My openEVSE

This page is dedicated to the build of a openEVSE device to charge out Toyota Prius Plug-in in our garage. EVSE stand for Electric Vehicle Supply Equipment and it´s basically a control and protection circuit to connect and charge the car from a ordinary 230V socket. The EVSE enhance safety by enabling two-way communication between the charging station and the electric vehicle. This two-way communication ensures that the current passed to the vehicle is both below the limits of the 240V socket itself and below the limits of what the car can receive. There are additional safety features such as a safety lock-out that does not allow current to flow from the EVSE until the plug is physically inserted into the car.

The Toyota Prius Plug-in comes with a OEM adapter cable that includes the EVSE and just plugs into a 230V wall socket. I find the cable a bit bulky and since it´s stored in the trunk below the floor cover it´s inconvenient to get it in and out every time you park the car in the garage for charging. A spare cable is more than 1000€ and so is the Toyota proposed wall charger from Electrodrive here in Germany.

Prius OEM EVSE electrodrive

Since 1000€ is a way off the budget I´m willing to spend for a additional charger I searched through the net and founr the openEVSE project @

The project is open source and hardware, DIY and therefore fits perfectly my needs. I have ordered the openEVSE v2 Plus kit along with the optional LCD+RTC. The kit includes only the partly assembled main board with required components. Some external components are required to build the complete device, they were ordered from Digikey.

openEVSE Parts

Count Digikey Order # Description
1 PB486-ND Relay 230V/30A, 12V driven
1 582-1018-ND Ground fault transformer
2 F5598CT-ND Varistor 250V
2 240-2119-ND Ferrite tubular bead
10 WM18717-ND Piggy back connector 6.3mm
10 WM2980-ND Connector 6.3mm
1 102-2664-ND AC/DC Converter 230V/12V/10W
1 CKN10008-ND Switch, red&green LED
2 P47KW-1BK-ND 47KOhm Resistor, required for AC detection circuit with 230V, not sure if they are supplied with the kit
2 486-1752-ND Fuse holder, 250V/30A
6 F4644-ND Fuse 250V/16A












 Crossed parts are not required since they are included in the openEVSE kit already.

openEVSE Plus kit arrived together with the LCD & RTC extension board.

openEVSE Plus Kit

Obviously the openEVSE Plus kit comes with a AC/DC converter already, correct resistors for AC voltage detection are included as well.

openEVSEplus_2 openEVSEplus_1

Kit and LCD+RTC built.

openEVSE_Version openEVSE_Selftest openEVSE_Ready

First power up…working! 😀

Box_1 Box_2

IP65 box designed for in-house electrical installations. Will be modified to take all the components and to have a nice front panel with LCD and button.

Front panel prepared Front panel Front panel back

Front panel made from acrylic glass. LCD and button installed. The whole front panel is glued inside the box where I trimmed of the inner frame.

Realy and controller Partly wired

Relay and controller mounted. Later on partly wired. Ferrite beads were placed just in case. Not sure if they are needed.

Inside finished

Final inside view.

Ready Stopped Box closedBox open with J1772 connector

My openEVSE operational and installed down in the garage:

IMG_20140103_145758333 IMG_20140103_145717450IMG_20140103_145704108IMG_20140103_145741726   IMG_20140103_145915653

2 thoughts on “My openEVSE

  1. The electrodrive EVSE in the picture looks identical to the Chargemaster unit available in UK.
    From Chargemaster website:
    A 3kW unit can be supplied and fitted for free to UK domestic customers.
    A 7kW unit, far more than you need for a Prius, is available including fitting for £95.
    These charges (or lack of) include UK government subsidy and only apply if your house passes a survey (for location and suitability of your existing consumer unit)

    The relay in your picture looks like others I´ve seen in commercial EVSE. These are often made in places where quality is as low as cost.
    Using one relay gives little or no fault tolerance against welded contactors, therefore a second relay is common practise to satisfy the design failure-mode-effect analysis (safety mitigation procedures normally used in design). Some EVSE use a second set of (redundant) contactors to add safety.

    Whilst the plug is finger proof, it is not intended to be live when not connected – anything such as dropping in a puddle is therefore something worth considering. A single failure such as a welded relay could lead to issues there.
    For home made EVSE, I´d recommend a pair of Tyco KiloVac relays to be very robust and reliable.

    • Thanks for your comment. Appreciate it.
      You are right, there is no safety backup for a stuck relay. Only a error detection and warning.
      I will consider you recommendation on a later design review. The actual is not yet in use and I need to perform some testing first.

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