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Thread: Deep discharge voltage question

  1. #1
    Variable Bitrate
    Join Date
    Jun 2007
    Location
    Boston MA
    Posts
    364

    Deep discharge voltage question

    Hey everyone!
    I'm using DCDC-USB power supply in my project. The specs indicate deep discharge voltage threshold to be 11.2V. I was wondering if it's at all possible to change that? Here's why:

    I want to use Hybrid Sleep, or Sleep and cold boot:

    When the ignition is turned off, the computer goes to sleep and the power supply is to NEVER shut off power to it from the battery. This will make the computer go into stanby and stay there.

    Now, lets say I haven't cranked the car in a week and the standby mode keeps draining the battery. When the deep discharge voltage is reached, the power gets cut off completely. If hybrid sleep is enabled - the computer will resume from hibernation, if not - it will cold boot next time the car is on.

    This works great in theory, but 11.2V is not enough to crank my car - I hear the engine turn over, but it's too slow to get a good start. At the same time, I don't think I found a setting in DCDC-USB software to change that voltage, but I might be missing it.

    If DCDC-USB has this voltage setting hardcoded, are there other automotive dc-dc regulators that would work for this scenario? Hard shutoff voltage should be settable, or at least 11.8V or so.

    Thanks!

  2. #2
    Raw Wave
    Join Date
    Nov 2009
    Posts
    2,118
    "Deep Discharge" probably relates to a deep discharge battery - not a cranking battery.

    Although deep discharge batteries can be discharged 50% (down to 20 % capacity remaining) according to many specs [even if it only lasts 1 year instead of 3 @ 50% etc], cranking batteries should only be discharged 20% (80% remaining).

    Adjust the voltage cutout up by ~0.6%. If it isn't adjustable, insert a diode in line with its sensing terminal. (Almost any diode if its a dedicated sensing wire. Else with whatever current rating that wires has - eg, input power wire.)

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