# Latching Relay



## VELOCI3 (Aug 15, 2019)

Do you have an auxiliary contact in your relay?


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## dronai (Apr 11, 2011)

VELOCI3 said:


> Do you have an auxiliary contact in your relay?
> 
> 
> Sent from my iPhone using Tapatalk


Yes lots of ice cube relays, and contacts.


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## ElectricMatt (Dec 29, 2016)

What exactly are you trying to do? What is the system and what components do you have To make it work?


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## splatz (May 23, 2015)

If you google alternating relay or flip flop relay you'll find lots, not expensive.


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## dronai (Apr 11, 2011)

ElectricMatt said:


> What exactly are you trying to do? What is the system and what components do you have To make it work?
> 
> Sent from my iPhone using Tapatalk


An alternator between two pumps. Latching relay, and a bunch of relays.



splatz said:


> If you google alternating relay or flip flop relay you'll find lots, not expensive.



I know, but I'm trying to make one using relays.


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## CoolWill (Jan 5, 2019)

You say "alternator" and I think "AC generator", so just stop that right this instant. You want to switch between two pumps? Under what kind of control? Where does the command come from?

Exact what is it you are doing?


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## ElectricMatt (Dec 29, 2016)

dronai said:


> An alternator between two pumps. Latching relay, and a bunch of relays.
> 
> 
> 
> ...


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## Wirenuting (Sep 12, 2010)

I use them all the time for remote pump switching. Diversified has a large selection and the last for years. 

https://www.galco.com/buy/Diversifi...CUMqVVFk7mAYutHV0ez-LhVge9xyjOJhoCfMoQAvD_BwE

https://www.marshbellofram.com/diversified-electronics/


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## splatz (May 23, 2015)

I think I have seen DC alternating latching circuits but you need relays plus diodes and / or capacitors. I don't think I've seen it done with AC and just relay logic. 

search search search ...

Look at page 8 here: 

https://www.ee.ryerson.ca/~phiscock/papers/relay-counter.pdf



> There are a couple of other interesting features of this circuit.
> 
> First, notice that the flip-flops are either both energized or both de-energized: they do not alternate, as one might expect.
> 
> ...


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## Wirenuting (Sep 12, 2010)

splatz said:


> I think I have seen DC alternating latching circuits but you need relays plus diodes and / or capacitors. I don't think I've seen it done with AC and just relay logic.
> 
> search search search ...
> 
> ...


The catalog I posted has diagrams for each controller someone might need. 
All you do click the relays download file and you can see each.


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## CoolWill (Jan 5, 2019)

I assumed you only have DPDT relays and the pumps were 120 V, so you may need to adapt accordingly, but this should do what you want.


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## Tonedeaf (Nov 26, 2012)

https://www.marshbellofram.com/diversified-electronics/types/alternating-relays-and-controls/


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## splatz (May 23, 2015)

Wirenuting said:


> The catalog I posted has diagrams for each controller someone might need.
> All you do click the relays download file and you can see each.


That's what I thought the question was too, but @dronai is looking to _roll his own_ latching alternating relay from ordinary relays on hand.


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## Wirenuting (Sep 12, 2010)

splatz said:


> That's what I thought the question was too, but @dronai is looking to _roll his own_ latching alternating relay from ordinary relays on hand.


That’s what’s what I thought also. 
The nice thing about this catalog is you pick the style of relay control needed and looking at the diagram you can build your own. Works great when your stuck in the field. I have the paper catalog in my truck and it saved me a few times. 
Some of these relays they sell are expensive, but the man hours needed to wire your own can be greater then the out of the box relay.


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## CoolWill (Jan 5, 2019)

dronai said:


> I'm trying to make an alternator using a latching relay, but I want to have one trigger. The relay uses a pulse to switch positions of the contacts.
> 
> Do you guys that use these types of relays, use a 2 position, or double throw switch ?





splatz said:


> That's what I thought the question was too, but @dronai is looking to _roll his own_ latching alternating relay from ordinary relays on hand.


Now that I'm awake and read the OP again, he already has a latching relay and wants to alternate pumps. So is there a separate means to turn power on and off, or is the latch currently doing that? Because if you have a power switch, then you could simple wire the latch to a regular double throw relay. One pump on the NC and the other on the NO.


