voltage display on the lamp i bought.

Discussion in 'General Electronics Chat' started by simpsonss, Jul 20, 2010.

  1. simpsonss

    Thread Starter Active Member

    Jul 8, 2008

    i have a 12v 3W lamp on hand. The 12V is refer to the RMS voltage or the Vpeak? if i have a Vrms = 15Vrms output which i measure using a DMM, will it blow the 12V 3W lamp i bought?

    thank you.
  2. someonesdad

    Senior Member

    Jul 7, 2009
    It almost certainly refers to 12 Vrms. You might be able to run the light at 15 Vrms, but you'll reduce the life of the filament, perhaps drastically.

    If you have to use the 15 Vrms, consider finding a 3 Vrms lamp and put it in series. Then the 12 Vrms lamp should work fine.

    Now 12 V at 3 W is 1/4 A, so you could also get away with using a resistor. The needed resistance is 3/(1/4) = 12 ohms. The power is (1/16)12 = 3/4 W, so a 1 or 2 W resistor would work fine. You could put four 48 ohm 1/4 W resistors in parallel.
  3. Jaguarjoe

    Active Member

    Apr 7, 2010