Power Consumption before transformer 1

[TerrenceM]

Morning all.

I'm working on a project where I have two power supplies (1 rated at 30W and another at 10W) and I would like to know how do you calculate the power rating of the cable that will be supplying mains to the two power supplies.

thank you all.
Regards
Terrence

 

[itsmoked]

Best method is to look at the data sheets for the supplies. They should specify the current draw at rated output.

Lacking that you can hook them up using obviously big enough wire and while they're running their expected loads measure the actual current. That can come in handy if you have to spec fuses.

Lastly you can take the supply power ratings. 30W or 10W

You don't specify the type; switching or linear, so take a worst case and consider 40% efficiency.

30W/0.30 = 100W
I believe you're in 240V land so 100W / 240v = 0.42A

Well.. That is a wire sooo small as to be too mechanically weak to be normally used. So abandon a calculated size and switch to a reasonable-to-use-size. That would be something around 18AWG. If this is all in the same protected enclosure and near each other you could maybe go down to 20AWG.

One caveat: If you're trying to meet some specification like UL or TUV, they have other specs that may override everything I've just said.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[TerrenceM]

Great Response. Thank you!!