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I want the possibility to charge my Laptop (19V/3.42A, Acer Aspire 5 A515-52G) from a power bank. Since my laptop only has the ordinary barrel power connector but power banks usually come with a USB-C PD 45W (20V/2.25A) port, I'm planning to use a USB-C to 20V DC Trigger (this thing requests 20V constantly from the USB PD charger.

The USB PD rev. 2.0/3.0 source power rules however define 2.25A as the minimum current for 20V. If my laptop is in a low power scenario and requires less than 45W, only the amperage may go below 2.25A. How does a USB PD charger/power bank behave in this scenario? Will it deliver lower amperage or refuse to work entirely?

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    Please edit your question to add info on the model laptop you are attempting to do this on. This is needed information because it all depends on make and model of laptop. I have a MacBook Air (2019) that comes with a 30W power supply. But I also have a 27W power supply and it charges fine; just slower. But if I try it with an 18W power supply it just keeps the machine running and not draining; no charging. – JakeGould Oct 10 at 2:06
  • I don't see the need for the laptop model. The laptops' power specs are there and my question has to do with the USB PD specification. Can less than 2.25A be drawn at 20V from a USB-C PD 45W power supply? – Morrow Oct 10 at 23:43
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The specs allow 20v at 5 amps max or 100w.

Basically, the more amps available the faster it will charge. There's a critical threshold after which it either won't charge at all or will be so slow it might as well not be charging.

Further there's a even lower threshold where it will drain the battery faster and faster as you amps decrease.

Your only chance of using the minimum is if your battery is 100% charged, and your laptop is off or near idling.

If you plug a USB type C into the laptop for charging, and its using super low power, there is a chance it might switch from 20v down to 5v where it can get 5v at 5a or 25w.

The barrel plug expects 20v (19v) no matter what.

  • The plug cannot switch down to 5V at lower power needs since the 20V DC Trigger I'm planning to use will always ask for 20V, hence my question. If my laptop requires less than 45W, only the amperage may go below 2.25A. How does a USB PD charger/power bank behave in this scenario? Will it deliver lower amperage or refuse to work entirely? – Morrow Oct 10 at 23:47

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