Calculating Power Consumption

[st11x]

G'day,

We have been given a couple of Christmas lights that you can find at Big C. I looked at the plug and it says 220V/3Amp.

Looking up Google, it looks like the Wattage is 220x3 or 660Watt. Is that correct? That seems to be quite a lot of power. So if each "strand" of maybe 100 lights use that much power, wouldn't a Christmas tree that requires maybe 10 of them consume as much power as an AC?

Thanks

Matt

[givenall]

3 amp is the maximum rating and it necessary the power consumption of the lights. They are normally a lot less

[Maizefarmer]

The 220v/3amp molded/stamped on the plug fitting is normally the plug manufacturers rating for that plug and nothing to do with the light manufacturer - who purchases it to use on his Xmas light production line, because 220v/3A is the closest standard AC type plug (and the therefore the cheapest!) he can get to what he needs

But 660 watts is not likley to be what your Xmas lights will be drawing (i.e. 220v @ 3Amps) - they will almost certainly, as givenall comments, be drawing siginificantly less amperage - if only because high wattage Xmas light arrangements are unusual because of the way they are used (e.g. Xmas trees) and the heat they produce. Chances are if they are the flashing string type lights common on Xmas trees, it's quite poss they'll be using not much more than around 200 - 300milliwatts (i.e. not even 1Amp - millAmps at most!).

[gregb]

As Maizefarmer said, that rating is for the electrical cable, not the lights themselves.

A good rule of thumb is 500 milliwatts per bulb. So if you've got a 100 bulb strand, then you can assume about 50 watts to run it. Of course, if they are blinking instead of always on, you only use power during the period of time they are actually on.

More correctly, the bulbs themselves are nominally 2.5v/200mA incandescent bulbs, so if you have a string of 100 you need a voltage of 250v to actually achieve the nominal rating. Most power here in Thailand is about 223v rms in my experience, which means you can expect 89.2% of that 50w figure, or around 44.6 watts for your strand. That neglects losses due to heating of the wire and second order effects, so the real number might be 1% or 2% higher than that.

[Crossy]

The above calculation bears out in practice

I just measured the consumption of my lights using my Kill-A-Watt.

Regular tree light string 100 lamp, 50W when in 'all on' mode, about 30W when cycling.

LED string 200 lamp, 10W all on, about 6W when cycling.

If you have a lot of lights the LEDs are well worth the 200 Baht a string

[Spoonman]

What sort of scrooge googles the power consumption of chrissy tree lights ??

[Garry9999]

What sort of scrooge googles the power consumption of chrissy tree lights ??

No idea, but maybe he should plant a couple of trees to offset his carbon footprint.

[st11x]

Thanks for the calculations.

We are using quite a lot of the 100 bulb strands, so it's good to know that it's not going to be that excessive.

Matt