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An OpenEVSE without relays?

An OpenEVSE without relays? I hope this question would not be too dumb. Assumed that the power wiring of my house already has safety devices (overcurrent and GFCI breakers), should it be feasible that an OpenEVSE operate without relays/contactors? Should the required configuration of parameters be done through LCD menus, RAPI or coding? 

The main purpose of a Charging Station Indoor or Outdoor is to only provide power when everything is alright. Each safety feature has a verification mechanism. OpenEVSE will not pass power until everything checks out and will disconnect power for many serious issues including:
Ground Fault
Pilot Error
Over Temperature
Missing Earth Ground

Can you hack the system to save a few dollers? Yes. But... there are many risks including fire or electrocution...

Many vehicles will throw errors if voltage is present on the line before it should be there.

OpenEVSE is inexpensive enough to do it right, its just not worth the risk to purposefully bypass the safety features.

Dear Chris, if I did not know the honest and helpful man you are, I would been offended. I am not looking to save a few dollars on relays.  I just want to know how the EVSE boxes work, as I am also interested in the improvement of the reliability of my OpenEVSE wall-box. My car depends on it to give me a reliable service every day.

Probably I am an old-fashioned engineer, but in my early days as an engineer, the term “solid-state” was not just a commercial term, but the holy grail of power engineering. Every time the semiconductors replaced tubes and electromechanical devices, it was a celebrated as technical success. This way, nowadays “solid-state” power converters in windmills are commodities able to handling dozens or hundreds megawatts without the use of electromechanical devices. Something that a lot of us believed were to be always unfeasible.

For mobile use, all the safety features available with an OpenEVSE and a dual-relay set are more than desirable. Even I guess that for this application, an overcurrent protection should be also added to the OpenEVSE firmware. I do not dare to plug my car in any of the free public charging sockets without an EVSE with all the safety features provided by the OpenEVSE.

However, for a fix service application let me try to understand what you mean with the safety terms you mention:

Ground Fault: I guess this means a leakage voltage/current appearing at the earth terminal. My house has a 10 mA earth differential breaker that shall be triggered if this condition should happen.

Pilot Error: I am not an expert in EV design, but I am sure that the control electronics of all the EVs are safe-fail on any deviation of the pilot signal. And if the EV electronics were fried, I guess the 20A breaker of my house shall be triggered.

Over Temperature: I suppose you are referring to the over temperature of the charging box, as the EVSE can’t do anything on the car over-temperature condition. In the former case the EVSE only need to set the pilot signal to a safe state.

Missing Earth Ground: I guess this condition should result in a missing pilot signal, bringing the car to a non-charge state.

Currently, my Renault Fluence is not the most power-hungry device at my home. With its mere 3.5 Kw load is behind my induction kitchen, pyrolytic oven and air conditioning compressor. None of them needs an EVSE to connect to my house power wiring. With all the engineering in the design of my EV, I feel safer plugin it that when I am close to my dish/washing machines, fridge and similar appliances.

The pilot signal is a simple and well-designed safety mechanism. It can switch on-off the charging mechanism, and of course indicate to the EV how much load can take from the power plug it is connected.

Then I reformulate my question. Assuming the devices at the both ends of an EVSE have the adequate safety features (a moderns house electric system and a decent EV), should the pilot signal alone able to control the charging process of an EV without old-fashioned relays? I understand from your answer that if the car senses the power lines active before the pilot one it blocks the charge process. Is it right?

After all that disquisitions, I will continue using my OpenEVSE with relays, just in case … for a mere few dollars, why take risks?

I apologize if my post came across as harsh or offensive, it was only meant to provide information.

Solid State devices are great, for a safety application they have limitations. They can block current but can not guarantee to block the voltage, they also tend to fail closed instead of open and their internal resistance causes them to run very hot at high current. In fact the National Highway Traffic Safety Administration (NHTSA) in the US forced a mandatory recall on a manufacture who used SSRs in their EVSE.

The systems of the charging station work together to provide safety plus long life with many connect/disconnect cycles. Most of your high load appliances are not plugged in every day or several times a day. My appliances were plugged in the day I moved in and have not been touched since so the risk of shock is low. The EV on the other hand is plugged in several times a day. My kids want to do it and I know it is okay since the pins are not energized.The combination of Proximity, Pilot and Relay provide other benefits as well like soft startup and shutdown.

Personally, I would not build without relays. I like knowing there is no voltage on the pins until everything checks out and the voltage will be removed if there is a problem.


Maybe I am missing your point, but the purpose of the EVSE per the J1772 standard is to provide absolute assurance that the charger plug and cable is not energized until the car detects that the plug is inserted (through the pilot signal) and signals "feed me".   I don't know how you would do this without a relay.

I go out to plug my car in all the time in the rain, barefoot, standing in (and maybe dropping the plug in) a puddle.  The absolute assurance the plug has no voltage until plugged in to the car is what makes this whole process safe instead crazy like handling a conventional electric cord would be under such conditions.  As Chris explained, only a mechanical, not solid-state relay will work for this.

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