Why the BMW i3-REx

Discussion in 'EV (Electric Vehicle) Discussion' started by bwilson4web, May 15, 2016.

  1. hill

    hill High Fiber Member

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    Bob thanks for filling in about the 75% rex issue ... as I was going through your read that did come to mind. I'd sure hope that BMW isn't so chicken $h¦t they'd raise that as a way out of traction pack warranty work. 12 volt aux battery may likely be the culprit & that's a frequent issue with Gen 1 ev RAV4s as well as the prius.
     
  2. El Dobro

    El Dobro A Member

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    The 12V battery problem has been known to pop up on the Volt, too.
     
  3. bisco

    bisco cookie crumbler

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    what is the cause?
     
  4. bwilson4web

    bwilson4web i3 and Prime

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    There is no single, root cause but a set of conditions that can lead to 12V failure:
    • charge-discharge - will lead to some electrode materials leaving the plates and becoming future short material
    • non-adaptive charge voltage - in reality a battery needs a positive voltage to absorb the charge the charge BUT it is a function of SOC and temperature. In ordinary temperatures, no problem, but high heat or very cold, the voltage drifts
    • there are other failure mechanism covered: Basic to Advanced Battery Information from Battery University
    Bob Wilson
     
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  5. bisco

    bisco cookie crumbler

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    is this because it's a bev? what is volt's problem, not enough engine time?
     
  6. El Dobro

    El Dobro A Member

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    The 12V battery is charged by the traction battery thru a DC to DC charger. Like any other car battery, they can go bad and when they do, funny things happen. I see this on the TDI boards, too.
     
  7. bisco

    bisco cookie crumbler

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    gotcha. i thought you meant they were more susceptible to going bad like prius battery.
     
  8. bwilson4web

    bwilson4web i3 and Prime

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    One trick the IONIQ is doing well is to provide 12V from the traction battery. I don't know the technical details but the potential of having traction battery energy available is an impressive approach and gets rid of that lead block, excessive weight.

    GOOD NEWS: my car just reported its status via the iPhone app! ('ET phone home.')

    Bob Wilson
     
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  9. hill

    hill High Fiber Member

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    Sounds like the defibrillator must have worked !

    .
     
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  10. bwilson4web

    bwilson4web i3 and Prime

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    Left rear motor mount bolt broke.

    Turns out a lot of parts to check and possibly replace including motor mounts, cables, and tubing. Parts are ordered. Hopefully better than original.

    Bob Wilson
     
    #330 bwilson4web, Dec 13, 2016
    Last edited: Dec 14, 2016
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  11. bwilson4web

    bwilson4web i3 and Prime

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    So I stopped by the shop to pickup some papers in the glove compartment. Talking with the techs:
    [​IMG]
    That is where the broken bolt used to be. The black, structural part is being replaced by an aluminum part. The whole motor and REx assembly will be dropped to do the repair.

    So one tech reached down and found:
    [​IMG][​IMG]
    The photo doesn't do justice but you could easily see the stress fracture, a horizontal 'bar' where it finally broke.

    Speculation, I suspect the threads provided a stress concentration point and small fractures developed. As the motor torque, both motive and regeneration rocked the transmission/motor back and forth, just like bending a coat hanger wire back and forth, the cracks grew until it failed.

    Sad to say, they had to order a special wiring assembly . . . from Germany. Looks like it will be down at least another week. Maybe I'll get it back for Christmas. <grins> In another 12 hours, my wife, her dogs, and I would have been starting a 1,600 mile drive to Arizona.

    I mentioned seeing 5mm and one 6mm tread depth and thinking after 10k miles, I'm down 40%. I used the Tire Rack specs for a new tire tread depth. The tech told me these tread depths are 'like new.' Huh!

    Bob Wilson
     
    #331 bwilson4web, Dec 16, 2016
    Last edited: Dec 16, 2016
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  12. bwilson4web

    bwilson4web i3 and Prime

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    This YouTube shows the type of motion in the engine compartment of an electric-only BMW i3:


    So I've ordered a special accelerometer: GCDC Human Activity Monitor

    HAM-IMU
    • 3-axis 16g digital accelerometer sensor
    • User selectable sample rates of 12, 25, 50, 100, 200, and 400 Hz
    • 16-bit resolution
    • Finite Impulse Response Filter to improve data quality
    • 3-axis . . . gyroscope, magnetometer
    • User selectable sample rates of 50, 100, and 200 Hz
    • Quaternion orientation solutions based on accelerometer and gyroscope data
    Affixed to the motor housing, these metrics can be correlated to driving style and road conditions. You don't know what you'll find until instrumentation and analysis. Hopefully, the magnetometer will give an indication of the power to and from the motor.

    Bob Wilson
     
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  13. bwilson4web

    bwilson4web i3 and Prime

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    So this is what the left and right motor mounts look like:
    [​IMG]
    [​IMG]

    Here is the underside of the 2" receiver:
    [​IMG]
    [​IMG]
    I wonder how it might impact removing the transmission/motor and REx.

    Bob Wilson
     
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  14. LasVegasaurusRex

    LasVegasaurusRex Active Member

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    I imagine it's just a big ol' DC to DC converter running off the traction battery. Can anyone confirm?
     
