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Thread: Where's the best place to get 12V?

  1. #1
    Newbie
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    Where's the best place to get 12V?

    I'm new to car electronics. I'm interested in putting an android tablet in my car and use a switching regulator to drop down 12V to 5V to charge the tablet.

    I'm a senior electrical engineering student but know next to nothing about car electronics, although I do have some experience with other electronic design.

    Do you guys generally just get your 12V directly off the battery terminals?

    Thanks

  2. #2
    FLAC SNOtwistR's Avatar
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    Hi and welcome to the forum! You can get from the battery directly if thats your preference. If you are removing the factory radio you can get 12v always on and sometimes 12v switched and ground from the radio harness. You can even get from the radio harness even with radio installed. Lighter socket is another option. I would try for a switched feed though as to not drain battery if sitting for a week or 2. Daily driver would be fine as the draw would not be that bad. Be sure to start a worklog so others can follow along. Hope this helps and good luck SNO

  3. #3
    Maximum Bitrate rray's Avatar
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    Another member just installed a Dell Venue Pro tablet in his car and used an Intelligent DC-DC converter to keep his tablet always charged as well as power a USB hub in his car. It charges while the car is running and for a timer set period after killing the ignition.

    The converter is connected to both the battery and ignition sense to start the timer after engine off is sensed. Car battery never dies, and tablet remains fully charged.

    -Robert

  4. #4
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    Thanks for the feedback. Are all the 12V connections in the car the same? Are any regulated?

    I guess I'd probably want either a 12V connection that is only there when the car is started, or have some sort of solution like rray mentioned. What would you call the wire that tells you when the car is being started? Ignition sense?

  5. #5
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    And one more question. When you guys are working under the hood, is there a good way to remove power? Do you guys just remove the battery typically? I'd rather not shock myself if I can help it.

  6. #6
    FLAC SNOtwistR's Avatar
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    You won't shock yourself with DC voltage just burn as the wire heats up from being shorted to ground. You just need to disconnect 1 of the terminals on the battery before working on the vehicle. The key-on wire is an ignition on wire, it has power only when the key is in the on position ( some would say ignition sense). Car 12v is not regulated it fluctates from 11.5 (or lower) to 14.3(average but could spike higher) Like rray mentioned using a dc-dc-usb power supply from mp3carstore it will give you the regulated power you need and will also supply an auto on/off feature to the power output. SNO

  7. #7
    Raw Wave
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    Disconnect the -ve battery terminal if there's a chance of shorts or equipment damage.

    The rule as to which battery terminal to disconnect first and reconnect last is simple - the GROUND/Chassis battery terminal(s) shall be disconnected whenever any work is being done to other terminals.
    And since modern vehicles are -ve earth/GND/chassis, that means the -ve battery terminal is to be disconnected whenever other work is being done.
    The only shorting hazard is therefore shorting to the other battery post when tooling the battery connectors. (And not similarly disconnecting other common-GND batteries if they are present.)


    As SNO said, 12V shock is a rarity. But there are other hazards like cooling fans turning on. 12V shocks only happen from ignition systems, de-energising coils, and power converters.

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