The key is the transition between the B and C state.
If the EVSE is not ready to provide power at any time the pilot should go High and PWM off.
The correct method would be to adjust pilot down to 6A and if lower is needed send pilot high to pause charging until the EVSE is ready again, then turn PWM back on.
Thanks for that - makes perfect sense. Qn now is whether Viridian Mainpine ECU supports this mode. In their docs it says :
"Input current resistance of < 100 ohm will cause the EPC to reduce the advertised current capability to 7A for 5 seconds after which the charging and the interlock will be disabled and the EPC will enter into a forced Status A until input current resistance is increased."
I think I'll have to test this out carefully. To me the "interlock disabled" means the contactors drop out exactly what I want to avoid, sadly. It's beginning to sound as though Mainpine doesn't quite do what I want.
I'm trying to restrict my wall-mounted charger's output to match solar generated free electricity. I have a Mainpine ECU in it, and can set a digital variable resistor connected to it to vary available current from 6A upwards, no problem. Problem is, when the sun's behind a cloud, and I have less power available, I have to set the Mainpine resistance to zero to turn it off, which makes it drop the available power & shut-down the charger. Mainpine docs say it effectively enters an error state, simulating "Status A" (car unplugged), until I increase this resistor back to normal. So the contactor goes clunk and the car stops charging.
Then when I restart the charger by increasing the resistor, it's as if I've just cabled the car up from scratch, and the contactor clunks in again as the car starts charging. Ok so far. But, being an Ampera, it also gives 2 Beeps on the horn to tell me charging has started successfully! No way in the car's settings to disable this! Will drive the neighbours, me & my wife nuts if it's doing this every time a cloud passes by!
I could fit a switch to disable the horn manually, but that's not nice, and I might drive off by mistake with the horn not functioning etc. Not ideal.
Are there any Ampera/Volt owners out there, maybe using Zappi/OpenEVSE/similar who have a solution to this?
One i3 owner says his car doesn't beep or anything when his Rolec clunks on again, so not an issue for him. Maybe most cars start heir charge silently, and it's only the Ampera/Volt which honks at you?
I only have an old version of J1772 off the web, Aug 2001, maybe the newer versions are clearer; as I see it, there's no "Status X" which means "charging is paused indefinitely but not yet stopped as the cable is still in but the charger doesn';t want to supply any current to the car".
The main states seem to be Status A = car not connected, B is transient as contactors pull-in, and Status C (or D, not relevant here) means "car charging at 6 or more amps". Statue E and Status F seem to be error states; whether I can use one of these to pause charging without the car shutting down he charge, I don't know. I can't see the difference between these 2 states, or why there are 2 of them!
Status A has oscillator off, Status B & C have oscillator on in general, acc to specs. But I couldn't see much detail as to what happens if the oscillator isn't on, in these states. I suspect the car would simply say "Unable to charge" yet again!
What would or should be the behaviour if, instead, I modified the CP signal so it tries to sit at 12V, the car drags that down to 9V or even 6V saying it wants power, but I refuse to drive the 1 kHz signal to tell it what's available?
It would be good to know if there's an "official" way to pause charging in these sorts of solar charging scenarios. Maybe J1772 never considered this need.