240v to 12v Circuit

28 Jan 2007
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United Kingdom
Want to add 12v downlighters in place of 240v light units and know a 5amp fused lighting circuit can take up to 1200w.

240v to transformer (transformer replacing a 100w bulb) to 8 x 20w LV downlighters.

What load is the transfomer putting on the mains circuit? as each 12v/20w unit is nearly 2A.

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:oops: yes you are right I am wrong, i was thinking it was 16 lights, but i don't know why i was thinking that
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OK Thanks but
8 x 20w = 160w but at 12v = 13A'ish which on 240v = 3000w 'ish

So a lighting circuit is 1200w however the volts are supplied ?
At 240V, a five amp circuit will carry 1200W maximum.

1200W is indeed 1200W, no matter what. 'Scuse the pun..
Just to point out the whys and where-hows of things:

Wattage is a measure of flow of energy in joules per second, it'll be roughly the same on the input and output sides of the powersupply, excepting of course internal loses (the laws of thermodynamics see to that! :) )

Current is amount of electrical charge per second, with an Amp being a coulomb per second

Voltage is the amount of energy on each unit of charge with a volt being a joule per coulomb

Which is why P=IV works :) , and as long as you keep it proportional you can shift I and V about (which is exactly what the grid does)

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