I’ve never had this error when using the AC50S and refrigerator except when charging. It has no problem running the fridge from 100% to 0%. Also the error for too much output current would be:
E27 “DC12V-1 output over current, Output current >11A or short-circuit”.
My error is:
E28 is “DC12V-1 input over current, Current >-1A”
Well, with your information and Bluetti’s reply above would make me now think that DC charging and discharging at the same time are not always compatible. Is this the first time you have tried that? If so, I would have to say it will not DC output significant amps while DC charging. If you have done this in the past several times without issue, that would seem more like a machine problem
It usually works and I’m charging and discharging right now and it’s fine. But it happens often enough that I’ve gone to my fridge and seen it sitting at 50 degree and E28 showing up that I want to know what’s going on. I wish Bluetti would respond what the error actually means, not just how to reset it. My guess would be the AC50S gets confused sometimes when discharging if you disconnect the DC charging input like when a car shuts off.
I wonder if it is as simple as the cig lighter plug or socket in the car is not making good contact and the combination of charging and discharging makes it more prone to a spike caused by a poor connection. The cig plug is notorious for poor connections. Just as an experiment, it may be interesting to try to improve the contact in the socket (clean with emory cloth on the end of a pencil eraser or try a little electrical tape wrapped around the cylinder part of the plug to tighten it. (make sure not to get tape on the metal side contact).