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10v regulator for car

Discussion in 'General Electronics' started by James Carruthers, Jun 2, 2004.

  1. Hi there,


    On my Triumph Spitfire - and most British cars I assume - I have the
    standard 10v voltage stabiliser designed in the 60s - but the things
    are always blowing and not working - in short - theyre a PITA. They
    provide the fuel and water temp gauges with 10v supply instead of the
    12-14 that everything else gets.

    Can someone give me some directions on how to build a modern solid
    state version of this ancient device? Im pretty sure it must be easy
    with a single IC - but I'd like some suggestions as to the most simple
    way to do it.



    James
     
  2. Nirodac

    Nirodac Guest

    I like to use the LM117 (LM317) voltage reg chip from National.

    http://www.national.com/ds/LM/LM117.pdf

    I've done this before on an American car (Chrysler) and it worked well (used
    8 volts instead of your 10).
    You are sure it's 10 volts, aren't you.

    You should be aware that the thermal regulator that you are replacing was
    designed to interrupt the current going to the gauges. Interruption
    frequency is based on the current flowing through it. The gauges actually
    only got an average voltage, based on the number of interruptions of the
    current flow in a given minute. Automotive gauges of this era are typically
    slow in responding to voltage changes, therefore you don't see the needle
    move as the voltage is interrupted.
    I'm not sure how you determined that the gauges needed 10 volts, but with
    this solid state regulator producing a constant voltage, you may find that
    the gauges read high, as the gauge won't be averaging out the voltage
    interruptions. Simply lower the output voltage of the solid state regulator
    to make the gauges read correctly.

    The app note shows a precision 10 volt output. For older cars you do not
    need this kind of precision. Just use the resistors on the ground (center
    pin) as shown in the app notes. Adjust the trim pot for your output
    voltage. Don't forget to put caps on the input and the output (it's all in
    the app notes).

    OBTW, mine got really hot when I used the Vreg., you may need a heat sink.
    Gauges from this era tend to draw a lot more current than you may expect.
    They were designed that way.



    Yar
     
  3. Dbowey

    Dbowey Guest

    James posted:

    << On my Triumph Spitfire - and most British cars I assume - I have the
    standard 10v voltage stabiliser designed in the 60s - but the things
    are always blowing and not working - in short - theyre a PITA. They
    provide the fuel and water temp gauges with 10v supply instead of the
    12-14 that everything else gets.

    Can someone give me some directions on how to build a modern solid
    state version of this ancient device? Im pretty sure it must be easy
    with a single IC - but I'd like some suggestions as to the most simple
    way to do it.
    ----

    I don't recall which car this was for, but I read a short piece many years back
    suggesting a Zener diode to replace the electro-mechanical gizmo. I was
    thinking of doing the changeover, but didn't need it at the time; it is
    misplaced now.

    I suggest you contact a MG and Triumph club. There are usually "Keepers of the
    Obscure" in the clubs.

    I think I was considering the conversion for my MGTD.

    Don
     
  4. no_one

    no_one Guest

    remember that all the english cars used a positive ground, so you need a
    regulator designed with that quirk in mind!
     
  5. Radio Tech

    Radio Tech Guest

    Many IC makers produce the LM7800 series three terminal regulators.
    Radio Shack is a good source for these. There is not one specifically
    for 10.0 volts, however, by placing a zener diode or series
    combination of forward biased rectifier diodes in the ground (center)
    terminal of these devices, you can alter the output voltage from say,
    a 5 volt regulator (LM7805), to 10 volts using a 4.7 volt zener and a
    forward biased rectifier or signal diode like a 1N4148 in series,.
    The zener and rectifier will have a small current running through them
    forcing a voltage drop of about 5.2 volts to appear across them. This
    voltage drop biases the ground (or reference) terminal of the IC up by
    that voltage so at the output, 10.2 volts will appear, and can provide
    up to 1 amp of current, short circuit and over temperature protected.
    There are 3 amp versions of these as well, but are not as common as
    the 1 amp types. I doubt if your gauges will need more than an amp
    anyway. Good luck!
     
  6. I've found the perfect IC now!... 7810 - 10v regulator - the version I
    have gone for is the 2A one (78S10 is what the one I have found is
    called) - which should give me enough I think.

    So the whole regulator will consist of 2 cables with a couple of spade
    terminals on the end. It will ground to the speedo using the tag on
    the top of the regulator... brilliant! This is an excellent solution I
    think.

    If it reads high then I will try a 9v regulator - more common than the
    10v one too.

    Thanks everyone for your help.



    James
     
  7. James,

    Most standard types of 78xx regulators require at least 2V between in- and
    output. So for the 78S10 the 12V battery voltage will be enough but you can
    run into probles when that voltage falls below 12V. Some low drop types
    require only 1V. Check out the datasheet of the regulator to avoid
    unpleasant surprises.

    petrus bitbyter
     
  8. Petrus,


    Cheers for the heads up!

    The standard voltage is about 12.6 and the regulator wants 12.5 - when
    the car is charging on the alternator this goes up to about 14.5 - so
    I should be fairly safe.



    James
     
  9. Quack

    Quack Guest

    So the whole regulator will consist of 2 cables with a couple of spade
    with some of the regulator chips i have used (i cant remember
    specifically which one right now), the tag on the top was Vout, not
    gnd!. double check that.

    Alex.
     
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