Regarding electronic devices, in terms of calculating how many watts a device draws, say a WiFi modem, does one calculate the input or the output on the dc converter?

the specs are as follows 

input 240v 0.8amps (192watts)

output  12v 2 amps ( 24 watts)

there seems to be quite a big wattage difference

 

 

 

15 hours ago, sunset1 said:

input 240v 0.8amps (192watts)

output  12v 2 amps ( 24 watts)

there seems to be quite a big wattage difference

Typically, input specifications are for the peak power ever seen, so you can design the power supply to cater for that need. A power supply often has a turn-on surge that lasts less than a second; that would be where the 192 watts comes from.

The power supply's output rating is generally a continuous rating; it should be able to supply 12 V at 2 A all day. So IF the load was at maximum, that's 24 W as you say, so most of the time the input power would be about 10% more than that, say 26 W, with a brief excursion to a maximum of 192 W at switch-on.

1 hour ago, Coulomb said:

Typically, input specifications are for the peak power ever seen, so you can design the power supply to cater for that need. A power supply often has a turn-on surge that lasts less than a second; that would be where the 192 watts comes from.

The power supply's output rating is generally a continuous rating; it should be able to supply 12 V at 2 A all day. So IF the load was at maximum, that's 24 W as you say, so most of the time the input power would be about 10% more than that, say 26 W, with a brief excursion to a maximum of 192 W at switch-on.

AH ok thanks for the explanation!  

I thought maybe the adapter was just burning the difference (192 watts - 24 watts) in stepping down the watts and was thinking, that sure is a waste of x amount of watts lol.

thanks for the help again.

 

On 2021/07/12 at 12:01 AM, sunset1 said:

I thought maybe the adapter was just burning the difference (192 watts - 24 watts)

If it was, it would be getting burning hot! 🔥