Off grid diversion EV charging

I'm looking at setting up EV charging from surplus solar. I can use aux from midnite classics or relays off the Batrium. Both can be set up to start/stop around float state, float voltages or SoC states. So I was looking at a level 2 charger and was thinking of using this or similar SSR:


But I was wondering if I need to go with a larger amperage rating and whether I should find a contactor rather than an SSR?

Anybody have experience setting something like this up? What I'm thinking is essentially the lithium iron battery will charge, hit absorb andbalance, then charge controllers will drop to float. At that point, start EV charge. And then terminate Ev charge at some SoC or voltage level. I expect this will toggle on/off in some situations, but maybe not so bad if the start voltage/SoC and kill voltage/Soc are wide apart.

thx!

Instead of cutting power to your EVSE entirely, which sounds like it might have long term consequences for the EVSE or EV, what about getting an EVSE that you can adjust the charge current? Or open up the EVSE and use a normal relay to open the prox circuit to stop the charge?

I believe opening the prox circuit would be the same a pushing the release lever on the EVSE.

I'm running this EVSE as an on grid dump load, but it would work for either of my suggestions above.

I thought about the abrupt on/off being a problem, but was thinking it might be OK given the equipment must be OK with having a breaker trip. But also I was wondering if the equipment would even resume charging on a breaker reset. For phantom loads this seems to be the best way tho.

On-grid systems look like they have a device that triggers the EV charger on when the system goes to sell (even at a certain amount of sell) and can soft kill when the system stops selling. Ideally an off-grid system would have the same capability, but I haven't found anything usable for that yet. I'm not sure what is available for adjustable EV chargers. OpenEV looks like there is a remote api. I'll have to look at that.

thx

+1 on the openevse with the latest WiFi gui firmware. I have ev solar charging if I have more than 1kw of grid export and it works very well with filtering for sudden cloud shifts, minimizing wear on contractors or relays. For totally off grid, you just need to find out that magic number that can tell the system there is excess and as it ramps up, it has to adjust to that value. I’m drawing a blank on what I would do if I were off grid though.

looked at openevse in the past, but seemed not-off-the-shelf. Was it easy to set up ? Emporia evse plus their load-management can dynamically adjust charging rate. It has good reports from forum members

I've been using openevse for about a year now. The amount of power that is available to charge is sent via a program (http ethernet) to openevse. I looked at Emporia and it did not do what I needed. I wanted a more hands on approach. Did not want their system. But their system is probably best for most users. Can Emporia deal with an off grid system?
I have a program that uses data from my PV system to calculate the power available to the openevse charger. Additional loads can be switched on if more power is available. Right now there are 3 loads. (3) 1500 watt space heaters. A good time here to test this setup since the heating season has started.
I would not just hook a relay up and switch the power on and off to the charger. It will most likely be fine but what you really want is to adjust the charge current on a minute by minute basis based on what power is available. The sun and clouds come and go and so do other loads in the house. The power available to charge can change alot and in a very short time. My system updates the data every 5 seconds.

thx.

That's kinda the crux of it. I've got no way to tell the amount of power that is available. For on grid, you have clamps measuring sell/export, so you have that number.

I was hoping there was more of a plug and play setup.

So I'd likely have to write something to poll one of my midnite charge controllers and then maybe ramp available power to the openevse starting at CC state==float and then back off when CC state changes or when SoC or voltage drops. With maybe some wait/delay periods configured in there so it doesn't flap too much on mixed cloud cover.

Yes, If I were off grid I'd be getting data from Sol-Ark inverter as to battery state of charge and power in/out of battery. Trying a balancing act to not draw any power from the battery. Then once that algorithm is working the loads can be prioritized. You won't be able to get it to be exact. Power will come out of the battery and then back in but it can be minimized and tuned until it works good enough. Numbers can be averaged over time and there can be min and max time limits.
Someone will come out with a plug and play system because the need is there and money can be made selling a box that does this.

Home Assistant may be able to do this. It does have some scripting ability as I recall. I don't know much about it. I did setup a Home Assistant docker image the other day and it discovered the charger and the Shelly smart plugs all by itself.

jtvt said:

thx.

That's kinda the crux of it. I've got no way to tell the amount of power that is available. For on grid, you have clamps measuring sell/export, so you have that number.

I was hoping there was more of a plug and play setup.

So I'd likely have to write something to poll one of my midnite charge controllers and then maybe ramp available power to the openevse starting at CC state==float and then back off when CC state changes or when SoC or voltage drops. With maybe some wait/delay periods configured in there so it doesn't flap too much on mixed cloud cover.

Click to expand...

For the OpenEVSE, all you need to do is send it a charge wattage, you don't need to calculate that wattage the same way an on grid installation would.

You could calculate available charge wattage by PV watts - other load watts.

It would be a slower calculation, but you could also increase or decrease EVSE watts to hold battery voltage steady.
Or look at battery current and increase/decrease EVSE to hold battery charging near 0 or wherever you want it.

summit said:

looked at openevse in the past, but seemed not-off-the-shelf. Was it easy to set up ? Emporia evse plus their load-management can dynamically adjust charging rate. It has good reports from forum members

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This is what I have

The emporia EVSE has an open source way to control it, still through the cloud, but can be done with local control. Need to have something to decide the desired charging current, and use the pyemvue python library to send the command to the cloud, which then sets the EVSE current and on/off. https://github.com/magico13/PyEmVue