openinverter forum

Does LDU / SDU case need to be grounded? I don't have ground strap or cable from motor to body chassis. What's the function of that, do I need it?

The case is meant to contain radiation inside. It can only do this when grounded, otherwise the case itself becomes the antenna when it is free floating. Also because of the small distances between semiconductors and cooling plates and the fast switching, currents flow over the so formed capacitors. You will feel a tickling when touching an ungrounded case, not sure if it can reach dangerous levels. These currents could also flow via the ball bearings of your CV joints and cause damage there.

Since the case is mounted to the chassis via rubber dampers you need to ground it with a strap to prevent above unwanted things.

So if not grounded, I can feel tickling if touching, but how can ball bearings get damage?

What happens when current flows over the so formed capacitors?

I guess I’m asking, what actual results might be? Can it cause motor not working? Things glitching on OI board? (like I’m experiencing with weird overcurrent etc issues?)

With the LDU, the housing is connected to ground via the circuit board and the external 23-pin connector. This line is very small and not suitable for compensating for potential differences. All EVs I have seen have grounded motors. Also chargers, battery boxes, DCDC converters, heaters, AC compressors. This is mandatory in Germany. With the Model 3 PCS, the CAN interface is repeatedly destroyed due to poor grounding.

Ok thanks!

I have had some random CAN errors every now and then but the biggest troubles I have with the OI board throwing random errors, even without moving the car. So it might be all related. I guess that's the next step, add that strap.

Is there any requirements for ground strap? I don't have OEM braided strap. Where to attach?

mane2 wrote: ↑Tue Nov 21, 2023 10:37 am Is there any requirements for ground strap? I don't have OEM braided strap. Where to attach?

You should be able to find a decent & thick ground strap at a local auto parts store. You'll want a loop so it doesn't pull tight when the motor toques back and forth. A U shape is preferable over running it straight. Don't make it longer than necessary.

You want as a good of a connection as possible. Sand the surface of each side of where it bolts up and add your favorite anticorrosion goop.

As for where, you'll want it connected to the chassis, not a rubber bushed thing like a subframe. See what you have for existing bolts to the chassis that won't disturb anything important. Motor side might have a bolt that seems to do nothing, that's your ground location. Any spot on the casting should work well though.

And chassis wax can be a second layer of protection on the steel chassis side of things if it has any winter / salt exposure.