Community
OpenEnergyMonitor

Community

Hardware needed for basic setup without emoncms

Let me know if I’m on my own wanting to roll out something not directly supported here, that’s ok.

I’ve got an exciting home assistant solution running for my home automation which has already got a bunch of other sensors that are then pushed out to influxdb.

I’m keen to measure my whole home instantaneous power usage to get a better understanding of my usage and so looking at different hardware solutions. What would I need to get a basic clamp reading pushing through to mqtt or home assistant directly? Could I use the Arduino shield easily for this purpose?

I’m comfortable with software but not completely sure I follow on the hardware so a ready made shield I could slap onto something would be awesome. Is there any gotchas I should know before going ahead?

Do you mean current via a current transformer? Not one of these:

I think the emonTx Shield - provided it is compatible with an Ethernet-equipped Arduino - together with an a.c. adapter, would give you real power readings that you could send to wherever, in whatever format you need.

I add the caveat “provided it is compatible” because a while ago, some Arduino Ethernet shields stole one of the analogue pins which the emonTx shield uses, meaning the two could not work together. I’ve not heard of the problem recently, so it might have been resolved. I’m not an Arduino expert, but I would think that an Arduino natively equipped with Ethernet wouldn’t have the same problem.

I added the a.c. adapter to measure the voltage, because that way you can calculate real power - which is what you get charged for. Reading current only, and multiplying by 240, only gives apparent power, which is less accurate as (a) it presumes a constant voltage (which it isn’t) and that you don’t have any non-heating loads (which you almost certainly do).

Check the size (and accessibility) of your main incoming cable before you buy a c.t. You need access to just one core (see parts 1 & 2 of Learn→Electricity Monitoring→CT Sensors)
If our standard 100 A split-core c.t. won’t fit your cable (it probably will, it’s good to 25 mm² - 100 A in copper), we can help point you towards an alternative.

you could try this method of hardware of emonetx sheild and wemos r3 and mqtt

i do it this way into influxdb though I have mine using a openwrt router to handle everything - all my home automation (domiticz , zigbee2 mqtt wifi etc -) and data capture (collectd-mqtt > influxdb). I like it this way it easy and self configuring and new device/sensor will automatically be added to influxdb data with out any configuration other then the format of the mqtt data publish)

1 Like

Correct :slight_smile: definately meant a current transformer.

How careful around routing those do I need to be? They look like they run a fair distance, would they cause interference with Ethernet?

Looks like the Arduino shield would suit me well, particularly if I can power it with PoE. In theory I should be able to use voltage readings from other power meters in the house already? I have one hooked up to the washing machine already for example.

That’s very unlikely. There’s an article in the ‘Learn’ section giving the details regarding extending the cables. The output is a current, the voltage it develops is around 1 V at maximum current.

That will give you apparent power only, as I mentioned. To measure real power, you must multiply current and voltage on a per sample basis (~ 50 samples per mains cycle, 2500 per second) and then average the power. If you average voltage and current separately and then multiply, you end up with apparent power. That’s never smaller than real power, it will be larger by a varying proportion depending on the type of load you have - a timer on a microwave oven for example might be reading a very small apparent power, but still 10× too big. The washing machine motor might read 20 - 30% high, only the heating element on its own will read correctly.

poe just use a security camera poe injector