# Questions tagged [voltage]

Voltage, otherwise known as electrical potential difference (denoted ∆V and measured in volts) is the difference in electric potential between two points (adapted from Wikipedia). Voltage can be constant (DC) or varying (AC).

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### Powering a 5v relay from a 12v power supply

I have a relay which is rated for 5v. My power supply is 12v. I have measured the resistance across the coil as 400 ohm. If I place the relay in series with a resistor that is 560 ohm, would it ...
2k views

### How can a capacitor in a disposable camera shock you?

The battery in a disposable camera is usually a single 1.5V AA battery. It charges a large capacitor. When the capacitor is fully charged, it will contain a voltage very close to 1.5V correct? If ...
21k views

### Converting and Stabilizing output voltage of a dynamo hub

Preface - I don't know much about electronics :P I have ordered a Shimano dynamo hub for my bicycle. I have done a little homework and here are my findings about it: The output of the above ...
1k views

### Do all inductors produce 1 weber after one second when 1 volt DC is applied?

A definition of magnetic flux (the weber) is stated here as: - If you take a loop of superconducting wire, and apply 1V to this wire during 1s, then the magnetic flux inside this loop will have ...
99k views

### Charging devices - Voltage and Amperage

When dealing with voltages and amperage, which one can destroy your equipment when not properly matched to the proper device? Am I correct in thinking that attempting to charge a device with an ...
10k views

### Single terminal of voltage source attached to earth ground

This is a conceptual question I continue to struggle with as I have started studying electronics. Say we have a battery, and one of its terminals is connected directly to a nice patch of highly ...
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### The voltage drops measured across very high value resistors do not add up - why is that? [duplicate]

I have a very simple series circuit which I originally built hoping to measure voltage from an Arduino, but while calibrating realized an irregularity, so stripped it down to its basic parts. ...
76k views

### What's more dangerous : 110V or 240V

There lots of people claiming that 240VAC is much more dangerous than 110VAC. Some even find it insane to have 240VAC. I think this claim comes mainly from the fact that 240V will draw twice the ...
12k views

### Why is it important not to exceed Vcc at the input to a logic gate?

What happens to a logic gate (besides magic smoke discharge) seeing a voltage greater than Vcc? Is it just because the gate was not designed to handle a higher voltage than the recommended Vcc, or is ...
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### What keeps the kickback voltage from reaching an infinite voltage?

We know that the voltage over an inductor is defined by the formula: $V = L * \frac {di}{dt}$ So in the case where the current flow is suddenly interrupted (like when a mechanical contact is ...
13k views

### Voltage drops and current for LED?

I created the following circuit on a breadboard and used the Arduino Uno 3.3V supply for the power supply: ...
13k views

### Why do batteries with the same voltage have different currents?

Experts say "current depends on voltage". So, if the voltage is high, current would be high. Agreed; (I = V/R) If the voltage is low, the current would also be low. Agreed -> I = V/R But why then ...
24k views

### What causes overvoltage in power grid?

In the region where I live there's a state standard that says that mains voltage deviation can be within 5 percent continuously and within 10 percent for short periods of time, so if the mains voltage ...
47k views

### Analog voltage level conversion (level shift)

I have a joystick that puts out analog voltage somewhere between 1.5V and 3.5V. I want to transform this range of voltage to control a motor controller that takes analog voltage between 0V and 5V. ...
44k views

### How many volts can a 1 Watt 8 ohm speaker take?

I am working on an Arduino project and the sound is too low because the output pins on my Arduino UNO is only 40 mA. I can hook up an NPN transistor to amplify the sound, but I don't want to blow the ...
33k views

### Switching 9V using a NPN transistor and an Arduino

First of all, I'd like to say I'm not an Electrical engineer so please bear with me. I haven't got a sketch for what I'm trying to achieve but hopefully I can explain it ok. I have an NPN transistor (...
17k views

### Input voltage range of opamps

I understand that, for an ideal opamp, Vo is bounded by Vee and Vcc (i.e.; Vee < Vo < Vcc). But, what about the input voltage range? What is the allowed input voltage range in which opamp works ...
2k views

### How could I power an IC over the Ethernet?

I was looking foward to powering a small Integrated Circuit using only the power provided by the ethernet outlet of my room. Is that even possible? I've googled and I've found that the voltage that ...
11k views

### How does autoranging work in a multimeter? What is the circuit?

I was curious how this is done. It seems you would have to vary the voltage and current to measure resistance from 1ohm to 10Mohm.
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### Can I swap an electrolytic capacitor with one with a higher voltage?

I wish I knew more about this stuff, but alas I do not. I have a radial lead aluminum electrolytic capacitor (rated 470mF and 25v) that died on me. Can I swap it out with one rated at 35V, or do I ...
850 views

### Does this circuit have marginal voltage level problem?

As a research for the problem I described here I found this circuit by Maxim: This is clock doubler, and must be a really good fit in my case as input frequency is very well defined. However looking ...
14k views

### Using a 5v voltage regulator - Capacitors necessary? Better options?

I am very new to electronics. I am learning as I go, and I haven't quite found the answers I need; when it comes to programming, I'm not afraid of mistakes as they happen constantly. With electronics, ...
300 views

### What if we want to clamp/clip current to a certain value or range as we do with diodes for voltage?

I have seen diode clamping/clipping circuits and can see that they can work well with such simple construction. However, what if we want to clamp/clip the current to some value rather than voltage?
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### Joule Thief - operation and the 'supercharged' version

I've made a joule thief, and it works fairly well, but not as well as I would like. It's powering a 3.2v LED from a 1.2v battery, but it's very dim. I'm hoping increasing the voltage from the JT ...
36k views

### How can voltage burn out an LED?

I understand how a current higher than what the LED is rated for can burn out an LED, but how does something equivalent happen with voltage? If the correct current is on an LED but the voltage is too ...
3k views

### Why are cables rated for current not power?

I was wondering, since resistors are rated for power, not current (so one can blow them with both overcurrent or overvoltage), then why are cables rated only for current? Aren't resistors just stacked ...
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### Does current flow on an open transmission line?

