What is Dc: Definition and 1000 Discussions

When a DC flows through a wire, does the electric field vary? If a changing electric flux produces a magnetic field, then electric field will have to vary constantly, right? If that's not the case, then what produces a magnetic field around a conductor carrying current?

Hi Everyone, This thread is a modified continuation of my "Digital Voltage Meter circuit " thread I started a long time ago here: https://www.physicsforums.com/showthread.php?t=180822 But with a few changes. In this case, I have a large DC capacitor that I want to monitor the voltage...

Hi I need help deciding how to design my DC motor. I know about series wound and shunt wound motors. I want to design a motor for the highest speed at no load. The limitations are 12V and 1A. I can only use copper wire (0.315mm, 0.2212 Ohm/meter) and shimstock for the electromagnet...

I want to know if I am figuring correctly. I am putting together a 12 volt 3 amp DC power supply. The formula in the instructions is C = Tc / R. I figured the required cap to be 20,750 uf. When I went to a couple of supply catalogs to check the price for the cap I found that no one had had a...

Hey all, i have a summary report coming up which is assessed. I was just wondering if u guys could help out on the know how, terms and all the other stuff to go along with that stuff. Apparently the Summary has a 'prac' layed out like a case study i guess. The teacher said that we would need to...

Hi fellow thinkers. I need constuctive criticism on the following:- Imagine a tube circling around into a closed loop - like a hoop. Inside the hoop is a ring of connected bar magnets all facing the same way. Pressurized steam is fed into the hoop - and exited in such a way as to spin the...

Hello! Lastly i was designing a toy car moving in both direction foward and backward using relays and switches. I thank everybody who helped me. Now i want to move to h-bridge. i have read many books about the h-bridge but one problem that i still have is how to chose power FET transistors...

I realize that this may be an unlearned question. Is switching DC current, on and off, let's say 60x/sec, similar or exactly the same as AC. From a laymans point of view it is not. I may stand to be corrected but, AC indicates that the current flows, or is switched to flow, in opposite...

Ok so for those of you who have followed my recent threads, you will know that i am trying to find practical ways of obtaining a 16 kA DC pulse to create a magnetizing field. I have tried to locate a strong spot welder, but the DC pulse is three phase and results in a non uniform magnetic field...

Hi, Question 1: can anyone tell me do we need a rheostat or face-plate starter for a 12V dc motor? I read in the book and it says the starting current for the motor is very high and it might burn out the armature. I was wondering if I could just directly connect the 12V supply to the...

I am trying to adjust the output voltage of my 12v DC adapter. Is it possible to wrap the wires of the adapter around a toroid in a closed circuit, and then wrap another wire around the toroid to have the output voltage of this wire decreased, and the current increased? Example...

Hi, Can any expert advice if I can control the DC motor to make it work as a stepper motor? I am using PLC to control the DC motor clockwise and counterclockwise in steps. Output O:1/0 controlling clockwise and O:1/1 controlling counterclocewise.I will use the timer say 0.5s pulse to...

Hello I have a project in the works that requires a DC motor to turn a somewhat heavy (but with good bearings) gear assembly. The whole thing will be running off of a common computer power supply at 12V. I haven't selected the motor just yet but am leaning toward maybe an old cordless power...

Hi,Good day to all. If 3 phases(230 volts phase to phase )are rectified (using a bridge rectifier: MEB00806)and no neutral is used ; what amount of DC voltage will be obtained(with and without filtration)? Thanking you. Prashsar.

Lets say I want to move a kick stand on a motorcycle by use of a motor. Hooked up to the battery and a button on the handle bar. Is there a way of controlling the motor so it will automatically shut off when the kick stand has swung down all the way? Also when it has swung back up? Thanks, Hoovy

Hello Forum , i have a spindle motor from a Hard disk , it's a 3 phases DC brushless motor . This motor has 4 wires , 3 phases and 1 common , how i can know the phases and the common ? Thanks in advance. Anita

Hi there :) I need to build or buy an inverter that transforms 12V DC to 14 AC 50Hz. It's for my guitar sinthetizer, i need to play with it in the street with my 12V batteries. I've tried with an 12V->220AC inverter pure sine (from Velleman) but it introduces to much noise in the guitar. Any...

