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Thread: Layout / Power

  1. #1
    Newbie
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    Jun 2005
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    Layout / Power

    Hi,

    i know it can be irritating question from a newbie but not an electrical engineer so all the technical jargon doesn't settle in too well.

    Plan: use my Dell Optiplex SX280 as a car pc(will modify casing if required cuz this goes in the trunk) use a valet switch (hidden) and a power switch to fire it up.
    Also to use another battery in the trunk so the main battery doesn't die on me(getting back home is more important!)

    Equipment:
    Dell Optiplex SX280 [already here]
    Lilliput EBY701-NP/C/T 7" VGA [on its way]
    CarNetix CNX-P2140 185W Dual Output Intelligent DC-DC Regulator [on its way]

    Questions:
    a) Whats the easiest way to get the second battery? will the alternator charge both batteries when the car is running or do i need to upgrade it?is it worth it or the main car battery enough?

    b) i found a lot of layouts for the carnetix P2140, so many - i completely confused how to wire it up, anyone who can explain this to me in simple English maybe ?? (or is it, like i think, battery>valet switch>carnetix>Dell's PSU?)


    all/any help is appreciated


    Thanks
    DMX

  2. #2
    Raw Wave
    Join Date
    Nov 2009
    Posts
    2,118
    Search for my posts regarding 2nd batteries.
    You need a fuse at each interconnecting-cable end and an isolation relay which can be as simple as a relay controlled from your charge light (actually, the "D+" aka "L" terminal from your alternator (regulator).

  3. #3
    Newbie
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    and the carnetix is hooked up to the second battery?

  4. #4
    Raw Wave
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    Nov 2009
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    Yeah - sorry, I thought that would be obvious. IE - 2nd battery for whatever (PC, audio, laser show) and still be guaranteed a cranking battery to start.... (ie, the 1st/main battery remains unaffected. The two batteries are connected together ONLY whilst batteries are charging (eg - by the alternator).

    You could also consider a LVCO (low-voltage cut-out) to protect the 2nd battery - ie, if you forget the PC or laser targeting system, the LVCO disconnects the load from the 2nd battery. Some of my posts mentions that, though none go into detail with potential problems - instead usually a latching output is recommended (ie, LVCO cuts load off, but a reconnect signal is required rather than depending on the battery to recover voltage - which it does after being unloaded...).

  5. #5
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    Thanks, will i try to dissolve and translate all that to English - i'll look up your other posts


    could you help/comment about this one please:

    b) i found a lot of layouts for the carnetix P2140, so many - i completely confused how to wire it up, anyone who can explain this to me in simple English maybe ?? (or is it, like i think, battery>valet switch>carnetix>Dell's PSU?)

  6. #6
    Newbie
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    Location
    Dubai
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    ref to 2nd battery - Will this do the trick?



  7. #7
    Raw Wave
    Join Date
    Nov 2009
    Posts
    2,118
    That looks like a diode isolator or similar.

    For most other types of isolator, you would have the normal alternator + to battery + connection (maybe with its fuse near the battery).
    Then from that battery, via a fuse to the isolator (input) and out to the fuse & 2nd

    If that isolator is a relay, then its solenoid/coil is grounded (85) and the other side (86) goes to the alternator's charge lamp output (D+ or L). (Usually its 87 will be from battery #1 fuse, and 30 to battery #2's fuse, though swapping 30 & 87 isn't a major issue).

    A voltage sensing (aka smart) isolator only needs the heavy connections to the batteries, and a ground. Its sensing connection is the main battery (to which the alternator is connected).

    In the fig below, a chargeLamp controlled relay is depicted.
    (Paraphrasing...) The "smart battery isolator" (voltage sensing etc) is usually the same connectivity as the relay but without the 86 to D+ (or L) connection.


    Uploaded with ImageShack.us

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