Introduction: Multi-Input Electric Vehicle Charging Station

This instructable uses the P50D-WV kit from the OpenEV Store to create an EVSE capable of charging a car such as the Nissan Leaf, Chevy Volt, BMW i8 from a variety of different supplies. As such, it may be useful while traveling, or if renting storage space with anticipation of moving.

The links and information in this instructable were valid in December 2016.


Most electric cars available in North America in the 2010's can be charged using a standard SAE J1772 connector. The charger (which converts AC to DC and controls the DC charging of the EV battery) is built into the car. The EVSE (charging station) consists merely of a relay to disconnect the charger cable when it is not in use, and a mechanism to tell the charger the maximum amount of current to draw. It may optionally contain a timer, remote control, a means to adjust charging rate based on intelligent load balancing etc.

OpenEV is an open-source project which makes hardware designs and software for an EVSE controller freely available (at They also sell pre-built modules, complete kits, and complete EVSEs. This instructable uses a complete kit, together with cable and connectors from other suppliers.

Charging Rates

  • Level 1 (120V) 6A - 24A in 1 amp increments
  • Level 2 (240V) 6A - 40A in 2 amp increments

Possible Supplies

  • NEMA 5-15 (120V 15A household outlet) at 12A
  • NEMA TT-30 (120V 30A RV outlet) at 24A
  • NEMA 14-30 (240V 30A dryer outlet) at 24A
  • NEMA 6-50 (240V 50A welder/EV outlet) at 30 or 40A
  • NEMA 14-50 (240V 50A stove outlet) at 30 or 40A

Step 1: Safety Issues

To paraphrase the British sitcom Never Mind the Quality, Feel the Width , never mind the voltage, remember the current.

This project requires voltages up to 240V (120V in North America), which is normal household supply. It also requires currents up to 50A. The potential available power is thus over 10KW, eight times the power in something like a toaster. That is easily enough to melt equipment and start fires - without tripping a protective breaker (the OpenEV kit relies on upstream overcurrent protection, in the supply circuit).

The key to high-current safety is minimizing resistive heating, which means that all connections should be well-made and all plugs and wires should be adequately sized.

The current-carrying capacity (ampacity) of wires and cable is typically regulated by government bodies, either independently or based on IEEE-835-1994. The basic principle is that resistive heating of the wires, in combination with the thermal insulation of the cable material, should not cause the temperature of the cable to be elevated beyond the temperature rating of the insulation. Essentially, you need to use thick cables otherwise they will get too hot and melt. Often, the standards themselves must be purchased, but guides based on them are freely available online. One such interactive guide based on the Canadian electrical code is here at Note that EV charging is a continuous load, and that the wire gauge in cables must be greater than that inside equipment.

Below are typical values for cable rated to 90C, taken from codemath for the Canadian code Table D3

12A  14AWG
16A  12AWG
24A  10AWG
30A  10AWG
40A  8AWG
50A  6AWG    

In principle, if the upstream protection (breaker) is 50A, then the household wiring to the outlet should be 6AWG, as should the cable from the outlet to the EVSE. However, many EVs cannot draw more than 30A. The continuous load in that case would be 30A, so 10AWG should be adequate for the EVSE cable.

The J1772 cable assembly uses two 12AWG wires in parallel and is only rated by the manufacturer for 40A, as is the contactor in the OpenEV kit. The EVSE should thus not be used for currents over 40A, even though the controller allows up to 80A.

When in use at higher currents (over 20A), the EV cable should be fully uncoiled and allowed to air-cool - it should not be covered with insulating material such as carpet.

(images from Cheshire Fire Service Electrical Fire Safety Week and Michael Pereckas)

Step 2: Parts Required

  • OpenEVSE Kit - Level1 Level2 50A from the openevse store

  • J1772 cable assembly, from the openevse store or e.g. quickchargepower

  • 3-conductor 10AWG cabtire cable, as required, e.g. AWC wire
  • NEMA connectors, as required, for connecting to wall outlets
  • NEMA L6-50 locking plug and sockets, for adapters
  • 12mm 3V lithium button cell (CR1220, 1225, 1216), optional, for time-of-day clock