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## gpop (May 14, 2018)

Biggest problem with trying to do this is there's 3 states on a standard relay.

At some point you have the contacts between n/o and n/c which maybe for a micro second but that's enough to end with logic that doesn't work or logic that sometimes works. Solid state relays do not have this problem but the cost starts to add up. 

I always carry a programmable relay on the van. Its expensive but its capable of being any relay i need in a emergency.


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## splatz (May 23, 2015)

CoolWill said:


> Now that I'm awake and read the OP again, he already has a latching relay and wants to alternate pumps. So is there a separate means to turn power on and off, or is the latch currently doing that? Because if you have a power switch, then you could simple wire the latch to a regular double throw relay. One pump on the NC and the other on the NO.


I am not seeing how a momentary pulse lets you alternate loads...


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## dronai (Apr 11, 2011)

Float 1 is the trigger for both pump 1 and pump 2

Pump 1 goes through the Latch contacts, or NC

Pump 2 goes through the U Latch contacts, or NO

Pump 1 goes through the NC contacts of Pump 2

Pump 2 goes through the NC contacts of Pump 1

Pump 1, and Pump 2 goes through the NO contacts of the Stop float relay

When Pump 1 energizes, it also sends the power to the change state, or Latch relay coil.

When Pump 2 energizes, it also sends the power to the change state, or U Latch relay coil.

This works great on a PLC, the engineer who drew it up for me said it will work exactly the same with a latching relay, and real relay's. 

I think it might be what POP said above. For a split second, both get power, and it won't allow the latching relay to work.

If I manually touch the Latch and U latch terminals, it works fine.


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## dronai (Apr 11, 2011)

CoolWill said:


> Now that I'm awake and read the OP again, he already has a latching relay and wants to alternate pumps. So is there a separate means to turn power on and off, or is the latch currently doing that? Because if you have a power switch, then you could simple wire the latch to a regular double throw relay. One pump on the NC and the other on the NO.


Yes that works, but I want it to be automatic


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## CoolWill (Jan 5, 2019)

splatz said:


> I am not seeing how a momentary pulse lets you alternate loads...


The momentary pulse controls the latch. With the latching relay off, the other relay is de-energized and the NC contacts power a pump. When the relay latches, the other relay is energized and the NO contacts power the other pulse.


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## dronai (Apr 11, 2011)

When guys use latching relay's for lighting loads, how do you automatically send separate pulses for latch and unlatch ? A timeclock sends one


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## paulengr (Oct 8, 2017)

Macromatic sells an inexpensive alternating pump relay. Sure you can do your own but it’s cheaper than a “smart relay”. Used a lot in duplex sewage lift stations.


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## CoolWill (Jan 5, 2019)

dronai said:


> When guys use latching relay's for lighting loads, how do you automatically send separate pulses for latch and unlatch ? A timeclock sends one


Latching lighting contractors are usually mechanically held and change state when the signal goes high.


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## dronai (Apr 11, 2011)

CoolWill said:


> Latching lighting contractors are usually mechanically held and change state when the signal goes high.


No, they are not mechanically held, that's the point, non energized solenoid to be more reliable, and not work, when the load is on.


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## dronai (Apr 11, 2011)

paulengr said:


> Macromatic sells an inexpensive alternating pump relay. Sure you can do your own but it’s cheaper than a “smart relay”. Used a lot in duplex sewage lift stations.


That's good to know, and you're right, that's inexpensive.
This is more of a controls exercise


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## gpop (May 14, 2018)

dronai said:


> No, they are not mechanically held, that's the point, non energized solenoid to be more reliable, and not work, when the load is on.


They are mechanically held.(at least the ones i have worked on)

Its a simple trick because a ac solenoid will try to get the metal plunger into the center of the coil. Once the plunger is moving if you cut power to the coil it has enough momentum to complete the switch (aided by springs to make sure it can not stay in the middle)


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## dronai (Apr 11, 2011)

"Latching relay is really a generic term that is used to describe the type of relay that maintains its position after the power is removed. The reason latching relays are used is because they allow control of a circuit by providing a single pulse to a relay control circuit."


