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12 & 24 Volt

Discussion in 'General Electronics Discussion' started by niallmcdermott, Jul 22, 2011.

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  1. niallmcdermott


    Jul 22, 2011
    Is it possible to make a circuit which will take a voltage in the range 12 to 24 Volts and always give a 12 volt output?
    I want to be able to power 12 Volt LED lights on a trailer with both a 12 Volt car & a 24 volt truck...

  2. poor mystic

    poor mystic

    Apr 8, 2011
    Hi Niall :)
    it is quite possible to do this. The question in my mind is what the best method would be.
    In this kind of application lives can be at risk if a circuit fails, so I think you need the most robust and foolproof circuit design possible.
    Perhaps this would involve having a separate 12V plug for the car and 24V plug for the truck on the trailer. The lights would be designed for 12V working, and would be directly connected to the 12V plug. The other plug, only used for the 24V truck, would be current limited by a series resistor.
    Last edited: Jul 22, 2011
  3. duke37


    Jan 9, 2011
    You will need at least four controllers, for side lights, brake lights and direction indicators. I would not recommend a resistor since if one bulb fails, the other bulbs will be overvoltaged and will soon fail.
    The controllers will either be complicated or dissipate a lot of power giving out heat.
    Perhaps the best solution would be to have a 12V battery on the truck and three 24V relays to feed this power to the trailer. A single commercial 24V to 12V could be added to keep the battery charged if the battery does not have sufficient capacity for the trip.
    You could also rewire the trailer so that the pairs of bulbs are either in series or parallel with a multiway switch to chage between the two. This would be subject to pilot error.
    Last edited: Jul 22, 2011
  4. poor mystic

    poor mystic

    Apr 8, 2011
    Duke has made a good call on the need to prepare for failure, although these are to be led's instead of filaments and are less prone to fail.
    It seems needful to decide which of several possible designs is least likely to fail. I can see 1) a constant current source in each led supply, 2) a set of relays controlling a separate power supply, 3) my resistor idea (which mightn't be so bad for led's since they don't tend to fail anywhere near as much as filament bulbs).
    I feel that the resistors are the best solution because there's only 1 thing to fail. Of course I have heavy industrial wire-wound resistors in mind, not circuit board types.
  5. nepow


    Jul 18, 2011
    Resistors are ok but if you want to use either 12v or 24v for your trailer then you are better off using a voltage regulator circuit which will give you a stable output voltage irespective of the input. If you are technical and understand electronic circuitry you can use either a fixed volatge regulator or one that allows the output to be adjusted. These circuits are relatively simple and use few components. You need to work the total load current you will require and select a suitable regulator that will handle the current. If you want to make up your own regulator circuit then a fixed output regulator of 9 volts would be can then decide on you LED lighting and work out what resistors you will need working on an avarage of 20mA (milliamps) per LED. You can Google for fixed voltage regulators and down load tecnical data in PDF format. You may require a heat sink for high current loads. I don't know your level of technical knowledge and my answer reflects some circuit knowledge necessary here, however the costs are relatively cheap and parts easy to obtain. Hope this helps.
  6. TBennettcc


    Dec 4, 2010
    Just keep in mind that LEDs work on a constant current. It doesn't matter what the voltage is as long as the current remains constant. Therefore, Mark's suggestion of a constant current power supply would be better than a constant voltage supply, especially if you have all the LEDs in series with a series resistor.
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