How to power laptop from Lab Power supply ? - Page 1
Forum section: electronics / beginners

author: tonycstech
author_rank: Regular Contributor
timestamp: April 15, 2024, 06:38:34 am
content: Looking for a power supply that i can use to power modern laptops with.My understanding is that they do not just take straight DC 19v but instead they communicate with the charger via data pins and charger responds back as requested.Obviously average power supply cant do that so is there anything i can look at ?Something that can limit the current also.Thanks !

author: Berni
author_rank: Super Contributor
timestamp: April 15, 2024, 06:56:53 am
content: For the classical 19V barrel jack there is no fancy communication or anything. Just give it power and it charges. The bigger laptops might be careful and ramp up the current until they see the voltage sag too much, but that's about it.But there are laptops with weird proprietary plugs that might do more fancy stuff. The USB-C charging port laptops is where you definitely have communication going on before it will actually charge, but at least it is standardized to the USB PD spec.Why do you need to power it from a lab PSU anyway?

author: Solder_Junkie
author_rank: Frequent Contributor
timestamp: April 15, 2024, 07:22:55 am
content: It depends on the laptop brand. I have an Asus Vivobook and apart from the awkward sized connector, it powers and charges correctly from a 19V OEM car adapter.On the other hand, my Dell Vostro uses what looks like a standard barrel connector... except the inside of the tubular barrel is a 3rd connection to the charger. Without the correct charger, the Dell laptop will not charge, however it can be powered without charging using a 19V supply.There was some discussion elsewhere on this forum on the subject of "fooling" these laptops, but it's far from straightforward as the device in the charger of the Dell is some kind of 1 wire data comms IC that appears to exchange data with the laptop before it will commence charging. I have been unable to find much information as to how it communicates, nor have I been able to source a 12V to 19V car adapter... other than using the clumsy approach of a 12V to 230V inverter to power a standard mains Dell charger.SJ

author: Jwillis
author_rank: Super Contributor
timestamp: April 15, 2024, 08:20:05 am
content: The sense wire is for the computer to determine the power capability of the power supply so it doesn't exceed it or to just turn on the power supply only when a demand is required. In most cases is just a matter of jumping the sense pin with a resistor to either ground or positive or both as a voltage divider. Did it to a Lenovo with a resistor from positive to sense. But can't remember the value of the resistor. In that particular case, the power supply can't be tested without the resistor because it won't turn on.

author: tonycstech
author_rank: Regular Contributor
timestamp: April 15, 2024, 03:02:45 pm
content: Great. So basically no such power supply exist and ill have to make something of my own.

author: Solder_Junkie
author_rank: Frequent Contributor
timestamp: April 15, 2024, 03:21:33 pm
content: Quote from: tonycstech on April 15, 2024, 03:02:45 pmI don't understand the problem you appear to have... what is wrong with buying a charger for your laptop? There are plenty around, both new from the manufacturer or OEM/second hand from eBay.SJ

author: tonycstech
author_rank: Regular Contributor
timestamp: April 15, 2024, 03:41:10 pm
content: Quote from: Solder_Junkie on April 15, 2024, 03:21:33 pmit does not let me manually limit the current or see the current.Some chargers cost $300+ on high end gaming laptops so......

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 15, 2024, 03:43:51 pm
content: Why do you want to limit the current. If the laptop needs a certain current and you limit it then the voltage will drop too low to work. For monitoring the current you can cut the wire and insert the ammeter. Which laptop do you have that requires a $300 charger?

author: tonycstech
author_rank: Regular Contributor
timestamp: April 15, 2024, 03:45:14 pm
content: because if something is short, i want to be able to limit the current so it does not blow up before i see it.

author: Berni
author_rank: Super Contributor
timestamp: April 15, 2024, 03:46:48 pm
content: Well easiest way to get a laptop charger is to buy a laptop charger, generic third party charger bricks are not even all that expensive (unless it is some powerful gaming laptop that needs some giant >200W brick)What is the actual problem you are wanting to solve with a bench PSU? If anything that is a dangerous way to charge a laptop since you are one bump of a voltage knob away from sending 30V into a laptop and killing it.If it is current draw you are interested in, then you can just as easily buy one of those cheap digital panel mount amp meters and wire it into a existing charger (be it by cutting the cable or adding a male/female connector pair to plug it in between the charger and laptop). Heck even easier is to simply plug the 220V side of the charger into one of those mains power meters and read off the consumed watts. Laptop chargers are pretty efficient so you can assume most of the watts that it is pulling from the wall outlet are being put into the laptop. All laptop chargers have current limits built in too, otherwise they would catch fire way too often when people damage the charging cable. Reducing the current limit doesn't make sense since that will likely cause the laptop to start cycling between charging and not charging as it tries to pull the rated current and the voltage collapses, this might even kill a poorly designed charger circuit in the laptop.

