Wikipedia:Reference desk/Archives/Science/2022 March 21

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March 21

Laptop charger questions.

Somewhat CS-related but my questions are more on the physics side. My laptop charger is 45W. 1 store closest sells them at 65 W. Is that too far of a range? The employee said it will charge my laptop much faster. But I'm worried about overheating.

My laptop charger at where it plugs into the computer is L-shaped. And it is such that when the next part is straight, electricity doesn't go through. But it does go through if I twist the wire in some direction. Then what is going on inside?

And why is it the input and output volts and amps are different numbers? Thanks. 67.165.185.178 (talk) 08:09, 21 March 2022 (UTC).

Probably the first thing you need to do is a bit of reading about electricity. There's quite a good article at Hydraulic analogy which models electricity by analogy with water flow. However, put very simply: the first one to watch is the voltage. If the charger is rated at a different voltage it will either not work, or else damage your laptop. The wattage is related to how much electricity the charger can supply without being damaged or shutting down. A 65W charger can supply up to 65W, but will supply less if required. As regards the twisting, either you have a broken wire inside the cable, or else the plug and socket are not making good contact. If you have to do this things will eventually fail, based on my son's experience! Martin of Sheffield (talk) 09:23, 21 March 2022 (UTC)

Do what things, fix the wire inside the cable, or the plug and socket? In any event, the laptop chargers in the store don't seem to label the voltage. And my problem is my laptop chargers have 2 voltage labels, input and output. So I hope if store does list voltage, it has to list both voltages. 67.165.185.178 (talk) 09:33, 21 March 2022 (UTC).

1: A 65W power supply can provide up to 65W, but will only provide as much as the laptop asks for. The charger just provides a voltage on the cable; the laptop decides how much current will run. So I don't expect it will charge faster, although with a very smart power control unit in the laptop it could happen. When you connect a 45W power supply to a laptop expecting a 65W unit, the power supply unit might overheat or the laptop might decide that it isn't connected at all. You have to make sure the charger handles the right input voltage, provides the right output voltage, has at least the required power and has a fitting connector.

2: It appears there's a mechanical problem with it. A loose or dirty connector, only making a connection when you apply some force, or a broken wire. Or a damaged insulator that causes a short if you don't apply that force. You really don't want a short.

3: The power going in must be equal to the power going out (minus a few percent losses). Power is voltage times current and the job of the laptop charger is to convert the 230V or whatever comes out of the wall in your area to the 18V or whatever your laptop needs, and at the same time convert alternating current to direct current. PiusImpavidus (talk) 09:39, 21 March 2022 (UTC)

Ah you're right for #1. My laptop charger can work in both USA and England. The input voltage being 100-240 V, and the output 19.5 V. Input amps 1.4, output amps 2.31. Is the change in amps a conversion of AC to DC? 67.165.185.178 (talk) 09:45, 21 March 2022 (UTC).

Amps are amps. The fact that the power supply takes AC as input and produces DC output doesn't have any real relation. There is a voltage and current that the laptop is designed to accept as input, and that's what the power supply is designed to produce as output. The power supply draws what input current it needs to produce the design output, with the input voltage being the mains voltage. As you noted, many modern switched-mode power supplies have circuitry that can adjust for the range of mains voltages in different parts of the world. See electric power for the relation between voltage, current, and power. --47.147.118.55 (talk) 07:08, 24 March 2022 (UTC)

The intermittent contact of your Plug may be caused by dirt in the socket of your laptop. Every time you plug in, some dust particles from the air find their way in and are squeezed by the plug against the back of the socket. Over the time, the dust builds up, layer by layer, until the plug doesn't properly lock into place anymore. Try to clean out the socket with a thin plastic pin or toothpick or some other non-conductive tool. I saved many devices from going to the scrapyard this way... 37.201.147.171 (talk) 13:00, 22 March 2022 (UTC)

So I see now the newer laptop chargers (or AC adapters) are getting less voltage. I looked at my older laptop of over 10 years ago, at 65 W. (Compared to the new 45 W). Old 1 uses output voltage of 20 V (compared to new of 19.5 V). In any event the heads don't match, but if they did, and assuming the new stores sells at 20 V, is 20 V for a 19.5 V laptop okay? 67.165.185.178 (talk) 10:00, 21 March 2022 (UTC).

For the output, 19.5 V × 2.31 A = (19.5 × 2.31) W = 45 W. For the input side, voltage times current gives a range from 140 W (for 100 V) to 336 W (for 240 V), which is implausible, both for being excessively high and for being very different from the output side. The two powers should roughly match, as also mentioned above. Both the voltage conversion and the AC–DC conversion entail some power loss, but nothing that humungous, like from 68% up to 87%, which would turn into heat and melt the charger. Typically, in non-critical applications, there is some tolerance, and one would expect 20 W to be close enough to 19.5 W, but this cannot be guaranteed a priori.  --Lambiam 10:49, 21 March 2022 (UTC)

• OP, you would be wise to provide a faithful reproduction of your charger and/or laptop electrical spec (easiest would be a photograph of the plate with voltage information, like the link in that other question). As it stands, the advice above is correct, but depends on whether you read/interpreted the plate correctly. It is not very hard to do and more likely than not you read it correctly, but your questions here are rather basic (no shame in that), and mistakes can be costly when it comes to electricity. Tigraan^{Click here for my talk page ("private" contact)} 16:26, 22 March 2022 (UTC)

Wow, 37.201.147.171 was right too. I took a plastic fork and poked into the laptop part socket, and plugged it back in, voila. Now the wire is not bent and the electricity still goes through. On top of that, touching the AC adapter area is no longer as heated. But wondering what did twisting the wire do, if it was a socket issue? Could be both? 67.165.185.178 (talk) 01:26, 24 March 2022 (UTC).

Maybe, but it's unlikely that there's also a cable break. It's typical for this type of failure, that you can momentary establish temporary contact by twisting the wire or tangle it into a specific position. By doing this, a force is applied to the plug, pushing it against the contact surfaces in the socket. But reliable contact is only possible, if the plug has the space to go all the way in. By cleaning the socket out you created that space, so that issue should be solved completly. 178.208.99.186 (talk) 10:54, 24 March 2022 (UTC)

Gardening pH of soil.

What is pH supposed to mean for soil? In chemistry pH is the measure of H+ ions. But ions only exist in the liquid and gas phase, not solid. So soil can have a pH in rainy conditions, then what about dry conditions? I see a soil modifier in hardware soils, to make it acidic the principle ingredient is S, and to make it basic, a whole bunch of ingredients that are solid bases. Can they pluck the H out of a molecule without an orbiting electron? 67.165.185.178 (talk) 08:13, 21 March 2022 (UTC).

It's the pH experienced by the plants' roots that matters. Soil testing meters and kits generally require the soil be dried, then distilled water is added and a reading is taken. Abductive (reasoning) 08:55, 21 March 2022 (UTC)

Soil contains water. The pH in this case is the pH of the water in the soil. --Jayron32 12:47, 21 March 2022 (UTC)