Our home Hydra EVSE failed this afternoon for the first time in as long as I can remember (don't let that fool you. It has failed before, it's just been a while, and not with the current revision). The plug for my eGolf started throwing error F, which indicates a ground failure. To recap, the current hardware has a GCM circuit tied to the load side contactor terminals. When the contactor is off, there should be no current, or it's a stuck relay. When the contactor is on, there should be current flow, or else it's a ground impedance failure. The latter was what was being indicated. Watching more closely, it was easy to tell that what was really going on was that when the contactor was being turned on by the logic board, there was no characteristic "kerthunk" indicating that it actually did it.

I sort of should have seen it coming. The eGolf exercise the EVSE's contactor far more than is necessary. In fact, the eGolf's charging system is the flakiest and most finicky I've encountered so far (and I've encountered quite a bunch more than I've actually owned). Most notably, in the morning when it's time to leave for work, you have to click the key fob to unlock the plug-lock. When you do so, the car turns on the power. There's absolutely no reason for it to do so, since the batteries are all charged, and the climate control warm-up has already concluded. But that's what it does. Then it unlocks the plug lock and when you remove the plug, it turns the power off.

That's a lot more contactor play than average. What failed was R6 - the 150 ohm resistor connected to the driver triac. It blew open. When I got it out of the circuit there was nothing obviously wrong with it on the outside. But it measured completely open. Replacing it brought the Hydra back.

This suggests that that component needs to be made beefier. I'd been using ordinary 1/8W chip resistors from a reel, but it looks like the thing to do is use a 1/2 watt part. Fortunately, DigiKey has 'em. While I'm at it, I'm going to use 1/2 watt for the 2.4K resistor in the HV triac circuit too. That means 1/2 watt parts all 'round (the 39 ohm resistor in the outer snubber already has been upgraded).