Tools Required

  • Screwdrivers (crosspoint, flat, various sizes)
  • Wire strippers (10AWG to 20AWG)
  • Soldering iron
  • Utility knife
  • Crimping tool (6-8AWG, for wire lugs)

Step 3: Unboxing the Kit

Identify the parts

  • 10 nylon lock nuts
  • 4 foam washers

  • 4 white nylon spacers

  • 4 metal 1-40 x 11/32 threaded spacers

  • 1 clear acrylic LCD window

  • 1 LCD foam seal

  • 1 nylon LCD window brace

  • 6 spade terminals

  • 1 drilled metal plate

  • 1 polycarbonate enclosure

  • 2 cable glands

  • 4 6AWG wire lugs

  • 3 red 3 black wires with spade connectors

  • 1 push switch

  • 1 4-way ribbon cable with 0.1" pitch connectors

  • 1 green cable with 3 position 0.1" pitch connector

  • 4 long screws

  • 2 hex bolts

  • 4 1/2" wide-head screws

  • 4 short wide-head screws

  • 8 5/8" screws

  • 6 short self-tapping screws

  • 1 DPST Struthers & Dunn contactor 450BXX40-12VDC

  • 1 OpenEVSE PLUS v4 board with 100-240V power module

  • 1 LCD colour panel v2 board with daughter-board

  • 1 green unstranded ground wire

  • 1 current sensor CT with 2-pin connector model CR8450-1000-T7QC

  • 1 GFCI CT with 4-pin connector CR8420-1000

  • 1 ground terminal block

Step 4: Assemble the Lid

  • Identify the four 1/2" wide-head screws. They fit the threaded metal spacers. Identify the four foam plastic washers.
  • Fit the foam washers on the screws. Remove the protective film from the clear acrylic window and from the white nylon window brace. The metal spacers have a slight depression one end - the flat end goes down. Fit the screws to the case, then stack the rectangular foam seal, the clear window, the nylon brace, and the spacers.
  • Tighten the screws. You may need to compress the assembly initially to start the screws in the thread. Do not over-tighten.
  • Fit the LCD board to the spacers with the short wide-head screws
  • Fit the 3-position socket with green wire to the 3-pin header on the daughterboard. The polarity is unimportant. Cut the wire mid-way and strip the ends.
  • Fit the button switch to the lid, with the O-ring on the outside. Do not over-tighten or the O-ring will be displaced. If that happens, unscrew the switch and start again.
  • Insert the ends of the green wires in the switch terminals and secure them with the screws. You may need to double over the wire to obtain more thickness.
  • Fit the 4-pin connector with the rainbow cable to the 4-pin header on the LCD board. The green wire should be connected to pin 1 (with the square solder pad, on the left)

Step 5: Assemble the Base Plate

  • Orient the metal base plate the correct way up. The plate is drilled for more than one style of relay and board; not all the holes are used. The mounting holes for the ground bar may be identified (silver nuts here).
  • Mount the OpenEVSE board on the nylon spacers with four 5/8" screws and lock nuts. The nuts should go on the back of the plate, not as shown in the photo.
  • Mount the ground bar to the plate with two 5/8" screws and lock nuts.
  • Mount the Struthers & Dunn contactor to the plate with two 5/8" screws and lock nuts. Ignore the extra holes.
  • The relay coil terminals are the two centre ones. Unscrew the philips screws and secure two of the spade terminals to the coil terminals.

Step 6: Review the Wiring Diagram

  • See PDF document. The OpenEVSE board is designed to drive either a 12V DC relay coil for the Struthers & Dunn DPST contactor, or a 120V AC coil for a Packard C240C contactor, or two SPST contactors. Different connections are used for each. For the Struthers & Dunn contactor, the terminal block marked "AC_RELAY" is not used.
  • Only one of the DC relay connections is used. I used the one marked DC_RELAY_1 on the board schematic (on github). The relay coil is not polarised, and AC has no polarity, so it does not actually matter what colour wire is used or which way round the relay is wired. I chose to use red for the +12V supply to the relay and for the L2 supply.
  • Green is used for ground. That does matter. The EVSE may be used on any line voltage between 100-240V AC, 50-60Hz. In North America the choice is usually 120V single-phase or 240V split- phase, though 208V single-phase may be available in some locations. For 120V, neutral (N) is grounded at the utility supply and is not always switched.
  • By convention, in North America, white is used for AC neutral and black or red for live. A split-phase supply may or may not have a neutral, with black and red used for the two lives. Since the EVSE may be connected to either 120V or 240V, for consistency I have used black for L1. L2 to the car is red, but L2 on the input is white.

