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Thread: Electronic Otterstat

  1. #1
    Senior Member Bitsyncmaster's Avatar
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    Location:  Leonardtown, MD

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    Electronic Otterstat

    I've started playing with LMT01 temperature sensor to design an electronic otterstat. This sensor can work to 150 deg. C so it should be fine running in our coolant. It is a digital pulse stream so it will be less susceptible to electrical noise. Accuracy is 0.5 deg C so I do not need to do any calibration.

    I've prototyped this sensor to a micro and wrote code to read the sensor value. My plan is to have the user set the "trip" temperature via a DIP switch. I also plan to put an audio warning (buzzer) if a problem occurs (coolant temp running to high).

    The plan is to just insert the sensor into an existing coolant pipe and the two small wires would get clamped between the existing hose and pipe. I'm interested in testing the "otterstat" in the return coolant line to see if that is a better way to turn the fans on and off.

    I've never had a problem with my otterstat in my car so really did not consider the need for this project. But I have been reading where some owner are have otterstat failures.
    Last edited by Bitsyncmaster; 04-01-2017 at 07:52 AM.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  2. #2
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    Definitely interested. My otterstat is failing intermittently and Toby's solution has been out of stock for a while.

  3. #3
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    Aweet

    Wow. With the availability issue with this part, it's the right time to intro this Dave!

  4. #4
    Senior Member Bitsyncmaster's Avatar
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    Pretty much done with my testing of the temperature sender. I set my prototype software to turn an output on at 80 deg. F and off at 75 deg F. So I could just put my finger on the sender to warm it up and see the output turn on. Then let it cool to room temp and see the output turn off.

    Have been thinking of the best way to package this unit so I can get a prototype circuit board made to run testing in my car. I need access to a DIP switch and my "buzzer" needs to be exposed to hear it. Right now I'm thinking of making it the size of a relay so it can plug into a standard relay socket. I have two spare relay sockets in my relay compartment (the AC panel light dimmer and the red resistor are blank). I need the 5 pins connected for the unit. So my plan is to have a double PCB board and the top board will remain exposed and the space between the boards will be potted.

    I was thinking the buzzer would sound 3 short notes to warn if your coolant is getting to hot. And maybe another three if the temp keeps climbing. I will also sound a warning if I detect a failure like the temperature sender is bad. With a failure I will keep the fans powered along with the warning.

    If you have any other ideas, let me know.
    Last edited by Bitsyncmaster; 04-03-2017 at 02:27 PM.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  5. #5
    Senior Member vwdmc16's Avatar
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    How about a tie in to your solid state fan fail relay that flashes the fan fail light along with the buzzer.

  6. #6
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    sweet

    Go for it Dave!

  7. #7
    Senior Member Bitsyncmaster's Avatar
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    Quote Originally Posted by vwdmc16 View Post
    How about a tie in to your solid state fan fail relay that flashes the fan fail light along with the buzzer.
    Both Fan Fail and the Electronic Otterstat use all 5 pins of the relay socket. So a hard wire improvement is not possible. Putting WIFI into units would make the price go to high.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  8. #8
    Senior Member
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    I have suffered Otterstat failure and very quickly the engine overheated, to the point of hissing and spitting out of the expansion tank overflow hose, before I could turn it off.

    I can't wait to see what you come up with!

    In the meantime I have a new Otterstat, which I don't trust so have a manual fan override switch in the cabin in case the Otterstat doesn't do its job. Which is only a matter of time.

    Possible do you think to have a free floating thermocouple in one of the accessible coolant pipes without leaking under pressure?

    Great work as always...

  9. #9
    Senior Member Bitsyncmaster's Avatar
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    Quote Originally Posted by Horsebox View Post
    I have suffered Otterstat failure and very quickly the engine overheated, to the point of hissing and spitting out of the expansion tank overflow hose, before I could turn it off.

    I can't wait to see what you come up with!

    In the meantime I have a new Otterstat, which I don't trust so have a manual fan override switch in the cabin in case the Otterstat doesn't do its job. Which is only a matter of time.

    Possible do you think to have a free floating thermocouple in one of the accessible coolant pipes without leaking under pressure?

    Great work as always...
    I think Toby's adjustable unit does a free floating sensor and the tubing is clamped under the hose. My sensor only has two wires and I will probably use 20 AWG Teflon insulated wire which will hold the free floating sensor.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  10. #10
    Senior Member Bitsyncmaster's Avatar
    Join Date:  May 2011

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    I finished the PCB layout and ordered one "barebones" board. That lets me get a working unit into my car so I can verify the hardware and software. My only concern is maybe electrical noise from the sensor. If I get noise I can filter it with software or maybe a hardware circuit change.
    Dave M vin 03572
    http://dm-eng.weebly.com/

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