Hello all, I was wondering if it is possible to increase voltage if you combine 2 DC motors together? I know that it is NOT possible to increase the voltage if you put it into a series circuit since it won't work. As for the batteries you can increase the volts if you put them into the...

http://img104.imageshack.us/img104/3557/1234uyq.jpg Ok, there are a few calculations on this problem that I am having difficulty with. This is a past homework assignment which is why the answers are filled in. They are all correct. Anyways I approached the problem in this manner: V...

I have a predicament. I'm trying figure out the P-P ripple voltage of a Half-Wave rectifier filter, but the only equation I have is: I / (f * C) yet to find the current I need the DC voltage which I don't have yet. The same goes for the DC voltage. I have the equation: VDC = VOUT P – (VR...

If direct current is applied to activated carbon, will it be drawn to the cathode?

I have a quick silly question for a first-timer at assembling circuits. I have a circuit with a photodiode input and a BNC/coaxial output to a scope. The circuit diagram is below. In assembling this circuit, I'm not sure where to ground to. I've put it in a metal enclosure. One book says...

Dear electronic gurus, (2 part question) I want to check that: If i got a 12V motor (such as http://scientificsonline.com/product.asp_Q_pn_E_3041860" ) would i be able to adjust its RPM if i got a: 12V dimmer switch box...

Im not formally trained in electrical engineering but have recently been forced in the last 6 months or so to get up to speed on many elec eng power type subjects. One of which is AC versus DC. I understand the history/science of it and why AC eventually won out. However, one story I encountered...

First off, I know very little. I want to install a cabinet in my garage. It runs on 120AC, and then provides me 16 DC outputs. As I understand it the total output is 10,000 ma. I have some DC powered items that require 500ma, and some that require 1,000ma. I'm only going to use 6 of these...

Hi all, I've got a problem which is so daft it hurts. I'm using lithium batteries, and I'm well aware of the dangers, so despite being fine with working on an un-protected cell, I changed to protected ones, and then issues appeared. The current is drawn from a pair of parallel 18650's...

i want to have dc to dc converter which accept a Vin (300,600,900V) dc as input and is able to give 1.25Vin dc as output. any commercially avaible converter?or how can i build one? thanks

Effect of a pair of slip rings in a DC motor Hi, I have a question here. Knowingly that the effect of a slip ring in a DC motor is to reverse the direction of the current in a loop whenever the commutator changes contact from 1 brush to another, so as to ensure the loop to be always...

Hello, I am new to this forum. I hope this can help me with my curious question. I know that the DC motor can be run by electricity, but also it can create electricity by torque force. The question I would like to know if this works or not? One 1.5v DC motor is powered by one...

I need to do dc recovery on a sine signal with a variable amplitude. (so its not between +U and -U but between +2U and 0) It is fast enough if the offsets adjusts within minutes. There is a quick hack in the Art of electronics, where they set a diode and a capacitor in series, but this leaves me...

Laplace help on a DC transient RC circuit ? PLEASE -------------------------------------------------------------------------------- I HAVE A RC CIRCUIT WHERE R1=100Kohm and R2=1Mohm and C=2.1micro farads with a Vin =10V, In order to calculate the voltage through the capacitor I...

I HAVE A RC CIRCUIT WHERE R1=100Kohm and R2=1Mohm and C=2.1micro farads with a Vin =10V, In order to calculate the voltage through the capacitor I deduce the following formula, Vc(s)=V/S {(((R2×1/Cs)/(R2+1/Cs)))/(((R2×1/Cs)/(R2+1/Cs)+R1) )} I then need to produce a laplace transform...

http://img42.imageshack.us/img42/2461/49889005.th.jpg My question is, why does the dc voltage vary with time in this way? Ply it is something to do with the diode allowing current to flow when it has 0.7V or more across it, allowing the capacitor to charge, and when the voltage drops to...

