OpenEVSE questions

Hi, Just joined this community, finding my way around.

I hope this is the right place to ask beginners questions about OpenEVSE.

I already have an EmonPi monitoring our Solar PV and grid in/out, it works really well and I love the graph displays.

We have an EV coming soon, probably April, so I’m looking to get a home EV charger. Here is my wishlist for it:

  1. Solar PV divert function
  2. Cheap rate overnight charge function (ours is cheap about midnight to 7am)
  3. Intelligent combining of the above two based on required KW to deliver by selected departure time.
  4. Limit charge rate if main grid import approaches limit of house breaker (100 Amps)
  5. Control from my PC or phone

Can the OpenEVSE do (or be made to do) all of the above?

I was looking at the Zappi, which seems to do all of the above, but I would really prefer the OpenEVSE because:

  1. I can build it myself
  2. It is all open source, so if it doesn’t do something, I should be able to modify firmware or control scripts etc to make it do it
  3. I can set up access from my PC or phone over the LAN without having to subscribe to, and be at the mercy of, some cloud server provided by somebody else

(item 8 is particularly important to me, given the way Sonos are just forcibly obsoleting a load of their kit by pulling server support for it, could the same happen to Zappi some time in the future?)

Does all of the above seem reasonable, and will OpenEVSE do what I want?

Will the EmonPi I already have do all the monitoring and control I need?

Will I need any more current clamps? (I already have one on PV generation feed and one on Grid in/out).

I have programming experience, so if necessary I can dive into firmware or wherever the software that controls these features lives, to tweak it to my needs (and share back anything that might be useful to the community).

Many thanks for any advice, and sorry for all the questions :-o

Hi Pete,

I’ve had a Leaf for several years and installed an OpenEVSE charger a few weeks ago. You can use your emonpi to provide the inputs to allow ‘solar divert’ charging… Answering your questions:

  1. Yes you can do this with various options
  2. There is a simple timer built in, but it needs some work to really make it do what you want it to
  3. The default system isn’t that intelligent - you can set it to a limit and put solar divert on - it will charge as much as possible and then carry on at low rate until you hit the limit, but it probably won’t do quite what you want it to
  4. You could program this, but you must have some pretty loads in your house to get to 100A!
  5. You can control from either PC or phone, but only locally unless you do some clever stuff with your network.

I have been trying to figure out how to make the kinds of improvements you’ve talked about. I’ve found it quite hard to get my head around some of it - it’s really just understanding the terminology. But finally this evening I think I have it roughly doing what I want from ‘Node Red’. I set two schedules - one is based on dawn/dusk times and ‘smoothed’ solar excess, the other is a simple off-peak timer. When the the off peak timer is active the EVSE switches to ‘Connected’ and the car will charge to the limit set in the car controls. An hour after dawn, the other timer switches the EVSE in solar divert mode and lets the existing software control the power diverted to the car. THis will switch off one hour before dusk and wait for the off-peak timer. The smoothed excess PV output variable is used to switch the EVSE into sleep mode if the solar output has fallen below the economic charging threshold for about 15 minutes. It will wake it up again if the smoothed output goes above the threshold. This prevents the contactors from going on and off lots if the clouds are rushing over. I have’t really tested it properly yet - and probably won’t with the expected weather this week!

Hope that helps.

Thanks for those answers, very helpful.

Sounds like you’ve already got most of my wishlist working with OpenEVSE.

100A (24KW) is just possible here. Whilst the normal background usage is a few hundred Watts, we cook electric, so at cooking dinner time we could get 20A or so peak loads, if somebody decides to have a shower (electric) that could add 8.5KW (35A), we are putting in a “hobby room” at the bottom of the garden which will be heated/cooled by a hot/cold aircon unit rated at 5KW (20A). If the EV is charging 7.2KW (30A), so it could total 105 Amps for a momentary peak, and then if somebody puts the kettle on that’s another 10A. And of course all bound to happen in the evening when the solar isn’t making anything. I hope to add battery storage to the solar at some point, but the money is going into the EV purchase right now.

