Exploring alternate methods for providing DC power to Raspberry Pi

Pin header is cool, I've done it. I like to use 7.4V or 11.1V LiPos, and an adjustable buck power supply, fed into a diode , then to the Pi header pins.

The buck PS can be adjusted for 5V + whatever voltage drop you get across the blocking diode. 

I tend to overdo the battery size mA hr, if you just want to make it thru the track once , a baby size lipo, maybe  wire qty 2 150mAhr 3.7 V in series would do the trick. 

  https://www.etechnophiles.com/rpi-zero-2w-board-layout-pinout-specs-price/

The DC-DC converter chip doesnt seem to have  significant transient protections built in. 

robogary said:

Pin header is cool

how did you do this, what kind of jumper wires did you use, one pin or 2? a Pi 4 can draw 3A, so the connector should be suitable for that. 

The Chinese jumper wires from my junk box are certainly not.

GP I would ask the same questions.

My thoughts would be a wire gauge similar to what is provided in the DC wall wart.

I appreciate the response but would feel more comfortable with a little engineering background.

gpolder mentioned a Raspberry Pi 4,which I didnt use. I plan to followup in measuring the RPI 4 load requirements with a NOIR camera, WiFi on, and a keyboard dongle inserted. 

I plan to repeat the same measurement on a Raspberry Pi 4 with WiFi on, a keyboard dongle, and an RPi  HD camera. I will use cheap chinese jumpers :-)

The Raspberry Pi 4 schematics ( as well as other schematics) didnt publish the solder run ampacity. If I were to use both 5V pins, I would also expect at the least to use 2 ground points as well. I cant tell by looking if the 5V solder runs are beefy, and if some are beefier than others. 

You have a RPi Zero 2W, different requirements. I found this article, the author stating a RPi Zero with WiFi only pulls 200mA, but the author also stated seeing other published loads of 300-400 mA. 

https://robertthewombat.com/power-requirements-for-the-raspberry-pi-zero_w/

 ************** more on the wire itself ***********************

Referencing this table. https://www.powerstream.com/Wire_Size.htm  

Definition: ampacity is the current carrying capability of a wire. In other words, how many amps can it transmit? The following chart is a guideline of ampacity or copper wire current carrying capacity following the Handbook of Electronic Tables and Formulas for American Wire Gauge. As you might guess, the rated ampacities are just a rule of thumb. In careful engineering the voltage drop, insulation temperature limit, thickness, thermal conductivity, and air convection and temperature should all be taken into account. The Maximum Amps for Power Transmission uses the 700 circular mils per amp rule, which is very very conservative. The Maximum Amps for Chassis Wiring is also a conservative rating, but is meant for wiring in air, and not in a bundle. For short lengths of wire, such as is used in battery packs you should trade off the resistance and load with size, weight, and flexibility. NOTE: For installations that need to conform to the National Electrical Code, you must use their guidelines. Contact your local electrician to find out what is legal!

28 AWG is rated for 1.4A in this table. The "Neltron" Flat ribbon cable sold for for GPIO is 28 AWG. 

26 AWG is rated for 2.2A,

24 AWG is rated for 3.5A. The Dupont jumpers sold on Amazon are 24 AWG. 

If your Pi is on a train, it will have loads for the camera & wifi. You'll probably use VPN to setup and connect to the Raspberry Pi thru a PC after the first initial setup. 

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I'm sure with some more internet surfing there will be other helpful information. 

Hi gpolder - seeing is believing  :-)     reminds me of the Journey song - Dont Stop Belivevn'       

To properly reply to your question on RPI 4, I just did an experiment on a Raspberry Pi 4 ,  I used an adjustable power supply to simulate a battery. Current limit was set to 3.1A in case I screwed up. From the + terminal of the power supply, I wired in a series 3Amp diode, Diode Anode to the + terminal.

I always use series diodes from a battery or external power supplies since I forget and will plug in a PC, or vicea versa, or both, and end up backfeeding somebody and unintentionally powering sensors & stuff. 

From the out side of the diode (cathode) I used an alligator jumper, to a cheap chinese Dupont jumper , with a socket end that plugged into GPIO Pin 2.

I put a voltmeter on GPIO Pin 4 to read the voltage directly at the RPI4.  I also used a single cheapy run of the mill jumper to GPIO 6 GROUND. 

The RPi 4  has a keyboard dongle installed on one USB port. The RPI 4 also has a NOIR camera installed. 

On initial bootup, the RPI 4 only drew 100-150mA, and increased as it went . The Power Supply was set for 5.2V ( 5V +  the measured no load Vf drop of the diode was .2V).

 As the RPi 4  continued in bootup, l had to turn up the power supply voltage to compensate for the diode IR drop. I dont think the load was so much the 28 AWG wires were dropping significant volts. 

The power supply ammeter does dance around a bit, and I'm sure I'd see some higher peak excursions if using a scope on CFB, BUT the largest amps I witnessed was  .6A. in the power supply's screen.    

This measurement isnt the absolute chart all for everyone's applications, but maybe instills some confidence in colporter that its not that bad. 

DISCOVERY !  5V at the 5V pin was not enough to boot up reliably. I missed this on my first pass because I didnt have a monitor plugged in.

