48 votes
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How does a USB C port provide the power to charge laptops?

USB-C will use the Power Delivery specification, a first connexion is done at 5V, then "negotiate" whether it can use a higher profile to charge. There are 5 profiles available : Profile 1 : 5V@2A ...
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  • 739
30 votes
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How do mobile phone chargers produce regulated voltage?

Phone chargers are indeed usually a 5 V regulated power supply. Here's an example of a simple circuit that is commonly used: Source. This is a flyback converter circuit. The output voltage is ...
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25 votes

Takes days to charge phone from 10W solar panel

First make sure everything is working as intended. Point the solar panel at full sun and see what kind of current you can get at 5 V. Try a 5 Ω power resistor. That should draw 1 A, which ...
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24 votes
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Heat lost in ideal capacitor charging

The problem with these theoretical examples lies in the fact the current is assumed infinite for 0 seconds. Crudely substituting this in the conservation law: $$ \frac {\partial \rho }{\partial t} +\...
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21 votes

Takes days to charge phone from 10W solar panel

You're hooked up wrong. The meter's big rotary switch has a legend around the outside indicating range. Obviously, there are as many range markings as there are switch positions. Only two of them ...
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21 votes
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Why doesn't my computer USB port break when I plug in a 2A device?

To be compatible with the original standard, USB devices should not draw more than 100mA (which is plenty to power the logic interface), until they have negotiated with the host, to find out what it ...
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  • 140k
16 votes
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Using LiFePO4 battery as car battery

LiFePO4 vs LiIon vs LiPo Some people have commented on LiIon batteries, but the question and this answer are about Lithium Ferro Phosphate batteries / LiFePO4 which I'll abbreviate in places as LFP4. ...
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16 votes
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Difference between battery and capacitor?

Capacitors and (rechargeable) batteries can both be used to store and retrieve electrical energy, and both are used for this purpose. But the way they store electrical energy (charge) is different, ...
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16 votes

Why doesn't my computer USB port break when I plug in a 2A device?

Historically: really old mainboards connect USB power pins to the 5V power rail, with no protection power on by keypress was added, which added a jumper or a BIOS setting that decided whether USB ...
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16 votes

What does an EV "wall socket charging cable" do?

It is for safety. It can't be omitted. The box tells the car how much current is available at maximum so the car knows how much is the maximum current it can draw. The box also turns on mains voltage ...
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15 votes

Are AA battery and 18650 battery the same?

An AA cell is not the same as an 18650 cell. 18650 designates lithium-ion batteries of nominal voltage 3.6 Volts each. These typially consist of the actual lithium-ion battery and some circuitry, as ...
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15 votes
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How do USB charging and "smart" charging ports (e.g. Anker's PowerIQ) work?

There are two additions to the USB specification that allow for more than 500mA current. usb battery charging specification 1.1. Allows for up to 1.3A. usb battery charging specification 1.2 (and ...
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  • 913
14 votes
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Lead Acid AGM battery testing - Why am I testing it this way?

You could do the entire discharge at the lower rate but then it would take a lot more time. When discharging at a high rate the voltage may collapse prematurely so the battery seems discharged before ...
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13 votes
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Are sealed lead-acid batteries safe to use indoors?

Actually SLA batteries have a vent... so the name "sealed" is a bit of a misnomer. VRLA (valve-regulated lead-acid battery) is actually a name for the same tech. Practically every UPS (...
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13 votes

Heat lost in ideal capacitor charging

When masses collide in an inelastic manner, momentum is conserved but energy has to be lost. It's the same with the two-capacitor paradox; charge is always conserved but, energy is lost in heat and EM ...
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13 votes
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Is this MOSFET upside down?

It is correct. You normally see PMOS connected like this to act as a reverse-polarity "diode". simulate this circuit – Schematic created using CircuitLab It has much less voltage drop ...
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13 votes
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Are smartphone cells actually charged with 9V using QC and other techniques or does the smartphone always step down the voltage?

Your friend is right in that you cannot charge a lithium ion cell with just any old voltage. The battery university goes into some detail about it. Short form: A single lithium ion cell has a voltage ...
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12 votes

How do USB charging and "smart" charging ports (e.g. Anker's PowerIQ) work?

In practice, 'smart' chargers use a special chip called a Dedicated Charge Port Controller. A DCP controller can act like different chargers, and picks the mode which seems to work best. That's ...
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  • 281
12 votes
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How come charging a phone with less current is just slower?

Typically: It just monitors the voltage of the power supply. If that drops too far (typically, for USB chargers, below 4.8 V), it reduces the current sink into the battery. A smarter charger might "...
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12 votes

What does an EV "wall socket charging cable" do?

It is required. The charger for the car is built into the car itself and this is a weather-resistant lead with some smarts in it. The dedicated wall chargers some people have installed in their homes,...
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  • 616
11 votes
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Why do three series connected 1.2 V NiMH batteries read 4.16 V when charged?

No, that’s perfectly normal. See the charge curve for NiMH below. It’s about 1.45 V / cell fully charged. NiMH are tolerant to overvoltage as long as the current is kept low enough. This is commonly ...
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11 votes

How do mobile phone chargers produce regulated voltage?

Complementary to main answers: It is crucial to note that attempting to charge a Li-ion cell by simply applying 4.2 V (or whatever maximum voltage is required) is an extremely bad idea because: One ...
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  • 142k
10 votes

Difference between battery and capacitor?

Wouter's answer is quite good. I would add this chart: Energy density is how much energy can be stored in a given weight of product. Power density is how quickly you can get that energy out. So you ...
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10 votes

Charging of capacitor in RC circuit

simulate this circuit – Schematic created using CircuitLab The current is determined by the voltage across the resistor, which is V1-Vc. As the capacitor charges, Vc increases while V1 stays the ...
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10 votes

About the torque-free charging operation

The paper is about using the EV motor windings as a transformer or inductors as part of the charger when the vehicle is charging instead of using a separate component. A common problem of doing so is ...
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9 votes

Does the charger consume power after charged device is disconnected?

These kind of AC to DC converter will always consumme a small amout of power to maintain the control IC alive. I do not see a way around that unless your USB port has some sort of mechanical switch to ...
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  • 316
9 votes

Can I charge 2.7 V 500 F capacitor with 12 V car battery?

It doesn't matter what voltage your power source is, as long as the capacitor is not subjected to a higher voltage than it is rated for. You could, for example, charge the capacitor from a 12 V ...
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8 votes
Accepted

Do cell phone batteries contain protection circuits?

Those batteries do have built-in protections, but not the kind of ones you see on sparkfun batteries. They have thermal protection required for charging the battery and sometimes low charge cutout ...
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  • 1,670
8 votes

How does a USB C port provide the power to charge laptops?

USB Type C allows for power negotiation, up to 5A at 20V, giving you your 100 watts.
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8 votes
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Charging a 3.7 V with a 5V usb charger

Ok, so you aren't actually asking the right question. I'm going to assume you mean you have a 5V power source (usb, battery pack, etc.) and want to charge a single cell lithium ion battery with ...
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