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## splatz (May 23, 2015)

You can get lighting contactors that are mechanically held or electrically held, they say the mechanically held last longer and of course they are green, they save the $0.02 of electricity per year the coil eats running all those hours. 

This one has two coils to latch and unlatch ... but they are operated by an alternating relay, the CA2SKxxx in the diagram operated by the pulse.


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## gpop (May 14, 2018)

dronai said:


> That's good to know, and you're right, that's inexpensive.
> This is more of a controls exercise


If you are learning to do your own controls for a lift station also add a back up system that starts both pumps on the HI-HI level float and pumps until you hit the low level. Add a additional time delay relay to one of the pumps if you have a generator bypass or the panel can not handle both pumps starting at the same time.


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## dronai (Apr 11, 2011)

gpop said:


> If you are learning to do your own controls for a lift station also add a back up system that starts both pumps on the HI-HI level float and pumps until you hit the low level. Add a additional time delay relay to one of the pumps if you have a generator bypass or the panel can not handle both pumps starting at the same time.


Yes, I have lots of experience with these. It's too expensive to build on your own, and compete with the prebuilt models on the market.


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## gpop (May 14, 2018)

dronai said:


> "Latching relay is really a generic term that is used to describe the type of relay that maintains its position after the power is removed. The reason latching relays are used is because they allow control of a circuit by providing a single pulse to a relay control circuit."


Must be different down south. 

If the latch turns the coil off its referred to as mechanically latched.


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## dronai (Apr 11, 2011)

Here's mine, looks like one coil, and a couple of diodes


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## dronai (Apr 11, 2011)

Terminals 4,and 5 are NC, and NO, connected to terminal 1 when energized

Terminals 6 & 10 is what you send the pulse on


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## splatz (May 23, 2015)

It is a great controls exercise. It illustrates how hard seemingly simple things could be with relay logic. 

But for real use, purpose made pump controllers are dirt cheap, I wouldn't roll my own with an alternating relay, programmable relay, or small PLC, you can spend about the same and have zero programming to get what you want. Unless you want some really complicated control. 

edit - beat me to it 



dronai said:


> Yes, I have lots of experience with these. It's too expensive to build on your own, and compete with the prebuilt models on the market.


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## dronai (Apr 11, 2011)

splatz said:


> It is a great controls exercise. It illustrates how hard seemingly simple things could be with relay logic.


Can you imagine wiring an elevator without a PLC !!!:surprise:


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## splatz (May 23, 2015)

dronai said:


> Can you imagine wiring an elevator without a PLC !!!:surprise:


I have a manual from a big milling machine's controller from the 60s that ran on relay logic. (I am not sure if you'd call it a CNC or the forerunner of a CNC?) The maintenance electrician at one of my customers was retiring, he was there since 1969. He was cleaning out his office and asked if I wanted it. It went through digital logic from the ground up like a textbook. It was in a big three ring binder, 500 pages.


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## dronai (Apr 11, 2011)

splatz said:


> I have a manual from a big milling machine's controller from the 60s that ran on relay logic. (I am not sure if you'd call it a CNC or the forerunner of a CNC?) The maintenance electrician at one of my customers was retiring, he was there since 1969. He was cleaning out his office and asked if I wanted it. It went through digital logic from the ground up like a textbook. It was in a big three ring binder, 500 pages.



That would be pretty cool to see. 

How about the assembly line at an automotive plant on relay logic !!!


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## Forge Boyz (Nov 7, 2014)

dronai said:


> Can you imagine wiring an elevator without a PLC !!!:surprise:


I've done it. It was a very simple elevator, just three levels in a feed mill. I didn't build the controller. Just a bunch of limit switches 2 times and about 8 relays.

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## dronai (Apr 11, 2011)

Forge Boyz said:


> I've done it. It was a very simple elevator, just three levels in a feed mill. I didn't build the controller. Just a bunch of limit switches 2 times and about 8 relays.
> 
> Sent from my SM-G970U1 using Tapatalk


I've done this with a PLC, but I'd like to give it a shot with a bunch of relays like you did


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## Forge Boyz (Nov 7, 2014)

To be clear I didnt build anything control related on it. It was a package that I wired up. If i remember correctly it took about 2 weeks to do. 

