LDU Overcurrent Sense Issue/Question
Posted: Sun Mar 10, 2024 10:12 pm
So as many know I've had my car running with an LDU for a while, and 2 weeks ago had what appeared to be a catastrophic failure. I now don't think that's the case, but have an enigma on my hands. I'm running version 4B of the control board.
For background, here's the sequence of events: driving home with DC-DC on the fritz, I had a falling 12V voltage, and started seeing the CANBus temp gauge go nuts (jumping around all over the place), while slowing and making a sharp right turn, I lost power. Pulled over, initially thought the 12V battery was dead so went and got one and my multimeter, turns out the 12V battery was ok (not great, but 12.4V). Then used my phone to connect to the inverter and go step by step through the start process. When it got the start signal, it immediately showed an OVERCURRENT error. I assumed a contactor had dropped killing a power stage, and got a neighbor to tow me the mile home. Once home I opened up the bus bars and did a diode test on the inverter per Damien's video and everything tested out perfectly fine. I opened up the inverter and found a significant amount of coolant (I had an external leak that I think made its way inside) and the bottom of the control board had been fully submerged. I cleaned out the connectors and tested (several times) but still got the same instant OC error when given a start signal.
I've pulled the board out, and connected to just 12V power to test. The board powers up ok, and it appears that all the IC chips are getting 5V as they should. I didn't find any chips with pins connected to ground that shouldn't be. I decided to test the pins going out to the gate drivers, and found each 12V supply and ground to be fine, but found what seems to me strange readings on the Fault pins. Here is what I measured:
Fault A High 1.1V
Fault B High 2.9V
Fault C High 1.5V
Fault A Low 2.5V
Fault B Low 0.5V
Fault C Low 2.5V
I measured the capacitors attached to each of the fault lines and they appear ok.
That looks to me like there's some sort of issue on the Fault B circuit, but I don't know. This is getting beyond my knowledge, frankly I'm not entirely sure why there is voltage here at all; as I read the circuit diagram I would have thought these were inputs to the control board not outputs, but when it comes to this level of detail, I'm still hopelessly uneducated.
For background, here's the sequence of events: driving home with DC-DC on the fritz, I had a falling 12V voltage, and started seeing the CANBus temp gauge go nuts (jumping around all over the place), while slowing and making a sharp right turn, I lost power. Pulled over, initially thought the 12V battery was dead so went and got one and my multimeter, turns out the 12V battery was ok (not great, but 12.4V). Then used my phone to connect to the inverter and go step by step through the start process. When it got the start signal, it immediately showed an OVERCURRENT error. I assumed a contactor had dropped killing a power stage, and got a neighbor to tow me the mile home. Once home I opened up the bus bars and did a diode test on the inverter per Damien's video and everything tested out perfectly fine. I opened up the inverter and found a significant amount of coolant (I had an external leak that I think made its way inside) and the bottom of the control board had been fully submerged. I cleaned out the connectors and tested (several times) but still got the same instant OC error when given a start signal.
I've pulled the board out, and connected to just 12V power to test. The board powers up ok, and it appears that all the IC chips are getting 5V as they should. I didn't find any chips with pins connected to ground that shouldn't be. I decided to test the pins going out to the gate drivers, and found each 12V supply and ground to be fine, but found what seems to me strange readings on the Fault pins. Here is what I measured:
Fault A High 1.1V
Fault B High 2.9V
Fault C High 1.5V
Fault A Low 2.5V
Fault B Low 0.5V
Fault C Low 2.5V
I measured the capacitors attached to each of the fault lines and they appear ok.
That looks to me like there's some sort of issue on the Fault B circuit, but I don't know. This is getting beyond my knowledge, frankly I'm not entirely sure why there is voltage here at all; as I read the circuit diagram I would have thought these were inputs to the control board not outputs, but when it comes to this level of detail, I'm still hopelessly uneducated.