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 I live in an off grid house and have a hybrid hydro/solar charging system. The solar produces little in the winter and the hydro little in the summer. They are connected to a 12kwh battery bank ( lead acid so only 6kwh useable) . I have a chevy volt that I plug into the house at 12 amps (110v)  and it drains the battery until the state of charge gets to 75%, then i unplug it. On the hydro only I can get 30km per day into the car... which would otherwise be wasted ... if I am attentive to plugging it in and unplugging it at very specific intervals. On solar it can produce enough to charge it nearly completely in perfect conditions and if my car is not at work with me. I want to control the charging with the relay output that is present on either the charge controller or the inverter of the off grid system ( which can be programmed to turn on or off at a specific voltage or battery state of charge). Is there a good place to interface the open evse with the 12v relay control present on the inverter/or cc. I have thought of a few:

At the panel: The 12v relay output could turn on or off a relay right at the panel ... this would turn on and off the branch circuit that the open evse would be plugged into. Is it good to cycle an open evse on and off by essentially unplugging it under load. This sort of is like turning the power off on your computer by pulling the plug. It is the easiest though as the inverter relay control is right beside the panel

In the EVSE :A secondary transistor between the transistor and power relay inside the EVSE controlled via a bluetooth or wifi link( or wire) that overrides the power being sent to the vehicle. It would .... or should be a softer disconnect method and the evse would remain powered up . Would the evse throw an error code?

Ground the Pilot: A transistor or relay that connects the pilot to ground inside the evse that was connected to the relay control on the evse would cause the evse to register an error and turn the relays off I think.

Any thoughts on this. Or other methods that may be easier that I have not thought of. I am looking for a soft method of controlling the on off of the evse charging with a 12 volt signal from an off grid inverter.

I would like to control the charge rate of the OpenEVSE using an Arduino. I do not do wifi but would prefer to wire it using whatever equipment is required. Please could someone point me to the "simple well documented" commands. I do not know emonpi or nodered. I would like to integrate the charging system with my offgrid solar to charge my car so I need a dynamic means of varying the charge rate to match the energy I have available from my solar system. My existing Arduino system can create a turn on/ increase / decrease / turn off signal of some kind but how to get it to the OpenEVSE puzzles me.

Any help with hardware or software that would be required I am grateful for. I have done a bit of work with RS232 interfacing my diversion control with the Midnite Solar Classic charge controller but do not pretend to be an expert. The location of information that could teach me what I ned to know would also be very helpful.

Thanks

Will

 As far as I can tell from a quick look at the code, the OpenEVCS is essentially an Arduino, and its external interface is a serial port running a nice simple CLI. Appaarently, when you plug in the WiFi adapter, it connects to this serial port and implements a TCP-to-serial interface. If this (extremely cursory) analysis is true, you can either buy the WiFi adapter and implement a trivial socket-based program on any computer on your intranet, or you can wire a little computer that has a serial port directly to the serial port in place of the WiFi adapter. In either case, you are completely free of the baggage of apps, development platforms, bloated libraries, and all that other garbage that is so trendy these days, unless you choose to use them.

I have a rasberry pie and arduino. I also have a battery monitor that has a relay output that can be turned on and off based on the house' battery state of charge.I could use all or some of these provisions.  You could also add or splice off of the current shunt to send info to a rasberry pie/arduino that has a programmed response sent to the evse. In reference to the comment above I guess I am not sure what wifi monitoring and control means. Does that currently mean that it is control from a web app or smartphone app. I want to avoid apps. I try to avoid looking at my computer and phone as you can easily get so wrapped up in them as everything has app monitoring these days (or can the app run on the linux rasberry pie). If wi fi monitoring and control means that I can easily integrate a rasberry pi or arduino to control and speak to the evse then the open evse is for me. If I have to rewrite the entire evse program to connect to the arduino/rasberry pi then I think the control of the relay directly via the arduino /ras pie is probably more likely possible for me. I have a reasonable level of programming knowledge and have a decent understanding of electronics... as well as access to people who are much more knowledgeable than myself in regards to programming. I still have not bought an evse . Do I want an open evse and use arduino / ras pi to connect to its wi fi monitoring and control or can i just use any old dumb evse and give it the smarts I need with integration of a rasberry pi/ arduino and just turn it on and off with the added smarts. Still I am not sure where the best place to turn charging on and off would be without setting off one of the alarms on the car or causing an error on the evse.

 

I thought the OpenEVCS was provisioned for WiFi monitoring and control. If so, you can monitor the Hydro and Solar power systems using little computers that report back to a central computer that in turn makes decisions and commands the OpenEVCS. A brute-force approach would use a Raspberry Pi Zero W ($10.00) with a $13.00 peripheral card a$5.00 SDmicro card,  and a $5.00 power supply at the Solar Power system. This is the part that accepts the 12V signal. The use of WiFi conveys the signal to the OpenEVCS with no need to hack into to CP wire. If you do not already have a central automation computer, that little Pi is quite capable of handling that job in addition to the trivial 12V monitoring.

I admit it's a strange new world when full-up Linux computers with radios are actually cheaper than relays and wire.

 

I just asked a related question. My idea is to add a small relay to open the pilot rather than grounding the pilot. I think this is equivalent to unplugging the car (from a signal standpoint) but I'm not that knowledgable about SAE j1772, so I asked.