The battery fires at ECU sense connector thread

Discussion in 'Generation 1 Prius Discussion' started by ChapmanF, Mar 19, 2015.

  1. landspeed

    landspeed Junior Member

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    I may well have detected this problem at an early stage. I have a 2008 NWH20, about 160,000 miles, and it has been parked up for a few weeks (still using it a little but not much). I have a Nissan Leaf which I have been using for my commute - work has been so busy I don't need to drive any further (for now).

    I fired up the Prius - red triangle of death - no big deal (still original 12v battery). However it was a bit different; the ICE stayed on, it kept charging the HV battery which went from full, to 1-bar, while charging. It had been fairly well charged when I last used it - and 12v battery was disconnected.

    The error code P0AFA came up; looking at everything in more detail - the cells are well balanced, but 'blocks' 1 and 2 (out of 14, so basically 1,2,3,4 of the 28) keep switching back and forth between positive and negative approx 16v (low SoC). They also charge more slowly. The car worked but now, the 'ready' light flickers on and off then stays off, and it can only go to neutral.

    I am planning to see if I can remove the upper case of the battery 'in situ' and see what the state of the voltage sensors are. The car has been fine and no HV battery problems have every occured before now. Hopefully it doesn't catch fire before I can figure out what is going on!
     
  2. bwilson4web

    bwilson4web i3 and Prime

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    Now if each sense wire had a 1-10k ohm resistor at each battery tap end, there would be no fire hazard. There would not be a low resistance path to short out the huge currents a module-to-module short can provide to 'let the smoke out.'

    Bob Wilson
     
  3. landspeed

    landspeed Junior Member

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    My thoughts exactly!

    Am about to get to the HV ECU. Looking at photos of the circuit board, each pin has a 1kOhm resistor on the circuit board. If my connector isn’t destroyed, I plan to get a new basic connector of some type, splice it in, and basically have a way of ‘inserting’ another connector between the two. Then, I plan to remove all the 1k ohm resistors on the HV ECU, and instead put 1k ohm resistors into this new loom which inserts between the sensor harness and sensor plug. Labelling it up and labelling up the ECU as ‘warning - DO NOT USE without special loom’ will do for DIY safety.

    Have also thought of a fuse for each line. 100mA fuses may do the job but may put the voltage reading off by up to 1% (or 0.1%??). These could go into a special loom too - would prevent that massive plasma arcing in some of the earlier photos.

    Anyway, off to check this ECU - maybe it isn’t what I think at all!

    I’ve had a few ideas about the reason for why these pins fail - will examine the motherboard once it is out - it may be there is a way to fix this problem for good!
     
  4. landspeed

    landspeed Junior Member

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    Edit : thinking about it - the short circuit must be ‘on the ECU’ side (be it the pins inside or outside - eg bridged by corrosion). As the connector keeps its pins apart (until it melts of course). The corrosion must be the short circuit issue - will do resistance testing at some point. I will look at the pins in great detail as there may well be another issue that could initiate unexpected plasma short circuits and then be gone after the event!
     
  5. landspeed

    landspeed Junior Member

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    Okay Houston, we’ve had a problem here.
     

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  6. landspeed

    landspeed Junior Member

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    The white dot inside the connector is light shining through where the connector has burnt through. Am inside sitting in front of air con (New Zealand summer). It appears that basically the NWH/XW20 and earlier with prismatic batteries have a major problem. My mum’s car which I will fix in a month probably has the same thing (NWH11 Prius). I’ve bought a second hand battery pack in my city, not inspected, $600US - it will be worth it for spares or forensic investigation. I will now enter forensic mode! And open the ECU.....

    The $600US battery has an ECU so I am going to inspect and swap, then the orIginal battery and ECU in this car (New Zealand brand new from dealer, no third party mods to battery ever.....) can be inspected and evaluated in detail!
     
  7. landspeed

    landspeed Junior Member

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    PS the pin in the corner is still present, just very charred - and is the main player it seems. This car never had any battery faults until 2-3 days ago, last power up was 2 weeks prior, drove it a bit, full charge cycle (on the road). So this is of concern.
     
  8. ChapmanF

    ChapmanF Senior Member

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    Hey, that's just what I was thinking back in 2008!

    Wish I'd sold Toyota my idea. :)

    That sounds like it might be more complicated than necessary, and at the same time still not be the optimal placement for the resistors.

    Since Toyota hasn't told us what the input impedance of their voltage-measuring circuits is, we're not yet in a position say how much the readings would be dropped by adding a given resistance in series. (We know the impedance is at least 1 kΩ, from seeing the 1 kΩ series resistors sitting there, but it may be much higher than that; voltmeter inputs usually are.)

    A little experimenting could be in order ... build up a battery where, in place of one block (or more than one), there's a stable 14.4-ish voltage source, and see how much the ECU readings change when adding a few different values of resistance in series.

    It could turn out that adding 1 kΩ in series (even without drastic mods like removing the resistors in the ECU) would make a difference so small it wouldn't matter.

    My favorite design for a harness would be to have the resistors right out at the battery ends of the wires. End of wire spliced to resistor, ring terminal spliced onto resistor, ring terminal attached to battery.

