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Christmas Tree Fairy Lights Confusion.

Zoomup
Season's Greetings all,


I have several sets of fairy lights by my front door. There are either 20 or 40 light sets with traditional filaments, not L.E.D.


 I only have 20 or 40 light sets and spare lamps for them.


One or two lamps had failed at the front door. There are several sets all tangled up and left there from last year. I can not be bothered to count the number of lamp holders in the sets with blown lamps.


When I put in new lamps they failed immediately, but maintained the set's other lamps due to the internal shorting wires in the new lamp.


If I put in a new 12 Volt lamp  all should have been good. (20 light set with 12 Volt lamps).


I took some 12 Volt lamps from a new set for the spare lamps to replace the blown ones at the front door.


If the new 12 Volt lamps were accidently put into a 40 light set they would just glow dimly as they would be supplied at 6 Volts.


So, why did the new 12 Volt lamps blow instantly?


Z.


.







Parents
  • 0
    I thought that we were back to one of Zoom's weekend quizzes. ?


    Then I had to see for myself.

    100 W lamp 240 V => I = 0.42 A => R= 576 Ohms

    40 W lamp 240 V => I = 0.167 A => R = 1440 Ohms



    Total R = 2016 Ohms

    240 V across both => I = 0.119 A



    Power = I²R

    100 W lamp => 8.16 W

    40 W lamp => 20.4 W


    So yes, the lower wattage lamp glows brighter. Interesting!


    ETA: Now for the fairy lights.


    Let's assume a current of 1 A in the 12 V ones

    Power of each lamp = 12 W and R = 12 Ohms

    To have the same power in the 6 V ones, I = 2 A and R = 3 Ohms

    39 x 6 V lamps + 1 x 12 V lamp = 129 Ohms => I = 1.86 A and there she blows! ?
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  • 0
    I thought that we were back to one of Zoom's weekend quizzes. ?


    Then I had to see for myself.

    100 W lamp 240 V => I = 0.42 A => R= 576 Ohms

    40 W lamp 240 V => I = 0.167 A => R = 1440 Ohms



    Total R = 2016 Ohms

    240 V across both => I = 0.119 A



    Power = I²R

    100 W lamp => 8.16 W

    40 W lamp => 20.4 W


    So yes, the lower wattage lamp glows brighter. Interesting!


    ETA: Now for the fairy lights.


    Let's assume a current of 1 A in the 12 V ones

    Power of each lamp = 12 W and R = 12 Ohms

    To have the same power in the 6 V ones, I = 2 A and R = 3 Ohms

    39 x 6 V lamps + 1 x 12 V lamp = 129 Ohms => I = 1.86 A and there she blows! ?
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