I’ve looked through other categories and topics but can’t find anything which is really answering my questions and so here goes.
What I’d like to do is:
Start monitoring immediate power use and log it historically.
Identify which appliances are drawing what power, again immediately and historically.
So here are my questions:
What should I buy? We have what I think is a relatively “normal” setup although we do have two consumer units, see photo attached. I assume I’ll be fine getting the “emonPi2: 6-Channel Energy Monitor”?
How many CT connectors will I need? I assume 1x 100A for the main feed coming in, are anymore really needed to achieve what I want? I saw in a YT video the others are rated at 50A and 20A, I assume I’d only need those if I wanted to monitor the two consumer units, or lines off those separately?
Do I need the optical pulse sensor? I’ve read somewhere it can provide more accurate readings?
Any gotchas I need to be aware of to get the most accurate readings? All help and advice gratefully received!
Hi @Peter_Aubrey - welcome to OEM. The 6 CT emonPi2 would be a good place to start. You’ll need the emonVs to go with it.
In terms of the number of CTs and their rating, you need to consider your desired granularity (e.g. do you want just the total draw, or split into sub feeds like your two consumer units) and then the maximum current draw - the power you can monitor is then the CT current rating times the mains voltage (note, if you undersize it won’t cause damage, it will just saturate so you won’t know the real maximum).
You don’t need the pulse sensor but it will give you some feedback on the accuracy of the CT monitoring as it reflects the power you are being billed for.
Hope that helps to start, there are plenty of people here with a lot more knowledge than me
I was wondering about the emonVs but I don’t see it for sale on the website, only power supplies?
Regarding the info about what I can monitor, thanks for the saturation point, can you start to identify an individual appliances’ draw with just the 100A or 20A CTs?
Or is it just the total for each CT lead I have at any one time?
It is a combined power supply for the emonPi and a precision voltage monitor so that, along with the current, the real power (which is what your meter charges you for) can be calculated. emonVS Power Supply: UK Plug - Shop | OpenEnergyMonitor (You clearly don’t have a 3-phase mains supply, so the single-phase UK one is fine.)
With experience, you can - looking at the graphs in emonCMS and knowing what appliances have been used at varying times of the day/week - make an educated guess. But as far as I’m aware, nobody has yet managed, with even a hint of accuracy, to automatically separate out individual appliances energy totals from the total. Despite the high hopes of many researchers, it’s proving a very, very difficult problem to solve.
This is where the multiple inputs of the emonPi come into their own. If you put a c.t. (current transformer - it’s not a “clamp”, I think that’s a Chinese mis-translation) on each circuit outgoing from your consumer unit(s), then you’ll record the total power/energy on that circuit. If it’s a ring main, then that’s the best you can do in terms of hard numbers. If it’s your EV, then of course it’s that alone and you’re OK.
You’ll be able to have a c.t. on the main Grid incomer, the incoming side of the two C.U’s and the EV, where you have access to the brown line conductor on its own. If you want data for individual circuits outgoing from your C.U’s, you’ll almost certainly need to get the c.t’s inside the consumer units. (I don’t think I’d have a c.t. on the main incomer if you have one for each C.U. You can add the powers using the maths inside emonCMS.)
Also note: if you get PV (solar) at some point in the future, a pulse input will no longer tell the truth because - depending on the meter - it either won’t register exported energy or it might count it as imported.
For individual items you could always use smart plugs, providing they are sufficiently rated. Otherwise monitoring individual items even with CTs is tricky because of the need to separate the live/neutral connections. I’ve used them successfully on fridges, dishwashers, washers etc.
