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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1answer
963 views

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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3answers
164 views

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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2answers
3k views

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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1answer
125 views

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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1answer
1k views

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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2answers
2k views

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 ...
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2answers
444 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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1answer
683 views

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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1answer
87 views

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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1answer
13k views

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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5answers
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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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1answer
6k views

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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5answers
193 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-...
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2answers
1k views

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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2answers
2k views

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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2answers
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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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2answers
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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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1answer
1k views

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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3answers
226 views

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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4answers
270 views

How do you prevent feedback in a relay or contactor (120V coil, 120V contacts) when coil and contact are both connected to one source?

I have a 2NO 2NC 120V coil, up to 400V contacts contactor. (Electrodepot 934022) I need to power both the coil at 120V and the contacts at 120V from the same source. Manufacturer says this is not ...
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5answers
7k views

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 ...
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2answers
561 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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1answer
719 views

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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2answers
3k views

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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2answers
560 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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3answers
544 views

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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1answer
1k views

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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2answers
83 views

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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0answers
330 views

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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2answers
249 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 ...
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1answer
118 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 ...
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3answers
186 views

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 ...
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135 views

Transformer Welfare

I know this circuit is dangerous, but i made it anyway (probably a mistake)-https://www.instructables.com/id/Variable-voltage-ignition-coil-power-supply/ In my circuit, I used a small ignition coil ...