What is Dc current: Definition and 51 Discussions

Direct current (DC) is the one directional flow of electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor such as a wire, but can also flow through semiconductors, insulators, or even through a vacuum as in electron or ion beams. The electric current flows in a constant direction, distinguishing it from alternating current (AC). A term formerly used for this type of current was galvanic current.The abbreviations AC and DC are often used to mean simply alternating and direct, as when they modify current or voltage.Direct current may be converted from an alternating current supply by use of a rectifier, which contains electronic elements (usually) or electromechanical elements (historically) that allow current to flow only in one direction. Direct current may be converted into alternating current via an inverter.
Direct current has many uses, from the charging of batteries to large power supplies for electronic systems, motors, and more. Very large quantities of electrical energy provided via direct-current are used in smelting of aluminum and other electrochemical processes. It is also used for some railways, especially in urban areas. High-voltage direct current is used to transmit large amounts of power from remote generation sites or to interconnect alternating current power grids.

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1. I DC current flows in a wire when two loops are brought close by?

Hi all, I have a question on the DC current flows, when two loops are close by. Consider a battery driving a loop with a finite resistance. There are charges on the surface of the loop, which exerts forces to direct the flow of the DC current. The changes also produce an electrostatic field...
2. B The historical war of currents in Mains Power Distribution: AC vs DC

So, if I get it right, the basic argument goes like this: AC was preferred to DC because its voltage can be stepped up by a transformer. This limits losses while the current is transported from the production plant to the final user. The voltage is subsequently stepped down when delivered to the...
3. DC current through a resistor circuit

Summary:: Current through a certain resistor in a mixed dc circuit. Hi, Sorry if this is the wrong forum. I'm trying to work out the current through R1.The answer I need is 2 Amp, which I have confirmed with a simulation software. I have calculated the source current as 8A, the current past...
4. If DC current is chopped on it's way to a load, what happens to the EM?

I am curious what happens if you draw DC power to a load, but as it approaches the load you chop the load connection say with a SSR or switch. The power will be traveling near the speed of light, following the wire toward the load. When the load is chopped by a switch just before the pulse...
5. Implement a DC current source - simulink

Homework Statement Homework Equations - The Attempt at a Solution Here's my work : When I add the DC current source , it shows a red dotted line and won't connect to other elements . Any help would be greatly appreciated !
6. Quick Question about a Piezoelectric shoe for project

I am currently working on a piezoelectric shoe and the objective of the project is to charge a phone I am aware a phone is DC and piezoelectric disc generate AC I know I need a bridge rectifier to convert My question is: Would I generate more volts if I Use a bridge rectifier to convert AC to DC...
7. Completely solar powered engine -- is my design good?

The engine of a solar car I am designing(for my fictional stories but I would like a scientific point of view on this) is literally a DC circuit combined with mechanical force. First of all, there is a rechargeable battery. I would say it is about 24V fully charged. There are 2 wires coming off...
8. Can I Use AC to Power DC LED Light Bars for Stage Production?

I need guidance in the explanation of utilizing LED light bars for a different function then designed. I do stage production, sound and lights for concerts and would like to adapt these LED light bars to "blind" to crowd. My issue is that each light bar operates 12-30 Volts DC @ 300 Watts. In...
9. Poynting vector and DC current

We all know that poynting vector could be used to calculate energy transferred in AC system, but I want to know if that theorem could also be applied to DC current? How to prove this? And how to prove energy transferred in AC system could be calculated via poynting vector?
10. Superposition with AC voltage source and DC current source

Homework Statement Using the superposition principle, determine the current i(t. 2. Homework Equations Zc = 1/jwC Zl = jwL V = I*R I = V/Z The Attempt at a Solution First, I converted inductor/capacitor to impedance: L = 1.5H -> jwL = j * 10 * 1.5 = 15j C = 10mf = 1/(jwC) =...
11. Why does AC have less copper loss than DC

Hi there everyone, I'm doing some study on electronics and the section on the advantages of A/C over DC mentioned that AC has less copper loss (I^2 x R), But to me this seems contradictory to the skin effect. Could someone please tell me why AC has less copper loss.
12. Current limiter for TIA, realizing dc current source

Problem: my photo diode receives pulses of width 10ns-150ns and repeating at rate of 1Hz-50KHz the current from photo diode depending on incident light can go from 10nA-100mA, so i have two photo diodes to cover the dynamic range, what i want to do is limit the current from a photo diode to...
13. DC current from an armature and converting AC to DC....

