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Constellation

Not Fast Charging while Screen is On

I have been a Samsung user since the S5, and have owned Every Generation in between. As far back as the S7 I remember that "fast charging" has not actually worked while the screen is on. Recently after upgrading to the Note 20 Ultra, I actually measured it. Here is what I found:

 

Disclaimers:

  • I am using the stock 25W "Super Fast Charger" and cable, and Fast and Super Fast Charging are enabled in settings, so please do not offer these as troubleshooting suggestions. 
  • I am measuring the Voltage draw from the Charger using an energy monitoring smart plug as my determination of Charge speed, not anything on the phone. 
  • When plugging in the cable, I get the notification on the lock screen and notification dropdown that the phone is "Super Fast Charging."

Results:

  • Simply put. When the screen is on, the phone only draws ~9-10Watts from the charger. 
  • When the screen is off The phone draws the full 25W from the charger.

 

Now my question:

  • I can't find this advertized anywhere by Samsung, and I have seen zero posts on the forums or elsewhere that say the phone will not fast charge while the screen is on. Is this really normal behavior? Do other brands behave the same way?

What I would expect:

  • The phone should still draw the maximum current/wattage from the charger regardless of whether the screen is on. 
    • I would expect the net charge rate to be a little slower in this case since the phone is in use.
  • I would not expect the charge rate the be cut by literally 67%. The net effect is that after offsetting power usage, the phone barely charges at all while using it. 
    • The only thing that should affect charge speed while in use is battery heat, which I would fully understand but is not happening in this case. 
  • I would also not expect the phone to say "Super Fast Charging" in the Notification Bar as this is a flat out lie, and the "estimated time until full" is complete in that case. It honestly takes 3-4 hours to charge to full while using the device. 

Can anyone confirm that the behavior I am seeing is as Designed by Samsung? Any other clues as to what is going on?