Step 7: Review the Cable Routing

  • There are some constraints on cable routing. The high-current wires have a limited bending radius, and must pass through the current-measurement toroids. Cable routing must not interfere with the contactor switching - wires should not pass over the contactor.
  • I chose to place the input power cable on the right, the output cable to the EV on the left, and lead the wires around the contactor, secured with cable ties. I drilled extra holes in the base plate to secure the ties. The toroids are placed on either side of the contactor. I also shortened some of the provided low-current leads.

Step 8: Contactor Wiring

  • Fit the cable glands to the polycarbonate box. The glands serve both as waterproofing and as strain relief, and should fit snugly around the power cables when tightened.
  • Feed the input power cable and the J1772 cable through the cable glands and pull through enough length to work with (a couple of feet). Strip back a sufficient length of the outer insulation on both cables - about 3 inches on the input cable and 9 inches on the EV cable.
  • To strip the insulation, bend the cable into a small-radius loop, then cut into the outside of the loop with a sharp knife. The cut should propagate into the insulation, allowing it to be pulled apart by hand, Repeat on all sides of the cable. Try not to cut the inner insulation
  • Cut and strip each of the wires in each cable to the appropriate length, bearing in mind the cable routing. There should be about an inch of outer insulation extending through the cable gland. The ground wires need to go to the ground bar, the pilot wire to the terminal block on the EVSE board. Crimp the connector lugs on to the L1,L2 cables.
  • EV cables from openevse and quickchargepower use two 12AWG wires for L1 and L2, together equivalent to 9AWG. Crimp them both into one lug. My preference is to solder after crimping, for corrosion resistance and better electrical connection. Do not tin leads before crimping - solder creeps under pressure and will loosen.
  • I would prefer to substitute 8AWG or 10AWG lugs that actually fit the cable for the 6AWG lugs provided. Failing that, double over the stripped end of the cable. The wire must be tightly secured in the lug and make a good low-resistance electrical connection.
  • One pair (either L1 or L2) of wires from the EV cable should be routed through the current sensing toroid. Both pairs (L1 and L2) should be routed through the GFCI toroid, in the same direction. GFCI works by sensing any difference in the flow and return currents.
  • Unscrew the terminal screws from the contactor, and bolt the high-current lugs in place with the spade terminals on top of them. The cable lugs should be in contact with the metal surface of the contactor terminal (bolts should not be used as current carriers).
  • Connect the low-current wires from the input side of the contactor to the AC_LINE inputs on the EVSE board. Connect the low-current wires from the output of the contactor to the AC_TEST inputs. Connect the contactor coil terminals to the DC relay outputs on the EVSE board. Connect the green ground wire from the EVSE board to the ground bar. Shorten the wires as necessary to make for neat routing.
  • Connect the 2-pin connector from the current sense toroid to the 2-pin header on the EVSE board marked A_CT. Connect the 4-pin connector from the GFCI toroid to the header marked G_CT. The orange test wires go on the inside, next to the power supply block.
  • Connect the pilot wire (usually purple) from the EV cable to the terminal connector on the EVSE board. The EV cable may have an unused wire, which should be cut flush with the outer insulation. Verify all connections are correct and secure, then fasten with cable ties. The contactor armature must be completely free to move.
  • Slide the power cables through the cable glands and drop the assembled base plate into the polycarbonate box. Fasten the plate to the box in several positions using the supplied sheet-metal screws. Tighten the cable glands so that they grip the cables firmly. It may be necessary to hold the nuts with a wrench. Do not allow the cables to twist while tightening the glands.

Step 9: Fit the Lid and LCD Panel

  • Connect the 4-conductor ribbon cable from the LCD board on the lid to the 4-pin header on the EVSE board. The green (ground) wire connects to the pin with the square solder pad next to the screw. Use the 4-pin header at the edge of the board, not the 6-pin header next to it.
  • Connect the power cable to a 120V power source. Verify that the LCD panel lights up, and is readable. Adjust the trimpot on the LCD board if necessary.
  • Optionally, insert a 3V 12mm button cell (CR1220, 1225, 1216) into the battery slot on the LCD board, to provide power for the time-of-day clock. Check the polarity (+ve is marked on the socket).
  • Fit the lid to the box, and secure with the 6 long screws.