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 15, 2024, 04:26:10 pm
content: Quote from: tonycstech on April 15, 2024, 03:45:14 pmAre you going to run the laptop without battery? If you have the battery in it and there is a short the battery will supply the current to destroy the computer. Besides monitoring the current going in to the charging port doesn't tell you much how much power the computer is consuming.

author: tonycstech
author_rank: Regular Contributor
timestamp: April 15, 2024, 04:59:23 pm
content: it tells me how many amps it pulls on idle.And ill be able to see how many amps it pulls on full load.

author: thephil
author_rank: Regular Contributor
timestamp: April 15, 2024, 07:38:04 pm
content: As others have already said, the traditional barrel style connectors often feature an additional pin that will signal the wattage of the power supply to the laptop via a simple resistor – no complex/fancy communication required. You can get cheap sets of brand specific connectors that have the required resistors in the connectors, already. I use such a set when working on defective laptops for the very reasons you mentioned: monitoring and possibly limiting current draw for the device under test.For the new generation of USB-C PD machines, I use a generic supply and one of those USB-power monitors from a brand with too few vowels in its name.... Not as nice and convenient, but it works.

author: tonycstech
author_rank: Regular Contributor
timestamp: April 15, 2024, 08:28:07 pm
content: I ordered my self the biggest connector kit i could.None of them had any resistors that i could see and also none of them fit my laptop either.Maybe i ordered wrong kit, i dont know.

author: Jwillis
author_rank: Super Contributor
timestamp: April 15, 2024, 11:54:38 pm
content: Quote from: tonycstech on April 15, 2024, 08:28:07 pmIt would help immensely if we knew what make and model the your laptop is. If you have dimensions of the existing power plug would also help.I only have 3 barrel type in my laptop adapter kit with a center sense pin. 7.4mm OD 400K Ohm between centre pin and positive. 7.8mm OD centre pin unconnected. 4.5mm 390K Ohm between centre and positive.

author: Andy Chee
author_rank: Super Contributor
timestamp: April 16, 2024, 08:22:27 am
content: Quote from: tonycstech on April 15, 2024, 04:59:23 pmI have one of bigclive's clone "Hopi" meters for that:Failing that, a consumer energy meter does exactly the same job:https://a.co/d/5JG83WZ

author: BTO
author_rank: Frequent Contributor
timestamp: April 16, 2024, 10:30:57 am
content: Quote from: tonycstech on April 15, 2024, 06:38:34 amOK....1. Given your question it would have been useful if you posted a picture , Since you didn't we need to assume it's a basic connector thathas only + and -a datasheet would have been good as well or wiring diagram.2. If it is the type that has only Positive and Negative, here is what you do if you plan to run it off a bench power supply.- First you find a connector that will actually comfortably and snuggly fit into the charging socket, Preferably one that you could butcher.You cut it off (Preferably) a non working power supply/ Charger , long enough so you have enough slack.- Now you need to apply power to it, so you CHECK THE POWER REQUIREMENTS ON YOUR LAPTOPNow you said 19V (it's likely that it's DC but you need to specify this) so let's make the assumption it's 19V DC on the output.THE TAKE AWAY OF VOLTAGE IS......... DO NOT EXCEED THE VOLTAGE RATINGas you will blow capacitors in your laptop.Voltage is Pressure, ... Too much pressure = BANG !!!However... Too Little pressure does not. so.. 17V-19V DC is going to be fine,If you stuff up, it will result in the laptop not starting up, or it will result in slower charge or not full charge.- Now you need to know the current rating (this is equally important as the voltage), since you have not provided it, i will assume one.Let's say your laptop has a current rating of 2A (May be written as 2000mA),Current is speed in a circuit, so....You need to AT LEAST MEET THE REQUIREMENT, But not go under it.So, You can have a 2A - 3.5A Transformer but i wouldn't go higher.so remember DO NOT EXCEED THE VOLTAGEhowever..........DO MATCH OR SLIGHTLY EXCEED THE CURRENTif you provide less current worst case scenario ,it will not switch on, Not because something blew, but because there is not enoughcurrent circulating through the circuit to keep everything powered.it's important to know these things up front, However, if you hook it up to a bench supply IN CONSTANT VOLTAGE MODEthe current should figure itself out,Assuming your power supply can supply at least that much- Lastly, YOU MUST GET THE POLARITY CORRECT. so , is it Centre Positive , or Centre Negative, chance are it's centre positive, BUT DO CHECK.

author: Vovk_Z
author_rank: Super Contributor
timestamp: April 16, 2024, 03:38:32 pm
content: Quote from: tonycstech on April 15, 2024, 03:02:45 pmNo, I guess what you need is almost any lab power supply (>=4-5 A) and an appropriate connector for that exact laptop. I mean a connector for exact laptop is the largest problem typically.

author: BTO
author_rank: Frequent Contributor
timestamp: April 17, 2024, 10:17:05 am
content: Quote from: Vovk_Z on April 16, 2024, 03:38:32 pmI Agree with the power supply ideaI disagree that the connector is USUALLY the largest problem.Usually people understanding the power ratings is the largest problem , the connector is the 2nd largest problem