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Grid import/export figure - SORRY which way round?

Long question, hopefully with a short answer! I've just got my OpenEVSE box working, MQTT and so on, but I am struggling with the wording around the grid feed:

If grid +I/-E (positive Import / negative Export) feed is available: charge rate will be modulated by available excess power.

I'm not using EmonCMS, just some cron jobs to fetch stuff from my 2 inverters & SQLite & Grafana to compile and show it all off. So I'm having to supply this "grid feed" figure myself.

Right now it's dark in the UK, and my Solax inverter gives a "feed in power" figure of "-762" which I take to mean "importing 762W from the grid".

Am I right in assuming that when I pull this figure to supply to OpenEVSE via MQTT, I need to *invert* it? I can see a +/- figure successfully updated on the web interface as I feed the figure, but I can't tell from the wording which way round it should be (and so when the Eco charging mode will kick in as I'd expect).

To self-answer after some investigation.

Yes, the Solax feed_in_power value is the opposite way round, so it needs negating for OpenEVSE to do the right thing in Eco mode.

*Additionally* my inverter charges a battery, and there's also a battery_power value. That reads positive when the battery is being charged (i.e. it's sunny and the power would otherwise be exported), and negative when it is discharging (when it's not sunny and it's time to use the stored power).

The feed that goes to OpenEVSE from the inverter ended up looking like this:


I added moving averages because the Solax is reactive to feed-in, and the readings are spikey when it decides to start charging or discharging the battery. If you give one power reading to OpenEVSE suggesting there's export happening, it starts charging, and then doesn't stop when the next reading goes back to normal.

Having said this... can someone explain how this calculation is worked out? If I've told OpenEVSE it's exporting 900W, surely it should reduce the charge current to the minimum 6A / 1440W? This is drawing from the grid instead:


I can (& probably will) fiddle the amount I feed it to get the result I want :) But I'm curious how it decides the charge current based on the export rate.

Hi Mathew,

Good effort getting up and running. The Grid Import feed is designed to be the reading at the connection to the grid (i.e the power in the cable leaving your house), This value should be positive when importing and negative when exporting.

The charge rate the OpenEVSE sets is simply the grid export current with the current consumed by the OpenEVSE subtracted:

Therefore a grid export of 912W as your screenshot shows above *should* result in a charge rate of 3.8A which is below the minimum of 6A therefore you are correct the charge rate should be 6A . Did the charge rate reduce within a few seconds?  Have you got the service level set to L2?

What version WiFi FW and OpenEVSE controller FW are you running? 

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