Step 10: Supply Connector and Adapters

  • This EVSE can operate at either Level 1 or Level 2, on different voltages and current limits, which are communicated to the charger on the EV via the pilot wire. The current limit must be matched to the connector and the available supply. In North America, there are a number of possible outlets, some of which are shown in the diagram.
  • In general, the current limit on the EVSE should be set to 80% of the supply rating. For instance, for a household 120V 15A outlet (NEMA 5-15, usually with a 16A breaker), the current limit should be set to 12A. For a 30A RV outlet, 24A.
  • For maximum flexibility, fit the EVSE with a NEMA L6-50 locking plug, and then create a number of adaptors L6-50 to 6-50, TT-30, 5-15 etc., which will allow the EVSE to be plugged into dryer outlets, campground RV outlets, welding equipment outlets as well as household 15A outlets.
  • Commonly, one can buy adapters to down-convert, e.g. NEMA 14-50 stove plug to 15-15 household socket, rated 15A. For the EVSE, we need to up-convert, 50A socket to 15A plug. Use 10AWG cable and 50A connectors for the EVSE end of the adapter, rated for the highest-power circuit used. If there is a fault in the EVSE when connected to a 50A supply, the supply-side breaker should trip, rather than the cables melting or the EVSE catching fire.
  • Since the contactor switches both AC lines (L1 and L2 for level 2 charging, or live and neutral for level 1 charging), it does not actually matter which way round or what colour the supply wires are (except that ground is by convention green). The cable from the EVSE to the adapter will be used for both single-phase (live,neutral) and split-phase (L1,L2). In North America, white is used for neutral when wiring e.g. NEMA 5-15 connectors.

Step 11: Setup

  • The EVSE controller is programmed with the push button. Push and hold the button to enter setup mode. A short press steps through the available options, while a long press selects one. A selected option is indicated with a +
  • If a battery is fitted, program the date and time. The clock is not necessary for operation, however.
  • The EVSE may be set to charge at L1 or L2, or Auto. In Auto mode, it will automatically switch depending on the supply voltage (120V or 240V).
  • The maximum charge rate must be set separately for L1 and L2 charging. In L1 mode, the current may be set in 1A increments from 6A to 24A. It should be set to 80% of the supply rating, e.g. 12A for a 15A outlet (16A breaker) or 16A for a 20A outlet.
  • In L2 mode (240V) the maximum current can be set in 2A increments between 6A and 80A. However, the Struthers & Dunn contactor is rated only for 40A, while the J1772 cable is also typically rated only for 40A. Do not exceed these limits. The EVSE will communicate the allowed current to the vehicle, which will in any case not be able to exceed its own maximum charge current.
  • Set the maximum current to the least of these : 80% of the supply breaker rating, 40A, the rating of the J1772 cable, the rating of the supply outlet, the continuous load rating of the supply cable, the rating of any adapters. E.g for a TT30 campground outlet or14-30 dryer outlet , use 24A. For a 50A welding outlet but 30A EV cable, use 30A.
  • Set all the other checks to "on". E.g. GFCI self-test, ground check.

Step 12: Supply Outlet Wiring

Strictly speaking, the supply wiring falls outside the purview of a build guide, and is typically regulated by a government body.

The supply outlet and wiring should be rated for a continuous load at least as high as the maximum current used by the EVSE, and be protected by a breaker or fuse 125% of that value.

The photo shows a NEMA 14-50 outlet (rated 240V 50A) with 8AWG supply wire. The outlet is the only load connected to a ganged pair of 40A breakers, fed from a 70A upstream supply. This outlet is used for a Nissan Leaf which can draw a maximum of 30A. (It would be usual to use a 6-50 3-pin outlet, with no neutral. 14-50 is commonly used for an electric stove)

Employ a qualified electrician to install the outlet, as required by local regulations.

Step 13:

Green Electronics Contest 2016

Participated in the
Green Electronics Contest 2016