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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Triggering a relay with a 0.7 - 2 Hz pulsating DC voltage between 0 and 12 V

50% duty cycle. I would prefer if there was a passive solution to this but it's not a necessity. The relay needs to turn on when the signal is pulsating and to turn off when the signal is no longer ...
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2 answers
68 views

Circuit not flowing as expected

INTENDED FUNCTION: In position 1, the voltage will feed the speed controller to modulate voltage to the Logic Controller, which will serve to modulate speed of the Basket Motor from the programmed ...
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Relay power feed question

These are the relays I have: https://www.amazon.com/dp/B07QXXNGHR So simply put, the circuit I'm trying to complete is using a single 24V/8A source, and one of my suspicions as to the trouble I'm ...
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Using relays to control two loads from two power sources [closed]

I need to reconnect a system that was disconnected without taking notes and I am having difficulty with the logic. There are two 12 V sources of power, one is 12V DC from the generator alternator and ...
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Auto switching between power sources using SPDT relay causes delay

I have a circuit with two DC Power sources, one is a 12 V, 1 A adapter and the other is an 18 V, 150 W solar panel. I have a DC buck converter LM2546 which turns that 18 V into 12.4 V. The 12 V power ...
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11 votes
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Is there such thing as a normally closed MOSFET?

Is there such thing as a normally closed MOSFET? Or can I somehow make a circuit? Can I control a circuit that functions like that with a control logic voltage of 3.3 V or 5 V so that when I give a ...
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Relay activation and power step down

I have one single pin and I would need to activate a relay. After half a second I need to step down the voltage of the relay from 12V to 3.3V. I've been able to accomplish this task using an LTV6994 ...
2 votes
4 answers
163 views

Do all relays need a diode in parallel with the coil?

I often see circuits with relays and diodes like this: Note the diode D1 in parallel with RLY1, at reverse polarity to the driving voltage V1. Per my research, the reason is that the relay coil is ...
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(Another) how do I choose an appropriate TVS for a relay?

I've seen questions about selecting TVS diodes before (for example, How to choose the correct TVS diode and how to size it?; there are others, but they aren't about TVSs for protecting relay coils). ...
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How do I cause a normally open solenoid to close when power is removed?

Background: I have an undersink 3-canister filter in my kitchen and wanted to monitor the amount of water going through the filter. I purchased a Digiten DFC15 water flow controller and a Digiten ...
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I'm looking to identify this IC. Number is CS2918EB

Markings: CS2918EB SZTA1T8005L It's 16-pin and is on a microwave oven control board and it's connected to relays and a control chip.
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1 answer
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Delay to a MOSFET switching

I have a very simply circuit which, when the sensing lines contact water, switches a relay. The circuit performs well on 12 to 15 VDC. I want to add a delay of approximately 3 seconds to the circuit ...
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How to use a sinking controller output to drive a N-channel MOSFET like a normally-open relay?

My controller has a sinking output (aka it supplies ground). I am able to use an N-channel MOSFET to switch the load as if the MOSFET circuit worked like a normally-closed relay, see diagram below: ...
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Momentary output from turning on and off a switch

I am trying to wire something up for my car so everything here is going to be running off 12/14 V and draw is well under 1 A, probably in the range of 200 mA. I am trying to find a simple way of ...
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5 answers
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Failsafe for relay contact welding

So, I'm fiddling with a design for a widget, and one of the "fun" parts is to ensure that power is reliably cut without human intervention. Power is normally controlled by relays, which have ...
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3 votes
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Could a vacuum-tube diode be used to snub a relay's coil?

I recently asked a question about inductor flyback in relay computers on Retrocomputing.SE. The preferred modern way to snub the inductive kick of a relay's coil is to add a flyback diode across the ...
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1 answer
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How can I detect a power failure on a 120V circuit and activate a battery-powered indicator light?

