I'm trying to decide on a portable AC power station to power four laptops for at least five hours. I have the charger units for the laptops, and I'm confused on how to figure out the power consumption from them. Mainly, I don't know whether to look at the input power from the AC source or the output power going to the laptop.

Here are the specifications I see on the adapter.

INPUT: 100-240V ~ 3.2A OUPUT: 19.5V - 10.8A

So I know that the input is AC and the output is DC. And I'm looking at a 500Wh portable power station, like this one.


How do I know that 500Wh is enough to power four laptop for five hours? I know that the laptop can consume 19.5V * 10.8A = 210.6W. Or should I be using the input power, which is 110V * 3.2A = 352W?

With those numbers, there seems no way that 500Wh can power four of these laptops for five hours. But the power station claims that it can charge a laptop 7+ times, run a mini fridge 7+ hours, and power a TV and game console for hours.

My question is: Can a laptop really consume that much power under light use?


closed as off-topic by Chris Stratton, Dmitry Grigoryev, PeterJ, MCG, Kevin Reid Jul 3 '18 at 22:42

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "Questions on the use of electronic devices are off-topic as this site is intended specifically for questions on electronics design." – Chris Stratton, Dmitry Grigoryev, PeterJ, MCG, Kevin Reid
If this question can be reworded to fit the rules in the help center, please edit the question.

  • \$\begingroup\$ If the specs relevant, the one that would apply is the input. But in modern computers the actual draw would generally depend on processing load; typically the highest consumption would be while doing a lot of processing and charging a depleted battery at the same time, but it's not a given that the adapter can support both. In practical terms, this is off topic as a question about the usage of consumer electronic devices. This is a site that is reserved only for questions about design for which full engineering-level detail can be provided. \$\endgroup\$ – Chris Stratton Jun 27 '18 at 23:50
  • 2
    \$\begingroup\$ Can't you just run the laptops off of battery power for 5 hours? In any event, you probably cannot be sure how much power the supplies consume unless you measure actual numbers. The numbers on the supply are maximums. So you need to get a power meter for the laptops. Check out the "kill-a-watt". \$\endgroup\$ – mkeith Jun 28 '18 at 1:48
  • \$\begingroup\$ Well, the batteries on these old work laptops last for maybe 1 hour on a good day. And I don't have the option to replace them with new ones. \$\endgroup\$ – user3211857 Jun 28 '18 at 2:22
  • 1
    \$\begingroup\$ Laptops can consume a ton of power under light use if their batteries are discharged. \$\endgroup\$ – Dmitry Grigoryev Jun 28 '18 at 10:58

Don't forget the margin on top of the supply for good measure, a lot of products power supplies are sized one size up from the current they normally draw when the max power rating is still lower than that listed to some degree.

The best way tio do this is to get a power monitor like a kill a watt To help you find the average and max usage of your device. The ballooning of requirements is called margin creep, at each stage of the design you keep on adding margin until the requirements get too unreasonable. Then you message or total then up and size the system appropriately


210W DC is worst case weak battery and full screen brightness at 100% CPU. Then efficiency I expect is 85% max so AC input current is for computing breaker capacity.

You can expect laptops use 10% bestcase of this power on very dim displays with charged batteries and 100% worst case. Try 50% or better and expect short life. Laptop consumption varies greatly from 65W Max types to gamer power hogs.

  • \$\begingroup\$ I looked up the specs on the processor that these laptops use, and they use up to 47W. However, the laptops aren't actually doing very intensive tasks in the field, they mostly sit there with a word document on or running a data collection program. However, I still want to allow for extra room. Without actually measuring in the field, I'm still not sure that the 500Wh battery will last 5 hours. \$\endgroup\$ – user3211857 Jun 28 '18 at 2:26
  • \$\begingroup\$ Can’t you test them? Or even check battery discharge time or know anything about their charger access times or battery power capacity in Wh \$\endgroup\$ – Sunnyskyguy EE75 Jun 28 '18 at 3:01
  • \$\begingroup\$ I will get a power meter to measure exactly how much the laptops consume. They get used a lot but perform pretty much the same tasks every time without being connected to the internet, so I'm hoping their power consumption should be fairly consistent. \$\endgroup\$ – user3211857 Jun 29 '18 at 2:08
  • \$\begingroup\$ Set brightness low \$\endgroup\$ – Sunnyskyguy EE75 Jun 29 '18 at 2:35

Not the answer you're looking for? Browse other questions tagged or ask your own question.