Laptop charger vs bench supply ??? - Page 1
Forum section: electronics / general

author: PwrElectronics
author_rank: Regular Contributor
timestamp: August 21, 2022, 05:08:13 pm
content: OK,A few weeks back I found a free circa 2014 Acer laptop in the recycling barrel. Had a wiped drive with a fresh (in 2018) install of win10 on it.I found a old charger in my stash of stuff that worked and the battery is even pretty good. This morning ran it for well over 2hrs and it was still at 55%I have several other old chargers around with the wrong plug size on the end but they are all 19v output. The one that did have the correct plug also is 19v.I found a chopped off cable end with correct size plug around and thought it would be interesting how much current this laptop would draw while charging the battery. The charger I had used earlier got pretty warm and could be undersized (pretty old charger from a circa 2001 Gateway).I set my bench supply for 19V and connected the chopped off cable (checked polarity of the plug compared to the charger that worked) and plugged it in. No current draw and laptop was not seeing it or charging....Connected up the real charger and it works fine.WhyI am aware that some chargers are "smart" and those have a double barrel and center pin in them (aka 3 wires). The laptop can throttle its power use based on what charger is there. My HP laptops supplied by work are like that. I doubt that old Gateway the charger came from and this Acer do not appear to have anything like that. Keep in mind the charger is over a decade older than the laptop and a different brand too.Just a Sunday morning mystery...

author: golden_labels
author_rank: Super Contributor
timestamp: August 21, 2022, 05:18:42 pm
content: Is the bench power supply capable of delivering enough current? Perhaps the laptop tries to pull multiple amps, the supply switches to CC, sags, the laptop detects that and stops charging.Also see what is the open-circuit voltage of the working charger: in case the laptop uses that as a hint that it should charge.I know those are obvious things, but I have no other ideas and we all happened to forget to plug the cable into a socket multiple times, right?

author: PwrElectronics
author_rank: Regular Contributor
timestamp: August 21, 2022, 06:39:52 pm
content: DMM measured on the plug of the charger was 19.0V +/- Set bench supply to be the same. Its a 100W bench supply and I set the current limit at max of 5A. There was no hint of any current draw from the bench supply....I am going to have to investigate more, like get a scope on the voltage somehow looking for a sag, etc....Also triple check the the plug polarity.There is no apparent reason for this to not work so far!My end goal was to splice the chopped off plug end onto a spare charger that currently has the wrong plug on it. The test charger comes from a 2001 Gateway that I occasionally use for interface (real serial port with WinME (!) ) with some 90s era Tek scopes so I would rather not use that for this other laptop when I have other spares around.

author: PwrElectronics
author_rank: Regular Contributor
timestamp: August 22, 2022, 02:01:03 pm
content: OK egg on face a littleThe OD of the barrel plug matched but the ID of the inside barrel did not. The ID of the inside plug on the cable I tried with the bench supply is ever so slightly larger compared to the charger one. So, the center pin on the socket in the laptop would not be contacting it and therefore no connection.It took inserting the shaft of a small screwdriver to tell the difference between them.Part of me was hoping there was some electronics reason for this but just simple mechanical issue.