I cannot find answers to this on the internet. Can a d/c be made using an armature? How? How does one convert a/c 2 d/c (or d/c to a/c) thirdly, why does the band a/c d/c come up as the first result on google? (don't answer the last question.)
14. Transistor 2N4401: DC Current Gain (hFE) for 5V/60mA

OK. On datasheet of transistor 2N4401 there are many DC current gains (hFE). Which one is useful. I want to use it over 5V and 60mA.
15. Solving a parallel LC circuit with DC current

Take the following circuit (capacitor initially not charged) : I am trying to solve for the current everywhere as a function of time. I set up the following equations (are they right ?) : Then, any way I try it, I end up with some messy integrals. Even using wolfram alpha to get those...
16. Solving a DC Current Magnetic Flux Problem

Homework Statement A direct current i=10 A flows in a long straight round conductor.Find the magnetic flux through half of the wire's cross section per one metre of it's length. Homework EquationsThe Attempt at a Solution I have spent quite a while thinking on this problem but I can't think of...
17. What wire size should be used for USB charging ports on a luxury coach bus?

Hello, I am an engineer working on a project and have several questions. I believe I have the answers I need, but this forum is such a great place to confirm my thoughts. I am installing USB charging ports on a luxury coach bus. There will be a charging module installed at every pair of seats...
18. Vacuum tubes and electronic oscillators

I've been reading up about vacuum tubes and (more specifically) the Audion, and how they were used for instruments/amplifiers. This isn't anything I'm learning about on my degree, just things I'm reading up on myself so forgive me if I'm a little slow to grasp some parts. I understand how the...
19. Losses in AC and DC power tranfer

Hello, I have forgotten most of the electricity physics we studied and I have problem describing/understanding a concept. Does AC current produce less loss than a DC current? I found this statement in a website: "AC electricity loses less power over power lines than DC"...
20. Corrosion in metal pipe carrying DC current?

Hey Given the simple electric circuit below, the connection between the negative end of the DC source and the load (R1) is a pipe where heavy oil flow with some H2S and CO2. The pipe is made of iron and copper alloy. Without the DC current, H2S and CO2 will corrode the pipe. After introducing...
21. DC current -- Find the 3 currents in this Battery + Resistor circuit

Homework Statement Find I1 , I2 and I3 Homework Equations I = E / R I3 = I1 - I2 The Attempt at a Solution its the trouble with parallel different emf . I know a formula how to combine them into one but it needs inner resistance . i don't know how to do it with the ideal circuit . The...
22. Understanding Propagation of DC Current Along a Conductor

I've been stuck on what I would of thought was a simple/common question but I can't seem to find an answer anywhere. I'm confused as to how a DC current propagates along a conductor (wire) in terms of it's E/H field. I understand that it is these fields that cause the propagation of current...
23. Generator for Bike to Charge Phone: AC or DC?

Hey, I hope I don't bother any of the serious electrical engineers, but I was wondering if anybody could help me with a project I'm working on. I want to build a generator that I can attach to my stationary bike that will charge my phone. It has a very simple design, two permanent magnets that...
24. Pulsing DC Current: Power Supply 15vDC

Hello, I am an Environmental Engineer with very little knowledge of electrical engineering, yet I am working on a project and need a little help. I need to pulse DC current. I have a power supply that will be putting out about 15 vDC and I need to pulse this current at this same voltage. At...
25. Calculate DC current through an inductor?

Hi everyone, Say I have a series DC circuit. The circuit contains a 100V DC source, a switch, a 1.5H inductor, and a 1nF capacitor (all in series). If I close the switch for 2uS what is the current at that time? Initially I thought I could rearrange V=L*di/dt to V*Ton/L = di/dt which would...
26. Does electromagnetic waves are generated by dc current?

I am beginner in physics.I have question that when dc current flow they flow with apparent drift velocity so it appears that it should not emit em waves.But in actual current flow electrons are accelerated due to applied potential and also deaccelerated during collision so even they appear to...
27. Limiting DC Current for Car Battery Use

Is there any way to take 12 volts dc from a car battery and have it go thru some components so that what comes out amounts to still 12 volts dc, but is limited to only 20 ma output? John
28. Optimizing DC Current Through Neodymium Magnets for Efficient Power Transfer

Hi I want to pass DC current through a magnet, essentially using it as connector. The magnet I am using specifically is Neodymium (NdFeB) grade N42. The DC current I would like to pass through it is 100mA ~ 150mA (3V DC ~ 7V DC) I would like to know if there is any downside to the magnetic...
29. Pulsing DC current through coils

Hi, What hardware do I need to buy if I want to pulse DC power, say 12v through some regular coils with iron cores. Can I use a regular power supply connected to some other device? How would I pulse the output of the power supply?
30. AC voltage, DC voltage, AC current and DC current

Hi, I know that existence of AC and DC currents but what exactly the same with AC and DC potential difference. Of-course it was very basic question and i apologize if it annoys any. Please explain the difference only in terms of voltage. Thank you.
31. Why does DC current not generate EMR?