  15. bwilson4web

    bwilson4web i3 and Prime

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    I could see two: a small, highly efficient one, < 1-3 W, and; 1.5-2.0 kW for normal operation.

    Bob Wilson
     
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  16. Trollbait

    Trollbait It's a D&D thing

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    No reports with details. Most articles treated not having a 12 volt battery as a minor detail. I've seen a "separate 12 volt tap", and one module of the battery dedicated to 12 volt needs mentioned in different articles.
     
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  17. bwilson4web

    bwilson4web i3 and Prime

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    I got a call that the parts arrived and they have the transmission/motor and REx down . . .
    [​IMG]
    Here we see the rest of the bolt in the transmission/motor mount. You can clearly see there was a rocking motion that just like a coat hanger wire, flexed and broke the bolt.

    The new mount frame is substantially larger, a solid aluminum piece:
    [​IMG]
    Notice the "U" shaped channel so instead of putting all the stress on the bolt, the shoulders of the "U" will transmit the forces to a much larger area.

    Here are the two new bolts and the remaining bolt from the engine side:
    [​IMG]
    Substantially larger, the new bolts will be substantially stronger. If I remember correctly, the strength increases by the the square of the diameter.

    The original bolt had a smooth shoulder which would minimize the stress on the bolt head:
    [​IMG]
    However, the stresses deformed the bolt attachment piece enough to lead to vibration and fracture in the threaded part, narrowest part of the bolt. In contrast, the new bolt is substantially larger and threaded the whole length.

    There is a new mount piece on the engine side:
    [​IMG]
    Again, substantially larger piece with the "U" shaped shoulders to take up the stress. It has to be "U" shaped as the engine is raised to fit into the body/frame pieces.

    The part that came from Germany was the air conditioner (AC) hose:
    [​IMG]
    When the mount failed, everything dropped and the refrigerant hose broke . . . and leaked it out. So part of the repair, after the hose replacement, is to draw a vacuum and recharge the AC. Had the repair been done under a recall, the refrigerant leak would not have happened and replacement hose would not have been needed.

    From the rear, here is the transmission/motor assembly and REx:
    [​IMG]
    Draped in the foreground is the cabling to the tail lights. I have a 2" receiver hitch but it has no lights. To add lights, I'll need a 12V power, 'relay' box that amplifies the light signals to generate the typically much higher current, trailer lights.

    Finally, here is a neat shot of the 5-point attachment holding the wheels:
    [​IMG]
    Truly brilliant, these five, links with rubberized bushings hold the wheels semi-rigid and aligned. Yes, there will be small displacements from bumps and normal operation but the 5-points bring the wheels back into alignment.

    Final repairs and assembly are in progress and I told the tech,"Take your time and do it right. I have my Prius which is working perfectly fine."

    On the way out, I suggested the service writers and staff take a minute or two to see what the repairs look like. I got the impression this is the first one in this area.

    Bob Wilson
     
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  18. bisco

    bisco cookie crumbler

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    at least you don't need a 12v.:cool: what happened with the hitch?
     
  19. bwilson4web

    bwilson4web i3 and Prime

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    Actually the 12V is being replaced too. When the car failed, it was obvious there was a load so when I came back Saturday morning, the 12V was dead.

    It got below freezing that night and over the weekend. To get the car around, the techs had to use a jump box. I usually expect 5 years of service but given what happened with freezing temperatures while discharged, I'm not surprised that the 12V is being replaced too. For what its worth, it is a motorcycle battery.

    The hitch was not a problem. It has just a couple of bolts holding it on they took it off easily. It turns out it didn't 'hold' the transmission/motor and REx off the road. Another expensive part, KLE that doubles the charging rate on AC charging, also helped hold everything inside the car . . . and of course the various hoses and electrical wiring. Once again, the expensive parts protected the cheaper ones.

    Bob Wilson
     
    #339 bwilson4web, Dec 22, 2016
    Last edited: Dec 22, 2016
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  20. bwilson4web

    bwilson4web i3 and Prime

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    It was a dark and stormy night . . . 42% SOC and charging at 4%/hr it would take 15 hours to reach 100%. So I decided to drive down to the high-speed DC charger. Hindsight, I could have just used the REx around town and stayed at home. Regardless, I met a Tesla model X owner with temp tags getting a charge to go home.

    A Leaf owner, he recently added the Tesla X which still had temp tags. He put it under his business so he can rapidly depreciate it. But he needed a charge to reach home and at '100 miles per hour', the 30 minute charge would meet his needs. This suggests since using a 40 kW charger, his typical usage is ~400 wHr/mile. He was using a CHAdeMO to Tesla adapter.

    I showed him my BMW i3-REx and how we'd used the engine to do a 700 mile trip to Oklahoma ... using the truck stops for refueling every 80 miles and relief for my wife and her dogs. I had used 'PlugShare' and only found a few 'Tesla NEMA 14-50 outlets along the route' and not enough to handle the EV range. He related taking four days to drive his Leaf from Florida to Huntsville and the growing SuperCharger network that means he can do the Florida drive in one day.

    I'm still skeptical about long distance, battery only but it is less bad.

    Bob Wilson
     
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