Guide to adding a current selection switch to the DIY Portable EVSE from ZCW Introduction This guide is intended for those who have built the Zero Carbon World DIY Charging Station kit as depicted in the #EVSE Build Day video, who want to take advantage of the current limiting capabilities of the EPC used in that project. What You Will Need Soldering equipment (Iron, Multicore solder, pliers, cutters, strippers) Hacksaw Mole Wrench/Vice Drill (selection of bits) Small block of wood. Two lengths (approx 8 ) of different coloured stranded wire (light guage) Rotary switch (see text) Specific resistors (see text) Optional: Silicon grease
Choosing your switch This part took the longest for me as I was having to rely on internet searches so I have shown you which one I chose eventually, which was inexpensive and adequately splashproof for my expected usage, especially when used with silicon grease around the shaft. It has an enclosed switch construction and a fairly flat form factor which fits in the cabinet comfortably. There are fully waterproof versions to be found if you expect your unit so be subject to a dunking from time to time. You have two choices to consider :- 2 pole / 6 position OR 1 pole 12 position. I favoured the 2 x 6 option so the mounting of the resistors would not require an insulated terminal post to be fitted. The resistors will be connected thus :-
Resistor Selection This is where you have to decide what optional charging currents will be right for you. If you own a Tesla Roadster then 7A should be the minimum. Ampera/Volt work OK on 6A minimum. 12A may be more useful if you want to use adapters to run off a13a plug (do mind the plug/socket doesn t get hot in use). Also, 16A is only useful if the car is capable of 32A Ampera/Volt won t take more than about 14A at UK mains 240V in reality anyway, so I relied on R5 (open cct) for my 16A and used 12A (280 ) in R4. Plan to keep one position Open Cct (5 in the diagram) which will allow 32A as per the breaker & EPC Max rating, and one Short Cct which causes the EPC to instruct the car to ramp down tidily and stop charging. This is a good feature to use when interrupting a charge before cycle complete. Decide the location of the switch I chose a position adjacent to the cable entry on the EPC end, simply so that it would be protected from knocks. Offer up the switch so you can see how much clearance you will have behind it, and mark the centre line for the drill hole. I use a small drill for accuracy to make a pilot hole, then enlarge in two steps until the correct size is achieved. You will notice that there is a position lock stud on the rotary switch, and you could drill a small hole just above the main hole for it to locate in. It would need to be sealed, however, and I decided to cut the stud off and rely on the lock washer and mounting nut to prevent unwanted rotation. Remember to place a small block of wood inside the cabinet as you drill to remove all risk of damage to the EPC.
Check the length of shaft required for your switch given how proud of the cabinet the threaded part will be and mark with a marker. Then cut the excess shaft off with a hacksaw. This is so much easier with plastic shaft types than metal ones, also you can de-burr and camphor the end of the shaft with a sharp knife. Solder the resistors into place I used the mole wrench to grip the shaft and provide a guide for the cut. It then was useful as a mount to hold the switch while I soldered the resistors in place. I found the leads of the resistors were stiff enough to arrange them without any shorts between them and left mine bare but, if you want, you can make your own sleeving by stripping lengths of insulation from thin flex inner core wires. For soldering tuition seek a separate guide. My only tip is keep the iron tip clean with wet sponge and use enough solder to get a good flow over the whole tag, having positioned the lead through the tag and bent over. Trim excess lead once solder is set. I chose to position the resistors around the circumference of the switch as shown. This avoided fouling with the lid flange of the enclosure, but any arrangement that works for you is fine. This shows why I chose 6 x 2 as it provides two mounting posts per
resistor. I used very fine single core insulated wire for the zero ohm position 6, as we are dealing with under 5v and signal level current only. The two wiper tags are where the flex wires connect and as these are not current carrying soldering is ok, even necessary, unlike we said for the crimped ferrule power terminations in the main build. The other end of the flex wires connect to terminals IC & 0v on the EPC. Once the switch is mounted with all the switch end wiring in place, test each switch position with an ohm meter to be sure you have the correct resistance in each position and no resistor leads touching, then connect to the EPC as shown.
I marked the current limits I had chosen on the side of the case.
A dymo labeller or similar, would have been a lot nicer! Maybe I'll get back to doing that later. I would be happy to answer any questions from would be constructors, just tweet me on @RickMGoldie