[eCRX]

I'm surprised that EV specific contactors don't always include auxiliary contacts for physical status of the contactor.

Does anyone have any opinions on how necessary contactor status is? Is it an unnecessary redundancy from yesteryear?

 

[remy_martian]

It still doesn't give you health of the contactor, just whether it's thrown or not.

 

[57Chevy]

If you are using a negative rail contactor and state machine logic then it is a necessary indication that the negative contactor closed. The positive contactor registers HVDC so don't need one for that. Negative contactor is IMO vital for failure shutdown/redundancy as it never closes with current flowing so can't weld/far less likely to. There is always some risk of the + rail contactor welding, if you don't have a second one, it is a high risk state with HV live and no way to get it off until you can Tonya Harding the contactor. Always a fun game...

Gigavac contactors seem to always include them as an option, not so much the cheaper ones. I have used, welded and TH'd a lot of cheaper ones. Will be using Gigavac this time.

 

[asymptonic]

I was planning on including loops of low voltage through the auxiliary contacts that would interrupt all HV command voltages if they disagreed. Sort of like HVIL on the cheap. I'd prefer to do HVIL properly but I don't yet understand the hardware surrounding it.

 

[57Chevy]

I don't yet understand the hardware surrounding it.

OEM HVIL uses resistors in some items so consumers can't easily bypass the circuit, plus they can use a PWM signal instead of just open/closed. You can just put microswitches on the lids of anything HV and join them up in series, it is just to stop wayward fingers going into places where there is unprotected live HV.

The contactor feedback signals are to drive the control logic, otherwise you end up with "leaps of faith" where a control command assumes that a corresponding action executed. This is very poor design and can result in unexpected outcomes.

 

[asymptonic]

That makes sense. My instinct was to avoid using the aux path as inputs to a VCU just because it added a point of failure. I'd rather the continuity or lack of in a circuit involving the aux paths through all contactors created a fail safe condition. I've read Texas Instruments' tech docs on their HVIL products, but it's very high level and it seemed the point of PWM was to be able to detect the difference between normal operation and abnormal ground to low or short to high, which makes some sense.