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Thread: Lights wired in series

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    Question Lights wired in series

    Good day folks
    If I were to wire two infrared globes in series - would this reduce the power consumed as well as the heat output? If so, by how much?
    I am trying to heat my dogs kennels and cannot source low wattage infrared globes in my area, so was thinking of using two par38 150 watt globes wired in series, one in each of the kennels. I was hoping to get the equivalent of a 75 watt globe in each for a total consumption of 150 watts.
    TIA

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    Diamond Member AndyD's Avatar
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    Yes, you're right if it's some kind of filament lamp which I assume it is. If you wire two in series and they're the same wattage the voltage is divided pretty equally between them meaning the heat output of each lamp will be approximately halved.

    Can't help thinking a heated pad under the bed might be a better way to keep the doggie warm, I think it would be more efficient and less likely to attract snakes and other unwanted animals. If you get a very low voltage heated pad it's also less likely to electrocute Fido if he decides to chew it.
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    Thanks Andy. I considered the heat pad, but my pooches have a habit of tearing up their beds so opted for the light mounted up high.
    Will the series wiring also halve the power consumed?
    I am thinking 2 x 150 watt lamps wired individually or in parallel will total 300 watts, using 1.25 amps (300 watts = 1.25 amps x 240 volts)
    What part of the above equation will change by putting the lamps in series, the watts or the amps, since the volts are a constant?

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    Diamond Member AndyD's Avatar
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    The wattage stated on the lamp is not a 'given', it's dependant on the lamp being supplied the voltage it's rated at so you can't use the wattage as a base point for any calculations. If you wire 2 lamps in series you're supplying them with half their rated voltage which means the power (wattage) stated on the box no longer applies.

    The lamp is 300 watts at 230v it has a resistance of 176.4 ohms. This resistance is the constant you'd use in any calculations.


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    The filaments will also be operating at a lower temperature, which may reduce the resistance a bit and may also affect the frequency of the radiation emitted.

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    Thanks guys, that makes sense now.
    I used to know some of this stuff, but time has not been good to the memory cells.
    Series will give me my desired results in terms of heat output and power consumption. Hopefully the globes may last a little longer too, as they will be running cooler.

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    Diamond Member AndyD's Avatar
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    With a PAR38 filament lamp it might last longer if it's run at a lower voltage like if two lamps are in series. With other types of lamp, especially halogen, low voltage can cause premature failure. https://en.wikipedia.org/wiki/Haloge...#Halogen_cycle
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