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Overheated Inverter - Need Expert Opinion

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by PDWhite, Jun 25, 2009.

  1. PDWhite

    PDWhite Junior Member

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    A few days ago, my 2005 Prius suddenly showed a number of warning lights, including the master clear. This was a first for my Prius. Never happened since it rolled of the showroom floor 53,000 happy miles ago.

    The dealer replaced the 12v battery which didn't fix the problem. On the way home from the from the repair, it overheated again, bigtime! -- It shifted into neutral and then wouldn't budge.

    The service manager took it for a test ride and not so unexpectedly, it happened again. This time the car would not power down. THe lights on the console went on and off. A day later they called and told me I had a bad inverter coolant pump and it would take 4-5 days to get a replacement.

    Now the question(s): What is likelihood that overheating the inverter several times could cause it to fail prematurely?

    The inverter is a very expensive part to replace and I have approximately seven thousand miles left before my drive-train warranty expires. I am also aware that it is very difficult to tell if an overheated solid-state component has been damaged until it actually fails. This is often the case with power supply components.

    I am afraid my overheated inverter may hang on just long enough to get past the warranty period and die. :eek:

    An expert opinion is needed here:

    Should I insistthat they replace the inverter, too?

    Please RSVP and let me know what you think...


    Thanks,

    PDWhite
     
  2. qbee42

    qbee42 My other car is a boat

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    Overheating is not good for electronics and can cause premature failure. You already know that or you wouldn't be posting this question. The real question is whether your inverter has been damaged. If it isn't throwing a code, there is no way to prove damage. I can't see a dealer or Toyota agreeing to replace an expensive part that has not failed. That said, if you don't have any codes, your inverter is probably fine.

    Tom
     
  3. donee

    donee New Member

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    Hi PD,

    I doubt your going to get them to replace the inverter. Possibly you could get them to extend the waranty on the inverter, based on the possible effects of a waranteed item that failed early.
     
  4. galaxee

    galaxee mostly benevolent

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    if there is no evidence of damage to the inverter and you choose to insist it is replaced, you will be paying for the replacement.
     
  5. PDWhite

    PDWhite Junior Member

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    donee, (& others,)

    Thanks for your advice. Considering your replies, I think it would be best to put the dealer & Toyota on notice that this overheat has occured and that if the inverter dies (resonably) after the expiration of the 60,000 mile drive-train warranty, I will still expect it to be replaced for no charge. -- I'm hoping that will fly. :confused:

    What say you on this?

    -pdw
     
  6. Patrick Wong

    Patrick Wong DIY Enthusiast

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    The inverter is covered by the 100K mile hybrid system warranty. So you've got coverage on that component for a reasonable amount of additional time and mileage.
     
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  7. Celtic Blue

    Celtic Blue New Member

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    Make sure that the problems and potential long term impact on the inverter are documented by the dealer. It doesn't make sense to replace it at this point. However, it if fails later due to the other warranted part that failed, you will have a pretty good basis for replacement. Of course, as Patrick noted, you already have a very long warranty on the inverter, but it doesn't hurt to have something to reference back to if they try to blame something on you later...

    Do they do a flush and replacement of the inverter coolant system when they replace the pump? If not, then it really should be done. What about the transaxle fluid? Would it get a bit toasted since MG1/MG2 lost coolant and ended up in lockout? Seems like it would be prudent to flush it as well.

    Seems like Toyota needs to give us some decent gauges so that we have some warning when parts like the coolant pump are failing. It's silly to have more ECU's than you can even list, and virtually nothing in the way of an interface for them. Even their dealer shops have trouble with stuff like this. A simple temp. readout on the inverter coolant would eliminate a lot of problems and guesswork.
     
  8. 2009Prius

    2009Prius A Wimpy DIYer

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    So I suppose Scangauge II would not read the inverter coolant T?
     
  9. PDWhite

    PDWhite Junior Member

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    Shawn,

    Thanks for the good advice. And I agree with you 100% regarding the need for improved built-in monitoring capabilities. - The Toyota Service Center had a hard time diagnosing the problem because the most recent error codes disappeared when the power died.

