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HELP: Whats the impedance of the PTC heater?

Discussion in 'Roadster 2008-2012' started by Logticom, Sep 7, 2019.

  1. Logticom

    Logticom Roadster Sport EU #243

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    Winter is coming here in the Netherlands and I am working on my cabin heating to start working again.
    I / we think the 400v controller is working fine, but the PTC heater is not working as it should be working.

    So we did some more research on the wiring to the PTC heater:

    upload_2019-9-7_22-5-48.png

    We are measuring around 390 ohms (on the red dots), and it should be around 70 ohms to get enough power at 400V. The other pins (blue dots) are shorted. We think this should be correct? Is it? (the PTC heater was at ambient temperature)

    Besides this I think there could be something wrong with a sensor that is malfunctioning and causing the heating control to think it too hot, like CSPHD mentioned here:

    Heating system has stopped functioning

    And John here:

    Heating system has stopped functioning

    Is there anyone who van measure the impedance of the PTC heater?

    My next step will be to take a better look at the HVAC assembly, but it would be great to get more info first. Thanks!
     
  2. X.l.r.8

    X.l.r.8 Supporting Member

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    2 of those wires function as the HV loop. I cannot check till tomorrow as I have my old one on the bench if no one can got it to you sooner.
     
  3. X.l.r.8

    X.l.r.8 Supporting Member

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    Is that not to the HVAC? (Plastic box below the 400v controller
     
  4. gregd

    gregd Active Member

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    The resistance is not linear with temperature, so a calculation of "70 ohms to get enough power at 400v" may not be relevant. That said, PTC means "Positive Temperature Coefficient", so does "positive" mean that the resistance goes up or down? I think up, which would be the safest as it makes the system at least somewhat self-regulating. Either way, there's no way to calculate what it should be at room temperature.
     
  5. Logticom

    Logticom Roadster Sport EU #243

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    @X.l.r.8 Thanks! I am very curious what you will measure (and if this helps me with more info on my problem). Please let me know when you have measured and what your aprox ambient temp was.
     
  6. Logticom

    Logticom Roadster Sport EU #243

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    @X.l.r.8 Yes, thats the HVAC assembly. The PTC heater is in there.
     
  7. Logticom

    Logticom Roadster Sport EU #243

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    @gregd Thanks for your input! I did not make the calculation of 70 ohms myself, but will share your thought with Peter (who is helping me with the electronics in the car).

    I think your right about the resistance going up when the PTC heater heats up and when the PTC heater is hot the power goes down.
     
  8. X.l.r.8

    X.l.r.8 Supporting Member

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    Good and bad news. The reading I got with ambient temp 15 degrees C but it’s in the garage so 13-15 would probably be more correct full continuity between 2 opposing pins, and 567 ohms.
    That being said. I just had that part replaced as it stopped my car from charging due to a ground isolation fault. So maybe not the best one to measure. I’m in the S today so cannot even check. However my heat and AC worked perfectly, it just wouldn’t let me charge.
     
  9. Logticom

    Logticom Roadster Sport EU #243

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    Thanks! I would think lower ambient temp, lower # omhs. But maybe I am wrong and it doesn't work this way (with lower temps). I think you are right about it not being the best one to measure, since your hvac assembly just got replaced. I will continue my search.
     
  10. X.l.r.8

    X.l.r.8 Supporting Member

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    ill be in the garage tomorrow and I can measure the brand new one
     

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