Getting started! Looking to self monitor multiple circuits

I live in the United States and, after my last electric bill, I’m looking to monitor my electricity consumption. I have 200 amp service and an additional 100 amp sub panel I recently installed. I would like to gather good metrics on what rooms/appliances(furnace,ac,stove)/circuits are pulling wha and tune my families usage from there. I’ll say there are up to 40 circuits/breakers I would like to monitor (24 in the main panel and up to 20 in the sub panel).

I was looking at a couple units on Amazon but I’m a Linux admin and like open source much better. I like the idea of modifying what I need and having the control to monitor what I want.

I have enough electrical experience to feel comfortable modifying my panel to do wiring (although I always have to resort to Google when wiring 3 or 4-way switches! Haha), but I lack the electrical engineering knowledge when it comes to specifics listed in the getting started guides without some guidance.

I’ve read somethings on here about using multiple Tx units reporting to a central EmonPi, but how many can you hook up? Is it like Voltron? (the more you hook up the better it gets lol)

I appreciate any guidance anyone can offer. Thanks!



Welcome aboard, Matt.

If you’re talking about the emonTx and the RFM radio modules on the 433 MHz band:
Definitely not a case of the more the merrier, because they use only one wireless channel so there’s competition and the possibility of collisions. There’s a limit of 30 in the software library that we use, and the practical limit will probably be a lot less than that. Unfortunately, the number you can have before the lost messages becomes a problem has never been quantified, as it depends on the frequency and length of the messages.

However, some people have been experimenting with the ESP8266 WiFi module, and there have favourable reports so far. I can’t tell you any more, but somebody else can probably fill you in with some details.

How many emonTx units you need depends to some extent on how many 120 V and 240 V circuits you have, and how you intend to monitor them. The options are in the “Use in North America” page of Building Blocks, accessed via “Resources” at the top of this page. Basically, you need 1 CT per 120 V circuit. You might need 2 CTs per 240 V circuit, but depending on how you connect them, you may need only one input. That article also lists many sources of current transformer suitable for your larger cables. If you can have one circuit (either voltage) per emonTx input, you need a minimum of ten, and you might need to modify the sensitivity of the 4th input on some or all of them. I wouldn’t like to say that you won’t miss the occasional message with 10 emonTx’s on the 433 MHz band. Whether that would be OK on WiFi, I’ve no idea.

I suspect from what you write that you’re not up for it, but if my memory serves, there are designs published here (on the old forum I think) for a high-powered Arduino with many more than 4 current inputs. You might like to seek one of those out. There’s one based on our designs here: Home Energy Monitoring System