I recently got a new septic system installed. It's a Presby/mound system whereas our old system was gravity fed to a single tank with fingers. The mound system has a pump tank and the tank is wired on ...
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Simple Model for AC Relay

Though for DC Relay this is almost immediately done with a Current Voltage Source, I've been having good trouble by modelling an AC Relay. Since the reactance part of the relay is an inductor, I am ...
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Securing a doorbell system with a tamper switch and a latching relay

I have a doorbell that has a relay to open the door. The issue I'm having is that my doorbell is outside the house and thus people would be able to come up to the doorbell, open it, and connect it ...
7 votes
3 answers
348 views

Coil suppression: Zener + diode: how to minimize the negative voltage?

I have come across these two app notes: Coil Suppression Can Reduce Relay Life Application of Coil Suppression with DC Relays Both of them agree on the fact that a common diode + Zener diode in ...
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2 answers
79 views

What are applications of an ideal switch?

Technically, every relay or transistor could be replaced by an ideal switch if there was such a thing. However, I learned that those parts are satisfactory in most cases. Thus, I'm looking for a ...
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1 answer
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How to design PCB traces for high-current applications

I am trying to make a WiFi switch using the ESP32 MCU. The PCB I am building will be switching high-power applicances, such as a kettle (which can draw around 14 A @ 230 VAC). The relay I chose is the ...
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1 answer
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Sizing a capacitor for a large relay economizer

I am trying to figure out the correct size capacitor (and resistor, but that's easier) to make an economizer for a Kilovac EV200A1ANA relay. The coil will burn up in minutes without any current ...
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2 answers
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Using a DC remote relay in low-voltage, high-current applications

I am trying to create a remote controlled miniature fog machine. My only issue is that I can't seem to find a wireless/remote relay that can work with low-voltage, high-current applications. It is ...
2 votes
1 answer
56 views

How to size track width for AC application

I want to run AC volatge through my relay shown below: My track width is 2mm for the COM, N/O, and N/C pins. These tracks go from the relay to the 3-pin connector. The relay (G5LE-14-12DC) is found ...
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Latching relay for MCU self power-off or high side MOSFET switch?

I am designing an ATtiny project that needs to operate for a specified amount of time on request, then power itself down completely. Although ATtiny MCUs are remarkable in terms of sleep mode power ...
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Controlling an automotive relay and a pulled up signal with one switch

I am trying to control an automotive relay and a pulled up signal. When I press the push-button switch, I need to trigger the relay and ground the signal on a microcontroller pin. When I simulate the ...
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3 votes
1 answer
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Help with understanding strange automotive relay schematic

I'm in need of help understanding a relay schematic from an automotive relay that has broken on my Triumph. I can find replacement relays of the same model number, but I was curious as to why the ...
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2 answers
379 views

MOSFET not driving a relay

I've been trying to drive a 24 V SMD relay with an internal coil resistance of 2880 Ω and an isolated 3.3 V logic input. I selected the 2N7002 MOSFET (Ic=115 mA) to drive the relay; the relay needs 24/...
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SSR firing problems

I am new here and do not have a lot of electronics experience, so please be nice haha. Anyways, I bought a 100W CO2 laser on eBay at a good price but the reason was that it is actually was sent to USA ...
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1 answer
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Need sort of 'one-way AC relay' for connecting two L-OUT sources to feed a single L-IN destination

I need an AC analog of what in DC world would be 1 x relay and 2 x one-way diodes. To clarify what I am doing: I am going to have a heating pump (...
2 votes
1 answer
78 views

How to solve for relay specifications?

I'm working with an unknown brand of relay and I need to know its specifications - most important is the minimum On current at approximately 42vDC, other values would be appreciated if possible. Does ...
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1 answer
51 views

Hall-effect pulse input to transistor for relay switching

I have a Hall-effect sensor on a water flow meter. I want to switch a pump on when if there is flow (Hall-effect signal). I was thinking of using a RC circuit on the base of my transistor that ...
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What component do we use to build a BLDC motor wye-delta transformer to achieve low resistance?

