@floobydust. Liked your idea but the main working principle limits a bit the use of such circuitry in my application.
The idea is to be able to detect the status of each contactor without relying on other parts of the circuitry.
The way I do it now with the auxiliary contacts is feeding a constant isolated signal (lets say 3.3V) with a very short pulse(just to eliminate the problems of signal stuck to high..).
There is a specific order in closing/opening the contactors and none of these operations happen at the same time.
For example:
1. Voltage/current across the HV bus is checked, should be ZERO(or very very close). States of all contactors are checked using auxiliary contacts. If everything is ok, discharge contactor which is normally closed is opened, voltage/current across the HV DC bus bar is checked again to verify that everything is ok, next.
2. Check that the rest of contactors are in the state they are supposed to be using the auxiliary contacts. Everything is ok? next.
3. HV- contactor that is normally opened is closed, verified with auxiliary contacts that everything is ok including the rest of the contactors, voltage/current measurement on HV bus..all good? next.
4. Testing circuit that ensures that the precharge resistor is still connected and has the right value is used. If all seems ok, precharge contactor is closed.
5. Precharge process in monitored voltage/current/time, when the precharge is over, the whole precharge circuitry is bypassed with the HV+ contactor.
and so on...
Perhaps there are some more inner checks that I am forgetting now, but the idea is that diagnostic coverage is quite high and basically everything is "doubled" in that sense. Haven't had a single failure during my 3 years working on this project and it has been daily used. Having another circuit for detection will improve the diagnostic coverage and also offer different ways for checking the contactors.