OK, with lots of help from Glyn and Robert I got my USA system up and running. I’ve got feeds showing my solar generation and my grid import/export. Now I’d like to integrate my openEVSE so I can use my excess solar power to charge the car (eco mode). I’ve got the openEVSE side all connected, and it is showing in my local emoncms inputs, but I’m stuck with the “grid topic” part. My system isn’t setup like most I think, see the attached drawing of how it all works.
So in principle I understand that I need to “tell” the EVSE when my emontx measures excess power going to the grid, but can’t figure it out. In inputs I’m already logging to a feed the sum of power1 and power2, the result being negative when I’m making excess power, positive when I’m using power from the grid. So someplace right in here I need to create a new process that will communicate with the EVSE. And you haven’t figured it out by now I am a complete novice (but pretty proud of being able to get as far as I have, albeit with lots of help!) electrical.pdf (14.4 KB)
You need to add a publish to MQTT line in emoncms under your emonpi.
I don’t really understand your wiring diagram. Do you have two live feeds as well as neutral in states? In the UK we have live (240v), neutral and earth (protective conductor). For power measurement we use 1 CT clamp on either the live or the neutral, just reverse the clamp depending on which is used. Trying to get my head around the need for 4 ct clamps?
To get a positive import figure or negative export figure you need to insert publish to MQTT in the emonpi setup page to get it talking to openEVSE.
Take a look at the ‘Learn’ section and in particular the article about using the emonTx in N.America. I won’t copy any of that here. Rick Wilson really does need four c.t’s for what he’s doing, I think I might just have noticed if I thought he’d got it wrong. What could be confusing you is Rick has drawn his power cables as two thin parallel lines, conventionally in the UK we draw them as a single thicker line, and he’s left the neutral off (which is where the 120 V is measured from).
Yes we’re a bit different here in the states, and indeed we have two 120v feeds with a central neutral and ground. So 2 CTs are needed to monitor grid import/export. The solar panels feed the house in the same way with two 120V feeds, so two CTs are needed there as well. It does complicate things because you have to combine the readings, but I got it all working (just don’t ask me how).
I should have updated this, but with some trial and error, and massive amounts of luck, I actually got it working. It had more to do with the names of my feeds and setting the EVSE to recognize those. How it worked I can’t say, but once I got the names right it just started working! The e-golf arrives tomorrow and now I can start charging with the extra solar!
For reference, and to help avoid confusing future readers of the thread…
In the US, what we’ve got is a single phase, center-tapped 240 Volt feed that is split into two legs.
i.e. the neutral leg is the transformer’s center tap. Hence the name, split-phase.
The neutral is connected to earth ground at the transformer.
Your PV connection is actually the same as your house, i.e a 240 Volt feed.
This is evident from the fact you’re backfeeding a double-pole breaker. It isn’t really a pair
of 120 Volt feeds as the neutral leg isn’t used to backfeed the breaker.
The need for two CTs (in each location) arises from the imbalance created by the 120 Volt loads.
When your house was wired, the electrician should have done their best to evenly distribute
the 120 Volt branch circuits across both hot legs in your load center.
Despite those efforts, there’s always some imbalance because of you almost never use the loads
with any regard to which leg they’re connected.
I had a look after posting on the emontx for North America. I see why now but it makes energy monitoring more difficult because you can only monitor voltage on one leg. The installation seem similar to three phase in the uk. Where you have three lines and a neutral and between phase and neutral you get 240v and between all phases 400v. If you have a house with I high demand then the three phase are split in the consumer unit and you try to balance all the circuits in the house so not to overload one phase. This is assuming most of the loads in a domestic house will be single phase.
I believe in Germany most houses have a 3 phase incoming supply as standard as there are benefits for high load applications such as heaters and pumps.
Indeed it does. I suggested a multi-voltage input emonTx a long while ago, which would satisfy the needs of our members who live in the three-phase world as well as our North American friends. Without that, it’s necessary to make assumptions about the voltages, which leads to inaccuracies that can’t be calibrated out.
Not really, it’s only vaguely similar in that there are more than two wires. In US system, as you read, both legs of the supply are the same phase - they come off the same centre-tapped winding of the final distribution transformer.
And most of Europe.
not necessarily for heating loads, but more particularly for motors, because the torque in a 3-phase motor is constant, not pulsing at line frequency (or a multiple).