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Thread: Electronic fused fan fail sales on hold

  1. #11
    Senior Member
    Join Date:  May 2013

    Posts:    120

    Quote Originally Posted by Bitsyncmaster View Post
    Yes the otterstat and it's wiring are critical. I need to do some changed to my engine harness and I was thinking of changing those two wires with new pins.
    Definitely worth doing. My otterstat connectors were pretty much new but the otterstat itself had packed up. I proved it by removing it from the car and boiling it in a saucepan whilst it was connected to a DVM set to measure resistance. Open circuit all day long.

    I think there is a lot to be said for running wires into the cabin and having a separate switch to manually override the otterstat in the event that the temp gauge starts increasing and the fans don't come on automatically.

  2. #12
    Senior Member Bitsyncmaster's Avatar
    Join Date:  May 2011

    Location:  Leonardtown, MD

    Posts:    6,317

    My VIN:    03572

    Units back in stock. Hold relased.

    The op-amps I was using on the prototype all worked 100% replacing the 20 TI parts on the build of the first 10 units. I may have just got a bad lot of TI parts but now I don't think I will ever use those TI parts again.

    Anyway, I kept the calculated current values because testing the lot of 10 units proved the accuracy was very good.

    Here is the recorded current results of those first 10 units. I measured three currents, the 4 amp minimum current for fan fail flash, the 18 amp maximum current for fan fail flash and the 20 amps "fuse" trip current.

    #1 pin 85 = 4.1, 18.1, 20.2
    pin 86 = 4.1, 18.2, 20.1
    #2 pin 85 = 4.1, 18.3, 20.4
    pin 86 = 4.1, 18.1, 19.8
    #3 pin 85 = 3.9, 17.9, 20.0
    pin 86 = 3.9, 18.1, ??.?
    #4 pin 85 = 4.0, 17.9, 19.9
    pin 86 = 4.0, 18.1, 20.1
    #5 pin 85 = 4.2, 18.2, 20.4
    pin 86 = 4.0, 18.0, 19.9
    #6 pin 85 = 4.1, 18.3, 20.4
    pin 86 = 4.1, 18.2, 20.2
    #7 pin 85 = 4.1, 18.1, 20.2
    pin 86 = 4.2, 18.5, 20.4
    #8 pin 85 = 3.9, 18.0, 20.1
    pin 86 = 4.1, 18.3, 20.3
    #9 pin 85 = 3.9, 18.0, 20.0
    pin 86 = 3.9, 17.9, 19.8
    #10 pin 85 = 4.0, 18.1, 20.1
    pin 86 = 4.1, 18.2, 20.1

    Voltage drop over each leg at 15 amps is 0.050 volts. Very little change in voltage drop after running the double 15 amp loads for 30 min. The current sensing value did not change at all after the 30 min. run.
    Dave M vin 03572
    http://dm-eng.weebly.com/

  3. #13
    Senior Member Bitsyncmaster's Avatar
    Join Date:  May 2011

    Location:  Leonardtown, MD

    Posts:    6,317

    My VIN:    03572

    The relay ground failing is really a larger problem then I thought. It's not really something you can test with an ohmmeter. A marginal ground connection will show up when a current is drawing after that bad connection. The fan relay is at the end of that daisy chained ground buss so when the fan relay turns on current flows in the ground and a bad connection makes the ground voltage rise. Probably a good test is to have the AC running and to measure the voltage on the fan fail ground pin.

    My electronic fused fan fail uses MOSFETs to turn each fan on and off and without a solid ground the gate voltage can be to low which overheats those MOSFETs.

    The old fused fan fail did not have MOSFETs so if the ground was lost it only upset the fan fail light circuit. I dropped the fused unit but it did have that advantage. The fused jumpers also don't use the ground on the fan fail socket. I wonder if the OEM fan fail would fail with a bad ground.

    So I may require using my electronic fused fan fail the user has to also install my front relay ground buss.
    Dave M vin 03572
    http://dm-eng.weebly.com/

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