Thanks to an astute poster in this forum from two years ago, I located a cooperative US distributor for the orange 22-pin Yazaki 7382-6100 connector in the battery management computer. This connector corrodes due to gases coming from the battery pack. I'm curious why the corrosion appears worst around pins #19, 20, and 21 of this connector. In the example below these pins are literally missing from the connector: Does anyone have access to schematics for the battery management computer and could say what voltages appear on pins 19-22? I'm betting that pin #22 is the bottom of the battery stack voltage-wise and pins 19-22 are (probably due to a design error at Toyota in the early 2000s) the opposite end of the battery stack with the highest voltages relative to pin #22. But on further examination there's a 400V electrolytic cap tied to pin #22 so it might be the opposite of what I describe: pin #22 is the top of the battery stack and pins 19-21 are at or near the bottom of the stack. My guess is that someone forgot to sequence the connector's pin-out so that adjacent pins never have more than one block voltage (14VDC) between them. The 2.5mm pin-to-pin spacing in this connector could not long tolerate 200VDC between pins. Nor could the PCB underneath the connector, even with conformal coating on it. I turned the magnification up on my microscope and can see that the skinny copper PCB tracks exiting pins #21 and #22 have served as electrical fuses and blown open as part of this failure mode. The battery block voltages from the Yazaki connector are fed to a group of 7 dual-channel Matsushita/Panasonic linear optocouplers.
Thanks, Chap. It looks like I was reinventing the wheel on my Yazaki connector study. Seems that others have pursued the matter to its conclusion. The photos of totally blown-up Yazaki connectors the posting you suggested are concerning. It would be difficult to sustain a pin-to-pin arc with only one block voltage between the pins. So that suggests that T's supplier didn't sequence his connector pins with adjacent battery blocks between adjacent connector pins.
Didn't realize that there'd been an entire book of postings about it some time ago. Everyone who works on Prii should read that series of postings. Sobering... Matt, the Texas BMS rebuilder, in his responses to Chap's comments a while ago, answered my question above about how much voltage appears between pins 21 and 22 of the orange connector. Matt's answer was 30VDC. Given that the voltage is DC, it's sufficient to sustain an arc in a narrow space. My guess is T's BMS vendor contaminated his Yazaki connector with rinsed-off reflow solder flux which has a ton of ionic crap in it. Subsequently, moisture in the air driven by the voltage differential between adjacent pins, will get the corrosion rolling.
So, to avoid it, what? Dunk the whole unit in distilled water, agitate for half an hour, and then dry thoroughly, perhaps in front of a fan? I recall trying to open that case and it had some peculiar sort of Japanese screw like fasteners in it that looked like Phillips but weren't. When none of my screwdrivers fit well and they wouldn't budge with moderate force I gave up. Because it would of course be better to pull the board out and clean it rather than to dunk the whole assembly.
That sounds like it would be a PITA to fix. Is the board still relatively flat there or did the heat pit it?
Pasadena, sorry for the delay in responding. I was out of town. My stereo microscope doesn't have sufficient magnification for me to say definitively that the damaged PCB copper tracks emanating from the orange connector have consequences in inner PCB layers. I think not, but I can test that. It's also likely that the PCB is only 2 layers, not 4. The PCB is not sufficiently complex to require 4 layers. Prior to any BMS internal fire I think these PCBs can be repaired. The orange Yazaki connector is available through Mouser and Digikey, including the matching plug. I also notice that one of the EBay sellers of fresh bus bars also includes in his kit a new orange wire harness with new plug. *** In the intervening week I've given this BMS orange connector failure additional thought. Poster "Matt" a couple of years ago on this corrosion topic remarked that the two most corroded pins in the orange connector are 0VDC (i.e. bottom of battery stack and the top of the second 14V battery block. The voltage differential between the pins is only 30VDC or so. 30VDC from a zero ohm source impedance can certainly sustain an arc but not likely start the arc. So how is the arc being initiated? I think the answer is tied to bus bar corrosion. Dr. Prius app reveals that the most stressful situation for the battery stack is high speed deceleration using regenerative braking. I saw battery currents during regen braking of more than 100 amps. Ohm's Law (I squared R) suggests that even 1 milliohm of resistance at the corroded interface between a cell's terminal bolt and the buss bar screwed to it causes 10 watts of heat dissipation. 25 milliohms of interface resistance (which is less than the internal resistance of my 2008's battery blocks) would cause 250 watts dissipation at that bolt/bus bar interface. I believe what's happening is that a heavily-corroded bus bar enters thermal runaway during heavy regen braking. The over-temp event is short (only as long as braking lasts) but the voltage across the bolt/bus bar interface briefly rises above 100VDC and arcing is initiated between the two corroded pins in the orange BMS connector. Said differently, the voltage seen by the two pins in the BMS connector is the sum of the two block voltages (30V) plus any voltage across the bolt/bus bar interface. If there's any corrosion on the other 3 bus bars associated with blocks 1 and 2, this voltage also adds. After the regen event ends, the 30VDC background differential voltage on the orange connector pins sustains the arc on the PC board. Some BMS modules flame inside as a result. Interior BMS fires are simply the final closing act of the bus bar corrosion drama. If Toyota had placed series resistors in the voltage sampling wires of the orange harness, the fires would not have happened. However, the corrosion leakage current at the two pins in the orange BMS connector would have disrupted the battery sampling and thrown block voltage errors. It's known that the corrosion at the bus bars is caused by electrolyte leaking out of the cells. The corrosion at the orange Yazaki connector is likely coming from wintertime driving episodes that also cause the vehicle's windows to fog up on the inside. The moist air in the passenger compartment blows across the cold BMS. Fine condensation probably occurs. Maybe there's even some electrolyte vapor wafting inside the battery enclosure to add to the list of corrosion accelerators.
