Electronics > Beginners
external battery pack for laptop, current limiter
ledtester:
A current limiting circuit will drop the voltage all the way to zero if necessary.
Current limiting isn't going to work. The laptop draws more current because it needs more power, but current limiting will reduce the output voltage which reduces the power supplied to the laptop. The laptop will respond by trying to draw more current resulting in even a further drop in voltage.
As Jeroen3 said you need to limit the power within the laptop itself.
soldar:
It is probable that it is not just the value of the resistor but that communication is going on through that pin. Have you checked with a scope to see if there is any signalling going on? Specially at startup?
https://kakopa.webcindario.com/Dell_PS/index.html
http://www.laptop-junction.com/toast/content/dell-ac-power-adapter-not-recognized
http://www.laptop-junction.com/toast/content/inside-dell-ac-power-adapter-mystery-revealed
http://www.laptop-junction.com/toast/content/dell-ac-power-adapter-id-chip-died
http://www.laptop-junction.com/toast/content/dell-battery-charging-system-d5xx-and-d6xx-laptops
purezerg:
--- Quote from: ledtester on October 03, 2019, 03:01:22 pm ---A current limiting circuit will drop the voltage all the way to zero if necessary.
Current limiting isn't going to work. The laptop draws more current because it needs more power, but current limiting will reduce the output voltage which reduces the power supplied to the laptop. The laptop will respond by trying to draw more current resulting in even a further drop in voltage.
As Jeroen3 said you need to limit the power within the laptop itself.
--- End quote ---
oh i didnt know that.
that said. i wonder how a 120w power adapter copes with 150w demand. how does it prevent itself from blowing up.
purezerg:
--- Quote from: soldar on October 03, 2019, 05:54:11 pm ---It is probable that it is not just the value of the resistor but that communication is going on through that pin. Have you checked with a scope to see if there is any signalling going on? Specially at startup?
https://kakopa.webcindario.com/Dell_PS/index.html
http://www.laptop-junction.com/toast/content/dell-ac-power-adapter-not-recognized
http://www.laptop-junction.com/toast/content/inside-dell-ac-power-adapter-mystery-revealed
http://www.laptop-junction.com/toast/content/dell-ac-power-adapter-id-chip-died
http://www.laptop-junction.com/toast/content/dell-battery-charging-system-d5xx-and-d6xx-laptops
--- End quote ---
from what i know HP adapters are resister based. the dell are digital chip id based. nope i dont have a scope to test. any other means to tell if it's not just plain resistor?
Zero999:
--- Quote from: purezerg on October 03, 2019, 06:56:55 pm ---
--- Quote from: ledtester on October 03, 2019, 03:01:22 pm ---A current limiting circuit will drop the voltage all the way to zero if necessary.
Current limiting isn't going to work. The laptop draws more current because it needs more power, but current limiting will reduce the output voltage which reduces the power supplied to the laptop. The laptop will respond by trying to draw more current resulting in even a further drop in voltage.
As Jeroen3 said you need to limit the power within the laptop itself.
--- End quote ---
oh i didnt know that.
that said. i wonder how a 120w power adapter copes with 150w demand. how does it prevent itself from blowing up.
--- End quote ---
It wouldn't surprise me if it can cope with more than 120W, especially if it's for short periods of time.
Navigation
[0] Message Index
[*] Previous page
Go to full version