Power adaptors for Arduino and R-Pi

Submitted by Guest on Mon, 03/12/2012 - 19:38

Which are the best and most energy efficient power adaptors to buy for the Arduino (emonTx) and Raspberry Pi (emon base)?

So far, I have found these:

https://www.adafruit.com/products/501 < for R-Pi and/or Arduino

https://www.adafruit.com/products/63 < for Arduino

http://www.amazon.com/Motorola-Micro-USB-Home-Travel-Charger/dp/B004EYSK... < for R-Pi

Is there any advantage to running the Arduino with 9V vs 5V?

How important is it that I monitor AC power with the 9V AC-AC converter?

Would love to get everyone's thoughts. Thanks!

Re: Power adaptors for Arduino and R-Pi

Submitted by Robert Wall on Mon, 03/12/2012 - 20:30.

I'll just answer this one: "How important is it that I monitor AC power with the 9V AC-AC converter? "

Crucial. It is used to measure both the line voltage and phase. Without that, you cannot properly measure power. Read up in Building Blocks for the technical details.

Re: Power adaptors for Arduino and R-Pi

Submitted by glyn.hudson on Wed, 05/12/2012 - 17:34.

We have tested this one with the Nanode RF and emonTx and found it to work well: http://shop.openenergymonitor.com/usb-power-adapter-uk-plug/

This one is a bit smaller (and cheaper), it's best suited to emonTx and emonGLCD: http://shop.openenergymonitor.com/emerson-5v-usb-mini-b-power-supply/

Re: Power adaptors for Arduino and R-Pi

Submitted by glyn.hudson on Wed, 05/12/2012 - 17:36.

Not all power adapters are the same, see this post for why is's worth getting a good quality adapter, there are some very poor units out there (usually sold cheap on ebay): http://openenergymonitor.blogspot.com/2011/08/not-all-usb-power-supplies-are-created.html

Re: Power adaptors for Arduino and R-Pi

Submitted by JP (not verified) on Wed, 05/12/2012 - 20:40.

Thanks guys. I have seen the post but it is hard to know before buying. I can only hope that the unit approved by Adafruit is a high quality power supply.

I am looking at switching power supplies because they are more efficient (although more noisy). Do you know if a switching power supply can be used for the AC-AC adaptor?

Re: Power adaptors for Arduino and R-Pi

Submitted by Robert Wall on Thu, 06/12/2012 - 00:23.

"Do you know if a switching power supply can be used for the AC-AC adaptor?"

Yes, of course I know. And if you had bothered to properly read and follow up my first answer to your question, then thought about what the output from a switched-mode power supply is, you would know the answer too.

[It's no].

Re: Power adaptors for Arduino and R-Pi

Submitted by JP (not verified) on Thu, 06/12/2012 - 02:13.

Robert, that response was uncalled for. I have a lot to learn about electronics, and I hope that this forum is a place where I am welcome to ask questions. I have not seen mention of switched-mode power supplies in the Building Blocks, which is why I posed the question.

Thanks for your help.

Re: Power adaptors for Arduino and R-Pi

Submitted by Robert Wall on Thu, 06/12/2012 - 14:01.

You're probably right - sorry. A SMPS invariably works at a high audio or super-sonic frequency so that it can use a minuscule transformer, and the transformer output is rectified, smoothed and comes out as a regulated direct voltage. That of course gives you absolutely no information about the mains supply, which is the whole objective of monitoring the mains. Read these in order to see how power is measured:

http://openenergymonitor.org/emon/buildingblocks/ac-power-introduction
http://openenergymonitor.org/emon/buildingblocks/ac-power-arduino-maths
http://openenergymonitor.org/emon/buildingblocks/ac-power-advanced-maths
http://openenergymonitor.org/emon/buildingblocks/measuring-voltage-with-...

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