# Can a laptop be run without an AC adapter present? **URL:** \ **Category:** Factual Questions\ **Created:** [January 19, 2008, 2:36am UTC](https://boards.straightdope.com/t/can-a-laptop-be-run-without-an-ac-adapter-present/434109 "2008-01-19T02:36:11Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![SweetHomeColorado](https://avatars.discourse-cdn.com/v4/letter/s/d26b3c/32.png) [@SweetHomeColorado](https://boards.straightdope.com/u/SweetHomeColorado)\ **Post date:** [January 19, 2008, 2:36am UTC](https://boards.straightdope.com/t/can-a-laptop-be-run-without-an-ac-adapter-present/434109/1 "2008-01-19T02:36:11Z")
Pretty self-explanatory but if I found a transformer large enough, could I plug it directly in to the laptop and power it safely or is the adapter necessary? ---
**Author:** ![Xema](https://avatars.discourse-cdn.com/v4/letter/x/9de053/32.png) [@Xema](https://boards.straightdope.com/u/Xema)\ **Post date:** [January 19, 2008, 2:45am UTC](https://boards.straightdope.com/t/can-a-laptop-be-run-without-an-ac-adapter-present/434109/2 "2008-01-19T02:45:38Z")
You need either to run the laptop on its internal battery or feed it the power it expects. This is typically a regulated DC voltage (often 14 to 18v) with a maximum current of perhaps 4 amps. A simple transformer puts out AC, which few laptops would like. Significant problems are likely if the power you supply isn’t what the laptop needs. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [January 19, 2008, 4:06am UTC](https://boards.straightdope.com/t/can-a-laptop-be-run-without-an-ac-adapter-present/434109/3 "2008-01-19T04:06:33Z")
[QUOTE=Xema] You need either to run the laptop on its internal battery or feed it the power it expects. This is typically a regulated DC voltage (often 14 to 18v) with a maximum current of perhaps 4 amps. A simple transformer puts out AC, which few laptops would like. Significant problems are likely if the power you supply isn’t what the laptop needs. [/QUOTE] Correct. To elaborate, “significant problems” including smoking your laptop. Don’t try this unless you know **exactly** what you are doing. ---
**Author:** ![Si\_Amigo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/si_amigo/32/2877_2.png) [@Si\_Amigo](https://boards.straightdope.com/u/Si_Amigo)\ **Post date:** [January 19, 2008, 12:41pm UTC](https://boards.straightdope.com/t/can-a-laptop-be-run-without-an-ac-adapter-present/434109/4 "2008-01-19T12:41:52Z")
Also, while on the subject, even if it is the proper type and has the right connector for the laptop you have it may work in all scenarios. I took a small targus travel adapter with me on a business trip last week (the factory one’s literally a brick) and found the its rated wattage was to low to boot my Dell M90. I had to remove the adapter and boot off of the battery. When my battery ran very low I plugged the adapter back in and it ran for days (but would not recharge the battery). Unexpected strangeness. ---
**Author:** ![ftg](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ftg/32/2801_2.png) [@ftg](https://boards.straightdope.com/u/ftg)\ **Post date:** [January 19, 2008, 8:56pm UTC](https://boards.straightdope.com/t/can-a-laptop-be-run-without-an-ac-adapter-present/434109/5 "2008-01-19T20:56:33Z")
In _some_ cases, the laptop is tightly coupled to an adapter in the sense that the internal resistance of the adapter must match as well. Too high or low and one or the other of the devices goes up in smoke. I do a lot of adapter substitution (and repair) when playing with 2nd hand electronics. But I would never dream of using a built-your-own adapter for a computer.