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## dronai (Apr 11, 2011)

Forge Boyz said:


> To be clear I didnt build anything control related on it. It was a package that I wired up. If i remember correctly it took about 2 weeks to do.
> 
> Sent from my SM-G970U1 using Tapatalk


ahhh, and two weeks :surprise: Christ !!


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## CoolWill (Jan 5, 2019)

dronai said:


> No, they are not mechanically held, that's the point, non energized solenoid to be more reliable, and not work, when the load is on.


Mechanically held means the coil is de-energized when the load is on. A momentary pulse latches and unlatches the contacts. Electrically held means an auxiliary contact is in parallel with a momentary switch to energjze the coil.

If you have a latching relay that takes a single polarity pulse to latch OR unlatch it, and that latch energizes and de-energizes a double throw relay, you have an alternating setup controlled by a single pulse.


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## Forge Boyz (Nov 7, 2014)

dronai said:


> ahhh, and two weeks :surprise: Christ !!


That included running IMC from the controller to all the limit switches, door switches and call stations. Pulling the wires took a while because a lot of the limits were daisy chained so the wires had to be pulled a few at a time. Oh and a good portion of it was done hanging off the emergency ladder that went up beside it. Climing 75 feet straight up and down can take up a lot of time in a day.

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## Jhellwig (Jun 18, 2014)

gpop said:


> Biggest problem with trying to do this is there's 3 states on a standard relay.
> 
> At some point you have the contacts between n/o and n/c which maybe for a micro second but that's enough to end with logic that doesn't work or logic that sometimes works. Solid state relays do not have this problem but the cost starts to add up.
> 
> I always carry a programmable relay on the van. Its expensive but its capable of being any relay i need in a emergency.


The cost of smart relays has dropped to the point that it would be cheaper than trying to figure out another solution or carrying multiple spare parts.


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## gpop (May 14, 2018)

dronai said:


> That would be pretty cool to see.
> 
> How about the assembly line at an automotive plant on relay logic !!!


I know of a feedmill in the uk that has over 90 motors and its all relay logic. Press one button (auto start) and it sequence starts over 50 motors and interlocks them. There control panel is a 4x20' story board with lights and analog displays with built in relays and a lot of indicator lights from pressure/temp switch's in the field.

The relay control panel is about the size of 4 double lockers and has probably 400+ relays.

Last i heard they still haven't upgraded as it works and they have no major reliability issues on the 40+ year old system. It was a great place to cut your teeth on relay logic.


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## dronai (Apr 11, 2011)

gpop said:


> I know of a feedmill in the uk that has over 90 motors and its all relay logic. Press one button (auto start) and it sequence starts over 50 motors and interlocks them. There control panel is a 4x20' story board with lights and analog displays with built in relays and a lot of indicator lights from pressure/temp switch's in the field.
> 
> The relay control panel is about the size of 4 double lockers and has probably 400+ relays.
> 
> Last i heard they still haven't upgraded as it works and they have no major reliability issues on the 40+ year old system. It was a great place to cut your teeth on relay logic.



Can you imagine troubleshooting that !


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## dronai (Apr 11, 2011)

Forge Boyz said:


> I've done it. It was a very simple elevator, just three levels in a feed mill. I didn't build the controller. Just a bunch of limit switches 2 times and about 8 relays.
> 
> Sent from my SM-G970U1 using Tapatalk


I just built one with regular relays on my bench, with only one floor, and it took 5 relays !

You had 3 floors with only 8 relays ? was that a dc motor for the Up and down motor with reversing contactors ? Also the door motor had to be dc for closure, unless it was a pull gate type door


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## JRaef (Mar 23, 2009)

There *is *a way to use a latching relay to create an alternating relay circuit, I learned to use them when I worked for a company that didn't make an alternating relay and insisted that I use parts that they made, which included latching relays. But to make it work, you need the command circuit to have a Late Break set of NO contacts to create the "pulse" that latched or unlatched the relay. Now 40 years later I can't remember exactly how it was all configured because by the time you get done with it, the whole scheme was way more complicated than just using an alternating relay and I convinced then that keeping it simpler was better, even though it meant using something made by someone else. 



We used the old Furnas Class 47 alternating relay, a product that can still be bought from Hubbell Industrial Controls. Alternating relays don't get any simpler than that.


