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Can I use a switch to perform momentary actions and also cut its own power source?

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dcwatson84

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This question sort of came up in another thread but I hate to de-trail the real topic of that thread so Im asking here...

I have a power source, which supplies current via a latching-relay to a switch.
Lets assume the latching-relay is closed.
When that switch is thrown I need it to perform a few momentary actions, but at the same time I need it to un-latch its own current stream (the aforementioned latching relay).

Is that a bad practice or error prone or impossible?
 

alec_t

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It's possible, but since no actions are instantaneous you would need to introduce a brief delay before unlatching the relay.
 

dcwatson84

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It's possible, but since no actions are instantaneous you would need to introduce a brief delay before unlatching the relay.
What would be the best/preferred way to introduce that delay? Or is it not as simple as a single component?
 
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alec_t

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I suspect the preferred way will depend on the relay characteristics as well as how much delay is necessary for the 'actions'. Slugging the coil with a capacitor might slow its drop-out sufficiently.
 

Tony Stewart

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a latching relay by definition is one that requires no power to stay in the latch position

is this what you have?

or do you mean a momentary input activates a relay with power on and another momentary input disables the relay.
is it a SPST or SPDT or DPST or?

In your other thread, it was clear that the series limit switch disables the relay at the end of travel in that direction.
 
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dcwatson84

Member
I suspect the preferred way will depend on the relay characteristics as well as how much delay is necessary for the 'actions'. Slugging the coil with a capacitor might slow its drop-out sufficiently.
The only actions being performed are unlatching 2 relays and throwing a DPDT switch.
 

dcwatson84

Member
a latching relay by definition is one that requires no power to stay in the latch position

is this what you have?

or do you mean a momentary input activates a relay with power on and another momentary input disables the relay.
is it a SPST or SPDT or DPST or?

In your other thread, it was clear that the series limit switch disables the relay at the end of travel in that direction.
The limit switch needs to do more than stop travel, the other assumptions were added by people in the thread. The switch needs to stop travel and also change the state of the system by unlatching relays. And yes I know they only require momentary power, they just need to be unlatched and then the system can cut all power.
 

Tony Stewart

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Your functions are not clear without more details. In general changing inputs and outputs simultaneously can be what is called a meta stable condition or a race and may cause glitches. But this may or may not apply without further explicit details.
 

Tony Stewart

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There are many scenarios; you can choose;

1) one momentary input button N.O.
2) 2 momentary input buttons N.O.
3) A toggle switch input (up/down) with a Pole and N.C. and N.O. throws (SPDT)
4) A winch reversal switch with 2in,2out
5) Two half bridge solid-state switches with 2in,2out
6) any sort of remote control with ?? functions

your input type is unclear.
....
I have a power source, which supplies current via a latching-relay to a switch.
Lets assume the latching-relay is closed.
So you have a low power relay used as an INPUT SPST switch. is that right? This controls the start of UP/DOWN ?? and changes how often?
The series limit switches would shut off power in that direction, thus only opposite direction power will function, when you flip the input switch.
got it?

if not pls clarify.
 

dcwatson84

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I don't think any of the up/down details are relevant to this question. This question is about the reliability of a switch which shuts off its own power source upstream.
 

Tony Stewart

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the full bridge has TWO inputs, cutting off one does not disable the other. It allows you to change direction. It does not disable your ability to do this.
 

Tony Stewart

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If you must avoid all power in each end stop state then the direction control relay must be a special ".latching " type which is more expensive.
 

alec_t

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Latching relays can take several forms:
1) A spare contact of a DPDT or DPST normal relay can be used to switch power to the relay coil,
2) A single-coil latching type requiring current in opposite directions to latch/unlatch it,
3) A double-coil latching type where one coil latches it and the other coil unlatches it,
4) A mechanical latch/unlatch type.

(I don't think any of these are necessary for your coop door application.)
 

Tony Stewart

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N

That's what I've been talking about... It's why I'm calling it a "latching" relay
You can't control a latching relay with a SPST switch

I agree with Alec.

http://media.digikey.com/pdf/Other Related Documents/Panasonic Other Doc/Small Signal Relay Techincal Info.pdf

If you had a SPDT ON-OFF-ON switch to a latching SPDT relay to dual coil DPDT Non-latching power relay switch I had specified.
That would work or the other wiring diagrams previously given but then you have no timer with a On-OFF-On control

so NG.

This is not the way to do it by specifying intermediate parts and ignoring the inputs.
 
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dcwatson84

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This is a very specific scenario, I do not want to expand it to anything other than the parameters I specified.

You made an incorrect assumption - I never said I needed to fully "control" the latch (i.e I dont need to do both operations). I only said that I needed to "unlatch" it. If the switch, when triggered, delivers the correct polarity of current to the latch (assuming the circuit is complete) - then it will in fact unlatch it, correct? So I believe you can do that with a SPDT switch right? Because all you need to do is apply the current and the latch will perform as it is designed.

I realize I may not *need* latching relays, but if it vastly simplifies the system then Im willing to use them, as they dont seem to be prohibitively expensive.
 
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dcwatson84

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If you'd like me to describe my thoughts on using the latching-relays I will, but when I have specific questions I sometimes need specific answers, otherwise I'll never understand the reasons behind certain designs.

And I should probably pose that design in the other thread - as I still consider this thread to be focused on my initial question.
 
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Tony Stewart

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if you read the Matsushita link on latching relays, it will explain how to use and not use them, especially fig's 18-22.

Latching relays are simple to use with a centre off switch and activate one coil exclusively.
They have set and reset coils.
They "latch" in either position while un latching from the other.

But not necessary for your application.

To answer this thread question.
simply put, it is a bad practise .. see fig 22
 
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