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I am looking at the 10.1 inch touch screen for RPi, and am puzzled by its power specifications.

Under Features tab in the above link, it says:

  • Power: DC12V/2A
  • Consumption: 5W

Obviously \$12 \times 2 \neq 5\$, I wonder what those numbers mean now. How can I correctly estimate the power consumed by the screen under normal operating conditions?

JYelton
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YumekaMengjiaLYU
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  • New math. Joking! Power is probably a switcher. 12V drawing 2A for a period of time consuming 5W. – StainlessSteelRat Sep 01 '20 at 22:28
  • those are chinese amps, divide by 3 for metric. j/k; it also powers the pi, so it needs more than just what the screen uses to have one power plug for the combined unit. nice of it to provide 5v! – dandavis Sep 01 '20 at 22:29

3 Answers3

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Looking through the photos on the site you linked, it shows that a 5V 2.5A USB power output plug is included. This means that in order to power both the LCD and that USB power output reliably, more than the 5W which the LCD (mostly its backlight) consumes must be available.

The USB output would be 12.5W, added to the 5W of the LCD portion, you could potentially consume 17.5W. The extra 6.5W would be for inefficiency and overhead.

JYelton
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  • So the power consumption is 5W + whatever the raspberry pi uses. – Jasen Слава Україні Sep 02 '20 at 10:06
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    @Jasen That's right. My answer might be a little misleading because it presumes that whatever is plugged into the USB connector is using all 12.5W. Rather, that is its maximum _capability_. If the Raspberry Pi uses 10W, then another 2.5W is "unused". (To be more technically accurate, power (watts) only exist when a load consumes energy. [This post](https://electronics.stackexchange.com/a/34746/2028) would be good to review.) – JYelton Sep 02 '20 at 15:45
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According to the data sheet, there is a USB connector on the board with a rated power output of 5 V at 2.5 amps which is 12.5 watts. Added to the 5 watts that the screen uses results in a potential power usage of 17.5 watts That is much closer to the specified 12 V 2 amps which is 24 watts. Part of the difference could be the power lost in generating the 5 V output from the 12 V input. The rest could be simply a matter of rounding up the numbers to get a nice even number like 2 amp rather than a fractional number.

Barry
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Additional to the USB output (whose power is passed on, not consumed) ...

Current ratings tend to be conservative, both to allow for tolerances, and to cover surge currents such as startup.

If imprecise, they must be on the high side, because they are used to determine the correct fuse if you are fitting one.

It's reasonable to round them up to the next even number or easily available fuse or PSU rating.