Please take a moment to look at the diagram below: The question is if the lightbulb will momentarily flash when the switch is closed. I think it will but I get the feeling I am wrong. The reason why ...
3k views

### Why doesn't it matter if a resistor is before or behind an LED wrt voltage drop?

I have read that current is always the same within a circuit, but as far as I understood voltage is not. Every electronic part I use lowers the voltage more or less, even simple wires do this. So far, ...
6k views

### Under what circumstances would 5V@2.1A be lethal? [closed]

Besides obviously sticking an output of 5V directly to the heart. Are there areas inside the body where resistance in ohms is so low that a 5V electric potential would be fatal? I got into an ...
17k views

### Trouble understanding Alternating Current (AC)

How does alternating current get anywhere if it travels "back and forth" in the wire?. I understand that Direct Current is a flow of electrons through a wire, but I have always been confused with how ...
152k views

### Why does fuse blow up sometimes?

Sometimes once in a year, either one of main fuses or a fuse in room blow up due to something. What is the cause of this? Why do we even use fuses? Is it because the voltage doesn't stay at 220V all ...
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### Using a microphone from the 1930s

I have an old Braun Cosmophon BMF2020 microphone at home, which I have long been wanting to use for good ol' fun. I have virtually no technical knowledge, so I am completely uncertain how to power ...
948 views

### What is the difference in this specific breadboard wiring?

As an absolute layperson in electronics I just found out that an LED only lights up when connected like in figure 1 but not when connected like in figure 2. And I just don't get why? I know an LED is ...
2k views

### Need help operating a transistor

I have a relay operated by an NPN transistor that needs some voltage applied to the base. I'm working with an arduino and if I give it a digital port, all's well. The circuit looks like this one: ...
16k views

### Why are 3.8V lithium-ion batteries used in mobile devices, rather than 3.6V or 3.7V batteries?

I've noticed an odd trend in the lithium-ion batteries used in smartphones and tablets: rather than the 3.6V or 3.7V per cell typical of most Li-ion batteries in other types of consumer devices, they ...
3k views

### PIC voltage measurement

I am running a battery powered device, and would like my microcontroller (PIC) to report on the supply voltage. This is so I can determine how many batteries is used in the supply, and also the state ...
28k views

### How does a non contact voltage tester work?

How does a non contact voltage tester pen detect voltages and/or currents? Are they limited to voltages of a certain range or type (AC or DC)? Here's some experiments I have conducted that lead to ...
3k views

### Bi-Directional Step up and Step down (3.3v <-> 5, etc)

So I've been reading a few threads here and on other forums. I understand there are various solutions for stepping down or up a voltage. What I have found are the LVC series shift regs that give a ...
2k views

### Ground noise and voltage drop problem

I have an RC device powered by a 3.7V poly battery, which includes a motor and a 40KHz sonar. The voltage across the sonar sensor is amplified and then adc-ed. The motor is driven by a 2KHz PWM. When ...
31k views

### What happens if an LED is connected to a supply voltage greater than its voltage drop?

My understanding of resistance and voltage is horrible. I heard that with Kirchhoff's law, (in my words, please correct) the voltage used by the circuit must equal the voltage supplied. For example, ...
7k views

### Can a 220V relay be used to switch 110V appliances?

Can a 220V relay be used to switch 110V power? If yes, then additionally to this question, does the amperage (A) rating on the relay change when the voltage (V) is 110V instead of 220V? To the risk ...
12k views

### What is the difference in meaning of a voltage signal and current signal?

This might sound like a crazy bad question. But I'm wondering even though current and voltage inevitability co-exist, why do we use the term for one concept(current or voltage)? If there is a signal ...
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### Implementing I2C to analog

How can I implement (or maybe there is an IC that already does that) a board whose input would be I2C and output would be analog voltage (0V - 5V) ? Eventually I would like to connect a couple of ...
1k views

### How is a DRAM volatile with capacitors?

There are a few things I understand: DRAM stores each bit of data to a tiny capacitor with some potential difference. Unless the capacitor is connected to low voltage end, the potential difference ...
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### Why to use 3.3V instead of 3V? [duplicate]

Why do we use 3.3V in circuits? Why not 3? Is there any specific standard? Or we use it because it was 3.3 from the beginning? Just curious to know.
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### Why are battery-powered appliances and tools specified in volts? [closed]

"Powered with a suction of 18 volts" Isn't this just a nonsensical "bigger is better" measure? The thing you really care about as a customer is the motor's torque or power or RPM or something like ...
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### What is the best way to convert 1.8 V to 5 V?

I connected HC-SR04 ultrasonic sensor, to single-board computer BeagleBoard-xM. Trigger pin requires 5 V DC. However, control pins of BeagleBoard-xM can provide only 1.8 V DC. What is the best way to ...
182k views

### How to calculate voltage drop over and power loss in wires

How do I calculate the voltage drop over wires given a supply voltage and a current? How do I anticipate on voltage drop so that the final load has the correct supply voltage? What will be the power ...
25k views

### Why is there a voltage drop in a twisted pair wires of an UTP cat.5 cable?

I put 12V DC through a pair of twisted wires of a 50 meters (~160 feet) UTP cat.5 cable and noticed that there was a voltage drop at the other end of the cable. It only had 5V. If I'm feeding the same ...