Raspberry Pi Forums

I'm considering a project where a Pi would be in a cabinet that has 208V 3Φ without a neutral. I'm having trouble finding a cost effective (cheap) way to get from 208VAC to 5VDC. I'm finding 208/240VAC 24VAC 40VA transformers cost more than a Pi. Once to 24VAC, there's most cost getting to 5VDC.

So, I'm asking for some ideas on how to power the Pi.

The project would control parking lot lights for a business. Some of the problems with traditional time clocks are:
- they turn the lights on at a set time rather than at, say, dusk. This means lights can burn when they're not needed or they aren't on when needed.
- they don't adjust to daylight saving time changes
- they need reset after power outages

I can solve all these problems with a Pi and an internet connection. I can also add some functionality like a web interface to adjust on and off settings or to turn the lights on for 10 minutes so people working late can get to their cars.

AFAIK, you should be able to get 120VAC from any two of the connections on a 208V 3 phase supply. A PSU to go from 120vAC -> 5DC should be easily obtainable.

mike_p wrote:AFAIK, you should be able to get 120VAC from any two of the connections on a 208V 3 phase supply. A PSU to go from 120vAC -> 5DC should be easily obtainable.

Only with a neutral and one phase, a 3 phase supply with no neutral will have the 208v between any two phases.

It should be possible to get a 5v dc power supply with a broad ac input range to work.

Many (if not just about all) laptop power supplies work fine in the range 115V to 250V. I think you may find the same for 5V USB supplies too. really worth checking the details plate on an mains adaptor.
So, when you have found one that will cope check for the double insulated symbol (2 concentric squares) connect it across 2 phases P1> adapter L, P2 > adapter neutral.

Doh, of course! A wall adapter like this https://www.sparkfun.com/products/12889

I'll open the case up, desolder and remove the board, and build it into my project.

Thanks for doing the thinking for me!