Calculating current draw

[pheran]

Apologies - I ought to know the answer to this and probably once did but old age is beginning to dull the senses.

I have relied on A = W/V to calculate the current draw of any electrical item. So (say) 6 x 20watt halogen down lighters in the main cabin use 10Ah (which is why I'm changing them to LEDs)

But suppose you run a mains voltage low energy bulb from the 12 volt supply via a DC/AC inverter. Is the current draw still W (say 10)/ V (say 240) = 0.04Ah plus an inefficiency factor (20%??) to cover the DC/AC conversion? TIA.

 

[nigelmercier]

I have relied on A = W/V to calculate the current draw of any electrical item. So (say) 6 x 20watt halogen down lighters in the main cabin use 10Ah ...

To clarify: they draw 10A, but use 10Ah in one hour.

There is nothing to be gained by using an inverter, but the calculation is similar. In your calculation the AC current is 0.04A at 240V, but is 20 times greater at the 12V end, plus an inefficiency factor of about 15% or more.