I am (very) new at this, so I apologize if it's a dumb question.

I am playing around with something. I have a momentary switch attached to a latching relay. Push the button, the light turns on. Push it again, the light turns off.

When the light is on, if I remove the battery and put it back again, the light comes on again. I don't want that. I want the default state to be "off" after the power cycle.

How can I achieve that?

 

What you most likely need is a magnetic latching relay, this device stays in the state it was in when power was removed.

 

Using a standard Non Latching relay, here is a latching circuit that seals in the relay with the D2 diode and a second set of relay NO contacts. SW1 can be a momentary NO button but once the power is removed from the circuit the realy coil will drop out and open the RLA/2 seal in contacts. Voltage depends on what is required by the relay up to 24VDC. To turn it OFF you can add a momentary NC button between the +V rail and RLA/2

 

What you most likely need is a magnetic latching relay, this device stays in the state it was in when power was removed.

that is what he seem to already have but does not like.

 

It appears that you are using a 'ratchet' or 'impulse' relay.

A 'ratchet' or 'impulse' relay changes state with a pulse input to its coil and reverts on the subsequent pulse.

In other words, it changes state on consecutive pulse inputs to its coil.

Here's an animation, courtesy Homofaciens.de, that gives an idea of how the impulse relay works.

Here's the ratchet-relay-based schematic.



The ratchet relay 'K1' gets mechanically latched, upon its coil being momentarily energised, when the momentary push button switch 'S1' is actuated . The lamp 'H1' is switched on through the 'NO' contact of 'K1' .

The ratchet relay gets reset, when the momentary push button switch 'S1' is re-actuated, and the lamp is switched off.

Your requirement of reset with power off necessitates the use of a standard relay instead of a ratchet relay.

Here's the standard-relay-based schematic.



The standard relay 'K1' is electrically latched, upon its coil being momentarily energised when the momentary push button switch 'S1' is actuated. Latching occurs when the 'NO' contact of 'K1', that's in parallel with the 'NO' contact of 'S1', gets closed. The lamp 'H1' is also switched on through the 'NO' contact of 'K1' .

The standard relay gets reset, when the momentary push button switch 'S2' is actuated, and the lamp is switched off. Reset occurs when the coil is de-energised by the 'NC' contact of 'S2'.

Nandu.

 

Welcome to AAC!
Can you post a link to the actual relay you have (to save us guessing), and post a schematic of your circuit?

 

Some sort of power-on reset circuit should do what you want.
The circuit complexity for that depends upon the details of the circuit you have, but it could be as simple as a large capacitor connected to the power supply.

 

What the TS has requested is the most common electrical circuit for controlling industrial actions. That is the self sealing relay circuit, as shown in the second drawing in post number five. But that drawing uses symbols that are not common.
The diode is not a functional part of the circuit, it is just a religious artifact included by many folks.

 

Thanks everyone. I am learning, this is super helpful!

 

. But that drawing uses symbols that are not common.

Not common to N.A, but common in Europe, a different drawing standard is used.
Different symbols and top down schematic flow.

The diode is not a functional part of the circuit, it is just a religious artifact included by many folks.

An odd person may believe it to be an "Religious Artifact" but essential in circuits that are sensitive to spurious BEMF 'spikes'. !
The AC equivalent is the R/C 'Snubber'.

 

For someone new to the electrical realm it makes sense to not add extras to a circuit without providing an explanation of why they have been added and what the purpose is. Also, having that diode present in an AC powered circuit will certainly cause problems.

 

Point taken, MisterBill2.

Agreed that the circuits are valid for AC as well as DC and that one tends to show the fly-back diode in the DC circuit while leaving out the RC snubber in the AC circuit.

Nandu.

 

This very simple "Non-restart" function has been mandatory for every machine with any motion elements that I have designed over many years. It is a very basic safety element of most motion systems..

 

"Non-restart" function has been mandatory

That's what he asked for. Somehow, it got skewed into stay started on repower.

 

I reviewed the posts and Sam is correct. Post #2 go tit wrong. Oh Well !
The single disadvantage of the sealed relay scheme for battery circuits is that the relay draws a bit of current while it is active.
How would I produce the same effect of non-restart with a scheme that did not use a bit of power to hold itself energized?? THAT will take a bit of thinking: How to provide the maintained power without consuming additional power to do it? "Low Power" would not be too hard, ZERO POWER is going to be a challenge.

 

Below is the LTspice sim of a two transistor latch, triggered by a push-button, that powers up in the OFF state, requires no current in the OFF state, and only the current through R1 when on:
Of course its output could drive a relay, if desired.

 

Here's another way.

1. DC version

A lamp may be toggled on / off, using an SCR (Thyristor) and two momentary push button switches.



The SCR latches 'on', when the 'on' pushbutton switch is pressed, and the lamp lights up.

When the 'off' pushbutton switch is pressed, power is removed when it's 'NC' contact opens, and the lamp goes off.

No power is consumed when the lamp is off.

2. AC version

This version uses a Triac.



Operation is identical to the DC version.

Nandu.