:*
> > > > The Raspberry Pi 3B+ power input schematic indicates use of an
> > > > Amphenol Micro USB connector as the power input to the Raspberry Pi
> 3B+.
> > > > The Amphenol specs for this part indicate a *_maximum current rating
> > > > of 1.8 amps_* for pin 1 of this connector.
> > > > https://www.amphenol-icc.com/micro-usb-101035940001lf.html
> > > >
> > > > *Input Fuse, Protection Diode and Filter Capacitor:*
> > > > The power input circuitry of the Pi 3B+ has a fuse, diode and filter
> > > > capacitor to protect the Pi from reversed power leads, too high a
> > > > voltage, and noise transients on the power supply.
> > > > The fuse is rated for a holding current of 2.5 Amps, and trip current
> > > > of 5 Amps. Importantly, *the fuse has a resistance of 0.1 Ohms*. That
> > > > doesn't sound like much, but we are working with a nominal 5 Volts.
> > > > *If you want 5 Volts exactly on the Raspberry Pi power bus, you need
> > > > about 5.25V on the Micro USB port* to achieve that. In fact, the
> > > > Raspberry Pi official AC power supply is 5.1V DC.
> > > > Question: Where do you buy a 5.1 or 5.25V power supply?
> > > >
> > > > The transient voltage suppression diode has a breakdown voltage of
> 6.4
> > > > Volts. Exceeding this voltage will cause the diode to short the 5
> volt
> > > > bus to ground, resulting in high current tripping the the fuse.
> > > > Should you wire up the power to your Pi with reversed polarity, the
> > > > diode will conduct, shorting the 5V bus to ground and blowing the
> fuse.
> > > > Fuse: https://www.bourns.com/pdfs/mfmsmf.pdf
> > > > Diode:
> > > >
> > >
> >
> https://www.littelfuse.com/products/tvs-diodes/surface-mount/smbj/smbj5_0a.aspx
> > > >
> > > > *Pi 3 B+ Voltage Regulator:*
> > > > On board voltage regulation is done by a new multi-voltage regulator
> > > > chip, the MXL7704-R3.
> > > > Previous Pi's used 3 separate voltage regulators. The MXL7704 was
> > > > created for the Raspberry Pi.
> > > > https://www.raspberrypi.org/blog/pi-power-supply-chip/
> > > >
> > > > The MXL7704 will operate from an input voltage of 4.0V to 5.5V.
> > > > At or below 4.63 Volts the regulator sends a low voltage signal over
> > > > the I2C bus to the CPU.
> > > > Below 3.9 Volts the regulator locks-out.
> > > > Spec Sheet: https://www.exar.com/ds/mxl7704.pdf
> > > >
> > > > image.png
> > > >
> > > >
> > > >
> > > >
> > > > *USB Cable Voltage Drop:*
> > > > Your power supply puts out a nominal 5 Volts, but the cable between
> > > > your power supply and the Pi will have a voltage drop.
> > > > The voltage drop increases with the larger current through the wire,
> > > > and the Pi 3 B+ draws more current the previous Pi.
> > > > Here is a chart I found at
> > > >
> > >
> >
> https://goughlui.com/2014/10/01/usb-cable-resistance-why-your-phonetablet-might-be-charging-slow/
> > > >
> > > > A voltage drop of nearly 0.5 V is possible with a hefty 22 gauge
> cable.
> > > >
> > > > image.png
> > > >
> > > > *Wireless Chip 5V Supply:*
> > > > While the Cypress Wireless chip on the 3B+ uses lower voltages from
> > > > the regulator for most of its operation, the WiFi power amplifier has
> > > > a separate 5V supply.
> > > > Acceptable operating voltage range is 3.0V to 5.25V, the optimum
> > > > voltage is apparently 4.8V
> > > >
> > > > *Measure the 5V rail on your Pi:*
> > > > GPIO Expansion pins 2 & 4 are 5V +, ground is available on pin 6, 14,
> > > > 20 2etc.
> > > > Ideally this should be 5.0 Volts DC. It's likely to be low if you're
> > > > powering your Pi via the Micro USB port.
> > > >
> > > >
> > > > *Header Plug as Power Input:*
> > > > I will be testing powering my 3 B+ via the GPIO Header.
> > > > I have ordered a 10 pin ribbon cable with female header connector.
> > > > My current plan is to have the ribbon cable connect to pins 1-10 and
> > > > extend out the slot in the case.
> > > > I may use an exacto knife and trim of unnecessary GPIO wires, leaving
> > > > only 2+4 for +5V and 6+9 for Ground.
> > > > I plan to use a 5V, 5A power supply that is not potted in epoxy so
> > > > that I can see the component values and ensure it has good filtering.
> > > >
> > > > Regards,
> > > > Randy W3RWN
> > > >
> > > > _______________________________________________
> > > >
> > > > ARM-allstar mailing list
> > > > ARM-allstar at hamvoip.org
> > > > http://lists.hamvoip.org/cgi-bin/mailman/listinfo/arm-allstar
> > > >
> > > > Visit the BBB and RPi2/3 web page - http://hamvoip.org
> > >
> > > --
> > > 73 Jim,KI7AY
> > > la ciruela de Panama
> > >
> > >
> > >
> > > ---
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