Pi 4 maximum power consumption

Question

What is the maximum theoretical power consumption of Pi 4? I had expected that I would be able to find some sort of specification table for that, but I could not. The only things I could find were third-party benchmarking results like this which says that Pi 4 uses 7.28 watts on "Load".

But isn't 5V*2A = 10W? Then, why do they say that Pi 4 requires a minimum 3A adapter? Is it because a 5V 2A adapter is does not actually output 2A due to some sort of conversion loss? Or because Pi 4 can use more than 10W?

Someone on the web says he recommends a 4A or 5A adapter. I could not find any 5V 5A USB-C adapter, but I could find a 5V 4A USB-C adapter. Is a 4A or 5A more recommended than the common 3A adapter? And does a 5V 5A USB-C adapter exist?

Answer 1

The "maximum theoretical power consumption" depends on device junction temperatures, thermal conductivity, air flow, etc, etc. I don't think that's what your question is really after - but if it is, you can stop reading here.

The amount of power the RPi 4B consumes "under load" is regulated by the device's firmware in a closed-loop system. In other words: At some measured value of device temperatures (CPU, GPU, PMIC), the firmware acts to "throttle" performance to limit further increases in the temperature. We don't know precisely how that is done, because the Raspberry Pi firmware is proprietary. For this reason, empirical limits of power consumption are of more practical interest than theoretical limits.

Test measurements from 4Q 2019 conducted by "The Organization" on the then-current firmware showed that the RPi 4B power dissipation tops out at approximately 6.4 Watts running with the latest firmware as of Nov 2019. However, the ambient temperature of the test environment was not given. It seems safe to assume that additional heat sinks and/or cooling fans were not used, as they are not shown in the graphics or discussed in the text.

The chart in the link in your question was taken from these tests. You can read some details on how they did their testing there. You can also read of similar testing done by an independent group (Tom's Hardware), and notice that the results are in reasonably close agreement. The Tom's Hardware test report indicates the ambient test environment was 24°C, and no mention was made of additional cooling.

You can also read the Power Supply Requirements published by "The Organization". Reading that, you will see that the "Recommended PSU Capacity" for the 4B is 3.0A - but also note that 1.2A are "set aside" for USB peripherals. This leaves 1.8A - approximately 9W for the RPi itself. That 9W figure is consistent with the measurements taken during testing, and it seems a prudent recommendation for most usage.

With respect to what "someone on the web" recommends, I can only offer this: With additional cooling (fans, heatsinks) and a lower ambient, it seems likely that the RPi could consume more power than in the tests referenced above - perhaps significantly more. Also, some will choose peripherals that may push the limit. But unless your usage case is extreme, the 3A recommendation seems sound - even conservative for many applications. If your usage case demands more power, I'll leave it to you to shop for a higher-powered adapter, but certainly they are available: for example Apple's Macbook USB-C charger is rated at 96W. And it's easy enough to assemble a 5V supply with very high amperage ratings.

In closing, if you're concerned about having enough power, consider purchasing a "USB Power meter". Plug one end of it into your RPi's USB-C input, and connect your USB cable to the other. This will tell you two things:

1. if your cable or your supply are sub-standard, the voltage may be less than the minimum (~4.8V)

2. you can monitor how much current your RPi and peripherals are drawing.

Answer 2

Power ratings of CPUs are intrinsically averaged over longer periods of time, at least tens of seconds. Sub-second power spikes simply don't have enough effect on the temperature.

The current ratings, on the other hand, are immediate, at least on the human scale. If your power supply cannot deliver the required current, its voltage will collapse within tens or hundreds of milliseconds, and the Pi may crash. The fact that the current consumption comes back to normal after 0.5s will not help.

So yes, it is possible to have a 7W device which requires a 5V 3A adapter. Note that if the adapter has a separate power rating (very rare), it doesn't have to be 15W, a 10W will do just fine.

Answer 3

In the case of perceived 'slow performance' you can force the CPU to run at speeds up to 2100, as I have done. You also need to 'over-voltage' to '6' to make that work. You can fiddle with the GPU frequency too, but that seems less effective, in my experience. This is all done by editing the 'config.txt' file in the /boot folder and is absolutely done at your own risk ... if you exceed 6 as an over-voltage amount, your warranty is immediately dead.

Answer 4

It's because the board is designed to be powered by random phone chargers. In my experience, random phone chargers often can supply the rated voltage at half the rated current, or the rated current at some lower voltage. But you shouldn't expect them to supply the rated current and the rated voltage at the same time!

The "3-amp" requirement is a simple-language way to exclude "2-amp" chargers that aren't likely to put out 2.0 amps at 5.0 volts +/- 5%. This product is aimed at a market that doesn't know much about electronic power supplies.

The SoC on the Raspberry Pi has internal voltage regulation. You need a regulated 5.0 V supply for the SDcard and USB hub. Thumb drives and whatever else you might plug in there may be unhappy running on the noisy 4.25V you might get from a "2-amp" phone charger, even if phones charge okay and the SoC can handle it.

IMO power supply is the weak link in the R-Pi architecture. I usually solder wires to pins 2 and 14 and mount a 3-amp buck converter next to the board. You can power the buck converter with any old 2-amp 12v or 9v wall wart and it doesn't matter how long the wire is.