4.4.2 build report

A project log for J1772 Hydra

Charge two electric vehicles at once

Nick SayerNick Sayer 01/24/2019 at 18:010 Comments

The combination of EVSE board 4.4.2 and HV board 4.4 is just about perfect, so far as I can tell. The schematic for 4.4.2 doesn't differ from 4.4.1 - the clock chip is just moved to the top of the board to be away from the AC wiring.

HV board 4.4 replaces the LM358 with an LM393 comparator. Since the LM393 has open-collector outputs, it's slightly better for the relay test outputs to be inverted, which requires altering the firmware. The circuit leverages the open-collector so we don't need diodes like we did with the LM358 output. The output is an RC circuit designed to slowly rise to Vcc. The LM393 output shorts that node to ground, discharging the cap. This arrangement allows the output to be constant given a 25 Hz pulse rate (as would be the case in Europe where they have 230v H-N wiring) so the firmware doesn't have to sample it repeatedly.

That said, v5.0 is coming from OSHPark next week sometime. It won't be operationally any different, but will be somewhat simpler for me to build. It will be interesting to see how it functions given that we're constructing both pilot voltages ourselves now.