latching relay

hgmjr

Joined Jan 28, 2005
9,027
hi, has anyone got any ideas on how to latch a relay using a pushswitch from a negative supply???

thanks
By the term "latching" do you mean to have the relay go to the closed state when the switch is pressed and then stay in the position when the switch is released?

hgmjr
 

Thread Starter

kirkyj78

Joined Jan 19, 2008
7
hi yes that's exactly what i need to do, it is basically to remove the power from a relay, i thought by latching another relay this could work. maybe there is an easier way???
 

hgmjr

Joined Jan 28, 2005
9,027
There is such a thing as a "latching" relay. It will stay in its last state even if power is removed. They are not cheap as relays go. These relays are most often driven using an H-Bridge.

Does that sound like what you would want to use?

hgmjr
 

beenthere

Joined Apr 20, 2004
15,819
Not necessarily - I an using a P & B latching relay to control lights in my basement from four locations. It just takes 12 VAC - P & B # S89R11DAC1-12. But they are $36.77 from Digi-Key.
 

hgmjr

Joined Jan 28, 2005
9,027
Not necessarily - I an using a P & B latching relay to control lights in my basement from four locations. It just takes 12 VAC - P & B # S89R11DAC1-12. But they are $36.77 from Digi-Key.
That sounds like just the thing for kirkyj78's application.

Is that a mechanically latching relay?

hgmjr
 

hgmjr

Joined Jan 28, 2005
9,027
No doubt about it. The relay that beenthere put forward and mrmeval kindly provided a link to is far simplier than the solution I had in mind.

I would like to join beenthere and mrmeval in recommending this as a proposed solution to kirkyj78's relay question.

hgmjr
 

SgtWookie

Joined Jul 17, 2007
22,230
See the attached schematic.

S2 through S4 are optional; simply there to show how you could connect a large number of switches to control whether the relay was ON or OFF.

If the coil voltage is the same as Vin, you can use a SPST relay. Otherwise, you'll need two sets of contacts.
 

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Thread Starter

kirkyj78

Joined Jan 19, 2008
7
hi, thanks for all the reply's,
I guess what i really need is some way of disconnecting power to a 12v dc relay using a one press of a push button supplied from the negative rail.

My problem is a latching relay needs to be switched between states manually.

But i need it to reset when the power is disconnected.

Hope this makes more sense.

thanks
 

hgmjr

Joined Jan 28, 2005
9,027
hi, thanks for all the reply's,
I guess what i really need is some way of disconnecting power to a 12v dc relay using a one press of a push button supplied from the negative rail.

My problem is a latching relay needs to be switched between states manually.

But i need it to reset when the power is disconnected.

Hope this makes more sense.

thanks
So let me see if I can understand what you are seeking to do

You already have a 12V relay that you want to be able to energize whenever power is applied by manually pressing a push-button. Then you want the relay to disconnect when power is removed but you don't want it to re-energize when power is re-applied until you press the button again.

Is that correct?

hgmjr
 

beenthere

Joined Apr 20, 2004
15,819
Then you use a DPST relay and use one set of contacts in parallel with the pushbutton. That way, the relay is self-energizing, and will drop out when power is removed.
 

John Luciani

Joined Apr 3, 2007
475
A latching relay maintains its state when the power is removed.
Some relays have two coils others have a single coil. The two
coil variety has a set and reset coil. To set/reset the single
coil variety you need to reverse the polarity of the coil.

The polarity of the supply doesn't matter as long as you connect
the positive terminal of the relay to the more positive potential
in your circuit (for the two coil version).

I have been using the NAIS DSP1-L2-DC5V two coil latching
relay. It is apx $7 from Digikey. You can also get a single version.

(* jcl *)
 
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