Building a latching relay circuit

Thread Starter

Kinoton

Joined Jan 20, 2014
30
Hi
I’m sure this is basic stuff but it’s something I’ve been struggling to understand so I’d appreciate any help or advice !
Am I right in thinking any relay such as this Beta BTA6-2C16-J-CW
https://www.beta.com.tw/download/downloadfile/9/1.htm
can be used to create a latching relay ? I’m trying to create a circuit that switches 230vac to a lamp . I’m using a momentary contact button as a start and a momentary closed as a stop. I’ve wired the 12v dc supply to the coil but I’m not sure how to wire everything else. I’ve wired the start button into the dc supply and connected the ac and the bulb via the other contacts . The bulb operates only when the start button is pressed , my understanding is that the relay can be wired so that the dc gets around the start button (once pressed) and keeps the coil energised . It’s this bit that I’m struggling with ! Any help gratefully received . Thanks , Jon
 

MrChips

Joined Oct 2, 2009
24,644
Any relay with spare NO contacts can be wired to latch. Connect the contacts across the pushbutton.
When the button is pressed the contacts will close and continue to energize the relay even after the pushbutton is released.

To reset the relay, install a NC button in-line with entire circuit or relay or latching contacts to break the power to the relay coil.

1630339259462.png
 

LowQCab

Joined Nov 6, 2012
1,368
That's what Schematic Diagrams were invented for.
It makes it quick and easy to follow where the Current is flowing.

You will need to change your "Off" Button to a "NC" (normally closed) Push-Button,
because it needs to interrupt the Current flowing through
the Relay-Coil to "Un-Latch" it.
 

eetech00

Joined Jun 8, 2013
2,659
This circuit allows the OFF button to override the ON button (both buttons are momentary action).
R1 reduces the holding current once the ON button is released and the relay is latched.

1630343289186.png
 

MaxHeadRoom

Joined Jul 18, 2013
23,949
Have you considered a magnetic latch relay if you are using DC to switch ?, the big advantage is, it has memory, i.e. retains state if you lose power..
Also there is a way with two relays and one P.B. to create a flip-flop circuit.
 

MaxHeadRoom

Joined Jul 18, 2013
23,949
Good to have on your bookshelf is the Square D Wiring Diagram pamphlet. Here it is in PDF. Sort of the bible of motors and control wiring.
Wiring Diagram Book (schneider-electric.com)
One issue I have with that publication, although it does not apply to this thread, is they show the old practice of placing the motor O/L on the RH side of the contactor/relay coil, instead of the present preferred method of using it on the LH side in the main rung.
 

xox

Joined Sep 8, 2017
609
One issue I have with that publication, although it does not apply to this thread, is they show the old practice of placing the motor O/L on the RH side of the contactor/relay coil, instead of the present preferred method of using it on the LH side in the main rung.
Is there a name for that convention? It must have something to do with grounding, I'm guessing...
 

MaxHeadRoom

Joined Jul 18, 2013
23,949
Is there a name for that convention? It must have something to do with grounding, I'm guessing...
Close! switching the grounded neutral or grounded supply common.
I don't think there was a name for it, evidently it made it easier for wiring up P.B, stations, (one less wire!).??
 

xox

Joined Sep 8, 2017
609
Close! switching the grounded neutral or grounded supply common.
I don't think there was a name for it, evidently it made it easier for wiring up P.B, stations, (one less wire!).??
I see. So more a matter of reducing costs rather than some particular safety concern.
 
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