5V 1.5A (7.5W) charger for a Rasperry Pi 4 8GB

[lurk101]

... which leaves me baffled as to why folks would use one, other than during the corner case of I blew up my supply and need to find something to temporarily power the Pi until I get another supply or forgot to bring the Pi supply to wherever.

A more common scenario might be to also use it to fast charge your phone.

[Joop99]

Can it work? The Rasperry Pi 4 can reach a maximum of 6.4W of consumption without peripherals connected, in theory as long as the voltage is stable at 5V there shouldn't be any problems right?

Why do you need a charger for a Pi (any Pi, doesn't matter what)? A charger is NOT a power supply, the electronics between a charger and a power supply do differ. So if the charger "thinks" your Pi is fully loaded it will switch off, it doesn't care if your in the middle of some bright idea. A power supply only switches off when the fuse is blown or if you ask too much power, if the supply is carefully chosen this won't happen.

[bjtheone]

Can it work? The Rasperry Pi 4 can reach a maximum of 6.4W of consumption without peripherals connected, in theory as long as the voltage is stable at 5V there shouldn't be any problems right?

Why do you need a charger for a Pi (any Pi, doesn't matter what)? A charger is NOT a power supply, the electronics between a charger and a power supply do differ. So if the charger "thinks" your Pi is fully loaded it will switch off, it doesn't care if your in the middle of some bright idea. A power supply only switches off when the fuse is blown or if you ask too much power, if the supply is carefully chosen this won't happen.

There is a terminology issue in that many folks tend to use "charger" and "power supply" somewhat interchangeably. Modern "cell phone chargers" are really power supplies (as Mr ame is fond of pointing out), with the actual charge management circuitry inside the phone. The "charger" just supplies a steady voltage. Good cell phone chargers capable of supplying well regulated 5V @ 3A work just fine, poorly designed cell phone chargers can have lousy regulation and may have voltage sags at higher current draws and create stability issues on heavily loaded 4Bs. 4Bs do not like voltage sags. Lousy charges work just fine as chargers, since the requirements are different.

Given those issues, the mantra is "buy the official power supply" and all will be good. Any other power supply that meets the requirements would be equally fine, the issue is being able to assess this equivalence.

[emma1997]

Modern "cell phone chargers" are really power supplies (as Mr ame is fond of pointing out), with the actual charge management circuitry inside the phone.

Absolutely correct. Although hard to convince average joe that his chargers are not actually chargers. After all what is it being plugged in to do? Just one of many myths and misconceptions perpetrated by almost everyone. Language evolves but not always in the right direction.

[FTrevorGowen]

Modern "cell phone chargers" are really power supplies (as Mr ame is fond of pointing out), with the actual charge management circuitry inside the phone.

Absolutely correct. Although hard to convince average joe that his chargers are not actually chargers. After all what is it being plugged in to do? Just one of many myths and misconceptions perpetrated by almost everyone. Language evolves but not always in the right direction.

A parallel issue is misinterpretation of labeling (both in the reading and writing thereof). Just because something has a label stating X volts and Y amps does not (always) mean it will provide both at the same time. This is something I've been monitoring for over a decade (initially whilst waiting for my first Pi from the second batch to arrive) and reporting on, originally within the old eLinux wiki, these days within my website.
Trev.

[HawaiianPi]

Technically, anything that supplies power is a power supply.

That being said, power supplies intended to charge batteries in mobile devices usually rely on the mobile device to control and regulate the charging. When used as a stand-alone supply for something like a Raspberry Pi, voltage regulation might not be within the tolerable range.

This is why many of us here categorize "chargers" as something different from power supplies. We can argue all day about what terminology is correct, but here on the forums it is important to know the difference. Raspberry Pi computers don't support any kind of power negotiation, and they require a power source that can supply a stable 5V over a wide load range.

Of course poor regulation is not true for all chargers, but most people don't have the equipment needed to determine the suitability of a charger for use with a Pi computer (a DVM is not enough, as it won't detect brief, transient voltage droops or spikes).

As for the question at hand (5V 1.5A charger...)
While headless power usage would suggest that a 7.5W supply should work, booting is a task heavy operation that could spike above that level briefly, and how that 7.5W supply behaves when it happens will be the key factor.

Another problem with "chargers" is that many of them use a separate USB cable to supply the power, and that introduces another common problem area with powering a Pi computer. USB cables that are either too long, or have power wires that are too thin (or both) will cause voltage loss under load.

So lets say you have a good charger which is rated for 5V at up to 6A (30 watts), like the one that came with my smartphone, and you have a good USB cable which is not too long and is rated for fast-charging (like the 30W rated charging cable for my phone). That should work fine as a Raspberry Pi Power Supply, right? Well, not really, because my phone's charger will only output 5V at up to 2A (10 watts) when it's connected to anything that is not the phone it was intended to charge. So you might get away with powering a headless Pi 4B, but you'll have little overhead for peripherals.

Similarly, the 45W charger that came with a friend's Chromebook will only output 2A at 5V when connected to a non-negotiating device. Some chargers will default to a lower "safe" output of 1.5A, or even as little as 500mA (0.5A).

This is why we always recommend using the official Raspberry Pi Power Supply.

Can it work? The Rasperry Pi 4 can reach a maximum of 6.4W of consumption without peripherals connected, in theory as long as the voltage is stable at 5V there shouldn't be any problems right?

Only way to know for sure is to try it. In most cases all you risk is possible software or data corruption on the SD card. There is a slim chance that an inadequate PSU could cause an SD card to go read-only (permanently).