Latching relay circuit

Thread Starter

Cipry777

Joined Oct 5, 2023
1
Hi everyone!
So, i have two push buttons, wich when pressed, gives 18v. I want to pun an LED light, so when one of them is pressed, turns it on, and the other one turns it off. I was thinking to wire the buttons to an latching relay module, but the one i found, changes states when pin A and B are shorted. Do you think i can manage somehow to wire them to achiev what i want? Thank you!!
 

MisterBill2

Joined Jan 23, 2018
17,814
A latching circuit with two buttons is a classic, been around for at least 75 years. BUT one of the buttons must be normally open and the other normally closed. And if they are all ready connected to 18 volts, then you need an 18 volt relay, with two normally open contacts.
For a more detailed answer we need a more detailed description of what really is desired.
 

MisterBill2

Joined Jan 23, 2018
17,814
A maintained contact relay with two coils,SET and RESET would certainly work quite well for this application.
But you will not find one to operate on 18 volts.

So you will need to use a 12 volt relay and include a resistor to drop the 18 volts to 12 volts. You will need to know the current drawn by the relay coils to calculate the value of the resistor.

In the past, such relays were fairly common in larger upscale houses, to easily provide control of lighting in the larger rooms where the lights would be controlled from different locations.
 

MisterBill2

Joined Jan 23, 2018
17,814
The bistable/maintained-contact 24 volt powered relay has been around a very long time. The ones that I am familiar with have one set of contacts rated for switching mains power for lighting. So tat device would be more than enough to control many LEDs. But it will exactly fill the stated requirements of only needing a short pulse of power to change state. It should be available from an electrical supply distributor, not an electronics distributor. It is as simple as it can get.
 

ThePanMan

Joined Mar 13, 2020
757
A maintained contact relay with two coils,SET and RESET would certainly work quite well for this application.
But you will not find one to operate on 18 volts.
The bistable/maintained-contact 24 volt powered relay has been around a very long time.
I've operated 24VDC relays using 13.8VDC on numerous occasions. 12VDC is not reliable for switching the relay.

Commonly it takes ~ 70% of the rated voltage to throw the armature of a relay and it commonly holds to ~ 30% of the rated voltage to drop it out. I said "Commonly". You will find exceptions to that statement, but in general operating a 24VDC relay (and I'm just assuming this is DC but I could be wrong) a 24V relay will latch at 16V. If you have a 24 volt relay in hand - give it a test at lower voltages to find out where it will click in. Also be sure the sources you're using has sufficient current as well.

A relay coil has resistance (not the correct term, but for the sake of understanding - - - ). Ohm's law states that the needed current to operate that coil effectively is the equivalent of the voltage divided by the resistance of the coil. If you have a coil that calculates to draw 200mA and you have a battery capable of delivering 30mA - it won't work.
 

ThePanMan

Joined Mar 13, 2020
757
I have a relay flip-flop latch circuit that uses one push button, push-on/push-off.
Assuming you're running LED lights at low voltages (not house voltages) then the FF approach along with switching transistors is the best approach.
You need a latching relay with two coils.
This is the easiest approach. All you need is a latching relay that will click in when you press the buttons. As long as the switch contact rating is sufficient for the load - you don't need to worry about the voltage of the LED lights. You didn't tell us anything about the lights.
 
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