For one of my (up to date) Raspberry Pi (SBC) installations, I have a 5v supply able to deliver sufficient power i.e. over 3 amps… I don’t need a full uninterruptible supply, but I thought it would be nice to use one of my USB battery packs in between the power supply and the Pi in case of short term glitches… the battery unit I have is able to shove out enough power also to keep the PI happy but its stabilisation is by the look of it rubbish, as such, from time to time the RED Pi power indicator flicks off momentarily.

No harm done yet but as I’m not using the Pi graphical desktop, I use the warning indicator as a sign I need better power supply. Even at 100% charge, I'm getting this warning on and off.  Anyone aware of a battery unit (doesn’t need a lot of capacity) or even one supplied without batteries that is KNOWN to be stable and deliver 5v, not 4.7v, , can send out 3 amps and charge at 3 amps at the same time??

This blog entry started off challenging battery solutions but now I’ve no faith in the validity of tests out there – it looks like a power voltage test (as against cpu, gpu etc) might’ve worked on Pi2 but not on later units. Thoughts? A problem with the internet is that sometimes incorrect or out of date info persists, often for years out there. No doubt I’m guilty of some of that myself but I do my best to update old blogs.

So I just found Python scripts for testing the power on Pi, but they don’t look right to me on Pi3 and people out there say that all the tests do on Pi3 is load the processor, not give actual power tests. Using an RPI3 upgraded this week (July 2019) from Raspbian Stretch to Buster, I’m getting power readings that don’t make a lot of sense to me so I’ve made a new(ish) script to cover this.

In my office right now, the temperature is 30c and the Pi stated temperature is up to 80c when running tests, maybe 58c otherwise (who would have thought a simple test with SSH output could cause such a rise). No heatsink or fan, clear plastic case. (an example of possibly old material out there, one fellow refers to the Pi3+  throttling to 1200Mhz from 1400Mhz at 60c, well, at 75c, mine is still running at 75c… and yes, I do plan to fit a fan when I find where I hid them.

 powermon.py

#!/usr/bin/python
import RPi.GPIO as GPIO , time

redLED=35
GPIO.setmode(GPIO.BCM)
GPIO.setup(redLED, GPIO.IN)

powerlow=0
while True:
    if(GPIO.input(redLED)==0):
        print "V below 4.63v on Pi2, just stressing on Pi3+" + " " + str(((int(open('/sys/class/thermal/thermal_zone0/temp').read()) / 1000))) + "c"      
        powerlow += 1
else:
    powerlow =0
    if (powerlow  > 3):
        print "Low power for " + str(powerlow) + " seconds"
    time.sleep(1)

This test suggests the voltage is dipping below 4.63v (and I’ve added the temperature monitor) almost constantly on my headless RPI3 (only a non-operating OLED display attached to the pi), erm, no, after discussions in here I’ve replaced my power supply with a QC3 charger perfectly able to keep the supply at around 5v (above 4.9v offload) and the RED light now never goes off. The script then in this case is merely loading the Pi as evidenced by the temperature rising over time – the “below 4.63v” reading being, I believe, nonsense in this instance.

I don’t have a scope handy but I do have a precision meter stating 4.9v to 4.95v while connected to the Pi3 edge connector, the red light on the PI is on constantly (visually).

Thoughts, ideas, am I right for RPI3 and Buster or am I missing something?

The Pi3 here was live upgraded from Stretch to Buster recently and generally works a treat, it is running Node-Red and Mosquito constantly.

In fact I’m running these tests on 2 near identical setups, one is running a Pi3 (hence 1200Mhz tops) the other a Pi3 B+ (hence 1400Mhz tops).

Right now it is looking like a carefully chosen QC3 charger and decent short lead is the way to guarantee sufficient power to run the Pi. Quick Charge 3 as you may know can ramp up the voltage given the right info, but this is NOT what we want for a PI. Mine runs at 5v as it needs to – standard practice for QC3 unless given the right signal by a connected device. No guarantees that if you get the wrong combination of lead and supply you won’t blow up your Pi. Note that in my tests using QC3.0 chargers which ALSO had non-QC3 outputs, the non-QC3 outputs were not as good as the QC3 outputs so it isn’t just a matter of overall capacity. 

And THANKS to Antonio (Mr Shark) and others for the feedback. I’ll cover Pi4 in later entries – see “Raspberry PI4 Arrival” entry.