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Thread: using universal car adapter

  1. #1
    Newbie
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    using universal car adapter

    i am jumping between the idea of either using an inverter or a car laptop charger. i know i would buy a carnetix psu but that is not in my budget right now. i was thinking of buying a universal car adapter like a igo or kensington and hacking off the cigarette lighter part and wiring in my car with an inline fuse. i was thinking of somehow wiring it up to a distribution block and adding a switch in the front to control when i want it on and off, so i can just sometimes run the laptop off of the battery

  2. #2
    FLAC SNOtwistR's Avatar
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    That would be fine to do, cutting off lighter end and wiring to car with switch . That's was how my first carputer was powered, but mine was an aopen bb10 with used a laptop power supply 19v. SNO

  3. #3
    Low Bitrate
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    I am powering my current rig this way and it works mostly fine. The only problem I've experienced is that it does not survive engine crank. I plan to add a second battery to the trunk that will only be connected to the main electrical system after the engine is started, which should solve this for me.

    Edit: If you are actually using a laptop, you won't have this problem. I'm using a mini-pc that takes 19v so I do.
    Last edited by timothy; 11-06-2012 at 10:57 PM. Reason: Additional Info.
    2008 Grand Prix GXP
    o Lilliput 669GL-70NP/C/T-HB-RV Double-Din Touchscreen
    o Zotac Mini-PC, Intel Atom D525 CPU, 2GB DDR3, 120GB SSD
    o JVC Headunit in bottom cubby.
    o Currently building custom power controller with Arduino

  4. #4
    Raw Wave
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    That's two good replies to a good OP.

    If I may humbly add:

    Hardwiring cig socket inverters etc is a good idea. Even a smallish 150W inverter is ~15A at full load, and some cig sockets can get hot at a few Amps due to bad contacts. (Hence why some devices like Engel fridges with a mere max of 2.5A or 5A have thermal fuses in their plug.)
    And hardwiring also removes the the risk of accidental disconnection - ie, knocking out of the plug, or vibration and bumps doing the same.

    Keep in mind that most cig sockets are powered via the ACC circuit which cuts out during engine cranking.
    However many inverters will not ride thru cranking voltage dips anyway. That does depend on the battery and the starter condition and type (eg, old batteries, and reduction starters draw less current), and the distribution to the target (ie, wiring and voltage drops to the cig socket).


    When hard wiring, I'd suggest its own dedicated +12V cable from battery +12V terminal with a nearby fuse and a relay. The -ve (GND) could also be from the batt- though that is less of a concern. (I often wire such add-ons including my HU direct from the battery using sheathed figure-8 (2 core) cable. The fuse or auto-resetting circuit breaker always "as near the battery +12V as practicable". The relay if used is after the fuse and may be near the battery, or in the cabin or boot/trunk or anywhere convenient in between.)

    Using a relay takes the strain off the switch and also allows smaller switches to be used. (30A etc relay coils are typically well under 500mA, hence is a huge selection of suitable switches.)
    The relay can be energised (turned on) by the ACC circuit (off during cranking) or IGN (on during cranking, but off when on ACC) or a manual switch or some other output - eg, the remote on from an HU etc.
    The relay can be energised by any or all the above by using a diode on each source and combining at the relay - ie, diode band-end's together at the relay coil (#86 for common Bosch-type relays). Dioding ACC & IGN means an ACC powered load that stays on during cranking. Add a manual switch for keyless loads. Any 1N400x diode will do - eg, 1N4004 or 1N4007 etc. (They are common 1A diodes. Even the lowest voltage-rated 1N4001 (50V) will do.)

    The new wiring with the relay may be enough to ride-thru the cranking dips (assuming it's on when cranking, eg, includes the IGN else its manual switch is on).

    The inverter could be engine bay or trunk mounted, but IMO it's better in the cabin. That's not only for the cooler cleaner environment, but negates the need to route "hazardous" AC wiring thru firewall etc. Instead normal 12V wiring need be routed - albeit maybe thick due to high-current requirements. Normal AC power boards can be used from the inverter.
    BTW, if you don't intend to run the inverter at full load, you can decrease the supply-wire gauge PROVIDED the fuse rating is decreased - ie, the fuse rating must never exceed the rating of the wire or relay etc that it is to protect!
    And with its remote controlled power relay, the inverter's power switch can be permanently on so it can be mounted out of sight etc.


    Next comes the 2nd battery if cranking kills the inverter, OR if you want an independent battery. IE, forget to turn off the inverter, or use it too long, and you merely flatten the 2nd battery but can still start your vehicle.
    The latter assumes a battery isolator that is NOT connected during cranking nor when the vehicle is not charging. If you have a charge-light, you might consider a relay energised by the alternator's charge-light circuit (D+ or L; search mp3car for "UIBI" - probably easiest using google and "oldspark uibi"; note too the risk if the alternator (regulator's) D+/L circuit is insufficient to power the relay coil), else a commercially available voltage sensing aka "smart" battery isolator.
    Though far less desirable, the battery isolating relay could be energised by the ACC circuit else a manual switch turned off when cranking, and before leaving the vehicle. (Not the IGN circuit in your case.)

    Note too that the inter-battery +12V connection requires a fuse AT EACH END as near each battery as practicable. Any isolator can be fitted anywhere in between.
    Also for battery interlinks I suggest self-resetting circuit breakers instead of fuses. These are available cheaply up to 50A, and are available in ATS blade-fuse style up to 30A, and maybe lower current in mini (or micro?) ATS types. Typically well under $10 each. Self-resetters mean automatic reconnection after unexpected battery charging or other current surges.

    Geez, that's simple isn't it? :wink:
    My other UIBI rants should cover the same as above, sometimes with more blurb or detail, and not uncommonly dishing it out to smart battery isolator (hence the name "UIBI").


    Though dc-dc converters are far better, I too started with an inverter (150W).
    As time progressed, I gradually obtained 12V converters for most of my devices like phone chargers, cameras etc, but I still often take an inverter (as well as the devices' original AC chargers) as a backup.
    Besides, occasionally there is still some AC device like a shaver, and let's not discuss my GF's hairdrier!


    Incidentally, if your still reading (LOL!), the above steps cold be neatly summarised, but I've added the full-blown (dis)course .
    It's merely a group of common procedures and tricks:
    - use a relay for remote control;
    - add a low-current switch to control it, or other triggers, optionally with diodes to combine triggers;
    - fuses as near the power source as possible (and at each power source).
    The rest are additional rules or learnings like fuse size versus downstream ratings; resetting protection for transient loads; & batteries should not be paralleled when not charging (nor cranking if the inter-link cannot handle its cranking current or its cranking voltage dip is undesirable.)


    Yep, yet another one of my small but humble replies. LOL!

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