Questions tagged [relay]

A relay is an electrically controlled switch. Electromechanical relays use an electromagnet to activate mechanical contacts, solid-state relays use semiconductor switches.

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13 votes
1 answer
26k views

How to properly use a relay module with JD-VCC from Arduino/Raspberry?

I got two 4-relay-modules and I am probably doing something wrong because none of them seems to work: My first try was using a breadboard 5v power supply, connecting VCC and In1 to 5V and GND to GND. ...
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46 votes
6 answers
183k views

Why is there a diode connected in parallel to a relay coil?

In most electrical circuits with a relay, a diode is connected in parallel to the coil of the relay. Why? Is it always a good practice?
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  • 571
4 votes
4 answers
8k views

Symbol or marking on safety relay

I found this relay inside an industrial x-ray machine. What does the rectangular box with a horizontal line through it, in the bottom left of the first picture, mean?
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61 votes
4 answers
159k views

How to choose a flyback diode for a relay?

A diode is put in parallel with a relay coil (with opposite polarity) to prevent damage to other components when the relay is turned off. Here's an example schematic I found online: I'm planning on ...
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14 votes
4 answers
22k views

Thermistor control of peltier voltage with Arduino (for DSLR chill box project)

I am mildly familiar with electronics, mostly from playing around with electronics kits as a kid. That was a long time ago, though, maybe as much as 20 years ago. I am currently working on a cold or "...
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  • 655
12 votes
6 answers
37k views

Need help calculating resistance for transistor base

I have 3 12VDC/40A automotive relays (datasheet) that I want to use with my Arduino. Based on the tutorial I am following (link) I need transistor, resistor, and diode. I am not an electrical engineer ...
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  • 443
55 votes
5 answers
48k views

Triac versus Relay

What are the scenarios where Triacs can not replace a relay or vice-versa?
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44 votes
8 answers
23k views

Why are relays so frequently driven by optocouplers?

Since the advent of the many microcontroller development boards, like Arduino, there have been a number of relay modules sold to drive mains AC loads. A lot of these seem to use an optocoupler, ...
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  • 1,924
14 votes
4 answers
24k views

Shutdown Controller for Raspberry Pi in a car

Following on from my previous question I'm trying to create a shutdown controller for my Raspberry Pi. The Raspberry Pi needs to be powered from the battery, but should power-down after the Pi ...
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24 votes
5 answers
33k views

When/why would you use a Zener diode as a flywheel diode (on the coil of a relay)?

I have just been cogitating on the tutorial at http://www.electronics-tutorials.ws/io/io_5.html, and in the discussion of flywheel diodes it includes this sentence without further elaboration: As ...
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29 votes
5 answers
12k views

Why does a relay have a minimum applicable load?

I am trying to find relays for my application and I read a data sheet which looks fine but specifies Minimum applicable load: 10mV 10µA In my circuit, it is expected that the relay closes but no ...
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1 vote
1 answer
2k views

How to control 4 relays with a not chip (7404)

I have a atmega8 that is working with 3.6V dc, I need to control some 12V relays with a not chip (7404), what is the simplest way to do this? I have connected a 12V dc to the relays, so when I connect ...
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0 votes
1 answer
208 views

Relay: higher voltage allowed at lower current?

Is it safe to use a 30VDC/1A relay for a voltage of 60V but a current of <100uA? E.g. this one: http://www.mouser.com/ds/2/315/mech_eng_gq-1075992.pdf
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41 votes
6 answers
18k views

What are some ways to use relays more efficiently?

We often seem to use microcontrollers to control relays, and a 5 V microcontroller is often used with 12 V relays. A relay may need several times more power than the microcontroller. Not a problem if ...
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  • 143k
7 votes
2 answers
8k views

Driving Solenoids from Arduino

I was wondering what the best way to run a solenoid would be from an Arduino board. I was thinking about using a MOSFET that runs into a relay to turn on the solenoid but am not sure how to go about ...
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7 votes
4 answers
25k views

Control 5v relay through 3.3v GPIO using NPN transistor

I'm not very pratical as I just started learning electronics and I'm planning to make some experiment with Raspberry Pi. I'm trying to control a 5v relay board that, I think, is made for Arduino, as ...
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  • 183
2 votes
3 answers
3k views

Snubber diodes for a DC Motor with 2 relays

simulate this circuit – Schematic created using CircuitLab Description: RLY1 relay switches 12v on or off. RLY2 changes direction of current flow to the motor. I have flyback diodes on RLY1 &...
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  • 76
0 votes
2 answers
544 views

Ordinary Differential Relay Problem

The answer given in my workbook to the above problem is A. The things I was able to point out secondary c-phase current = 300A and other secondary phase currents = 0A since the entire current ...
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88 votes
5 answers
102k views

Relay vs. Transistor?