During current flow , electrons are certainly being accelerated and decelerated betweeen two successive collisions with the metal lattice. Since accelerated charge generates EM waves , why doesn't a DC current emit EMR?
32. Understanding Capacitor Polarity in DC Converter Circuits

Hi all. Good day to you all. i want to make one thing clear. In converter circuits, how to trace the polarity of capacitor circuit. Is it following the polarity of capacitor or follow the current flowing in it? I understand that the capacitor is open at dc. So it means it is like a brake part in...
33. Poynting proof for a dc current?

A comment in another thread led me to think about an experiment which can hopefully test the validity of the pointing vector theory for a dc current. I’m very unsure of the outcome of this experiment but what the heck. Here it goes: the Poynting theorem states E x H is power per unit surface...
34. Is DC Current Truly Direct or Does it Have Alternating Components?

Or does it have a hint of alternation in it as well? I know that if AC current is "direct enough" it's considered DC current. I was wondering if DC current can also be "alternating enough", and therefor might be even considered AC current.
35. How does AC compare to DC in terms of power and energy flow in a circuit?

Is that right to see AC as current that flows like that? (marked in red) http://img864.imageshack.us/img864/5056/10vac.jpg Whereas DC would just be a straight line. Is that right?
36. How do I turn a DC current on and off very quickly?

I want to make a DC current (from a battery) oscillate between full voltage and zero voltage (not negative) really quickly, at least 30 Hz. I tried using an electromechanical switch, but the current from the battery is too low to produce any appreciable electromagnetism, so the switch didn't...
37. Proving DC Current Loop Does Not Radiate w/ Lienard-Wiechert Potential

Homework Statement Hi guys, on chapter 14 in Jackson's classical electrodynamics, problems 24 asks to prove that a dc current loop does not radiate, starting from Lienard-Wiechert potentials for the individual charges q. The distance between them is \Delta. We should move to the continuous...
38. How can i pulse a DC current at a rate of Ghz

how can i "pulse" a DC current at a rate of Ghz i need to pulse a dc current through a circuit in at 2.45Ghz. astable multivibrator style How might i go about doing this
39. How do I convert a small AC current into DC current?

I am constructing a small wind generator for a college project. I want the 0.1 V AC output of the generator to charge a battery. To do this, I need to convert the current into DC. I am familiar with things like bridge rectifier circuits, but the smallest diodes I can find have a forward "turn...
40. Multemeter - dc current warms wires.

Just curious why the red & black leads from my multimeter get quite warm when measuring higher dc current under a 20A setting? First I measured 4-5amps for 20secs & the leads didn't get warm, then measured another system with 16-17amps draw & within 5 seconds it got quite warm. Not like its...
41. Is High Voltage DC Current Dangerous?

I have heard that 'we don't get shock from dc current because it is constant but we get shock from ac current because it is alternating'.Is that true? If it is HIGH VOLTAGE DC CURRENT THEN?
42. How capacitor blocks dc current?

hello Capacitors are widely used in electronic circuits to block the flow of direct current while allowing alternating current to pass,how it does the job? samieee
43. Shouldn't a DC current emit EM waves?

So in a DC current we have a relative uniform movement of electrons in one direction. If we would have a very narrow coil around the dc current carrying wire, (like an atom wide), every time an electron pass trough the plan of the coil, should induce a voltage in the coil, so theoretically we...
44. How does a DC current polarize

from my understanding polarization is a way of causing objects to be diametrically opposed (North and South poles for example) What I don't understand is how a DC current polarizes a metal. Obviously for something to be magnetic it MUST be polarized but why does a DC current have to be used...
45. : 50mA-500mA constant Dc current source

URGENT: 50mA-500mA constant Dc current source Hi everyone, I am trying to design a 50mA-500mA constant current source for my project. I found the following link. But I think it would give slightly less than the required or designed value...
46. Engineering RC circuit with dc current source

Homework Statement Solve for the current in each branch of the following circuit as a function of time & derive and expression for the time dependence of teh emf of the constant current source in the circuit below. Homework Equations Zc = Xc = 1/(wC) = t/(2pi*C) The Attempt at a...
47. Multimeter measuring full-wave rectified DC current?

I have this question as a pre-lab for a physics electricity and magnetism lab. (I attached the question as an image.) I am having difficulty answering the second part: A full-wave rectified DC current is just the absolute value of the sinusoidal AC current...
48. AC vs DC current Tesla vs Edison

hey all, another quick question for ya The modern system for transmission of electric energy using alternating current (AC) originated with an inventor named Nikola Tesla. An American entrepreneur, George Westinghouse, bought the rights to Tesla's system and managed to convince consumers that...
49. Difference between AC and DC current

What's the difference?
50. Understanding DC current in automobile electrical systems

Ok so yesterday, I had to jump start my chevy blazer because I left the dome light on and the battery went dead. once it started, I let it run at high rpms for 8-10 minutes to semi charge the battery before I left. I know it was charging, because my alternator gauge was reading 16, and a fully...