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My reasons are 2 fold. I'm curious how the safety circuits work (ground fault test, etc) and I want to make a J1772 extension cable. I looked at buying one and found that either the cables are cheaply made and don't carry control pins or are very overpriced and do have control pins, but are better built. I would prefer an L2 but I'll take what I can get.
 

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How do you envision the extension cable will work? You'd plug your existing charge cord handle into a dummy charge port connected to another J1772 cable/charge handle?
 

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Basically, yes.
Well, if you do it, please post pictures of the wiring and the sealed container you put the charge port into. People (and I include myself in that category) love to see the step-by step pics of mods :)
 

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Well the safety circuit is just a simple chip that reads the pilot signal and does a handshake with the car's onboard charger. The car tells the chip what voltages it can take or is set for and if the EVSE agrees it closes a high voltage contactor and the juice flows. All the ones I've seen also have a GFCI loop around the main to measure amperage to ensure there isn't a problem.

You can look at OpenEVSE to get a pretty good idea how it works and the troubleshooting section for the technical stuff.
 

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You can start very simply, by only reproducing the Pilot logic to make a functional EVSE. Then add the J1772 standard protection circuits as you learn. You can make a simple functional EVSE (without protection circuits) with only a 12V source, a quad op amp chip, and a few transistors. You don't even need -12V. The trickiest thing is actually the 12V source, since it must be isolated from L1/L2/N.

The Proximity signal is only used at the (car side) plug. It doesn't travel across the cable. So you only need a 4 wire cable from EVSE to plug (if you want to splice in some wire). To make a pluggable extension, the Proximity at the EVSE plug is ignored, only L1, L2/N, GND, Pilot are sent down the extension cable. The normal Proximity circuit is used on the extension J1772 plug. Plug the extension into the EVSE first. And since you only really need 4 wires, any 14/4 SOOW or SJOOW type cable from you local hardware store is fine (for 12-16A).
 
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