I've considered using three relays to implement a wye-delta transformer, so I can turn the motor to wye or delta to change its Kv at any time, high Kv for high power and low Kv for high efficiency. ...
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3 answers
124 views

How can I decrease the relay release time when the current on relay coil is reduced slowly?

I'm trying to make a backup power supply for a home WiFi router (12V, 0.5A) and observe that the relay release time for a QYT73 relay is around 1 second. That is enough for the router to reboot, which ...
2 votes
1 answer
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Safe load for the Panasonic DW relay (ADW1205HLW)

I'm lost and can't understand what are safe operating conditions for the relay I have. In the datasheet (https://mediap.industry.panasonic.eu/assets/download-files/import/mech_eng_dw.pdf) it is stated ...
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1 vote
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Can a dual pole (mechanical) relay switch HVAC and LVDC at the same time?

As I understand it, a dual pole relay is one which (mechanically) switches two independent circuits. Is it safe to use such a relay (I'm looking at an Omron MJN2CE, specifically) to simultaneously ...
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1 vote
1 answer
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What is a suitable resistor value for this circuit?

See the small circuit of a PIR motion sensor below. I've tried to find more than one circuit online but every single time it shows a different value for the resistor. I would be grateful if anyone can ...
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1 answer
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Should a start-stop interrupt positive or negative? (Why?)

This answer shows a "standard" start-stop circuit. I was trying to design my own, and came up with a design that is essentially the same, except that it interrupts negative, with positive ...
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AC to DC conversion speed

I am using a relay and an arduino to quickly turn on and off lights for a Christmas light show. So far all of the lights have been AC power. However I just got a snowman that runs on 12v DC power ...
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Disconnecting lithium battery pack during charging

I'm building a smart battery consisting of a 3s6p Li-Ion battery and Arduino. The battery pack I'll be using came with a 12V 5A PSU which overheats when charging the battery from empty. I have a 20V 3....
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6 votes
2 answers
656 views

Does it matter how HV contactor is connected?

I have these contactors for my DC application. I never cared about which terminal to connect to HV, because I treated them like any mechanical switch (or 12V automotive relay). But recently I noticed ...
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Sensing a 24 V AC signal

I have a sprinkler controller with no separate output for a pump relay. I need a 16-input logic OR circuit that can trigger the relay when one or more of its 16 channels is live with 24 - 30 V AC. One ...
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1 vote
2 answers
100 views

Free wheeling (back EMF) diode for latching relay

I'm designing a circuit to drive a single coil latching relay. This uses two MOSFETs, arranged so current flows one way through the relay coil to switch it on, and then the other MOSFET activates to ...
1 vote
2 answers
69 views

Detection of mechanical relay sticking

I'm exploring new methods to find if relay contacts have been stuck together without using auxiliary contacts of the relay. while searching I find out this block circuit: at this Toshiba page as far ...
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Do I need a relay or can I wire this circuit with diodes?

Background I'm doing some automotive wiring to add a light to a cargo area with the following requirements: The light turns on/off when the cargo door is opened/closed The cargo light can be turned ...
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Variable input voltage relay circuit

I'm trying to devise a way to switch 12 V, 25 A using a relay. The problem: the trigger has two states, the OFF position 4.8 V, 0.3 A and the ON position 25 V, 0.3 A. I tried with a regular 24 V relay,...
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Replacing SPDT relay with MOSFET

I'm having trouble replacing a SPDT relay with a MOSFET circuit. I have an SPDT relay that serves as an emergency brake of a small motor when the power goes off, shorting both motor inputs. It's slow ...
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Controlling a solenoid valve with a relay and a 18650 battery

I have a 12 V 18 W (1.5 A) solenoid valve that I want to control valve with an RF relay. I use a Sony 18650 li-on battery to power this system. A 1S 10 A BMS unit is protecting the battery. Even ...
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2 votes
1 answer
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Common Source GaN HEMT breakdown

I had recently designed an array of GaN HEMTs to be used as a solid state relay. At low voltages (Vin = 24V) everything was working fine. However, when I bumped up Vin to 70V, after a couple cycles ...
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