    That would protect from damage anywhere along the harness. I don't see the need for a fuse, because just having the resistors there would limit the worst-case fault current to about a fifth of an amp, in a short between the worst choice of two wires.
     
  9. landspeed

    landspeed Junior Member

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    I agree. I am going to repair this HV ECU!!!

    Question - does the NWH11 ECU swap with NWH20? I am getting a spare NWH20 Ecu. It doesn’t matter if your guess is wrong but I am going to take the spare ECU back home anyway!

    Also, the pins that have experienced such high voltage that they have literally melted are not limited to the pin in the corner.
     
  10. landspeed

    landspeed Junior Member

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    On further exploration, my ECU has a pin melted internally in the middle. In fact about 3-4 pins are melted on the actual motherboard; will do more research as the connector on NWH20 may be different to NWH11 or 10. But probably not much different!!!
     
  11. landspeed

    landspeed Junior Member

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    On even further exploration, it can be seen that the final ‘catastrophic’ shorting occurs inside the ECU (on the thick metal pins that link the voltage sense connector to the motherboard). This shorting does not seem to be a fault of Toyota, and if it is what I think it is, it is of concern to many of us!
     
  12. landspeed

    landspeed Junior Member

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    On even more detailed visual exploration, the culprit is obvious. It is not Toyota’s fault but technically might require replacement of all ECUs up till 2008 (NWH20). I need to do more research but - if you get sudden anomalous cell readings, fluctuating readings, please get a brand new ECU from Toyota. If you are a DIY person who knows your way to avoid death by electrocution from the battery, you may wish to consider disconnecting the ECU immediately, then consider your options.

    An open-source ECU seems to be required. It appears the same ECU was used in version 11 / 20 priuses, probably also ‘prius C’ / aqua. Maybe more. If anyone knows how the HV Battery ECU communicates over the CANBUS ‘ethernet’ please get in touch (is it paired or encrypted?).
     
  13. landspeed

    landspeed Junior Member

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    I will be away for a bit, but, these two photos show two things; the first shows something extreme happened - an extreme thermal event, yet the HV ECU kept ‘working’; the second shows that the connectors were not overheated in the underneath of the motherboard........
     

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  14. landspeed

    landspeed Junior Member

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    I've made a thread about the diagnostic stuff I've done so far; to avoid spamming this thread. I would be interested to know your thoughts (particularly the implications of how pin 5 has totally burnt up on mine which, given the lack of the usual pin 22 corrosion, may allow further investigation as to the root cause of all this!)

    Troubleshooting HV ECU burnt connector (causes P0AFA, red triangle, 'replace hybrid battery' etc | PriusChat

    Would be good to hear your thoughts on this! (I think, for one, putting some resistors before the voltage wires enter the ECU makes a lot of sense, maybe even just some fuses!)
     
  15. ChapmanF

    ChapmanF Senior Member

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    I'd go with resistors. Really more predictable than fuses ... you know all the voltages involved, so knowing the resistance, you can calculate the maximum current that could flow in any fault, and keep it well below the temperature limits of the wires and connectors ... as opposed to having a higher current flow and counting on the fuse to then cut it off.

    Resistors are probably cheaper, too, and come in a nice form factor for just crimping to the ring terminals. (Though some non-replaceable small fuses do come in a similar axially-leaded package. Those are probably not the kind of fuses capable of interrupting this battery's available fault current, though.)

    I would watch with interest any effort to experimentally determine the ECU inputs' actual impedance, as suggested in #88.
     
  16. landspeed

    landspeed Junior Member

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    I agree re: resistors; basically I2r, and be obsessive about where they go / electrical isolation / working out max temp. I do like the idea of fuses, but it would require a dismantling of the car to get to the HV ECU. But I agree - I doubt they could tolerate the currents involved (given the thick connectors inside the ECU got vaporised, likely in a plasma arc, a fuse will likely do an even better job at keeping the arc running).

    I should add : I personally believe the cause is something which is unpredictable, which worsens over time, worsens with thermal cycling, worsens with mechanical stress, worsens with humidity, worsens with exposure to some chemicals. Specifically ‘Tin Whiskers’. That is the only thing I can thing of for my pin 5 short. Just my opinion for now though :) But, reading some NASA papers where they take actual tin whiskers, silver-solder them to ‘Jacobs ladder’ test rigs (like our connectors), then the plasma that is created can be created well below the voltage between sets of pins, and well below the current.

    I want to recoat the whole connector in lead solder, repair the burnt sections, repair the area where the circuitboard arched back to a pin, and see if it works. But - I will wait for my secondhand ECU to arrive; I want to use a microscope to look for tin whiskers on this ECU (note - if they didn’t use tin, then zinc whiskers etc!)

    Once my car is back in the road I will do some impedance tests on this ECU!
     
  17. landspeed

    landspeed Junior Member

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    A possible further clue; I took the a good battery computer from another battery and plugged it
    In; the ECU didn’t burnt out despite the damage to the connector on my battery; in fact it (and the battery) worked fine!
     
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