OpenEVSE charging Zoe

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doggy
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Real Name: David Kerr
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OpenEVSE charging Zoe

Post by doggy » Fri, 19 Oct 2018, 16:00

I thought some people might be interested in the use of OpenEVSE which I use to charge my Zoe using excess Solar power which would otherwise be exported to the grid.

I tried to put this in a more general category such as charging. However, for some reason, the system will only let me add attachments in a few spots- such as this.

1. Environment is 4.3kW system with 14 Enphase inverters linked to an Envoy. Garage is down about 80 stairs and contains the Zoe and OpenEVSE.

2. OpenEVSE is a one/three phase unit which I use in single phase mode at home. It handles 1.44kW to 22kW. Current is adjustable in 1amp steps from 6amps (the Zoe minimum) to a user settable limit (I use 18amps in the garage). The OpenEVSE has WiFi and automatically connects to my home network. Thus I can turn it on/off, set current limits, set start and stop times plus energy limits (that is, turn off after xx.yy kW) from the house.

3. I wrote a small Python script which runs (on a Linux server) and harvests production and usage data from the Envoy. This data is posted to EmonCMS which runs on the Linux server. There is also a MQTT broker running on that same server. Both these products are available on public servers if you don't have a Unix box.

4. OpenEVSE has a standard interface to MQTT and also to OpenCMS. There are Apps available on EmonCMS so NO code is needed. Even if I use the OpenEVSE somewhere else (e.g. a Showground with three phase outlets), it send usage data back to EmonCMS so I have a permanent historical record and graphs of all my Zoe charging using OpenEVSE.

5. When you click on the "Eco" button on the OpenEVSE web interface, the unit will wait until there is 1.44kW of excess power being exported to the grid and then start charging the Zoe. Once it starts, it keeps going until the solar output drops below a sustainable level for about 30mins and then terminates the charge. To avoid contactor wear and tear in the OpenEVSE and the Zoe, charging continues when there are periods of heavy other use or clouds etc.

In the images below, I manually started OpenEVSE a little (~15mins) before there was enough surplus solar. After that, it tracked the excess solar very nicely. It was a difficult scenario because I also had running the following:

a. Washing machine.
b. Bread Maker.
c. Microwaved coffe from time to time.
d. Dishwasher.
e. Water bed which uses 700W and turns on for 30secs every 2mins.
f. Fridge.
g. Some testing of a 2kW lithium charger which I am building.

Here is a standard graph showing the tracking. Near the top, the high usage is the dishwasher heating with a 2.4kW element. So, the Zoe charge is continuously varying between 6A and 15A depending upon what else is using power in the house. When I add a 24V Lithium battery charger, it will also talk to MQTT and will ensure it only uses exportable power. Unlike the Zoe, it will be able to vary its charge rate from zero to 2.2kW.

This image shows the Eco options from the OpenEVSE web interface:
Screen Shot 2018-10-19 at 11.57.12 am.png
Screen Shot 2018-10-19 at 11.57.12 am.png (68.31 KiB) Viewed 212 times
This image is a graph showing house usage and solar (yellow). You can see where I started and then a little while later when I turned on Eco mode:
Screen Shot 2018-10-19 at 11.28.48 am.png
Screen Shot 2018-10-19 at 11.28.48 am.png (130.57 KiB) Viewed 212 times
This image is the top half of the OpenEVSE web page. You can see the Eco button. Just under there is a realtime display of export/import. This updates every 10seconds.
Screen Shot 2018-10-19 at 11.27.22 am.png
Screen Shot 2018-10-19 at 11.27.22 am.png (143.36 KiB) Viewed 212 times
This image is the bottom half of the OpenEVSE main web page. You can see the sorts of things that can be configured such as energy limits, start times and durations.
Screen Shot 2018-10-19 at 11.27.41 am.png
Screen Shot 2018-10-19 at 11.27.41 am.png (152.67 KiB) Viewed 212 times
Best Regards,
Dave

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LouB
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Re: OpenEVSE charging Zoe

Post by LouB » Sun, 21 Oct 2018, 14:09

Hi Dave,
OpenEVSE appears to be a very capable unit. I especially like the charge scheduling function.
Have you any idea as to how it handles PV connected home batteries? And especially batteries that connect to DC side of inverter?
I understand that charge in AC side batteries, like the Tesla Powerwall, is much easier to monitor and react to. Usually just requires an extra CT clipped to the Live cable from the battery inverter.

Cheers
Lou

doggy
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Re: OpenEVSE charging Zoe

Post by doggy » Mon, 22 Oct 2018, 05:27

Hi Lou,
You can actually program it to do anything you want because it is fully Open Source and the code is freely available. There are two main branches- a US branch and a European one. I use the European code.
Basically, you send it a value via MQTT (it also supports other methods) which is labelled "Grid Import/Export" and you can see it in the screenshot just near the Eco button. If the value is more than about 300watts either positive or negative, OpenEVSE changes the Pilot signal to match with the only proviso being that the Pilot will not go below 6 amps.
So all you have to do is factor your battery behaviour into the data being sent to the OpenEVSE. If the battery is charging then I would expect that OpenEVSE will behave perfectly well because battery charge, turning on a toaster etc all have the same impact. If the battery is supplying power, that is a different matter and you would probably want OpenEVSE to shut down if that happened for more than a few minutes. So you would need to introduce the battery providing power into the export/import data being fed to the OpenEVSE and/or make use of the RAPI interface:
There is an even nicer capability which I did not mention previously. There is a full set of API commands which you can issue to the OpenEVSE to do absolutely anything you want. I attach a screenshot with some of the commands. These can be issued via web interface or across the internet. You can issue them manually for testing purposes via the interface in the screenshot.
Screen Shot 2018-10-22 at 8.17.35 am.png
Screen Shot 2018-10-22 at 8.17.35 am.png (268.29 KiB) Viewed 158 times

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