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Technical How to Build a Voltage Regulator for $3

Discussion in 'The Hokey Ass Message Board' started by 49 Custom, Feb 19, 2010.

  1. 49 Custom
    Joined: Apr 17, 2009
    Posts: 282

    49 Custom
    Member

    Here's a straightforward way to build your own "Runtz" type voltage reducers so that you can use your 6 volt gauges on your 12 volt system.

    The regulator is based on the LM7806 integrated circuit, which is able to reduce voltage while maintaining a constant current. Use one regulator for each gauge; this allows you to keep each circuit separate which is useful for sorting any troubles you might have. While it is possible to use one regulator for all gauges using a power transistor, it has a bigger footprint and produces more heat, requiring it to be carefully mounted away from any heat sensitive parts.

    Here are the components:

    [​IMG]

    1x LM7806 voltage regulator
    2x 1μ 25-35 volt tantalum capacitors
    1x Heat sink (around one inch long)
    3x wires cut to 3 or 4 inches in length

    You will also need a soldering iron, solder, some pieces of shrink tubing, and a bit of heat sink paste.

    First, bend the leads on the capacitors into an "L" shape. Usually the longer lead is the positive side and since we want to attach the positive ends to the outer leads on the LM7806, make sure the capacitors are bent in opposite directions.

    [​IMG]

    With the LM7806 sitting with the tab side down, solder one capacitor to one of the outer leads of the LM7806, then solder the other capacitor to the other outer lead. Again, be sure these are the positive ends of the capacitors. Carefully bend the remaining lose capacitor leads to make contact with the center lead of the LM7806. Solder them in place.

    [​IMG]

    Next, trim the three posts on the LM7806 so they are just long enough to solder the wires into place. First solder the center wire (ground), then the left (12V) and the right (6V).

    [​IMG]

    Cut some short lengths of shrink tubing and slide them along the wires all the way to the regulator side and heat them. Then take a larger piece and wrap the three leads together. This will both insulate the leads from each other and protect the connections.

    [​IMG]

    Finally, put a dab of heat sink paste to the back side of the LM7806 and attach it to the heat sink with a screw.

    [​IMG]

    When connecting them, select the appropriate connectors for your application. In the photo below, the red lead is connected to a switched 12V source (usually your ignition), the white lead is connected to the positive post on a gauge, and the black lead is connected to a ground.

    [​IMG]

    Finally, attach your harness and reinstall your gauges!

    [​IMG]

    Each voltage reducer cost about $3 and I learned a bit about how gauges and reducers work. Please don't hesitate to post questions and comments and I'll do my best to respond.

    -Stefan


    EDITOR'S NOTE - LINK TO ORIGINAL LIVE THREAD HERE: http://www.jalopyjournal.com/forum/showthread.php?t=448038
     
    Last edited by a moderator: Feb 21, 2010
    Woogeroo likes this.
  2. Ruiner
    Joined: May 17, 2004
    Posts: 4,145

    Ruiner
    Member

    That's badass man!...sure, it kind of sucks to have to make one for each gauge, but it's definately worth it to keep the stock gauges safely...my question is, does it allow you to use the stock Amp gauge safely?...I've got a bunch of 6v Stewart Warner gauges that I'm saving for a 40's style project, and being able to use 12v for the starter and such while using my 6v gauges without costing an arm and a leg is a hell of a good deal to me...
     
  3. 49 Custom
    Joined: Apr 17, 2009
    Posts: 282

    49 Custom
    Member

    Hey there, Ruiner. Amp gauges are a totally different story. They actually measure the current flow from the battery. Voltage regulators maintain a specific voltage by altering their resistance in response to changes in current.

    In theory, you should be able to run your amp gauge as is. In practice, many people convert them to volt meters.
     
  4. 440roadrunner
    Joined: Mar 30, 2008
    Posts: 55

    440roadrunner
    Member
    from live?

    Absolutely awsome. My only comment is that if you mount the regulator tab to a good solid piece of sheet metal in the cluster, you don't need anywhere near that much "heat sink" or any at all. Very well done
     

  5. Yep...I use a short piece of 1" square tubing. Plenty of surface area plus air flow path.
     
  6. Where do you get those parts, like a radio shack or something?
     
  7. 440roadrunner
    Joined: Mar 30, 2008
    Posts: 55

    440roadrunner
    Member
    from live?

    Sort of . I don't believe RS sells a 7806, but they sell a 7805, which is "OK"

    Otherwise Mouser electronics or Digikey

    The RS 7805 is RS part no 276-1770

    For the caps (at RS) you could probably sub RS # 272-1055 which are 1uf, 250v metal film caps.
     
  8. 49 Custom
    Joined: Apr 17, 2009
    Posts: 282

    49 Custom
    Member

    The 7805 is a 12V to 5V regulator, while the 7806 is 12V to 6V. As 440 mentioned, it probably would be ok, but I suspect the gauges might read a little on the "low" side; even original 6V batteries didn't always put out 6V. The capacitors can be anything between 0.1 and 10ų as they are just to reduce noise.
     
  9. tdoty
    Joined: Jun 21, 2006
    Posts: 821

    tdoty
    Member

    You can probably get away with using more than one gauge on an LM7806 circuit, as they are rated for 1.5A. There are more parts involved (thus bumping the price), but an adjustable LM 317T regulator could be used as well. The 317 is also rated for 1.5A.

    I have often wondered why this wasn't discussed more often around here.

    Tim D.
     
  10. HotRodMicky
    Joined: Oct 14, 2001
    Posts: 1,767

    HotRodMicky
    Member

    For 5A there is a 5Volt version availible...i just forgot the number.
    78L05 or something.
    And if you put a diode(is that english , too) on the middle pin(connectet to ground)
    then you end up with 5.7 Volts as the diode "eats" 0.7 Volts.

    That way you need only one for all.
    Michael
     
  11. MARTINSPEED
    Joined: Nov 18, 2007
    Posts: 294

    MARTINSPEED
    Member

    thanks alot! fo you have any ideas for a 6 volt heater motor, or say a 6 volt horn? i m going to need both. -andrew
     
  12. Flat Ernie
    Joined: Jun 5, 2002
    Posts: 8,410

    Flat Ernie
    Tech Editor

    Run your 6V horn on 12V....it's nice and loud! Don't run a 12V horn relay though, stick with the 6V relay. The 12V ones often can't handle the increased current.




    I've done several of these conversions and never used the capacitors. And while it may make a more technically correct power supply for small electronic projects, personally, I don't think they're required in this type of circuit. Any "noise" that made it through the IC will be largely irrelevant to the bimetallic strips in the gauge circuits...they don't react quickly at all.
     
  13. 49 Custom
    Joined: Apr 17, 2009
    Posts: 282

    49 Custom
    Member

    I can definitely testify for the increased volume of 6V horns on 12V! And you are absolutely right that the capacitors are not required for old electric gauges; its a hard habit for me to break, plus at about $0.10 a piece, it was hard not to use them.

    There was a question above about heaters and wiper motors: a high load ceramic resistor is more appropriate for those. I've seen a few threads that provide more details.
     
  14. peeduh
    Joined: Aug 26, 2007
    Posts: 70

    peeduh
    Member
    from atx

    Awesome! Going to be using this to save money!
    Thank you 49 custom!

    Sent from my SGH-T999 using H.A.M.B. mobile app
     
  15. bobbytnm
    Joined: Dec 16, 2008
    Posts: 1,394

    bobbytnm
    Member

    Excellent tech!!

    Thanks
     

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