Laptop PSU - Page 1
Forum section: electronics / repair

author: vidarr
author_rank: Frequent Contributor
timestamp: June 08, 2019, 02:56:16 pm
content: Hi guys. I have an unused PSU for a laptop that I want to use for a different laptop. The new laptop requires 19V 3.42A. The PSU supplies 20V 11A.Way back when, I saw a laptop PSU opened up and inside was something that was adjusted to change the voltage output. I cannot find this video anymore.Do you guys think that was maybe just specific to that PSU, or is there a chance my PSU would have some similar setup inside? I don't mind opening it and making adjustments, but I don't want to do anything to it at all if this is going to be a lost cause.Any thoughts/opinions would be appreciated.Thanks guys.edit: I wasn't sure where to post this. Seemed to make most sense here. Move if necessary. Thanks.

author: madires
author_rank: Super Contributor
timestamp: June 08, 2019, 04:06:00 pm
content: Usually those SMPSUs have an optocoupler for the voltage feedback. The optocoupler is driven by a TL431 for example and the voltage is set by a voltage divider. Look for the feedback circuitry at the secondary side and let us know what you find.

author: vidarr
author_rank: Frequent Contributor
timestamp: June 08, 2019, 06:26:10 pm
content: I researched and read both these posts below and looks like there is some modification of the SMPSU required for what they needed. Not sure for me though, because they are not doing the same as what I need to do. If this is going to require "hard" modifications to the actual device, I would rather wait and find a used laptop PSU somewhere. The one I have is for a very expensive ($10k +) "laptop", aka desktop replacement. The original post I saw a long time ago, the guy had two variable resistors (I think?) that he was able to adjust with a small screwdriver that he could raise/lower the voltage output. After reading these two posts, I don't see how that is possible safely. (It was a long time ago when I saw that video.)https://www.eevblog.com/forum/projects/convert-smps-(laptop-psu)-to-variable-voltage-and-current-source/https://hackaday.io/project/3469-modifying-a-notebook-power-supplyIf there is any hope I can do this easily, I will crack this thing open and take some pics.Thank You!!!

author: extide
author_rank: Regular Contributor
timestamp: June 08, 2019, 06:30:43 pm
content: Honestly you can probably just use it as-is. Most laptops run from 19V but that one appears to be for a high end gaming laptop so they are probably pushing 20V to combat voltage drop at higher loads. I would imagine that the circuitry inside the laptop you actually intend on using it with will be fine with 20V instead of 19V. It's going to go through further regulators inside the laptop anyways as pretty much nothing actually runs directly from that 19V input voltage anyways.

author: vidarr
author_rank: Frequent Contributor
timestamp: June 09, 2019, 02:38:47 pm
content: I was wondering this, but too scared to try it. I think I'll do it now.If I am not back with a "Broken Laptop" thread, you'll know it worked.Thanks!

author: soldar
author_rank: Super Contributor
timestamp: June 09, 2019, 03:05:00 pm
content: Manufacturers specify precisely odd voltages and currents because most people will buy the exact PSU from the manufacturer.The PSU should work fine unless the laptop is one of those DELLs that have the third bus pin.Just the cable from the PSU to the laptop will have a voltage drop and you can increase it by just making the cord longer.

author: vidarr
author_rank: Frequent Contributor
timestamp: June 09, 2019, 07:02:27 pm
content: I made a custom adapter (it had 4 pins, you can see the diagram in the pic above) and it worked perfectly fine. It has been running for a few hours now. Thanks for taking the fear away.

author: Gyro
author_rank: Super Contributor
timestamp: June 09, 2019, 07:21:21 pm
content: It's pretty unusual to see a laptop adapter with an11Acurrent rating. That's about twice the norm.

author: magic
author_rank: Super Contributor
timestamp: June 09, 2019, 07:31:10 pm
content: Look at the plug pinout diagram printed on it, it wasn't originally for laptops.

author: vidarr
author_rank: Frequent Contributor
timestamp: June 09, 2019, 08:54:01 pm
content: Yeah, this "laptop" is actually a very, high-end machine -- they call desktop replacement". The machine that uses that PSU was about $11k. People use lesser versions of this for gaming and this sort of thing. I use it for work. I have to run intensive applications for 3D modelling, animation, graphics, virtual reality worlds, and this sort of thing. My desktop is even crazier than that laptop -- more room for RAM and also PCIe SSDs, liquid cooling, etc.Thanks!

author: coromonadalix
author_rank: Super Contributor
timestamp: June 10, 2019, 11:21:03 am
content: I have an 12 amps 19volts laptop psu, and its big, for an old p4 3.4 ghz alienware .... loll 4 fans in it, need lots of juice

author: DDunfield
author_rank: Regular Contributor
timestamp: June 10, 2019, 01:03:45 pm
content: Quote from: Gyro on June 09, 2019, 07:21:21 pmYeah! - that's impressive. I thought the 9.2A rating of the PSU for a laptop I was given recently was somewhat over the top!Had fun figuring out "BIOS customization" with that laptop:https://www.eevblog.com/forum/chat/anyone-with-experience-ami-bios-customization-amibcp/msg2413323/#msg2413323Dave