Relay Help

[Oxia]

Hi,

I'm working on a small project and need some help with relay wires.

I have two relays that get turned on by different items but i need both relays to be able to turn a third relay on when one of them gets activated (the third relay powers a sounder) i then need for the third relay to be turned off by a momentary push button to "silence" the alarm but allow any other of the two main relays to power it up again if it needs to...

How do you wire this?

 

[bernardgreen]

Can both relays be operated at the same time ?

Can this sequence happen ? -- de-energised ++ energised

Relay 1 ----------------++++++++++++++++++-----------
Relay 3 ------------------++++++++++cc------------------------ cc = cancel button
Relay 2 -----------------------------------------++++++++++

If relay 1 and relay 2 cannot ( or will never ) be energised at the same time then a simple circuit is possible.

Make contacts on Relay 1 and on Relay 2 are wired in parallel to supply power to the siiren via a normally closed contact on Relay 3

The cancel button latches relay 3 ON to the siren power from relay 1 or 2. Power to the siren is removed when relay 3 energises and relay 3 remains latched ON until the source of power ( relay 1 or relay 2 ) de-energises. If relay 1 and relay 2 can overlap as above then relay 3 will remain energised when relay 1 denergises and the siren wil not sound when relay 2 energises.

 

[Simon35]

Hi,

I'm working on a small project and need some help with relay wires.

I have two relays that get turned on by different items but i need both relays to be able to turn a third relay on when one of them gets activated (the third relay powers a sounder) i then need for the third relay to be turned off by a momentary push button to "silence" the alarm but allow any other of the two main relays to power it up again if it needs to...

How do you wire this?

Wire a contact from each of relays 1 and 2 in parallel to power the coil of relay 3. Wire a contact from relay 3 in parallel with these 2 parallel contacts. That way, relay 3 will stay on after 1 and 2 have switched off. All these contacts should be n/o. Wire a normally closed contact from the pushbutton in series with the relay 3 contact outlined above. Pressing the button will remove the power to relay 3 coil, therby muting your alarm.

 

[Oxia]

i'm so confused

 

[Simon35]

i'm so confused

How much do you know about relays? Do you know what normally open and normally closed contacts are?

Try drawing out what has been described above, much easier to see what's what.

 

[Oxia]

i know what the contacts are it's the circuit i'm stuck with. i can't draw it as i don't understand it

How much do you know about relays? Do you know what normally open and normally closed contacts are?

Try drawing out what has been described above, much easier to see what's what.

 

[EFLImpudence]

I have two relays that get turned on by different items

Does one (or both) of these items use momenary switches or do they remain 'on' when you want to silence the sounder?

 

[Simon35]

i know what the contacts are it's the circuit i'm stuck with. i can't draw it as i don't understand it

Ok.

Draw three normally open contacts in parallel with your supply voltage connected to the top of all three. The bottom of all three contacts connects to the coil of relay 3. These three contacts are from relays 1, 2 and 3.

If either relay 1 or 2 contact closes, relay 3 coil is energised, then the contact from relay 3 also closes and keeps relay 3 energised even if relays 1 and 2 switch off.

Does that make sense? There's another bit involving the pushbutton.

 

[ban-all-sheds]

Can both relays be operated at the same time ?
.
.
If relay 1 and relay 2 cannot ( or will never ) be energised at the same time then a simple circuit is possible.

Why does it matter if #1 & #2 can be energised at the same time, or not?

The cancel button latches relay 3 ON to the siren power from relay 1 or 2. Power to the siren is removed when relay 3 energises and relay 3 remains latched ON until the source of power ( relay 1 or relay 2 ) de-energises. If relay 1 and relay 2 can overlap as above then relay 3 will remain energised when relay 1 denergises and the siren wil not sound when relay 2 energises.

Using relays to implement the logic of reacting to state changes rather than states does not always work well. They are fine for combinational logic, not so good for sequential logic.

 

[bernardgreen]

Using relays to implement the logic of reacting to state changes rather than states does not always work well.

Strange then that the electromechanical telephone exchange equipment worked so well.

Why does it matter if #1 & #2 can be energised at the same time, or not?

because if they do over lap after the siren has been silenced then energising the second relay will not restart the siren ( that is in the very simple ciruit I suggested )

 

[Adam_151]

Off topic, ...an interesting trend I've noticed is things that your'd expect would have a handfull of descrete components, or a couple of common ICs, tend to end up with a custom programmed microcontroller.

Remember seeing an industrial fan that has to run for a set amount of time when a push button was pressed, the time could be adjusted between 10secs and 3mins using dip switches, there was also the option to lock it out for 30 secs after it stopped to limit thr duty cycle a bit. The controller had failed (the power supply section[linear] had gone pop) before it went back to the supplier's service dept. I was having a nose at it, and it was clear that the heart of it was an 18pin MCU, evident by the 4mhz clock crystal nearby, not sure what it was as the chip was simply indentified by a part number on a sticky label that the microfacturer deemed to reprersent the programmed MCU, peeling this back (yeah I am nosey!) revealed that the actual part numbr had been abradded away!

It struck me as ironic that something that could be done with a timer chip and a couple of counter ICs was actually using something with more processing power than the systems which landed teh apollo astronauts on the moon....