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## dronai (Apr 11, 2011)

JRaef said:


> There *is *a way to use a latching relay to create an alternating relay circuit, I learned to use them when I worked for a company that didn't make an alternating relay and insisted that I use parts that they made, which included latching relays. But to make it work, you need the command circuit to have a* Late Break set of NO contacts to create the "pulse"* that latched or unlatched the relay. Now 40 years later I can't remember exactly how it was all configured because by the time you get done with it, the whole scheme was way more complicated than just using an alternating relay and I convinced then that keeping it simpler was better, even though it meant using something made by someone else.
> 
> 
> 
> We used the old Furnas Class 47 alternating relay, a product that can still be bought from Hubbell Industrial Controls. Alternating relays don't get any simpler than that.


Yeah, I couldn't get it to work with the latch. I even tried a time delay to create the late break.

This was just an exercise, using the latch. 

By mechanical means, it seems like you can only create a pulse to two different locations (latch & Unlatch) by using a momentary single pole double throw switch.

So using only one trigger (the Float) I couldn't get to do it.


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## Forge Boyz (Nov 7, 2014)

dronai said:


> I just built one with regular relays on my bench, with only one floor, and it took 5 relays !
> 
> 
> 
> You had 3 floors with only 8 relays ? was that a dc motor for the Up and down motor with reversing contactors ? Also the door motor had to be dc for closure, unless it was a pull gate type door


It's a one man elevator in a feed mill. The door is a manual bifold. The number of floors doesn't make any difference as it just adds limit switches at each level which are wired in series. 
Each level has:
1 door switch
1 locking arm switch
1 level switch
It also has over travel limits top and bottom. It is not automatic as you have to hold the up/down buttons in to make the car move. It has an AC motor run on a VFD. 
It been a while since I wired it so I'm a little fuzzy on the details. It has a safety, up, down, motion allowed and also brake release and retiring cam relays. There are also two TDR's in there as well. 


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## CoolWill (Jan 5, 2019)

dronai said:


> Yeah, I couldn't get it to work with the latch. I even tried a time delay to create the late break.
> 
> This was just an exercise, using the latch.
> 
> ...


Did you look at my picture? I have made similar,in the past with success.


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## dronai (Apr 11, 2011)

CoolWill said:


> Did you look at my picture? I have made similar,in the past with success.


Looked at your drawing, but do you have to terminals, one for latch ,and one for unlatch ? Don't see it


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## dronai (Apr 11, 2011)

Forge Boyz said:


> It's a one man elevator in a feed mill. The door is a manual bifold. The number of floors doesn't make any difference as it just adds limit switches at each level which are wired in series.
> Each level has:
> 1 door switch
> 1 locking arm switch
> ...


1) Door switch for the bifold door.

2) Locking arm switch- Is this just a solenoid to latch the lockset ?

3) What do you mean by level switch ? Floor levels are indicated by limit swicthes right ? or are your limits in series like an e stop ?

4) By having to hold the button in, eliminates the holding contact, and possibly a relay.

5) Maybe the TDR's are for the delay to let the other features have time, before the up down is allowed.


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## CoolWill (Jan 5, 2019)

dronai said:


> Looked at your drawing, but do you have to terminals, one for latch ,and one for unlatch ? Don't see it


No. The way I understood you was that there was a single pulse source. Pulse once and it latches. Pulse again and it unlatches.


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## dronai (Apr 11, 2011)

CoolWill said:


> No. The way I understood you was that there was a single pulse source. Pulse once and it latches. Pulse again and it unlatches.


One *trigger* (the lead float)

My latching relay has two terminals, each one takes a pulse to operate, Latch or Unlatch.

This is besides all of the other terminals NO, and NC


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## CoolWill (Jan 5, 2019)

dronai said:


> One *trigger* (the lead float)
> 
> My latching relay has two terminals, each one takes a pulse to operate, Latch or Unlatch.
> 
> This is besides all of the other terminals NO, and NC


So could the float just energize a relay that then controls the latching relay? So if the float is low, the relay is off and the NC contacts send the power to unlatch. When the float is high, the NO contacts send the power to latch?