Rather basic, I'm afraid, but when would you use a relay, and when would you use a transistor? In a relay the contacts wear out, so why are relays used at all?
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19 votes
4 answers
13k views

Equivalent circuit of a solid state relay

I want to switch 50V AC voltage. Maximum drained current will be 5A. Frequency is 50Hz. Switching speed is not important, can be real slow, it is not a problem in my application. I wanted to use ...
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  • 13.5k
10 votes
2 answers
16k views

Using TP4056 module to charge battery while load remains connected

I need a circuit that utilizes the tp4056 breakout board to power a NodeMCU ESP like so: tp4056 USB port connected: 18650 battery charging and NodeMCU running of USB tp4056 USB port not connected: ...
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  • 149
8 votes
2 answers
54k views

Do I need a flyback diode with an automotive relay?

I have two relays to convert +12 volt circuits to "ground" inputs into a fuel injection ECU. If I connect the relay coil ground to the same ground as the "source" will I need to install a diode to ...
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10 votes
5 answers
78k views

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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10 votes
3 answers
52k views

how to use a 3v output to control a 5v relay

I have some circuit where my board (Electric imp) can output up to 3.3v, and i need to control a relay with atleast 5v in order to effect the coil and close the circuit. i have a power supply of 5v, ...
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  • 227
9 votes
1 answer
2k views

Spikes induced on PCB. EMC problem?

I designed the following PCB, where after testing a faced a severe (EMC related?) problem. This board houses an STM32F103 developing board. On the right of the PCB, there are 6 thermistors connected ...
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8 votes
2 answers
6k views

How do I connect a relay and transistor to an Arduino?

Ok, so this is what my relay looks like. I can't figure out what pins I hook the arduino and transistor to, and what pins to hook the the other device. Please help.
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8 votes
6 answers
8k views

PIC16F628A Resetting after relay turned off

I am having problems with controlling a relay with load on it. I am using PIC16F628A. The problem is following: The relay has load. At first it is off. When the microcontroller's output is on, the ...
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  • 916
6 votes
2 answers
10k views

Driving a relay directly with a microcontroller?

Are there any microcontollers on the market that would be able to drive this relay directly? If not, what is the most cost effective way to have a microcontroller control 5 relays?
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  • 2,669
2 votes
2 answers
7k views

Can I convert a toggle switch to momentary switch using a transistor and capacitor?

After searching online for an answer to how to convert a toggle switch to a momentary switch I found the circuit below. I've simulated it and it works in CircuitLab. simulate this circuit – ...
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0 votes
1 answer
4k views

How to control a motor with only relays and push button?

Hello I´ve been working in this project for some days, I need to make a circuit with only relays that can make a dc motor start, stop and a reverse. The thing is that when you push the start or the ...
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  • 3
3 votes
1 answer
2k views

How can i drive a 5v 120VAC 80mA with 15A contacts with a raspberry pi?

I don't have a very good knowledge of electrical engineering yet but I'm working on it. I will like to know as simple as possible, how can i drive a latching relay that needs about 70-90mA if the ...
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  • 61
25 votes
5 answers
18k views

Why don't relays incorporate flyback diodes?

Warning: this may be an extremely naive question (if so, please enlighten me). Many applications of relays require a flyback diode to protect against inductive voltage. I'm unable to find any relay ...
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  • 353
15 votes
5 answers
32k views

Simple and safe solution to control a power plug with Arduino or PC [closed]

What solutions are available to control a power plug (or even if possible a light socket), i.e. turning it On and Off? I have looked for xbee/zigbee solutions but there doesn't seem to be a solution ...
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4 votes
3 answers
14k views

Selecting the right relay

I'm looking for some advice on what type of relay I should use for my circuit. I have a 5v power supply and I want it to act just like a switch. I will be controlling it with an Arduino like ...
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10 votes
7 answers
69k views

