When the car is plugged in, but not charging, if I slide the "Slide to begin charging" thing on the icon of the charging connector on the Battery page in OVMS, it doesn't start charging, it just goes into the "Charging -- Prepare" state (according to the "stat" command) but never actually charges.
OK, after a couple of months delay, I have implemented a fix for this in the OVMS firmware. I've tested it on my Roadster 1.5 but I'd appreciate further testing by others, especially 2.x cars. You can flash my build with this change from here. If it doesn't work satisfactorily in some way you can switch back to the other OTA partition. If you'd prefer to build your own firmware, you can fetch my changes from the roadster-wakeup branch on GitHub.I should also say that if the OVMS app can cause the charging to start by doing whatever it does when Wakeup is triggered then it should also do that same operation when you slide the switch on the charge connector icon. I'll take a look at the code.
In order to make a valid test, the car needs to be plugged in and ready to charge but waiting for a scheduled start time. If you've just plugged in the cable, you need to then wait for the car to go to sleep (that is, for the coolant pump to stop).
As proposed, the fix required issuing a "wakeup" CAN message first, but then before issuing the "start charge" message the firmware needs to track the car stepping through a sequence of states while it checks whether the pilot signal from the charge cable is present. During that time the status messages sent to the app need to not include the true status as indicated by CAN messages that indicate no pilot signal because that would cause the app to hide the charge connector icon. Instead the status is faked to keep the app happy until the car detects that the pilot signal is actually present, then we can issue the "start charge" message. With my new code the charge connector icon should show "PREPARE" for some seconds as the car gets ready, then charging should start. You can then stop the charge by sliding the slider on the app or the real one on the car if you don't want the charge to happen at that time. You might try repeating the test after the car goes back to sleep. You could also try a test when the car is already awake; that should start charging with less delay.