How can I drop 24V to 12V w/2A draw

Discussion in 'General Electronics Chat' started by Jje1222, Nov 13, 2009.

  1. Jje1222

    Thread Starter New Member

    Nov 13, 2009
    6
    0
    Hi all, I'm trying to reduce the voltage at the trailer plug on a 24V truck to run 12V trailer lights with a draw ranging between 1 to 4A, but I'm not sure what value of resistor to employ. Any suggestions?:confused:
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    Don't you need three different voltage reducers? One each for RightTurn/Stop, LeftTurn/Stop, and running lights? You can do it with some power transistors mounted on a large heatsink (i. e. the truck).
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Hi Jje1222,

    I apologize for the earlier rudeness; some of us are tired and a bit cranky after a long week.

    Resistors are definitely not the way to go; they will waste a lot of power, which means you'll burn extra fuel and generate lots of waste heat.

    Additionally, if some of the bulbs burn out, the remaining bulbs will get too much current, and rapidly burn out; sort of a "domino effect", but faster.

    I'm assuming that you have a commercial trailer? I don't know how they are wired, but I'm familiar with wiring of boat trailers; etc.

    Following along with the boat trailer type wiring ... Usually, there is a single ground.
    There are three +12v circuits:
    1) Parking lights
    2) Left turn/brake light
    3) Right turn/brake light
    Each of those circuits will need their own regulators/step-down/supplies.

    It would help a great deal if you could confirm what your trailer wiring was like.
     
  4. ifixit

    Distinguished Member

    Nov 20, 2008
    638
    108
    Connect a similar 12V bulb in series with each 12V bulb on the trailer, however, the two tail lights could be wired in series.
     
  5. Jje1222

    Thread Starter New Member

    Nov 13, 2009
    6
    0
    Thanks for the input guys. This will use a flat 4 plug, ground, park, left, right. I plan on running a 12V hot line to the rear and using small 24V relays to then switch the 12V to the lamps. This will work fine, but its less than elegant to say the least. I'm just curios to see if there is a simpler way.
     
  6. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Well, the 24v relays switching a 12v "hot" lead isn't a bad idea; as long as the relays are either rated for outdoor operation, or enclosed so they won't get exposed to the elements.

    Using 12v linear regulators would be simple but terribly inefficient, and generate a LOT of heat that would have to be gotten rid of.

    Another possibility might be to use a PWM circuit set at 50% duty cycle. However, if you are a complete newbie to electronics, that could seem quite complicated.

    A switching DC-DC power supply would be better, but even more complex. If it broke, you'd have to either have a spare, or know how to fix it AND have the parts available.
     
  7. Jje1222

    Thread Starter New Member

    Nov 13, 2009
    6
    0
    Thanks for the help guys. It is a simple flat 4 trailer wiring set up (ground, taillamps, left, right) I am planning to run a 12V hot line to the back of the vehicle, then use 24V relays to switch the 12V line to the trailer lamps. This seems like a overdone way to do it, but I'm unaware of a simpler way at this time.
     
  8. Jje1222

    Thread Starter New Member

    Nov 13, 2009
    6
    0
    I plan to place the whole afair in an weatherproof box, if you would like to explain the Pulse width option, that would be great to explore. Thanks again.
     
  9. Jje1222

    Thread Starter New Member

    Nov 13, 2009
    6
    0
    I plan to place the whole afair in an weatherproof box, if you would like to explain the Pulse width option, that would be great to explore. Thanks again.
     
  10. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Using PWM would mean that you'd need to build a circuit using a timer IC (like a 555 timer) and a number of components.

    Unless you had a fair amount of experience in circuit assembly and soldering, you may run into problems with it on the road, which could be a safety issue - and the DOT folks wouldn't be pleased to see a trailer on the road in the dark with no lights.

    Have you worked with small electronic components before, like resistors, capacitors, and integrated circuits?

    How good are your soldering skills with a 20w to 40w pencil iron?
     
  11. Jje1222

    Thread Starter New Member

    Nov 13, 2009
    6
    0
    I'm good with soldering, but I think this might be a bit beyond my scope. I'm thinking the relays will be a tough, simple and easily serviceable way to go. Thanks for your help Sgt.
     
Loading...