9v DC to 12v DC?

Discussion in 'General Electronics Chat' started by killercripple, Apr 15, 2010.

  1. killercripple

    Thread Starter New Member

    Apr 15, 2010
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    I want to build my own RC car light kit. I want to use a 9v battery for the power suply, But the LED lights i want to use are 12V car lights.

    Is there some type of small cheap converter i can use?

    I can post the LED's if it well help any
     
  2. retched

    AAC Fanatic!

    Dec 5, 2009
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    You may be better off to spend $1 or 2 on getting some regular LEDs. You then would only need a few cent resistor, instead of a voltage pump or transformer to increase your voltage.

    Post the LEDs you have now so we can see if they can be used with 9v
     
  3. killercripple

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    Apr 15, 2010
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  4. retched

    AAC Fanatic!

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    Where are you located?
    I can probably show you many other retailers that will have what you need. It depends on where you are.
     
  5. killercripple

    Thread Starter New Member

    Apr 15, 2010
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    Wa state. They were just the cheapest and pre wired. i dont mind spending more if need be or wiring them. if it will be easier in the long run
     
  6. kingdano

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    Apr 14, 2010
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    someone please correct me if i am mistaken.

    i think those are pre-wired to illuminate to the correct level at a 12V supply - those LEDs may have a high forward bias drop and 9V may not leave enough juice to light them properly.

    it looks like something designed to run off of a cigarette adapter almost...12V in the car?

    if you want to, you can wire your own - but if you dont feel comfortable working with equipment, why not just buy a 12V battery pack?
     
  7. retched

    AAC Fanatic!

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    Well, if thats the route you want to take, that fine.. But to get 9v to 12v, you will have more work to do. It would be easier and better to get quality stuff.. Those import cheapie LEDs have a habit of burning up in short order.

    Can you solder?
     
  8. retched

    AAC Fanatic!

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    A few questions... How many leds do you want to put on the radio-controlled car?
     
  9. retched

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  10. SgtWookie

    Expert

    Jul 17, 2007
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    Trying to boost the 9v to 12v to run LEDs would be a bad deal all the way around.

    A 9v "transistor" battery might be rated for around 500mAh; that's at a 20-hour discharge rate, or a load of 25mA.

    Let's say you could build a DC-DC boost converter that's 80% efficient, which is reasonable.

    Let's also say that the 12v LEDs need 20mA current each.
    12v * 20mA = 240mW

    So, you'd need 9v*80%/240mW = 30mA current from the 9v battery - for each LED you wanted to light.

    However, just ONE LED would have the battery go flat in around 16 hours.

    By the same token, individual white LEDs have a Vf of around 3.4 to 3.8v at 20mA current. You could wire two in series with a current limiting resistor, and have twice the light output and use less current.

    Rlimit >= (9v - (2 LEDs x 3.4V))/20mA
    Rlimit >= (9 - 6.8)/0.02
    Rlimit >= 2.2/0.02
    Rlimit >= 110 Ohms. 110 Ohms is a standard value of resistance.
    See this page for a standard decade table of resistance values:
    http://www.logwell.com/tech/components/resistor_values.html
    Bookmark it. Refer to the E24 (green) columns.
     
  11. killercripple

    Thread Starter New Member

    Apr 15, 2010
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    my last post never posted wierd.

    I can solder some what.

    I would like at least 6 leds. 10 would be what id like
     
  12. SgtWookie

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    Using what for a power supply?
     
  13. killercripple

    Thread Starter New Member

    Apr 15, 2010
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    i would like to just use a 9v battery or a AA battery pack. I only need it to run for 30-45min at a time. Theres not much room so i cant use a larger battery pack
     
  14. SgtWookie

    Expert

    Jul 17, 2007
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    You can get a lot more out of a NiMH AA batteriy than a 9v battery.

    See the attached; scroll to the bottom of the 3rd page.
     
  15. Bychon

    Member

    Mar 12, 2010
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    Brilliant!!
     
  16. killercripple

    Thread Starter New Member

    Apr 15, 2010
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    first things first. i barley under stand what that is lol, im sure i can figure it out But while i was looking for that 555 timer and transistor. i found a few videos that show that it blinks. Is that just how they made theres? or is that what it will do? I dont want mine to do that. i want to use it like head lights in the grill and fog lights along the roof
     
  17. SgtWookie

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    The circuit on the bottom of page 3 of the PDF that I uploaded is a simple boost converter.

    The 555 timer in the circuit is not a standard BJT timer, it is a CMOS timer. The timer operates at very high frequencies to charge/discharge the 220uH inductor. Technically, in that circuit the LEDs do flash - but they are flashing at a frequency so rapid that it looks like constant light.
     
  18. killercripple

    Thread Starter New Member

    Apr 15, 2010
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    ok cool.

    I found the full article on that PDF file. Do i just use the parts shown in the picture to make the lights stay on constantly? or is there parts i need to get?

    I've never done anything like this, But know its got y wheels turning. So now i want to try it
     
  19. SgtWookie

    Expert

    Jul 17, 2007
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    Yes, you use the parts shown to make the lights stay on constantly.
     
  20. killercripple

    Thread Starter New Member

    Apr 15, 2010
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    Quick question. Is a 4.7uF capacitor the same as a 470uF capacitor?
    Also, does it maker what voltage rating i get?
     
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