I'm trying to power my Raspberry from my TV's USB port (originally intended to show pictures from an usb stick).
It mostly works, but I get some random reboots, while it works perfectly with an external USB power supply. Usually it will work correctly for a couple of minutes, so I suspect that particular USB port gives enough power for most of the time but not enough for some spikes in power usage.
It is a Model B (not by choice, it's just what I have lying around, I bought it on launch day) with a WiFi dongle and a TSOP32238 on GPIO. I control it using an IR remote and I already shut it down before turning off the TV (even if the Raspi is running on a separate power source).
I don't have a space problem (behind a typical TV you have plenty) but a cabling / power outlets one (in this particular location I don't have space to hide power bricks and the like).
I'm thinking about adding a large capacitor to help it survive those spikes:
- Does it makes sense at all?
- How large could be large enough?
- Instead of building a custom USB cable, it would be much cleaner to plug it on the Pi's pins. Is this going to cause any problem? I'm pretty sure it could not overvolt the Pi (typical risk when trying to power a Pi from those pins using an external supply) but I'm not sure about other kinds of problems.
I already do a clean shutdown every time I turn off the TV (either before or after it) so having the requirement to remember shutting it down is not a problem.