Questions tagged [coil]

A coil is an electrical conductor such as a wire in the shape of a coil, spiral or helix. Coils are used in applications where electric currents interact with magnetic fields, in devices such as inductors, electromagnets, transformers, and sensor coils.

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What are the differences between an AC and DC coil relay?

If a DC coil was just a coil, it would saturate. If an AC coil was just a coil, the magnetic field would drop to zero at 120 Hz and the relay would chatter. Presumably the designs in some way prevent ...
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Why is it impossible to connect these two doorbells in series or parallel?

I have: one 220 V AC -> 10 V AC transformer one push-button switch (at the door) two bells for two different places of the house; they should ring together when the (single) door push-button ...
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Any simple short range metal detector?

I'm looking for a simple short range metal detector. I've looked everywhere and I can find only complex metal detectors circuits to find metal at several cms of distance, most over 60cm, they are an ...
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Inducing an intense varying magnetic field with a coil and audio amplifier

Disclaimer: I'm computer scientist I want to test a system described in an old (~1990) french patent and experiment with it if it works. The system requires to generate an "intense" varying ...
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1 vote
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Voltage exceed source voltage over a coil when opening a switch

Well, I have the following circuit: simulate this circuit – Schematic created using CircuitLab When the switch is closed for a long time, the current that is flowing trough the resistor $R_1$...
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What is the point of the transistor to drive the relay coil

In the circuit the relay is controlled from a manual switch on a 12v bus. I can't understand why you would want to add the extra components of the transistor and diodes to the circuit? ie why are D4, ...
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Mutual inductance vs coupling coefficient

Question regarding this and this question about mutual inductance and coupling coefficient. I'm trying to analyse a two coil system: It consists of two coils like in the picture with 2 cm air gap ...
1k views

Voltage spike at the coil when opening the switch [duplicate]

I've the following circuit: simulate this circuit – Schematic created using CircuitLab In my book they stated the following sentence: After that the switch is closed for a long time, I let ...
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Inductor Design - How do I know what value of Bmax and Current Density to choose?

In order to decide what type of core I need, I need to calculate the Area Product Ap which is given as: $$A_p \simeq \frac{LI^2}{JK_uB_{max}}$$ Where I is the current, L is the inductance, J is the ...
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Transformer testing

I connected an ignition coil to 240v in an attempt to make a Hv generator. The ignition coil was connected I series with a capacitor and light dimmer. When turned on the ignition coil did nothing at ...
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Is this (working) 2-doorbell system dangerous?

In a previous setup, I had two doorbells, each one with its own 10V AC transformer, as detailed in Why is it impossible to connect these two doorbells in series or parallel?. I now know it was ...
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How many turns do I need for the primary coil of a transformer?

I need to know the number of turns that should be connected to 220 volts AC. I can measure resistance only, I don't have a device that measures inductance. If I need the primary coil to be 220V / 1A (...
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How to properly wind coils for a solenoid?

I need to wind a small electromagnet "solenoid?". About 3cm high and 2~5cm wide running at 5V/0.5A. This magnet will be put into a desk bell so it pulls the clapper down and rings the bell. I have ...
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Controlling an electromagnet strengh with arduino

This previous question Controlling an electromagnet with Arduino deals with binary control (ON or OFF) only. On my side I need to choose the strength of the magnetic field. It is a home made ...
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H-Bridge with emitter followers

I am currently reverse engineering a circuit which requires controlling of a magnetic field. For that, the circuit has a pair of D882 and B772 each. The PCB traces suggest that the transistors are ...
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What do you call a relay that self-opens on power loss?

I'm programming the simulation of some circuitry. These are relays that will open automatically when they lose power: Do relays such as this have a particular name? "power hold relay"? "single ...
816 views

Measuring faint varying magnetic fields with a coil

Disclaimer: I’m computer scientist. I want to measure a faint varying magnetic field with a coil. The frequency domain I’m interested in is ultra low (< 10kHz). The source of the varying magnetic ...
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How does a magnetic material "confine" a magnetic field?

I'm slightly confused as to how the magnetic core below "confines" the magnetic field generated by the coil to flow so nicely. What stops it from generating the same pattern as in the first ...
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Why my two coils don't repel each other?

I'm experimenting with two coils. I drive them with two MOSFETs and one consumes around 1A and the second ~0.7A (12V power supply able to deliver 15A). While the coils work with permanent magnets and ...
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increasing metal detector range

I am working on my senior project. As part of my project I need to use a metal detector. I am using the following circuit schematic. The principle is based on the properties of inductor coil: L=N^...
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How to compare a magnetic loop antenna to a conventional antenna

I want to build a compact 1 MHz receive coil (antenna for very near field). For that I need to make a choice on whether to build a simple RF coil only consisting of wire and capacitors or using a coil ...
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Induction heater circuit problem

I am trying to build induction heater with the help of the following schematics(taken from this page): So I am using 220:10Vrms(15Vpeak) transformer with fullbridge rectifier and a capacitor to get ...
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Switching kicker solenoid with an idea out of the box

From my previous posting some may know I am planning to make a kicker solenoid. The circuit specs: Coil - 3.5 Ω, 3.4 mH (inductance) Capacitor 1000 μF, 450 V DC booster up to 410 V 12 V DC battery ...
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Why are the vertical deflection coils in a CRT deflection yoke so different from the horizontal coils?

