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EV safety-chassis HV trip

545 Views 9 Replies 4 Participants Last post by  remy_martian, 
E
Hello everyone,
I am currently assembling an electric vehicle, and am looking for a little advise on safety components.
So far I have planned a switch to cut the inverter's enable signal when the hood is open, and I think it would be a good idea to have in place a system that turns off my HV contractors in the HVJB and on the charger if the chassis ever experiences positive voltage. Does this sound like a logical thing to do? I am no EE, but it seemed like a good precaution in case of a catastrophic failure, like in a crash. I do have an easily accessible manual disconnect on the battery, and I am using an EVSE charger that will have a ground fault connected to my chassis. My battery is 360v and my wiring has a 350A fuse, so I am trying to avoid having to buy a dc breaker of that capacity with a ground fault in order to achieve this. I am wondering if there are any other options to cut 12v power to my contractors that would be reliable and effective.

Thanks for the help!
Ember
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kennybobby
i would not want my car to disable itself while crossing a busy highway to make a left turn into traffic, or crossing railroad tracks, due to a sprung hood latch.

In addition, i would not want my main contactors to suddenly open while under load with current flowing, either in drive or while charging.

A test for HV in contact with chassis is a good idea.
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E
Valid points. I know a sudden cut of power can damage an inverter, but I am using a prius inverter so I was more focused on making sure things are safe
kennybobby said:
A test for HV in contact with chassis is a good idea.
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Do you mean something regular/built into the car? Like possibly a warning light?
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R
It's a lot more than a warning light. A light would ruin the isolation you are trying to ascertain.

"Heisenberg (yes, the Breaking Bad reference) Uncertainty Principle": Measure it and the measurement wrecks the result.
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VintageVolts
Not sure what BMS you're using, but the Orion BMS 2 has isolation fault detection (if wired correctly). see p30 of the operational manual PDF. Explained here better than i ever could!
Other BMS's's's may have it too but i only have experience with the Orion.
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VintageVolts said:
Not sure what BMS you're using, but the Orion BMS 2 has isolation fault detection (if wired correctly). see p30 of the operational manual PDF. Explained here better than i ever could!
Other BMS's's's may have it too but i only have experience with the Orion.
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That's a nice feature! I am using a simpBMS which unfortunately does not have any isolation fault detection.
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E
I have found a bit more discussion about this here: Isolation fault detector
and here: Hazardous Voltage Isolation - openinverter forum
Seems mostly like an unsloved issue, except for people using BMSs with components built in.
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R
It's solved as posted in the links you provided.

Both TI's app note posted on OIF, which I attached here, and Tom's Github have the circuit to do it.

GitHub - Tom-evnut/SimpISO: An Open Source HV Isolation monitor

Note that "ground fault" is not the same as "HV Isolation."

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E
True the solution has been engineered. I don’t think either of those are available for for sale, likely something I will see about ordering/assembling once I have a bit more progress on the other major components of my conversion.
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R
You wrote it was unsolved, backing that untrue statement up with links. I happened to go down the rabbit hole you dug, primarily to see where the dead ends in thinking/design were in those links, to find out there was indeed a reference design (it hasn't been merely "engineered") from Texas Instruments.

Now you change your tune to it's not available for sale, which is an entirely different problem from "unsolved." Yes, Texas Instruments does not sell reference designs. Tom may have a board design on that Github link - I didn't waste more of my time on this to look at the details there.
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