    As for replacing "warning lights" with guages; there is a good reason why they are called "idiot lights..." BTW: I am seriously looking at the ScanGuage II as a potentially good alternative.

    I am also looking for a good 3rd-party repair warranty. I've found one, but need to find a few more for comparison...

    My thanks to everyone! :rockon: -pdw
     
  10. JimboK

    JimboK One owner, low mileage

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    If it had the proper X-gauge set up for it, it could, but to my knowledge no one has figured out the X-gauge code for it from the CAN data stream.
     
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  11. richard schumacher

    richard schumacher shortbus driver

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    Ask the dealer whether SSC 50P needs to be performed or repeated.
     
  12. kohnen

    kohnen Grumpy, Cranky Senior Member

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    I realize this is about 6 months too late, but here goes...

    You're fine. The behavior of the system (all of the warning lights) tells you that there are temperature sensors in the inverter that cause the computer to shut it down before there is actual failure of the system.

    The high-power parts in the inverter are IGBTs (Insulated Gate Bipolar Transistors). These parts can function well above 100 degrees C - common testing temperatures of these parts for qualification testing is on the order of 140 degrees C, so there's quite a bit of margin.

    If the IGBTs themselves overheated, they would short (catastrophic breakdown) causing the bond wires attached to them to blow open.

    Because your inverter is still working, you didn't damage anything. You might have marginally reduced the component reliability, but not significantly so.

    If it were my car, I wouldn't bother having them replace the inverter.

    (I work in the extremely high reliability electronics business - stuff we put out has to run for 15 years straight with NO possibility of repairing it, so we're pretty anal about this sort of stuff).
     
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  13. Mjolinor

    Mjolinor New Member

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    It should be pretty easy to measure the gate current. If there is any damage at all then this will show as a gate current increase, problem is you need a reference or the IGBT datasheet.

    I wonder if it is actually measured by the ECU.
     
  14. kohnen

    kohnen Grumpy, Cranky Senior Member

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    I don't think so. The IGBT has an insulated gate (meaning that there is effectively no DC gate current). The Field Effect Transistor (FET) structure of the IBGT isn't the thing that breaks down during overheating - in fact, FET structures are well-behaved during overheat, and tend to decrease in current (because they are majority carrier devices).

    During overheating of a bipolar transistor, the current increases (because the resistance of a minority carrier device has a negative temperature coefficient). Unless the circuit is otherwise current limited, this causes more power, more heat, and even more current, until the transistor blows.

    When the transistor is overheated and overcurrented, the emitter region punches through to the collector region, and the transistor goes into secondary breakdown. At this point, the transistor fully conducts and can't be shut off. Unless the collector current is otherwise limited, the bond wires of the transistor will blow (spectacularly I might add).

    None of this happened though - the thermal sensors in the inverter told the computer to shut things down way before this happened. Don't worry, be happy, drive the car.
     
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  15. Mjolinor

    Mjolinor New Member

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    Note to self, don't post before breakfast and stop posting crap.

    :)
     
  16. 2009Prius

    2009Prius A Wimpy DIYer

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    Where are these temperatures measured? I imagine there is a large temperature gradient from the active region to the surface of the device packaging and on to the coolant.
     
  17. kohnen

    kohnen Grumpy, Cranky Senior Member

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    The temperatures that I mentioned would be junction temperatures. Those are the temperatures within the devices themselves.

    There will be some thermal resistance between the part and the cooling plate, but I'd be surprised if it was anywhere near one degree per Watt.

    The neat thing about the design of these switching systems is they waste very little power. Either the transistors are off and the current is ~ 0 Amps, or the transistors are turned strongly on, and the Voltage across them is small. Either way (since the power consumed in the transistir is Current x Voltage) the transistors themselves burn very little power while controlling lots of juice.

    But the key point is my original one: The inverter's fine - drive it and be happy. I would.
     
  18. 2009Prius

    2009Prius A Wimpy DIYer

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    This is good info to know. Thanks again! :)