Discuss Current draw? in the Electrical Forum area at ElectriciansForums.net

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Adrian768432

Hello everybody.

Can I ask what is probably a simple question?

Not long been living in my new flat, just got the first electricity bill, scary!!! Looking around and every room has down lights, the living room has 18 alone. I had a look and they're all 12v 50w, now I remember from school the old idiots triangle, and I was trying to calculate how much power, and load there is.

But my problem is the 12v being transformed from 240v part? Say 12 downlights, that's 600w, which at 240v is 2.5a, but at 12v its 50a! So which is correct, or is there another way to work this out?

Its not for any real reason really, I was just trying to get my head around it!

many thanks.
 

Strima

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To make life easy get an energy monitor. My supplier, Southern Electric, gave me a unit free and it allows me to track my energy usage on-line and make savings from there. I spent an h our wandering around the house turning things on and off to see what they draw and have managed to save myself roughly £120 a year by making a few basic changes.

Although you can calculate how much energy an appliance draws it never reflects its actual draw due to environmental issues, location, installation method, actual mains voltage etc etc...
 

AndyL

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Hi Adrian, you are almost correct the primary side of the transformer that feeds your lights would be drawing 600w/230v = 2.6 A
If it was one big transformer feeding all of your lights then you would also be correct on the secondary side i.e 600w/12v = 50 A

However it is more likely that each lamp will be fed from its own individual transformer 50w/12v = 4.16 A

Either way you get charged the same amount for the electricity because thats based on the watts per hour

Hope that helps
 

topquark

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Both your sets of figures (V & A) are correct. It's still 600W of power being consumed however it's being driven! From your source supply (you're assuming 240V) it's 2.5A.
 

telectrix

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time to invest in some good quality LEDs. bin the transformers and fit GU10 LEDs. take a year or so to recoup the outlay, but the saving on the 18 alone will be 810 watts. that's about 12p/hour.
 

Brightspark2

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time to invest in some good quality LEDs. bin the transformers and fit GU10 LEDs. take a year or so to recoup the outlay, but the saving on the 18 alone will be 810 watts. that's about 12p/hour.
What he said.

Ditch the 12V and get GU10's with GOOD quality LED downlights. Dont go for the cheap ones, they wont last.

Or just swap the 12V halogens you have now for LED downlights. Even swapping the 50W halogens for 20W will save you some money...
 

needasparks

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watts is watts, don't matter the voltage, watts is what your billed in and thats what your burning. just tot them up. simples. :)
 
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A

Adrian768432

Well many thanks to everybody. I've already found a fused switch in a kitchen cupboard(?) that feeds the towel rail in the bathroom, which has been on non stop since before we moved in! My first quarter electricity bill was £600, and that wasn't an estimate!

There are a total of 49 50w halogen downlighters in a two bed flat? And they're burning my money! I will contact a local electrician to come and replace with something less costly to run!

Thanks again.
 

telectrix

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49 x 50w = 2.45kW. that's around 30p/hour. or if left on 24/7. £50/week.
 

IzzyS

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In the the bright and distant past, people used to get by with a "planet destroying" 100W light in the middle of the room. Then some dim spark invented the CFL.

I recently stayed in a small cottage on holiday - 1 bedroom, a combined lounge/kitchen and a bathroom - it had just over 2kW of lighting.

We're all dooooomed....
 

telectrix

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but then again, the heat generated by tungsten lamps means less energy required from the heating system to warm the rooms, so the " wastage" on the lighting leads to a saving on the gas bill.
 
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