9v & 12v LED's

Discussion in 'General Electronics Chat' started by Acorn82, Jul 23, 2013.

  1. Acorn82

    Thread Starter New Member

    Jul 23, 2013
    Hi All,

    I have a project where I am using 9v LED bulbs & 12v LED Strips that are all on the same circuit.

    The LED bulbs have built in resistors. I tried to light it all via a 9v battery but it would not light the 12v LED strips.

    In order to light the 12v LED strips i would need to use a 12v DC adapter.

    What i would like to know is, if I use a 12v adapter will it damage / burn out the 9v LED bulbs that are in the circuit?

    Many thanks
  2. tracecom

    AAC Fanatic!

    Apr 16, 2010
    It's very possible. Post the specifications for your LEDs and/or a link to them; only then can anyone say for sure.
  3. LDC3

    Active Member

    Apr 27, 2013
    Let me check my tarot cards...


    Hmmm, it's "The Fool" :D I'm going to go with yes :( until I know more about your 9V LED lights. There may be a chance that it will be fine.
  4. Acorn82

    Thread Starter New Member

    Jul 23, 2013
  5. WBahn


    Mar 31, 2012
    That's not gonna help much. We need manufacturer and part number to really tell anything.
  6. bertus


    Apr 5, 2008

    It looks like the leds have been pre wired with a resistor under the Heat shrink tubing.
    It is stated that the current would be 30 mA at 9 Volts.

  7. Acorn82

    Thread Starter New Member

    Jul 23, 2013
    thanks for the reply. The thing is I don't understand what 30 mA at 9 Volts means lol i am a total noob.
  8. bertus


    Apr 5, 2008
  9. Austin Clark

    Active Member

    Dec 28, 2011
    The straight answer you're looking for is that you'll have to replace the resistors. Now, what you need to replace them with depends on the forward voltage of the LEDs. Or, if you want, you can let us know what the resistors are that are already installed, and we can calculate the adjustment from there.

    if you want to be sure your LEDs won't blow up, let's say Vf = 2.0 which is the safest assumption, it may be higher.
    In which case 350+ ohm resistors will suffice ((12-2)/30mA = 333.3 ohms), if placed before every LED. 30mA * 10V = 300mW lost as heat in the resistor, so you'll want a 1/2 Watt resistor.

    However, you should really figure out the real Vf, if it's higher, you will know it's safe to use lower-ohm and lower-wattage resistors, resulting in brighter LEDs and cheaper resistors.

    Good Luck!
  10. domino82

    New Member

    Aug 30, 2013
    You aren't going to get so much light out of them if you drop the voltage to 9V, but it will not hurt anything, since I did test my 12V led strips with 9V PS, they were dim, but still workable.
    Is that Mailbu 12v DC? It needs to be, connected with the correct polarity.
  11. KJ6EAD

    Senior Member

    Apr 30, 2011
    If we take the 9V, 30mA LED/resistor at face value, we need to drop another 3V to make it compatible with 12V, so just add 100Ω in series and run everything at 12V.