Prevent Stereo Shutdown During Ignition

Question

I've got a Honda Civic 2006 that I've recently added a nice aftertmarket Android Auto head unit to because I got used to the one I had in my old work car (a 2018 Audi A3).
This unit works great, however,  when I start the engine, all of the electronics go dead for a couple of seconds and it has to restart and reconnect. This isn't the end of the world but it's annoying.
Now, I'm an electronics engineer, so I know that theoretically, I could just add a diode and capacitor to the power rail and that'd probably keep it juiced for long enough for the engine to do its thing. That being said, I don't know much about car electronics specifically and want to check this won't break anything. Furthermore, is there a "standard" part I can buy and fit to do this? It seems like it should be a fairly simple thing to get as most modern cars don't seem to have this issue.

HandyHowie · Answer

If your supply is cut for a couple of seconds, then you will need quite a large capacitor to keep power supplied to the head unit, especially if the volume is turned up quite high at the time.
You will also need to think about the choice of diode that will be able to cope with the current demands of the head unit and also the inrush current of initially charging the capacitor.
If you wire this up correctly, you shouldn’t affect any of the car electronics, since the diode will block any reverse current.
It could be that the action of turning the ignition switch is disconnecting the power to the head unit, so an alternative could be to wire the head unit to the battery via a fuse, so that power isn’t disconnected when starting.   You would then need to ensure that you turn the stereo off when leaving the car.

Prevent Stereo Shutdown During Ignition

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