Can a USB-C Power Bank be used to power a Pi 4 for off-grid or mobile uses where the Pi cannot be tethered to either a mains electric socket or a POE switch?
Many of my contributions to this forum have centered around innovative ways to power a Pi which is awkwardly out of reach of a mains socket, specifically using POE. But what do you do if there's no mains power source at all, ie: Pi used in off-grid conditions or mobile use where the Pi is not stationary?
As the Pi 4 now had a USB-C Power socket, I thought it would be useful to revisit using a USB Power Bank as a power source which although worked with earlier Pi models threw under-voltage warnings.
Yes, USB-C Power Banks CAN be used to power a Pi 4 without triggering an under-voltage alert, but with following notes:
- USB Power Banks: Can vary widely in quality, affecting results
- Cables Used: Using long, thin-gauge cables reduce voltage supplied to Pi
- Pi Applications: Test Pi in use-case configuration to determine how much power it will consume for required period it must remain powered. For example, video encoding for a security camera will burn through power a lot faster than just running an SSH server on the same Pi.
- Under-Voltage: Despite only a single "Under-Voltage" warning seen during testing, neither USB Power Bank tested achieved a full 5v (but came very close). Although electrical equipment can be damaged by OVER-voltage conditions, it's also possible (however much less likely) that damage could result to hardware from UNDER-voltage conditions. Given the negligible cost of a Pi, I'm not terribly concerned
If interested in HOW my conclusions reached, please continue reading...
Determine relative power performance of different USB-C Power Banks & cables combinations to power a Pi 4
Identify combinations which resulted in Pi throwing an under-voltage warning ("Lightning Bolt" displayed in top upper-right screen corner)
Record sufficient detail to enable independent verification of results
Testing: How Power Measured
- Wait until Pi fully booted
- Take pics over a period of a minute to identify high-low voltage & amperage ranges. Not totally precise, but good enough
NOTE: Only (1) snap for each high & low value for each test will be shown
Equipment used in tests was employed because I had it in my office at hand. There may be better or worse Power Banks & USB-C cables then those used in my tests.
- Pi 4: Configured w/ cooling fan- which itself has additional power draw- as a wireless AP with "pi-ap"
- Official Pi USB-C Mains power cable
- USB-C Power Tester: Satechi USB-C Power Meter Tester Multimeter
- USB Power Bank #1: 20100 mAh Zendure X6 USB-C Hub and Power Bank with 20100mAh
- USB Power Bank #2: 20100 mAh Reka Power Bank (Aldi's supermarket £29.99)
- USB-C Cable #1: 21" Cable packaged w/ Zendure Power Bank
- USB-C Cable #2: 40" Cable packaged w/ Reka Power Bank
NOTE: Both USB-C cables were end-to-end USB-C with no adapters used between the Pi or nor the USB Powerbank
Zendure USB-C Power Bank:
Reka USB-C Power Bank:
Test 1: Measure power connecting Pi to mains to establish baseline
Test 2: Compare Power Banks Connecting Pi w/ USB Cable #1
Overall Results: No Low Voltage warnings observed on EITHER USB -C POWER BANK despite not quite reaching 5v. Also, best voltage performance achieved using the shorter 21" Zendure USB-C cable over the 40" Reka one.
Power Bank #1: Zendure Tests w/ 21" Zendure Cable:
Power Bank #2: Reka Tests w/ 21" Zendure Cable:
Test 3: Compare Power Banks connecting Pi w/ USB Cable #2
Overall Results: A palpable reduction in voltage from using the Reka cable which at 40" was nearly TWICE as long as the Zendure's (21"). This was enough for the Pi to throw a Low Voltage warning when connected to the Zendure Power Bank using the longer cable. However, the Pi 4 did NOT show the dreaded "Lightning bolt" when connected to Reka Power Bank using it's own 40" USB-C cable.
Power Bank #1: Zendure Tests W/ 40" Reka Cable:
Result of Reduced Wattage:
Using Zendure Power Bank with longer 40" Reka cable resulted in an Under Voltage warning
Power Bank #2: Reka Tests w/ 40" Reka Cable:
Test 4: Determine power overhead of dual monitors vs headless Pi 4
Finally, we'll examine power with the dual monitor cables DISCONNECTED using just the ZENDURE CABLE with each Power Bank.
Since low voltage is the problem we'll review only the HIGHEST recorded voltages observed to see how they were affected
Overall Results: Since we're using a battery- a DC power source- and negative resistance is at play, less amperage sees increased voltage getting us closer to 5v the Pi wants. I'm not an electrical engineer, but this appears to be the relationship evidenced in my tests results shown below.
Zendure Power Bank powering Pi4 w/ Zendure 21" Cable:
Reka Power Bank powering Pi4 w/ Zendure 21" Cable:
With the Reka using the Zendure cable we are now achieving 4.92v at 0.96 a whereas before with both HDMI cables connected the best we managed was 4.87v when amperage was 1.31a. Getting within touching distance of 5v now...
It very much appears that using short, thick-guage USB-C cables and a quality USB-C Power Bank you can power a Pi 4 while avoiding the "Under Voltage" warnings. However, although I managed to get close to 5 volts with my test bench, I never fully managed to attain it. YMMV depending on your own combination of Power Bank & USB-C cables-
To add just a minor point to F1Linux's answer...
Wrt the question:
Can a USB-C Power Bank be used to power a Pi 4...?
Yet another caveat to the answer is that you must use a
NON e-marked USB-C cable.
If you're interested in some details, see this answer. Also note the requirement to use a
NON e-marked USB-C cable is due to a design flaw in the RPi 4, and therefore not limited to Apple-manufactured USB-C power supplies. A
NON e-marked USB-C cable is required for any USB-C-compliant power supply.nothing to do in particular with an Apple-manufactured power supply.