My "battery" ended up being 6.6V for 5.3V to 5.5V at the RPI4 GPIO pin, I'd feel better having a better regulated voltage there as well. Its worth a test without the HDMI plug again tho.

For robots &  roving vehicles, I will tend to use a 7.4 V or 11.1  LIPO batteries, and a buck power supply to feed the 5.x volts, and often several for peripherals power, at 6V (RC receiver), 3V (sensors) 5V (sensors) , 12V (fans if any, some LED drivers,) etc...  

Where volts were measured

. 

the test setup. I'd like to check to see if the HD camera load makes any difference from the NOIR camera.

The power supply volts and amps, and the volts read at GPIO4. 

its still bugging me why I needed 5.5 V onto the 5V GPIO pins.  This is from the RPi4 schematic

its still bugging me why I needed 5.5 V onto the 5V GPIO pins. 

a guess: even though your meters don't show it, the voltage drops under what the Pi needs. Briefly.

You'd need a fast meter or an oscilloscope on the input that can check - if you set 5V on the pin -
if that 5V drops somewhere down the boot process. The meter you use doesn't have the capability to do that.

A fast meter with min/max may be able to check this. Or an oscilloscope in DC mode that is set to trigger on negative flank, level (say) 4.9 V.

The scope is a great suggestion, thank you.   

I also may need to reconsider the choice of blocking diode. I used a 3A .diode for this test, really want a diode that has a much smaller load dependent voltage drop from 0-3A, like .1 or .2V.  

If you suspect that the diode is the cause, you could *test* it without one, with PSU set at 5V.

It's a lab setup, so the only one that can connect it wrong is you . Check 5 times before powering on.

thanks for the thorough test, anyway it is clear that you loose a lot of voltage over the Dupont jumpers.

Note that the official 3A Raspberry Pi power supply uses 18 AWG cable.

thanks for the thorough test, anyway it is clear that you loose a lot of voltage over the Dupont jumpers.

Note that the official 3A Raspberry Pi power supply uses 18 AWG cable.

18 AWG would do the job for sure. I've had to make my own cables for wire sizes that big using Mate-N-Lock pins and hot glue as a homemade connector housing to keep pin separation & keep the sockets straight on the pins. It does look like an ugly hack job tho.  Please share if you find a nice solution for terminating 18 or 16 AWG wires into the GPIO header. 

I also considered the standard GPIO ribbon cable, usually at 28 AWG. The case against them is the users dont often feed 5V to the RPI , the pins are used to source 5V for sensor use.  The 40 pin connector tho allows for a good mechanical fit. I'll have to give them a look too, do more measurements to check on voltage drop using multiple conductors in parallel, 2 for 5V and 2 for GND, on both the GPIO ribbon.

I also need to the load measurements while the RPI is running code, for sure that also has impact.

At the end, its mostly curiosity, a bigger wire size ultimately the simple answer, as long as it is mechanically stable and has some covering that keeps pins from shorting together. 

Some of the smaller boards like Zero and Pico can likely get by with a smaller 5V feeder wire size. 

Use an IDC connector with strain relief.

In the past, if larger gauge wire was used, I would solder the wire to a 2.54 pin. You can crimp it but it can make a mess of the insulation on the wire depending on how thick it is. I then heat shrink to protect the pin. It has worked for me and since I don't have another solution, I will use it again.. This will be the first power connection I have done using this method. I have always managed to make the PS work. This project doesn't afford me a PS.

these connectors are 1A per pin, so with two 5V input pins you have 2A max.

I would propose to buy an official raspberry pi 4 power supply, cut the wire with the cable and throw away the power supply.

They are really cheap, price is comparable to a bare cable:

Buy Now

I was thinking the same. But colporteur wrote in the first post that there's no room for the USB connector in his design.

ok, you are right, forgot about that, I was more thinking for a solution for my own project 

On the other hand he is not using a Pi 4, so in that case it could work with proper pin headers and wiring.

much appreciate the input just the same.

Found these adapter cables on Amazon, sez 16 AWG, I have my doubts on that .....but here is a link to have a look https://www.amazon.com/Jienk-Terminal-Connector-Extension-Screwdriver/dp/B096RQNN8C/ref=sr_1_3?crid=1R8PJRO6AT2FN&keywords=Screw%2BTerminal%2BBlock%2BConnector%2Bto%2BUSB%2BC&qid=1649344174&s=electronics&sprefix=screw%2Bterminal%2Bblock%2Bconnector%2Bto%2Busb%2Bc%2Celectronics%2C132&sr=1-3&th=1

Another option to backfeeding GPIO with 5V. 

Looks interesting, much appreciated. I have been doing some reading about power supplies and their impacts on Pi4s. 16gauge is a step up from the typical 18 found in some power supplies. I have added it to an Amazon wish list for the next time I place an order.

The RPI4 uses the USB-C connector, the link is for that adapter. The RPi 3 uses a micro USB.   https://www.amazon.com/gp/product/B07PJYVH12/ref=ox_sc_act_title_2?smid=A3MDC9KUHU6B27&psc=1

There are a variety of these adapters depending on the USB type. 

I'm starting to really like the idea of powering a project this way. It makes it easy to unplug the upstream battery, interlocking & buck power supply, and plug in the AC power supply when doing the project development & debugging.