Looking at a typical raster CRT deflection yoke, there appear to be two very different pairs of coils. There is the pair on the inside that curves outwards, and the pair on the outside, which are ...
518 views

Relay coil fast demagnetisation

In the past few days, I've encountered an application note on the Maxim Integrated website about rapid demagnetisation of an inductive load: https://www.maximintegrated.com/en/design/technical-...
738 views

Why won't my JFET Hartley oscillate

I built this Hartley oscillator (taken from the November 1990 edition of Popular Electronics) as part of an AM modulated signal generator project. But, it steadfastly refused to oscillate. I was ...
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LM317 - Why could I not get more than 200 mA from the output?

My task is to heat a coil, with a resistance of approximately 0.8 ohm. I need to make a constant current source to make it work correctly. I want to use LM317T as a constant current source, but I ...
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What good is an induction coil in a dimmer switch?

I asked about a dimmer switch, and was told one has an induction coil. What benefit is an induction coil in a dimmer switch? ZE-02S has induction coil built-in on the circuit board, so it is 5/8" ...
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ULQ2003 not driving a Relay properly

I am driving a 9V DC (5 PINS) Relay from darlington array ULQ2003. The ULQ2003 COM pin is connected to 9V power supply while the Relay coil is connected to +12V supply. The Ground of both are ...
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If I pass electricity through heating coils will it make heat?

This may sound like a silly question. But if I strip some wires added the connectors and connect them to a heating coil will it heat the coil up? What else would I need to produce heat?
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Amplifying the output voltage from a coil (10Hz-20kHz) using an AD620 module

Disclaimer: I’m computer scientist. I would need some help to get an AD620 amplifier module to work. Some context is available here in a previous question. Here is a physical view of the amplifier: ...
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How to protect bistable latching 2 coil relay with diodes?

I know that a revers diode is required to protect a DC coil relay. But to protect this relay RT314F05? It has 2 coils, are 2 diodes enough?
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Effect of core losses on inductance in high-frequency LC circuit?

How will the core loss (hysteresis and eddy current loss) in an LC circuit at high frequencies (about 800kHz) affect the inductance of the inductor. When I measure the frequency I can see that it will ...
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How to make the electromagnet of a magnetic-levitator?

I saw pictures of magnetic-levitators on the internet. That's amusing. I wanted to make one of those. So I started searching in Google. And I found out that these devices have a big electromagnet ...
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Designing AC kick solenoid lock

I am making a kick solenoid lock with AC. I designed the circuit to run on 220 V, 50 Hz (household plug.) The inductor (coil) is air core 500 turns, 150 meter (500 ft) in length with inductive ...
1 vote
285 views

How to make a 220 V AC solenoid lock

I need to make a powerful solenoid lock using 220 V AC. Let say I will use 21 gauge wire and get a length of 24 Ω. This will draw 9 A from the 220 V, so 1980 W. This will be great force ...
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Inductor core permeability much lower than expected

I am interested in creating an inductor with a large inductance/large mag field in core. However, when empirically measuring the inductance of the wound core, I calculated a relative permeability ~...
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Voltage induced in aircraft high-tension magneto ignition system

Why is there no voltage induced into the secondary winding (in high-voltage step-up transformer) when the ignition switch is closed (OFF)? When the current flows in the primary winding of the coil a ...
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Could anyone identify the manufacturer or a similar product to this ~6x7mm inductive charging coil?

I had this smart ring from a company called Oura, and I took my charger apart recently. Inside, I found an incredibly small inductive charging coil printed inside of a little FPC. Could anyone ...
785 views

My Tesla coil is not working

I made a Tesla coil, but it doesn't not work. I used this circuit: I used 200 turns for the primary coil with 0.5 mm wire and 5 turns for the secondary coil with 1 mm wire on a wooden rod. Back to ...
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Strength of a pulsed electromagnetic field

Forgive me if my question sounds a bit naive: I have built a coil (no solid core) out of an insulated copper wire, and I calculated that it has 8 ohms of resistance. I tried it and it gave me the ...
185 views

PWM control Coil

I'm trying to use the coil with a PWM of motor drivers(DRV8837). But there are some problems. I'm using stm32f1 MCU, IN1 : 80% 400hz, IN2 : 0% 400hz PWM output of the coil is abnormal... When you ...
2k views

How to design wireless charging coils so they are resonant?

I am continuing from this question: What can I use to increase efficiency of inductive wireless energy transfer instead of factory manufactured ferrite plates? I am trying to make somewhat efficient ...