Homework Statement Is it possible to find the P.D. across the 10ohm resistor. Homework Equations Kirchoff's second law. The Attempt at a Solution Well KSL states that the sum of the pds is equal to the sum of the emfs. I(10) + 0.25(12) = 2 Gives the wrong value for...

Hi all, :smile: My understanding of harmonics in general is quite sketchy and as a result my query might appear a bit lulu! :rolleyes: I tried the net but could not get suitable info on the same. This is what I'm looking at; Assume a battery hooked up to an inverter (1 phase or 3 phase...

Diode ac and dc resistance? here is my question ...saturation current of a silicon diode is 2uA.and forward current is 20mA...i want to find out the AC and DC resistances of the diode in 300k... so i know that , I(forward)=I(saturate)[exp(eV/nKT)-1] ..so by differentiating both sides...

I'm trying to design a system that will source DC power while transmitting a high impedance sourced AC signal superimposed onto this power signal. I'm sure this has been done in many applications, but I'm new to it. Currently I'm trying to use a basic adder circuit with an opamp to superimpose...

Homework Statement Explain what is meant by "DC Offset" in an amplifier and how can you eliminate it ? 2. The attempt at a solution I think it is the deviation from the real voltage, but I am not sure

Hi I'm new here and I just would like to ask for help regarding our surge suppression system. Our surge supression system is designed to eliminate transient voltage spikes on the 3 phase AC lines to protect the SCR pucks on the scr system. The surge supression system consist of a 3 phase...

Hello all. First off, I am a total newbie and need some help in getting my "project" up and running. Here goes, I'm trying to get a dolly (weighing around 50lbs. or so) to move at a fairly slow constant speed. I'm thinking my best option is to find a 12 volt DC motor along w/a speed control...

I am trying to make a simple electric (DC) motor using a battery (9V), wire, and magnet. For some reason the coil isn't spinning though. I scraped the entire insulation off one side, and half of the insulation off the other. Why isn't it working?

Homework Statement Hey, For one of our final lab projects, we have to (less design and more build) an electric DC motor on a 6V DC battery. Restrictions/Requirements: No plastic parts can be used The motor must run for at least 60 seconds No simple motors allowed "not-simple" means, it must...

hi, thanks for taking time to try and help me out, i have hit a brick wall with these questions, i have made an attempt and don't no where to go from there, and feed back would be great thanks alot... The problem Using both Norton’s and Thevenin’s theorem determine the power dissipated in the...

I'm wanting to build a dc power source of 1 million volts more would be nice but ill start with a million and work my way up from there. Any suggestions would be helpufull. Is it possible to build a 1 million volt capacitor or should i build a capacitor bank to smooth out the ac current after...

Hi out there! I've been handled 3 questions which for me is rather hard and therefore I'm asking the experts. Any help would be great:) Donkey Kong Question 1) A circuit consists of a 15Ω and a 30Ω resistor connected in parallel across a battery of internal resistance 2 Ω. If 60W is...

I have a 500v, 50A dc generator (~25kw) and need to get 240v ac (rms) for operating typical household and shop appliances including those sensitive to quality of the ac. (this 240 would be run through another transformer for 120v appliances) I've found an abundance of information on various...

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...

I have a device that generate a pulsating current(2s 2A,2s 0A), and i would like to convert it to a continuous dc current. i have no idea of how to do it. Thanks for your help.

I'm trying to understand the converter in this link: http://en.wikipedia.org/wiki/Power_inverter I don't see how the two transistors and the DC source cause the curretn to alternate through the windings. It seems that both transistors would be passing current constantly, not alternating...

Good day everyone I'm implementing a speed controller for a DC motor 220 v 2.7 A 1500 rpm. I've already made and tested the firing circuit and the motor works fine in an open loop. Now big problem the parameters of the motor are unknown and impossible to find. No time for mechanical...