Latching Relay question

[mkruger]

What's the difference between a standard relay and a latching relay?

 

[NewYorkDave]

A latching relay... well, it latches. In other words, it holds its state until a second pulse is applied to change it back to its original state. A standard relay requires a sustained current through its coil to maintain its "switched" state. A latching relay requires a "switch" pulse and a "reset" pulse.

 

[mkruger]

oohhh!!! Yes! then that is what i shall use :guinness:

 

[NewYorkDave]

Only if the circuit is designed for a latching relay. The two types are not interchangeable.

Dual-coil latching relays have one coil for "operate" and another coil for "reset." Single-coil DC latching relays use one voltage polarity for "operate", and require reverse polarity for "reset."

 

[CJ]

You can "unlatch" a latching relay by tapping it with a screwdriver, so make sure that there won't be any mechanical vibration around the circuit you are using it in, ie: tape recorder for instance.

 

[mkruger]

no prob, i will use a DPDT Center Off Momentary switch...

 

[daArry]

ahhh, so with latching relays momemtary switches would be the choice and non-latching the push on/push off type switch would be the order the of day? Coo... :thumb:

 

[SSLtech]

[quote author="CJ"]You can "unlatch" a latching relay by tapping it with a screwdriver[/quote]Some 'sticky' relays perhaps, but I bought a latching relay about 15 years ago to use in a home-made, self-designed car alarm circuit for a show car that I had built, andd the internal mechanism was rather like a click-click retracting ball-point pen, or perhaps a schadow switch alternating action latching mechanism.

You wouldn't be able to unlatch that one, unless you 'tapped' it hard enough to smash it!!! :wink:

Keef

 

[Mark Burnley]

...plus you can "blag" a latching (or "Flip Flop") relay using a T-type ("Toggle") flip flop (made from D-type CMOS 4013) with an R-C debounced push switch driving a transistor driving the relay. But a proper latching relay has the no-power-between-states advantage!

Mark

 

[CJ]

I just thought I would show you that latching relay's are nothing new.
I scored these old timer Leach relays at Andy's last week.
You push that black button to set it:

and when the coil is energized, it allows the relay to latch until it is re-set by the maintainance guy at the drive in.
Even if the relay coil is accidently re-energized, nobody gets electrocuted.
Definately will not come un latched if you bang on it with a hammer.