Automotive voltage limiter to 12.6V

Discussion in 'The Projects Forum' started by bobank, Jul 10, 2007.

  1. bobank

    Thread Starter Member

    Nov 19, 2005
    21
    0
    What would be the simplest method to make voltage limiter. It should use automobile battery and limit voltage to 12.6 - 13V, preventing higher voltages if they occur
    Thanks, Boban Klasnikov
     
  2. cumesoftware

    Senior Member

    Apr 27, 2007
    1,330
    10
    The best is to use a voltage regulator, but you won't have much choice. Or you choose a low dropout regulator, that is one that doesn't need a overhead voltage, or you have to choose a regulator that regulates to 9V for instance, like the LM7809, since it's input needs 12V minimum.
     
  3. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    Just tossing out a half-baked idea here...


    1) Battery feeds voltage doubler chip which in turn feeds a regulator with o/p of limit voltage level

    2) feedback signal (see below) and regulator i/p into comparator

    3) Comparator o/p controls MOSFET or IGBT passing battery current across big capacitor and into load. Take feedback at this junction.
     
  4. bobank

    Thread Starter Member

    Nov 19, 2005
    21
    0
    Originaly I was thinking about using resistor and Zener Diode paralell with receiver(DVR in this case) but not sure if this works. Becase I do not have enough voltage to play with and it is not important to keep voltage constant, just to protect from spikes (like accidental connection with 2nd battery ( this is for working van) or any other reason for increasing voltage. If Zener diode 12 -13V, I thonk there is 12.6 available is parallel with DVR, voltage drop over Zener will stay constant for variaos changes in voltages... or I am missing something. I play with electronics when I have free time, but having business that is on call 17 hrs/day really do not leave free time, so I can say I am not very good in this, I can follow circuit and make small expperiments on my own, but that is that .
     
  5. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    Resistor and zener will be fine for what you suggest. Zeners usually run around 5 or 10 percent accuracy, but that will be good enough for your need. Note that only the zener is in parallel with the load - the resistor dissipates the "left over" power and is therefore in series with the zener and the load. This is more eloquently explained here: http://www.allaboutcircuits.com/vol_3/chpt_3/11.html

    Your resistor will need to have little enough resistance to avoid degrading performance of your load. It will also have to be able to dissipate power in your "fault condition." Something like a 3-Ohm 50-Watt resistor would work - but try to keep it away from heat. Those things de-rate their power rating like mad over 25 Celcius.
     
  6. Gadget

    Distinguished Member

    Jan 10, 2006
    613
    0
    Perhaps a 16 volt zener with a fuse to blow if the zener voltage is exceeded..... a concept we used to call "Crowbar" protection, as it is like shoving a crowbar across the circuit to blow a fuse when a fault arises. A value or 16 to 18 volts should still offer the spike protection you are after. Nowadays more elegant solutions are normally used.
     
  7. a_kent

    Active Member

    Jun 12, 2007
    30
    0
    I have done quite a bit of automotive work with devices that 'had to have' 12v outputs. This was initially harder when these things had to also work with 24v systems.

    I used switching power supplies that worked from a nominal 9v up to 40v and maintained 12v output.

    There are a few companies out there who make these switchers. My favorite are several from Linear Tech.

    Granted, the layout is critical on all switchers, but you can successfully dead bug build em. I've done it more than once...
     
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