I am running a Raspberry Pi 3A+ in my car as a DIY Android Auto head unit (using Crankshaft).

In order to not have the RPi immediately shutdown when you remove the key from the ignition (or have it reboot when you start the engine), I am powering the RPi directly from the car's battery. Using the ignition state, the RPi is booted and shutdown gracefully (after some time-out).

In other words, the RPi's 5V input is always powered. The RPi is just shut down when the ignition is off.

Well, the problem now is that the RPi keeps powering the USB port when it's shut down, which means the entire system still draws about 0.190 A (at 12V, so ~2.3 W). That is too much to run 24/7 because of the risk of sucking the car battery dry when left for multiple days.

Is there any way to get the RPi to cut the power to the USB port when halted, or is it hard-wired to the 5V line? I found some info for the B models, but nothing for the 3A+.

Is this not possible on the 3A+?

  • The alternative approach would be to run the PI in read-only mode so that a power loss is not a problem.
    – Robert
    Sep 19, 2021 at 20:44
  • @Robert Yes, I did that for a while and that works, but it has two problems: first, the RPi will reboot when I start my engine, so you have to sit and wait for it to boot before you can setup you navigation, etc. Second, you cannot set a time-out on the shutdown: it powers off immediately when you remove the key from the ignition. This is a better, more sophisticated solution.
    – Compizfox
    Sep 19, 2021 at 20:50
  • Ok, makes sense. But then you need a relay and a "stairway circuit" that enabled power for a fixed time. That would you to use a power button to start the Pi, as well as ignition. One the Pi is up it can periodically trigger that circuit to keep itself "alive". Once you shut down the Pi the circuit comes to a halt and disconnects the Pi from power using the relay. BTW: The post you have linked to is to cut power the Pi is providing to other devices, not the power it consumes in power down state.
    – Robert
    Sep 20, 2021 at 7:11
  • @Robert the RPi power supply is taken care of already. The RPi is woken from halt state by pulling GPIO3 low momentarily (I built a circuit that does this when the car's ignition is on). I am indeed talking about cutting the power on the USB port to accessory USB devices, because those are kept powered on when the RPi is in halt state and they consume too much power for comfort.
    – Compizfox
    Sep 20, 2021 at 9:22
  • Sorry, I thought you simply want to cut the power the Pi consumes in shutdown state (which is also not neglectable).
    – Robert
    Sep 20, 2021 at 9:54


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