Not sure how to wire my 5VDC to 120VAC arduino relay board

I have a board with 8 relays on it that will take 5v from my arduino and the relays will flip on my 120VAC devices. I'm not an electrical engineer by any means so I am wondering how to wire my 120V ...
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  • 101
9 votes
2 answers
4k views

Zener Diode Selection for Relay

I am using a Zener diode along with a flyback diode with a relay in order to speed it up a bit. This works very well but I am currently using a rather over-sized zener from the inventory. For proper ...
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  • 5,229
7 votes
2 answers
24k views

Why do I need a transistor to control a relay with an arduino, and which one should I get for this circuit?

I need to control a coffee machine plugged into a wall outlet using a relay connected to an arduino. Apparently I need to connect a transistor to the relay. Why? Is it because the arduino can't supply ...
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  • 459
6 votes
1 answer
12k views

Connecting microcontroller 3.3V output to relay using ULN2803A

I have a need to connect an ARM micro-controller with 3.3V digital output pins to a few 12V solenoid water valves. I figured that I can use a ULN2803A for this task. The internal circuit for each ...
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  • 373
3 votes
4 answers
21k views

How can I drive a 12V automotive relay with a uC running on 5V

I have a project where I need to engergize a 40A relay in a car. My uC based circuit is running at 5V via a 7805 and is mainly doing its own thing, but I need a digital out to energise the 12V relay, ...
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  • 705
15 votes
5 answers
24k views

Is it good practice to parallel relay contacts for increased current capacity?

Say I have a DPDT relay, like T92S7D12-24. The contacts of this relay are rated for 30A, but there are two sets of contacts. Can I parallel the contacts to get an effective 60A relay? Further, could I ...
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1 vote
3 answers
3k views

What is the difference beteeen a solenoid's make current and inrush current?

Sorry if I'm just being noobish, but as I understand it, the make current is the maximum current that the solenoid can handle when switched on, but the inrush current is the maximum current it can ...
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5 votes
7 answers
6k views

What is the most economical way to drive an array of single coil latching relays?

Please read the question to the end. The answer to this question may be non-trivial. Replacing a number of 2-coil latching relays with single coil latching relays ...
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  • 3,152
1 vote
3 answers
24k views

Make a Latching Relay using SPDT Relays

I want to make circuit which can working like a Latching Relay which Hold Current using SPDT Relays. So i can use this circuit to Pules ON/OFF switch. Using limit switch when pressed a pulse goes ...
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2 votes
2 answers
14k views

Relay "sticking"

We are experiencing a problem where the mechanical switch of a SPST NO relay (COTO 9007-05-01) is not opening back up when the coil is de-energized. Current keeps flowing through the switch until we ...
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  • 1,013
2 votes
2 answers
2k views

LCA717 SSR connected to Arduino Digital Pin

I am trying to figure out how to go about using this LCA717 SPST-NO relay in my project. I will be sending 12V (car voltage) to a radar detector and I want to be able to turn it on/off whenever via ...
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  • 645
2 votes
1 answer
8k views

relay power ratings - AC vs DC

I'm in the process of finding a suitable relay for switching the elements in a mini oven I want to use for solder reflow. I've found what I think will be a good candidate, however I'm a bit confused ...
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  • 3,275
0 votes
2 answers
8k views

Choosing a relay to control outlets from Arduino

I'm working on a project that involves an Arduino Uno and some external electronics. I have a 12 V power supply that will connect to an outlet, and I want to be able to control this power using a ...
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  • 543
0 votes
2 answers
282 views

Trigger relay at different voltages with voltage comparator

TL;DR - I need help on making a relay with voltage comparator which accepts two reference voltages. Aim My project needs to run a Raspberry Pi on solar power. Solar panel will be connected to a power ...
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-1 votes
2 answers
4k views

DC Motor reversing relays using a micro switch [closed]

I'm looking to use relays and 1 micro switch to reverse the polarity of the circuit. I will need a simple ON/OFF switch to have the motor turning in one direction and then when the micro switch is ...
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65 votes
8 answers
19k views

Why are there so many relays used in a car, instead of transistors?

Recently I did some work on my car electric circuits. I see many relays are used in car circuits. These relays are used for simple switching, and I wonder why these circuits are based on relays and ...
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