Arduino Automatic Coolant Temp Hack for Better MPG's

Discussion in 'Gen 2 Prius Accessories & Modifications' started by TheForce, Feb 23, 2011.

  1. wjtracy

    wjtracy Senior Member

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    I have not tried this project, but lately I have been downsizing my Arduino projects, putting the Arduino code into a smaller LilyTiny (ATTiny) chip for smallness. Not everything can be done this way of course.
     
  2. TheForce

    TheForce Ron Paul 2012

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    As small as the code is and as simple as the circuit is I would think the ATTiny would work well as a finished device. I have not looked into it though. I have plenty of Arduino micro's laying around so I dont really need anything else.
     
  3. mindogas

    mindogas Junior Member

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    Could you detail this problem more? Did arduino read bad temperature from analog input or digital pot didn't holded desired temperature throw transistor? This happen then ambient temperature was hot? I'm asking because eventually i will face same situation sooner or later becouse setup is the same.

    Already finished prototype of my standalone arduino:
    DSC_0784.JPG
    Done simulation and seams all things are OK:
    DSC_0780.JPG
    Tomorrow I'm going to try it in car. For longer term testing this form of device will be safer and more reliable solution. We all know whats happens with losing jump wires and accidents during hard breaking.
     
  4. mrbigh

    mrbigh Prius Absolutum Dominium

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    It is nice having this thread resurrected and with positive results
     
  5. TheForce

    TheForce Ron Paul 2012

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    The transistor is temperature sensitive and you will most likely see a difference in readings during the summer with a 100F+ degree car and in the winter when its below freezing. This may result in the fake temperature being below the 157F point needed or close to or above 190F and I think if the temp gets above 200F the fans kick on. I never got around to see what the exact range is. Just let your car set out in the sun for a few hours and see what the result is. I don't remember if the fake temp gets hotter or colder during the summer/winter. Use canned air up side down to spray the transistor to get a good idea on how temperature changes the results.
     
  6. mindogas

    mindogas Junior Member

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    Attiny or smaller package Atmega's could be used. But if I look more to Automotive family of AVR's. Thous have better temperature range, stable performance and the most of all buil-in voltage protection for short-circuit monitoring.
     
  7. mindogas

    mindogas Junior Member

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    After two days and about 10 trips i must say things are stable. The only question for me is calibration quality. In original design The Force uses +12 power line and internal arduino VREG. In this case voltage reference on car vas a little bit different then arduino's +5V, so calibrations should be different if i'm using +5V for Atmega power from ECU. The force, could you explane what temperatures there you targeted as setpoint? I will check if i'm getting same results or not.
     
  8. TheForce

    TheForce Ron Paul 2012

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    I really dont remember. I think my target was between 160-175F. As long as your not above 190F and not below 160F you should be fine because below 157F you wont get into full hybrid mode and above 200F you kick on fans and throw codes. What I was doing was forcing the engine to run to heat it up and turning on and off the ACTH to see what values it got vs the actual temp from the car. As long as you stop faking the temp when the actual temp gets to around 180F you should be Ok and not damage the car. You kind of have to play with it and see what values works best.
     
  9. mindogas

    mindogas Junior Member

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    So now my temperatures are facing 175F (or 79-80C) so it's OK. Also faking starts from about 112F (44-45C) and i'm OK with that too.

    I'm interested about other thing. If i look to arduino serial out during faking temperature near cold point i see high digital pot value:
    RTA;=;294;ADC;=;102;Average;=;101;DP;value;=;233

    If transistor are not so good on passing voltage on hot environment it will be problem because to compensate pot will go to the max 255 value. I will test this thing then i'll have laptop in may car during hot day.
     
  10. ccdisce

    ccdisce Active Member

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    Vbe will vary with temperature to the tune of 26mV/C.
    You may want to consider using a LV Rail-to-Rail OPAmp in a voltage follower mode as a buffer and remember to match the + and - input impedances for optimum thermal stability.
     
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  11. Radu Stauceanu

    Radu Stauceanu Junior Member

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    anybody have a good working version of this, i would like to build it. can I use MCP40D18T-502ET Dig. Potentiometer 7bit 5k ?
     
  12. TheForce

    TheForce Ron Paul 2012

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    Is there a reason you need to use the 7bit over an 8bit? More steps gives you more control over the target temp. You could put a few of them together to get a higher resolution though.

    I never finished this project. I ended up getting one of ccdisce's versions. It has worked great but I have had issues with it not working all the time the past few years. I never tried to diagnose the issue with it either. I've had too many things break over the years ( some car related ) and not enough time to work on any projects.
     
  13. Radu Stauceanu

    Radu Stauceanu Junior Member

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    Ok, I found some 8 bit ones.
    Did you have a problem with the car because of the mod?
     
  14. TheForce

    TheForce Ron Paul 2012

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    No issues with the mod. I just have bad luck.

    Car related issues I've had...
    1. My Hymotion battery will only give about half a charge sometimes. Dont know why and live too far away to have it looked at.
    2. My in car PC bit the dust. Sucks having to listen to the same thing on radio every day.
    3. My MFD stopped working about 5 months ago but I can still drive the car.
    I think there is a few minor things I'm forgetting but those are the major 3. Dont have the money to fix those because of other things breaking around the house.

    Good luck getting this working and let me know how it goes.
     
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  15. ericbecky

    ericbecky Hybrid Battery Hero

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    Thanks for the update The Force.

    Sidenote.. I'll likely be removing (another) dead Hymotion system next week.
    Very few of these remain working anymore.

    If you are ever up this way, give me a ring.
     
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  16. TheForce

    TheForce Ron Paul 2012

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    I doubt I will ever travel that far by car again but if I do I will let you know. Thanks.
     
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