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Thread: PDM and battery isolators.

  1. #1
    Smoke em if you got em! LINCOLN's Avatar
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    PDM and battery isolators.

    Does anyone know if the following wiring theories are workable? Do I need to worry about the alternator charge going somewhere? Should I be switching the positive or negative? I am trying to replicate (but not spend the money) of the cartek isolators which shut the motor down a fraction before isolation.

    Lincoln.

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    Convicted User data_mine's Avatar
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    I've got the cartek isolator,

    It breaks the negative line.

    it also has a positive line you splice into your ECU power.

    so more like your second diagram, but unsure how you'd reset the PDM having it that way.
    GT-P
    Bandsenkowagon

  3. #3
    Smoke em if you got em! LINCOLN's Avatar
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    Thanks.

    With regards to resetting the PDM that is why I thought I would have to do it like the first diagram with the B- running back to battery.

    Have asked motec and will see what they say.

  4. #4
    Smoke em if you got em! LINCOLN's Avatar
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    Got any suggestions for power relay? I was thinking one of these.

    https://www.ebay.com.au/itm/KiloVac-...oAAOSwXf1aT5Tk

  5. #5
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    Direct from the Motec PDM User Manual -

    Battery Isolator Switch
    Battery positive must generally be connected via an isolator switch or relay.
    The isolator must isolate the battery from all devices in the vehicle including the PDM, starter motor and alternator. The isolator must be rated to handle the starter motor current.
    When the battery is isolated, the engine may continue to run due to power supplied by the alternator. To avoid this, the isolator switch should have a secondary switch that is connected to a shutdown input on the ECU.
    Attached Files Attached Files

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    In the MoTeC drawing, it wont stop the alternator dump.

    The battery switch should be a relay and controlled by the PDM much like your first drawing except the relay is on the + side of the battery.

    Then with a shutdown of the engine first then the relay, load dumps will be avoided

    Your second drawing will never turn on, You will need a switch across the relay contacts to power up the PDM ground.
    Last edited by SprinterTRD; 15-06-18 at 10:36 AM.

  7. #7
    Smoke em if you got em! LINCOLN's Avatar
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    Quote Originally Posted by SprinterTRD View Post
    In the MoTeC drawing, it wont stop the alternator dump.

    The battery switch should be a relay and controlled by the PDM much like your first drawing except the relay is on the + side of the battery.

    Then with a shutdown of the engine first then the relay, load dumps will be avoided

    Your second drawing will never turn on, You will need a switch across the relay contacts to power up the PDM ground.
    Is first design OK? Or is stuff still not isolated because of B- link needed to keep PDM alive?

    I guess this is the only way? Assuming PDM output does not mind (or put a diode inline)

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    Last edited by LINCOLN; 15-06-18 at 11:07 AM.

  8. #8
    Owns a Ferrari BeverlyHillsCop's Avatar
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    /csh Racing

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    Owns a Ferrari BeverlyHillsCop's Avatar
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    And here is the motec webinar explaining how to wire it to avoid the alternator still powering the car.

    /csh Racing

  10. #10
    Smoke em if you got em! LINCOLN's Avatar
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    Thanks mate.... am I missing something or does that still not address the power flow of simultaneously isolating battery and turning off engine? (alternator power)

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    Quote Originally Posted by LINCOLN View Post
    Is first design OK? Or is stuff still not isolated because of B- link needed to keep PDM alive?

    I guess this is the only way? Assuming PDM output does not mind (or put a diode inline)

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    To be safe I would put a diode from the battery +12V to the reset PB as well as a diode in the PDM output to relay.

    This will stop any feedback in either direction if the PB is held down for any reason.

    Set the ECU and IGN outputs to turn off 2 -3 seconds before the relay is turned off to stop the load dump into the PDM.

    I must say that the PDM is protected from load dump however there is a limitation on how much energy that it can handle for a given period of time.

    The Video does not address the load dump issue. It assumes that there is enough things turned on to dissipate the energy.
    Last edited by SprinterTRD; 15-06-18 at 01:28 PM.

  12. #12
    Smoke em if you got em! LINCOLN's Avatar
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    Much appreciated. Better advice than motec.

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    Registered User glenn's Avatar
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    Quote Originally Posted by LINCOLN View Post
    Much appreciated. Better advice than motec.
    Motec video shows how it kills the power even with the alternator There is an input into the PDM that kills all power when the tyco relay coil is switched off.

  14. #14
    Smoke em if you got em! LINCOLN's Avatar
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    Yes mate I got that. Old school mechanical isolators used to use a big resistor on the other pole to abosorb the load when switching off. Again the video does not address where the alternator load goes when switching off engine and isolating the battery simultaneously. Fancy $500 cartek isolators address this issue by sending a signal to ecu and then isolating 500ms later. I would not like to wire it like motec says and switch the isolator off when under load. I sure it would let the smoke out of something.

  15. #15
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    Quote Originally Posted by LINCOLN View Post
    Yes mate I got that. Old school mechanical isolators used to use a big resistor on the other pole to abosorb the load when switching off. Again the video does not address where the alternator load goes when switching off engine and isolating the battery simultaneously. Fancy $500 cartek isolators address this issue by sending a signal to ecu and then isolating 500ms later. I would not like to wire it like motec says and switch the isolator off when under load. I sure it would let the smoke out of something.
    have had zero issues wired up exactly that way and my PDM30 has not decided to smoke up every time ive tested it.
    /csh Racing

  16. #16
    Smoke em if you got em! LINCOLN's Avatar
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    Got to know thanks for real world experience.

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