Voltage Drop Solution for Car

Discussion in 'The Projects Forum' started by JohnB7, Jun 11, 2009.

  1. JohnB7

    Thread Starter New Member

    Jun 11, 2009
    2
    0
    I need some help with ideas to overcome this problem.

    I have 2 LCD screens in my car (12 volt) as per this Page. When the car is parked and a DVD movie is watched, all is fine, but when the car is started (cranked), the unit resets completely and the DVD movie starts up right from the beginning. Needless to say it is very annoying. Research done shows these LCD screens need a constant voltage supply, even a 0,8V drop will cause them to reset they told me. Of course I ran the 12V supply wires directly from the car's battery. So this is not a wiring issue, but a unit design isssue - other makes of these DVD units do the same. It is common on these products the suppliers said.

    I came up with an idea to overcome this "reset" issue:
    Add small 12V battery, with a charger circuit to drive this DVD unit, instead of the supply coming from the car's battery.

    My question is, will this work, or have an effect on the car's alternator and other electrics ?
    Can anybody supply me a link to such a charger circuit ?
    A friend of mine suggested a large capacitor (subwoofer type), to maintain the voltage momentarily when the starter motor turns and the DVD units will stay "up". Not sure if this would work.
    Any other ideas or circuits to oversome this problem would be appreciated.
     
  2. Externet

    AAC Fanatic!

    Nov 29, 2005
    758
    57
    Hi.
    Both should work, extra battery or capacitor.

    +12Vcar------------------------|>|------------B+----BAT2---gnd

    +12Vcar------------------------|>|------------C+-----||------gnd

    Supply the screens with B+ (added battery) or with C+ (added capacitor)
    Diode --|>|-- should be capable of ~ twice the current consumption of the screens. Initially charge the capacitor with a light bulb in series.
     
  3. JohnB7

    Thread Starter New Member

    Jun 11, 2009
    2
    0
    Thank you for the answer.

    One last thing - could the second battery to be used, be a small 12V 2A SLA (sealed lead Acid) type to install under the dash ?
     
  4. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,741
    759
    U know if u add a SLA, then you should have an online charger.
    But if you use a capacitor like 0.1F to 1F 12VDC caps and a appropriate series diode, then it will be much simpler and effective.
    _____
    Rifaa
     
  5. Steve C

    Active Member

    Nov 29, 2008
    86
    0
    It's nice to have solution that requires no maintenance, but be aware that .1F caps are huge. Ballparking toilet paper tube size as an absolute minimum and a good chance they will be larger. And space comes at a huge premium in a car. If you've got nothing else in there, I'msure there will beplenty of space. But if you have two LCD screens then I'll guess you have amplifiers, DVD players, maybe a full computer. Lots of stuff. And the cap will be most effective as close to the DVD players as possible. Same with the battery, for that matter.

    My local surplus stores sell SLA batteries in the 2Ah range for less than 5 bucks. Usable lifetime is only around 5 years at best, but they can be tiny. At less than 2Ah you are looking at the size of a D-cell battery or smaller.

    That can be an especially attractive solution, limited lifetime or no.
     
  6. Steve C

    Active Member

    Nov 29, 2008
    86
    0
    also be aware that some electronics REALLY do not like to remain on while cranking. One big reason the car shuts off ACC1 and ACC2 is for exactly that reason.
     
  7. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,741
    759
    :D

    and that too.
    Ignition introduces erratic operations :eek:

    ______
    Rifaa
     
  8. Steve C

    Active Member

    Nov 29, 2008
    86
    0
    BTW, if you have $100, you can buy a 12v-12v DC-DC converter (I think it's called the Vinfinity s12d12 or something along those lines) that takes 9-18v in and outputs 12V out with a 6 amp capacity, and will even isolate grounds if you need.
     
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