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# How many amp 240v for 5v 10a

#### Stuee123

##### Member
Hi, i need so supply 5v 7amp for a couple of lights,
I want to use a step down converter 240v to 5v but wondering if there is a simple calculation to see how many amp the 240v supply needs to be.
Thanks

5V x 7A = 35 watts power out of the supply
240V x ?A = 35 watts power into the supply
The power supply is not 100% efficient so if it is 90% then add 10% more to the 35. (38.5 watts)
I don't know if 90% is the right number but this is what to do.

Load current efficiency considerations (impact on input current calculation) :

Regards, Dana.

Hi, i need so supply 5v 7amp for a couple of lights,
I want to use a step down converter 240v to 5v but wondering if there is a simple calculation to see how many amp the 240v supply needs to be.
Thanks

To be fair, it's a pretty pointless question - 35W is a very small load for a mains supply, and any possible mains supply would easily provide much more than 35W.

Generally there's never any need to work out the current from the mains, it's only the wattage which is a concern - which is why everything is usually rated in watts.

For example, a UK mains socket/plug will provide 13A, just over 3000W (actually 3120W) - almost 100 times the power you require. 120V sockets in the USA for example won't provide as much power (only 1800W), nor will some European sockets, although the most common Schuko type will provide 16A (3840W).

So it's not an issue.

Shipping costs are often the biggest expense. But Alibaba is working hard to make these low. https://www.aliexpress.com/item/32792812301.html
Google or Bing could easily answer that power equation question. A shopping need can also easily be solved there too. Distributor's profits must be recognized and Banggood is a trusted brand. Many others copy them. Connectors must be chosen too. Voltages can be universal(120/240). You can use hard wiring with crimped spade lugs or wire, or looped tight CW around screw terminals. Compare with pictures to do it right to avoid finger touching unsafe input voltages. If you need weatherproof or outdoor approved include those words in your search with 12V 35W or 3A

Last edited:
In reply to the actual post #1 question,
Input Amps = Output Watts / Input voltage = 5V x 7A / 240V = 35W / 240V = 0.15A. Allowing for inefficiencies, reckon on 0.2A as a minimum.

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