OpenEVSE performs a self test of the safety features by checking for the presence of voltage on each line using Optically Isolated detectors connected to the AC_Test terminals.

The Welded Contact (Stuck Relay) check is performed during Power on Self Test (POST) and before each charge session.

Theory of Operation:

The two AC line monitor chips act as opto-isloators. The presence of an AC voltage potential relative to ground on either L1 or L2 will result in a state change from High to Low appearing on PD3 and PD4 of the Microprocessor. 

The circuit tests both stuck relay (voltage present when there should be none) and continuty to Ground (voltage present when it should be). Stuck Relay is tested whenever the relay is open and Ground is monitored when the relay is closed.

If the display reads "ERROR Stuck RELAY" check:

• The AC_Test Headers are connected to each line on the load (J1772 cable) side of the relays/contractor.
• The OpenEVSE board is connected to Ground with the AC Input Ground, J1772 Ground and Chassis Ground (if applicable) 
• The Relay Contacts are not stuck closed