Precharge relay staying closed at power on

[Zieg]

I'm not sure if this is a new issue or if it's always been doing this, but today I discovered my precharge relay is turning on and staying on as soon as I turn the key. I discovered this because it's causing my dc/dc converter to start running and it draws power through the precharge circuit.

Pressing the start button will close the main contactor and open the precharge.

What could be causing this? I've traced it right back to the external pin so I know it's not the wiring or the relay being welded. Hardware is a gen2 Leaf inverter with the mini mainboard / OI drop in board running 5.35.R

with no power to the board there is no continuity to ground through that pin so I'm hoping it's not a damaged or shorted component. I have to remove the stack from the car to access the mainboard so I'm hoping there are some other things to check before it comes to that.

I did see an older post with a change to the bootloader that would prevent clicking on powerup, but I don't think that's the issue because the relay just stays on. Also, the post was dated late 2020 and I purchased the board in 2022, so it probably already has it installed.

params (1).json

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[johu]

It's always been like that. Why should it drop out?

Your DCDC should only activate once the main contactor is closed

[arber333]

I'm not sure if this is a new issue or if it's always been doing this, but today I discovered my precharge relay is turning on and staying on as soon as I turn the key. I discovered this because it's causing my dc/dc converter to start running and it draws power through the precharge circuit.

Pressing the start button will close the main contactor and open the precharge.

What could be causing this? I've traced it right back to the external pin so I know it's not the wiring or the relay being welded. Hardware is a gen2 Leaf inverter with the mini mainboard / OI drop in board running 5.35.R

.....

That is a good way to burn precharge resistor!
1. If you switched outputs between DC and PC could cause this. Verify operation without HV and fake Udc value within interface.
2. Also you can see this in web interface. When you push start button system should change state either to "running" or "error"

[Zieg]

Ah, so it's intentional, good to know. I did verify the outputs weren't switched and that with the precharge relay disconnected, I get the expected precharge error.

I don't know how I can make the dc/dc wait for the main contactor. Maybe switch its 12v power through a relay controlled by DCSW? How are other people handling this, when not using a VCU?

The good news is my resistor is 100w with cooling fins and mounted to a big aluminum plate, so that's probably why it hasn't burned yet. I'm also usually pretty quick to press start after turning the key, so for now I'll just make sure to keep up that habit.


Another option, what would be the best way to keep the precharge relay off until start is pressed? With my very rudimentary understanding, I wonder if I can just add

Code: Select all

DigIo::prec_out.Clear();

to the top of vehiclecontrol.cpp? I can't tell where it gets set active in the first place, but I suppose changing that would be the better way.

[arber333]

I don't know how I can make the dc/dc wait for the main contactor. Maybe switch its 12v power through a relay controlled by DCSW? How are other people handling this, when not using a VCU?

For some builds i had dcdc connected to HV directly via 20A fuse. I controled it by 12v pulse from my VCU.
For Outlander system i control DCDC via 12V start signal when precharge is complete and DC contactor is on.
You could simply use that contactor signal to turn on DCDC as well.

[johu]

In Audi A2 I actually use the dcsw signal via an aux relay to power up the dcdc.
Changing the code takes more than just one line and I'm not home now.

[jrbe]

You could add a fuse to the pre charge and main contactor that you can pull if you're doing work.

Why would this kill a pre charge resistor though, or do you mean while feeding a dc-dc converter too? Ignoring the dc-dc in question, it's main current pull would be getting the capacitors up to voltage. After that it should be minimal.

Could out pwm be used instead? Could potentially have the oi board watch 12v battery voltage and turn it on only when the main contactor is closed (as arber says.)
Or use the same main contactor output to delayed turn on the DC-DC. This option of watching the 12v battery voltage and only turning on the DC-DC when needed has safety implications. Say key is on, 12v battery is just above threshold of turning on the DC-DC so no high voltage. You're doing work, consuming the 12v battery, then the DC-DC kicks on. Now you have high voltage connection you weren't thinking about and likely won't be prepared for unless you hear the contactors clicking.
This also has the potential implication of missing the pre charge time and going straight to main if not done well.

Does the key switch have an accessories only mode that could be used instead? I think this is all around safer and has the typical running off the 12v battery people should be used to from ice vehicles (no DC-DC on in accessories only mode.)

[Zieg]

In Audi A2 I actually use the dcsw signal via an aux relay to power up the dcdc.
Changing the code takes more than just one line and I'm not home now.

Oh don't worry about it, I was just curious if it would be that simple to change. Trying to learn more about coding but it's a lot to take in. I think I have one spare relay in my relay box so using that the same way you have seems like a good option.

Why would this kill a pre charge resistor though, or do you mean while feeding a dc-dc converter too? Ignoring the dc-dc in question, it's main current pull would be getting the capacitors up to voltage. After that it should be minimal.

Yeah, that's exactly it, the dcdc is drawing power through the resistor. At least the car doesn't have a lot of 12v demand, so the draw must be pretty low. My key switch doesn't have accessory mode, if it did I would be very tempted to use the second position for the start signal.