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## gpop (May 14, 2018)

dronai said:


> 3) What do you mean by level switch ? Floor levels are indicated by limit swicthes right ? or are your limits in series like an e stop ?


The last one i worked on years ago the floor levels switch's (micro-switch's with a roller on the end) were wire individually to unlatch the floor selected relay.


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## dronai (Apr 11, 2011)

CoolWill said:


> So could the float just energize a relay that then controls the latching relay? So if the float is low, the relay is off and the NC contacts send the power to unlatch. When the float is high, the NO contacts send the power to latch?


I'll try that. Sounds like it should work. Remember my test drawing was from a plc program, but the engineer said with relay logic, it should work exactly the same, it didn't ! Maybe it just needs to be tweeked like you showed ?


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## Forge Boyz (Nov 7, 2014)

dronai said:


> 1) Door switch for the bifold door.
> I forgot- safety switch on car escape hatch
> 
> 2) Locking arm switch- Is this just a solenoid to latch the lockset ?
> ...




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## dronai (Apr 11, 2011)

CoolWill said:


> So could the float just energize a relay that then controls the latching relay? So if the float is low, the relay is off and the NC contacts send the power to unlatch. When the float is high, the NO contacts send the power to latch?


Looking at the drawing

Wont work 

You two pumps, that needs to alternate.

The way you have it. the float is high, it changes the state of the NC, and NO

and repeats everytime the same, no alternation


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## CoolWill (Jan 5, 2019)

dronai said:


> Looking at the drawing
> 
> Wont work
> 
> ...


Walk us through the process that you want to accomplish. You have a float and two pumps and then....


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## dronai (Apr 11, 2011)

dronai said:


> Float 1 is the trigger for both pump 1 and pump 2
> 
> Pump 1 goes through the Latch contacts, or NC
> 
> ...


Here is the logic


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## CoolWill (Jan 5, 2019)

dronai said:


> Looking at the drawing
> 
> Wont work
> 
> ...


I just re-read this. The way I have it drawn, the resting natural state is for pump 1 to be energized. A trigger pulse causes a latch condition and changes the state of the pump relay, causing pump 1 to turn off and pump 2 to turn on. A second trigger pulse opens the latch and resets everything back to pump 1.

With your latching relay, what happens if the latch or unlatch terminals are left energjzed continuously?


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## dronai (Apr 11, 2011)

CoolWill said:


> I just re-read this. The way I have it drawn, the resting natural state is for pump 1 to be energized. A trigger pulse causes a latch condition and changes the state of the pump relay, causing pump 1 to turn off and pump 2 to turn on. A second trigger pulse opens the latch and resets everything back to pump 1.
> 
> *With your latching relay, what happens if the latch or unlatch terminals are left energjzed continuously?*


They make a shorting sound !


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## dronai (Apr 11, 2011)

dronai said:


> They make a shorting sound !


I'll try out what you say on the bench


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## dronai (Apr 11, 2011)

CoolWill said:


> I just re-read this. The way I have it drawn, the resting natural state is for pump 1 to be energized. A trigger pulse causes a latch condition and changes the state of the pump relay, causing pump 1 to turn off and pump 2 to turn on. A second trigger pulse opens the latch and resets everything back to pump 1.
> 
> With your latching relay, what happens if the latch or unlatch terminals are left energjzed continuously?


Doesn't work, because the latching relay doesn't reset. You have to send the next pulse to the second terminal


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## CoolWill (Jan 5, 2019)

dronai said:


> Doesn't work, because the latching relay doesn't reset. You have to send the next pulse to the second terminal


You misunderstood. I'm just curious what the actual relay does if the trigger to either input stays on. Let's say that the relay is unlatched. If you supply signal to latch it, but don't turn the signal off after the change of state, does the relay behave normally?


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## dronai (Apr 11, 2011)

CoolWill said:


> You misunderstood. I'm just curious what the actual relay does if the trigger to either input stays on. Let's say that the relay is unlatched. If you supply signal to latch it, but don't turn the signal off after the change of state, does the relay behave normally?



Yes, you can leave the voltage on, instead of just a pulse


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## gottspeed (Mar 8, 2010)

I prefer the relay base style of alt relay.


https://octopart.com/s89r11app1-120-te+connectivity-39661832


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