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Vehical battery level.

 Using the USB to serial cable am I able to:

a. Control the max current from say a raspberry pi

b. Query the vehicals battery level during a charge (so it tells me it's 85% full for example).

I want to get one of these to integrate into my automation system and just want to be sure it will do what I want before I commit to buying.

I meant vehicle.


Hi Nicholas,

OpenEVSE can be fully controlled via RAPI over the USB Serial device or via WiFi module with HTTP requests or MQTT.

a. Yes, you can adjust current, start, stop and change settings via.

b. The charging station does not have any information about the vehicle, this information has to be pulled either from the vehicle directly via CAN/ODB or through the vehicles online portal. What kind of vehicle do you have?


Hi Chris

I currently have a Mitsubishi PHEV and a Nissan Leaf.  I think I can get the information about battery level from the Leaf via other means but the PHEV I'm not so sure about.  I have a WIFI ODB for the PHEV but haven't got round to playing with it yet.  I had hoped that the the charger and the vehicle communicated with each other about such things but alas it seems not.  It's not vital anyway, just would have made life a bit easier.  So long as I can control the max current that is the main thing.

Good last name btw ;)



Unfortunately, there is no digital communication between the vehicle and charging station.

Yeah, max current is no problem. I would recommend WiFi and MQTT for automation.

Yeah I was in two minds about the WIFI module.  Does it have any kind of security to prevent unauthorised access?  Feels like the USB to serial (lengthened with some ethernet cable) will provide the most reliable connection.


Yes, WiFi has standard security protections:

WiFi will connect to your local network with encrypted WPA

The Admin console requires authentication, both default username and password can be changed

Requests via HTTP require authentication

MQTT connects to the broker with username and password

USB serial will work fine, it just requires an additional host like a raspberry pi or PC.

I've gone the USB to serial route and am just wondering, is the 5v and 0v lines necessary?  As the computer has power and the OpenEVSE has power, why does 5v need to be supplied down the cable?  Sorry if this is a dumb question but it seems like I should only need Tx and Rx lines.

Is it still true that it's not possible to get the car's state of charge. I only say that because I regularly use my local NRMA station in town (A Tritium DC charger) and it knows what % level my car is. It displays the percentage on the charger's display. It's must be communicating with the car via the charge cable somehow.  


DC Fast Charges use digital communications which can pass along State of Charge. AC charging stations use an analog pilot signal. It is not possible to send data on the analog pilot.

That explains it :-) Thanks. Not to worry, I can use the original state of charge from the dash as a starting point, and the KWhrs reported by the OpenEVSE as an alternative.

While everything said above is true, you may be able to do something, but it would be rough and limited in scope. You may be able to infer some information about the battery state of charge by observing the current drawn by the charger and how it's changing over time. You would need to observe this over several charge cycles and correlate that data with states of charge reported by the car throughout the charge cycle. There would likely be a big portion of the charge cycle in the middle where you won't be able to tell much unless you started outside of that region, because for a large portion of the charge cycle, the charger is probably just going to pump energy into the battery as fast as it can, which means maxing out the current it's allowed to draw from the EVSE. If you are below or above that region, though, you may be able to infer an approximate state of charge. How accurate that inference can be and how reliable the model you use to make the inference remains over time and under all temperature conditions, I don't know, but it's something. It might be an interesting project to investigate if you're suitably motivated.

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