With the Christmas to New Year break, we managed three EV days this week. Amazingly, it took us nearly all that time to get the three contactor boxes that are required to operate the vehicle finished (as far as possible) and installed. We're so confident about two of them that they actually have their rubber gaskets installed
Part of the delay was figuring out where to route some of the conduits. I've already mentioned the one behind the headlights, and we've had to move another one that would was fouling the headlights already. We've decided that now that we can see where all the cables have to go, we really need to redesign one of the contactor boxes completely for next time (if there is one).
We decided to test the pre-charge circuit, to make sure that the voltage across the motor controller contactor was low enough when it connected after the pre-charge delay. This was a little tricky; we had to convince ourselves that the pack was properly floating, so we could connect one end of the pack (the positive end, as it turned out) to mains earth at the Digital Storage Oscilloscope probe. All worked well, and we saw the classic exponential rise (from negative voltage towards zero) as expected, then the very low and very steady zero volts when the contactor connected. There were two slight surprises. The voltage, even after about 5-7 time constants, didn't rise completely to zero; there was about 10 V across the contactor that would just not go away.
We assumed that this was probably due to a small load from the motor controller of about 10/100 = 0.1 A (our pre-charge resistor is 100 ohms), or about 24 Watts. Perhaps this drives some DC/DC converters or something, but I thought those should run off the 12 V from the CAN bus. Later, we noticed how slowly the capacitors on the motor controller bled down (the manual says 10 minutes). It seemed to bleed down a lot faster with the ~ 10 megohms of load from the multimeter! So now that I write this, I think it can't be a load on the motor controller high voltage input, or certainly not one as high as 100 mA. So that's a bit of a mystery.
The other surprise was that the voltage across the motor controller contactor appeared to have spikes of voltage on it, some of which were fifty volts in magnitude. I remember heading an ethereal voice saying "You have noise in your future!" and thinking "what chance does the digital BMS have in an environment like this?".
So we finally got to run the latest BMS software while running the motor up on stands. The result is: as far as we can tell, there is no problem. Arrgh!
The best we can tell is that the way we were monitoring for faults way back when was actually injecting noise into the system. [ Edit: and that still happens, if we monitor that way. ] But there are other ways we can monitor, and while there are some corrupted characters to the monitoring system (e.g. the "V" in the voltage string will corrupt to an "R" or "F" about one in a hundred times), the communications between the BMS master (in the Driver Controls computer) and the actual cell-top BMUs (Battery Management Units) seems to be unaffected by noise. We can tell this by the lack of retrying, and the counts of checksum errors.
But can we really be sure the problem is fixed / never was there in the first place? Damn it, no we can't be sure... not unless we run the car as close to "real life" as we can get it!
So we were reluctantly forced to take the car down off its stands, and run it under its own power. Well, nothing we could do seemed to provoke any errors.
We want to give it one last try next EV day, to make sure we've provoked the BMS as much as we possibly can. (Damn! Another day when we have to move it around under its own power
). Maybe we'll temporarily attach one of the DC/DC units to keep the auxiliary battery charged, and maybe we'll even hook up the charger as well (after all, it's also a source of PWM noise; presumably less strong than the motor controller, but we should not make unnecessary assumptions). Also, the charger process (which happens under the control of the Driver Controls software) uses BMS communications, so this will be another test of BMS comms.
Nissan Leaf 2012 with new battery May 2019.
5650 W solar, 2xPIP-4048MS inverters, 16 kWh battery.
1.4 kW solar with 1.2 kW Latronics inverter and FIT.
160 W solar, 2.5 kWh 24 V battery for lights.
Patching PIP-4048/5048 inverter-chargers.