Very much the exception for all that to happen at the same moment, but since it could, it would be nice if the car charger could back off just until things return to normal, rather than tripping the main house breaker. I know the Zappi has that feature, and from what you say it sounds like it wouldn’t be too difficult to program into the OpenEVSE system.

I use a Draytek router which has a built in VPN server, so I can access my LAN from elsewhere. I already use it to log in and have a look at my EmonPi solar monitoring, so I should also be able to use it for the OpenEVSE.

It seems counter-intuitive that if the App I am using goes via a cloud server, I can’t connect to something via the LAN I am standing next to if the broadband is down or the cloud server unavailable (or withdrawn x years from now). If there is a pretty cloud based app with a sensible subscription price, I might well subscribe to it, but it will be good to know I have the direct LAN fallback if I need it, which seems not to be the case with the Zappi.

I’m just reading through various other topics on here, no doubt I’ll have more questions shortly!

I’ve found VPN access to OpenEVSE not to work for me and whilst I haven’t properly investigated yet I suspect it is likely to be that the ESP8266 protocol stack may not by default support packet fragmentation/reassembly and/or path MTU discovery due to resource constraints. Maybe one of the developers could comment? If my supposition is correct there are potentially workarounds and hopefully the upcoming ESP32 platform will not be so constrained.

David, thanks for that insight. I guess I can always use the VPN to RDP to my desktop PC, and then browse to the OpenEVSE from there. Hopefully the move to ESP32 will sort it. Which leads me into one of my other questions.

I’ve been browsing other topics on here, and as a result I’m afraid I have more questions :-o

  1. If I don’t specify wi-fi gateway with the order, does the OpenEVSE still have a CAT5 type Ethernet hard wired connection I can use?

  2. If so, would that give me all the functionality in the OpenEVSE as if I used an ESP32 Wi-Fi module?

  3. In this discussion Telling if car is connected Glyn Hudson mentions that there is an upcoming update that only works with the ESP32 wifi module. So am I better not specifying wi-fi when I order OpenEVSE and sourcing my own ESP32 for future compatibility?

  4. In this discussion openevse and wiring regs changes Glyn Hudson posted in June 19 “We are working on integrating DC leakage detection into our unit, but this is probably about 6-12 months away and will probably add about £100 at leat to the cost of the unit.”. So we are about 8 months on, is there any update when this is likely to be available, or should I just go ahead and order the current unit and type B RCD?

  5. There is mention that I could still get the OLEV grant if I get Ecoplugg to install my OpenEVSE. Is this still likely to be an option if I buy the kit version and assemble it myself?

Thanks again,


OpenEVSE has a serial interface and the WiFi gateway communicates with it over that using the RAPI protocol.

My understanding is that the shop will be offering an ESP32 module in the not too distant future but probably best to await confirmation from those involved. I have yet to try the beta code on an ESP32 module I already have which has both WiFi and CAT5.

Yes, the OpenEVSE / EmonEVSE supports this function in conjunction with an emonPi to monitor solar PV / Grid export:

Yes, the OpenEVSE / EmonEVSE supports a time charge to stop/start a charge between a specific time. See demo UI

Charge schedule is not currently supported at the same time as solar PV divert (Eco Mode). Currently you would need to manually turn off Eco Mode to stop the solar P divert at the end of the day. However, we’re currently adding a feature to automatically stop the charge when solar stops generating. This feature will be ready in the next couple of weeks:

Not supported

Yes, the OpenEVSE / EmonEVSE is controlled via a web interface. This is available locally when connected to your local network. It’s not currently possible (without opening ports on your router) to acccess this interface outside of the house. See demo UI

No, you wont need any additional current clamps. The emonPi will do all the monitoring you need for solar PV divert with OpenEVSE.

The OpenEVSE has an advanced API to allow any aspect of the device to be controlled via HTTP or MQTT. This is very useful for advanced integration into home automation systems etc.

We’re currently developing a smart scheduling feature to automatically choose the best time to charge (cheapest / lowest carbon) if your on a time of use tariff e.g Octopus Agile