Linked Questions

3
votes
1answer
8k views

How does my phone get charged via laptop USB port at lesser current (compared to wall charger) [duplicate]

Today's typical smartphone chargers are rated at 5 Volt & 1+ Ampere. The laptop USB can supply 500mA 100mA. Why is it safe to charge the phone with 1/2 the rated current? Is it like a slow ...
1
vote
2answers
666 views

How much current will I get from the 5V rail of a Teensy 3.2 powered over USB? [duplicate]

The microcontroller in question is a Teensy 3.2. My understanding is that the most current that you can get from a standard computer USB port is ~180mA; how much of that will current devices attached ...
0
votes
0answers
37 views

Usb charger not charging only with vcc and gnd [duplicate]

I want to charge my tablet on the wall. And I have a charger behind the tablet and connected 2 wires to vcc and gnd, the same pins as usb female, it turns out that I can't have more than 10 mA. If I ...
13
votes
5answers
9k views

How does a USB 2.0 Wall Charger negotiate current output?

I'm trying to use a mobile phone charger for my projects, and want a high current output. I have read this, however my measurements show something else. Here is a link to the Battery Charging ...
9
votes
6answers
1k views

USB Power - The basics

I am new to designing something to be powered by USB. Ideally It can either be plugged in to an adapter to a UK wall plug, or a powered USB port on another device. I have the circuit design in place ...
5
votes
3answers
18k views

Voltage requirements for charging Nokia phone

I have an old Nokia phone which charges fine from the adaptor, but refuses to charge using a USB charging cable. Note that this isn't a normal USB cable, as you can see from the picture, it's got a ...
8
votes
3answers
2k views

Best way of making a battery powered USB charger?

I recently made a USB charger that takes a 9V battery. I've noticed it doesn't work with a lot of devices though. It was very simple though, just a 5volt regulator hooked to a USB plug and 9V battery ...
0
votes
4answers
4k views

USB PC Current Limit

I want to build a USB device that can draw 1A. Some of the PCs at my office can supply 1A, some only 800mA. The USB 2.0 specification says a device can only draw up to 500mA. I cannot build a ...
4
votes
3answers
1k views

What's needed to get 100 mA from a USB port?

I'm trying to build a stereo speaker system for use on a laptop. I want to keep it as simple as possible, so I'm thinking of using laptop's audio output to for the audio signal and a USB port for ...
6
votes
2answers
3k views

Critique of my Data logger's Power circuit design

I am laying out my first full device, a fairly simple sensor-data logger, with these specs in mind: I'm running microcontroller and sensor @ 3.3V, with load varying from 10 mA to 400 mA device will ...
2
votes
5answers
6k views

How to adapt a string of 10 LEDs powered by 3 AA batteries to work off a USB port?

I have a string of Christmas lights made up of 10 warm white LEDs. The lights are connected in parallel (not in series). The string works with 3 AA batteries (that is, 4.5 VDC). And all that stands ...
3
votes
2answers
6k views

Make a tea mug heater with a USB power source

For a school project, I have to make a mug heater which draws its power from a computer's USB port, such as this one. I don't mean one that boils the tea, but one that keeps it warm-ish, at at least ...
2
votes
4answers
4k views

Max current for USB powered Arduino?

My plan is to use a Teensy logic output pin to switch a transistor to switch an infrared LED The LED handles up to 1A peak current. I will use it as a computerized IR remote transmitter so the duty ...
3
votes
3answers
1k views

Connecting a higher-current power supply to a lithium-ion charger will damage the battery. Why?

I am not asking how the battery gets damaged, because that answer is straightfoward. What I am asking is why lithium-ion chargers allow batteries to be damaged by excessive charge current in the ...
2
votes
3answers
2k views

Feeding 2*5V to a 12V fan?

How would I amend a 12V fan to take 2*5V? The 12V fan has 2 wires on it. one would take 12V the other GND. I'd like to be able to feed it 5V and 5V, instead of just 12V. What do I need to do it? ...
0
votes
3answers
1k views

Why USB wall chargers don't reach their amperage rating? [closed]

recently I bought a power bank that requires 1,6A of charge current. I tried charging it with a 2A Samsung charger, which came with my tablet. Unfortunately it charges very slow. Then I tried another ...
0
votes
4answers
2k views

Creating Li-Ion charger with step up to 700mA from 500mA?

Canon apparently hasn't ever herd of something called USB-charging. The factory AC adapter for this battery(NB-5L) output's 4.2V's at 700mA. Most standard USB chargers output 5V at only 500mA. Would ...
0
votes
3answers
3k views

Three-prong / USB power outlets in wooden desk [closed]

I am trying to mount a strip of three-prong outlets and a strip of USB charging outlets on an old wooden desk. I can handle the carpentry aspect, but I am struggling with the electrical aspect. I ...
2
votes
1answer
2k views

Risk of overloading a usb charger

I just bought this product: "Jackson PT1USB" as an attemp to get a portable charger for my netbook, ipad 2 and smartphone. Now I am bit worried after reading in the product "total connected load to ...
3
votes
2answers
626 views

Lengthen a AC to microUSB phone charger cord?

Can I effectively take a 3 ft standard cell phone charger (AC to microUSB, 750 mA at 5V) and lengthen the cord to 6 ft by splicing the cord or am I going to lose something in the mix? Do I need to ...
2
votes
2answers
362 views

connect LEDs to USB keyboard – but they turn off after a second

I have a USB keyboard. As I work many times in the darkness, I put some LEDs into the keyboard case. I connected two pairs of yellow standard LEDs serially to the USB power lines (Vcc and ground, pin ...
2
votes
2answers
1k views

Convert low power USB to high power USB in car stereo.

Could I connect the D+ and D- to my car stereo's USB input, then connect the red and brown (+/-) to a 2amp cigarette plu'sg USB? My issue is that the USB in the head unit is low power and doesn't ...
-2
votes
1answer
1k views

Can I use my Android tablet charger for the PlayBook? [closed]

I got a BlackBerry PlayBook and it came with the wrong charger plug. It's for the US that I can't use here in Germany. Can I use my Android tablet charger for the PlayBook instead? The information ...
0
votes
1answer
605 views

LM317 to charge a NImh battery from usb [closed]

Hi want to charge my 4000 mAh 1.2V nimh cell battery simply, I do not use them very often. So I wanted to plug this kind of voltage regulator which I think is like that : https://en.wikipedia.org/...
1
vote
1answer
727 views

How to configure USB OTG as power supply

I have an ARM computer with an USB 2.0 OTG port, and I want to use it as 5V 100mA power supply (to drive a couple of leds). However, when I connect a load (LED+resistor) via an OTG cable, the power is ...
2
votes
2answers
443 views

Can you charge a battery to run a device at 5V from the USB port?

Say you had a device that requires 5VDC to operate. It can actually run safely at about 4.8VDC. It normally runs off of USB power but I would like to rig it up to run off of a battery. Would it be ...
0
votes
2answers
122 views

USB powering batteries without OS support?

On a bare-metal project I have in mind, I would like to know if I can avoid to implement the multiple USB specs (O/E/xHCI) and still benefit from usb charging my battery. It will run on a almost ...
0
votes
2answers
141 views

Drawing too little current from PC USB

If I connect this very small load (3 LEDs) to a mains to USB adapter, it's fine. Full brightness, great. I can't even measure the current it's so low. However, if I connect it to my PC it does 3 ...