Relay question that requires thinking and theory

Microcontrolled

View the attached picture. Remember the when the coil has current flowing through it, the switch inside the relay will close, allowing current.

Now tell me, what happens when you push the pushbutton?

Does the circuit stay on, or does the relay close up again?
I haven't tried this yet because I want to see what theories are generated here. :-)

txmarsh

I vote for Stays On... looks like a standard relay logic latch circuit. No?

John R.

The circuit stays on. This is used routinely with the addition of a NC switch and/or contact in series with the load. This provides a "push me for on" (the switch you have), and a "push me for off" (the NC switch that would be added). In motor controls it is not uncommon to have an additional contact from the "heater" also in series with the load and the NC switch to shut down for thermal overload.

On large motor (or other loads) circuits, the actual motor load is on a different set of contacts driven by the same relay.

John R.

Edit: The above ***-u-me-s that "circuit" goes to ground, which is probably not the case and a matter of misreading the partial schematic.

Shawn Lowe

Its a latch circuit. Itll stay on

erco

Not a latch, won't stay on, won't activate . The switch and relay contacts are in parallel, that's all.

To latch, the coil would have to be in series with the relay contacts. As shown, it goes to an external circuit which is controlling the relay.

Ron Czapala

If the coil wire labeled "to circuit" is ground for the supply voltage, the relay will latch on.

W9GFO

If the coil is energized, the button will have no effect. The external circuit has control.

If the coil is not energized then the external circuit will not be able to energize it unless you hold the button down.

Rich H

txmarsh

Won't do anthing because it is just lines on a computer screen! ; )

I still say that, as drawn, it is intended to convey the idea of a latch... of course it is dependent on the "circuit" not shown.

erco

Ron: Yes, if the "to circuit" wire goes straight to ground, it will latch. But "to circuit" is purposefully vague, counselor, and this court will not dispute it!

txmarsh

Erco... funny thing... when I read your response I thought... hey, he answered it like a lawyer! Now I'm thinking you probably really are! : )

skylight

Firstly it depends on whether the "circuit" has any reference to the relays supply.
If so then it depends on whether the circuit shows enough negative reference to energise the coil, if so and the button is pressed and the relay then closes it will stay latched until the circuit is interrupted

zappman

Can't tell, you have not shown any connection to ground (or your power - lead). Also need to know what "to circuit" is connected to.

davejames

Some assumptions must be made:

- IF as drawn (connections and normally open switch)
- IF the "supply" is the required voltage for the relay coil
- IF the "to circuit" is near 0v

...then the circuit does NO-thing initially. The relay switch will not close as it's in series with the coil and supply voltage.

Given the above assumptions, pressing the button will energize the coil and the relay switch will close - thereby maintaining coil current. The button becomes ineffective at this point.

Raise the voltage potential of "to circuit" above the minimum required by the coil to keep the relay switch closed, and it will open.

DJ

Dr_Acula

First answer - what Zappman says.

Second answer, trying to second guess the statement Remember the when the coil has current flowing through it, the switch inside the relay will close, allowing current.

Which I think is making the assumption that the "to circuit" is a low resistance load connected to ground. Otherwise current would not flow, right? So "to circuit" is not open circuit, and it is not a 1meg resistor, and it may not be a direct connection to ground, but it probably is something like a light bulb or a motor. In which case the relay latches on.

BUT - if "to circuit" is a propeller chip, no, the relay does not latch on. There is not enough current.

Peter KG6LSE

It depends on the Ω of the "other circuit"

I do not have sufficient data to render a sound and safe engineering decision .