Best method for powering my emontx shield

Sorry if this is has been asked before but I struggled to find a post that answered my question.

To set the scene, I’m using an Ardunio UNO to power my emontx shield along with my emonbase, all this is to monitor my solar PV power generation stats. Everything is up and running now and I’m loving the whole emon ecosystem (great work guys).

So, a couple of basic beginner style questions if you don’t mind:

  1. I’m after some advice for the best method of powering my emontx shield. I’ve been writing software for 20+ years but new to hardware (especially soldering electronics but thoroughly enjoying it!). To highlight my naivety I bought myself a 9v battery and powered up my Arduino thinking it would last maybe 6 months or so, well, you can imagine my shock when I woke in the morning and discovered the battery was dead So, back to the
    drawing board. Is my best option to purchase the AC-AC Power Supply Adapter from the OEM shop, is that all I need?

  2. I’ve noticed in my sketch (Shield_CT1234) that the voltage is hardcoded to 240v, if I use the AC-AC power supply is there a way to detect/calculate the actual voltage for a more accurate reading? My voltage is measuring around 248v.

Thanks guys!

  1. No, you need a d.c. supply for an Arduino. We use the ac adapter not as a power supply for the Shield, but as a means of obtaining a sample of the mains voltage to measure. It’s also used at the same time as a power supply for the emonTx, but when serving both purposes, the power that can be drawn is strictly limited. I’m sure there’s much on the Arduino website about the power supplies they recommend, and it will pay to get a decent quality one. Many of our users have had trouble with cheap 5 V phone chargers which can be used with the emonTx.

  2. That’s true. The way to get an accurate value is to use an ac adapter and the Shield_CT1234_Voltage sketch. In that one, it measures the voltage (and you’ll then get real power, not VA), and it’ll have a direction too - useful if you have your own generation.

Superb, this is just what I was looking for!

Thank you.!

Discussion on why it’s preferable to power an Arduino from the DC-in jack, vice the mini USB connector: