Correct use of HVIL

1457 Views 5 Replies 4 Participants Last post by remy_martian, 3 mo ago

asymptonic

Discussion Starter · Nov 13, 2021

Still in the very preliminary design of my conversion. Mostly hypothetical CAD design lacking the donor vehicle yet. I've been looking at a number of the smaller components like HV connectors that support HVIL. I've read that HVIL can be pretty complicated including square waves monitored by controllers.

Long story short, I am big into safety in this design. How is the DIY crowd wiring HVIL into their systems. At minimum I'd like to use it to prove continuity through the battery system prior to allowing the traction controller to come online, but I can't find much info on how it's typically wired and/or used. Would love some help on this one, especially in the early design phases.

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balex97

· #2 · 3 mo ago

This thread is quite a few months old but I have the same question:
For our build I want to add HVIL. I use the Dilithium BMS system, so I could use a 5V signal for the HVIL line, which is monitored by a input of the BMS. If the 5V is interupted, the BMS shuts down all relais. Unluckily there is no report, which component has caused the disconnect but this would be a simple method, wouldn't it?

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remy_martian

· #3 · 3 mo ago

Sorry - I somehow missed the first posting.

You can't use 5V for HVIL. It's a current loop that series connects through the HV battery contactor coils. So, if you use 12V contactor coils, it's 12V/24V.

As far as sensing where it went open, that could be done but:

1) HVIL is a rare event
2) You know which cover or enclosure you accessed HV with in most cases
3) The sensing system adds a level of failure to the HVIL that can defeat an open loop. Very dangerous if that happens, so don't do it, imo.

So, just because it could, doesn't mean it should, be done.

Pull an access cover, the power has to be shut off by the HVIL, reliably. Every time.

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asymptonic

Discussion Starter · #4 · 3 mo ago

Commercial HVIL loops are more complicated, they use PWM and can sense interruption and grounding separately, as well as where in the loop the fault is (not sure how that works, something something resistors). So presumably they use HVIL to close the contactor via a separate relay/voltage.

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oudevolvo

· #5 · 3 mo ago

Agree, OEM HVIL is a current based signal.
HVIL itself does not power contactors.

But there might be another reason why 5V from the BMS might not be the best idea.
What if this wire shorts to ground?
Will that damage the BMS?

I’m using a 12v signal to power a relay that creates an active low for the BMS to detect.

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remy_martian

· #6 · 3 mo ago (Edited)

I stand corrected. With a relay, you could use 5V.

As far as fault location, you can come up with high resistor values that when paralleled to ground come out to a unique resistance as each node in the loop goes open. Your "PWM" is not "M", but static in duty cycle. On times are long enough to keep relays closed (I stand corrected on needing the contactor coil voltage for the HVIL - 5V could be made to work with relays), and off times is when you can measure resistance, including detecting a malicious short/powering/bypass by someone trying to defeat the HVIL. Bypass detection with resistors may be a bit trickier.

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