How to Reset and Control Latching Relay

[abuyaser]

Hello,
I am responsible for safety in a team project. The prototype is an aquarium light system and my part is to open the main power supply circuit when the prototype falls in water. So, I am using GRI2600T water detector to detect if the existence of water. I am REQUIRED by my professor to use a relay as a switch (I know a GFCI will be the best choice but I am not allowed to use that), I picked up G6BK-1114P-US-DC5 dual coil latching relay which will save the last state it was in even after losing power and I have to reset it if I want to unlatch it.

Now, I am sending a signal from my GRI2600T water detector to the relay to latch it (5V/56mA), I am considered using pushbuttons to do the job, one normally open and one normally closed pushbuttons but I am not shore how to set up these pushbuttons!!! I guess I need something that can sense the off state of the relay so I can use both of my pushbuttons.

Please advice on how to set up the pushbuttons and what device do I need to detect the off state.

Thank you,
abuyaser

 

[carbonzit]

Here's how industrial equipment is started and stopped using momentary pushbuttons. The circuit is called a "locked-out relay":

**broken link removed**

Notice that this uses an ordinary relay, not a latching relay. You don't want a latching relay in this application.

The idea is that it's extremely easy to de-energize this circuit: just hit the "STOP" button, which is normally-closed, which removes power from the relay coil, bringing the whole show to a screeching halt. If there's a power failure, you don't want the machine returning to the last state it was in, which may have been powered on.

I'm not saying this is the circuit to use. You could use it, however, by replacing the "off" switch with a solid-state relay connected to your water detector through an inverter (depending on the logic level output by the detector).

Anyhow, just an idea.

 

[abuyaser]

Thanks carbonzit for your replay,

But I do not want the user to unplug the wire and plug it back again to get the power back and change the last state of the relay. I want the relay to keep the circuit open even if the user unplug and replug the wire to the outlet. How can I do that without a device that has some kind of memory of the last state?
What do you mean that I do not want my relay to save the last state if there is a power failure?

Regards,
abuyaser

 

[carbonzit]

That's why you don't use a latching relay. Why would you think you'd want to use one? You want it to forget its last state, not remember it.

This circuit will keep the circuit open if either 1) the user trips it off with the NC pushbutton or 2) the power goes out. In either case, it will always revert to being off. It's what's called "fail-safe".

 

[Reloadron]

You began this in this thread. so why haven't you kept it in that thread? Your choice of relay, if unchanged from your original post is not a good choice. My read is your sensor is N/C which would be placed in series with S2 in the basic circuit that Carbonzit provided. Once triggered (open) the user would need to momentarily press S1 to get it closed again.

Ron

 

[Reloadron]

The attached drawing is about what you want. For your sensor you mention "the GRI2600T water detector to detect if the existence of water". According to this data sheet that particular sensor is NC (Normally Closed) and opens with water sense. Also, though you mention 5 Volts that unit is 12 volts.

2600 Operating Voltage 12 Volts DC
2605 Operating Voltage 5 Volts DC
2624 Operating Voltage 24 Volts DC
Operating Current 12 mA

I used 12 volts in the attached because you mentioned the 2600. Now let's look at the circuit:

SW1 is a normally closed push button switch, current normally flows through SW1. SW1 is followed by the normally closed switch contacts of your sensor. SW2 is a normally open push button switch. Pressing SW2 will cause RY1 to "Latch" through the action of RY1 pins 1 and 3 which are normally open and will close when SW2 is pressed. That action causes a self latching of RY1. When SW2 is released RY1 will remain latched.

RY1 is a 3 pole double throw 12 volt coil relay. The purpose of D1 the 1N4002 diode across the relay coil is to "snub" the inductive kick of the RY1 coil whenever it de energizes. RY1 has additional unused contacts which would be used for your load, be it a lamp or whatever. The LED is simply an indicator to show when RY1 is energized and is not required.

If the moisture sensor detects water the normally closed contacts of the sensor will open. When that happens RY1 will open and the load will lose power. Power can also be removed by pressing SW1. If either the sensor opens or SW1 is pressed RY1 will drop out and become un latched.

Look at the circuit carefully and try to understand how it works. This circuit is a very, very common circuit used everyday in general electrical applications. You will note the circuit is based on the circuit Carbonzit initially posted. Remember as to the term "Latching" that RY1 is latched through it's own contacts. If SW1 or your sensor opens then RY1 will drop out. Once RY1 drops out it will remain un latched until SW2 is pressed causing it to latch.

While your initial choice of a relay could be used it would require additionally circuitry which is something you do not want in safety circuits. You want the circuit to be simple and reliable.

If you want the circuit to work on 5 volts just find a 5 volt coil relay. The 12 volts and the relay I show are just a matter of example. Make sure the relay contacts for the relay you choose can handle the load current (lamp or whatever) for your load.

Hope that helps.

Ron

 

[abuyaser]

Thank a lot Ron and carbonzit,
Your comments are really helpful and please keep it up.

OK, so I should have my own independent power supply instead of depending on the main PS as it will be open when I latch the relay

Thanks,
abuyaser

 

[carbonzit]

Just so long as we all understand that by "latch the relay" you mean energize it and keep it energized, right? You're not physically latching anything. The relay self-energizes, so I suppose you could say it's self-latching.

You can use the main power supply, as it's still present even though your circuit may shut itself off.

 

[abuyaser]

But the idea is that I should open up every thing including the main POWER SUPPLY for the safety of the circuit which will result in power lose for my sensor.

I would like to use the main power supply if it will work so that I get my power from the same source that I will shut down when water is detected

Regards

 

[carbonzit]

But the idea is that I should open up every thing including the main POWER SUPPLY for the safety of the circuit which will result in power lose for my sensor.

But can't you just power your sensor "upstream" of the shutdown circuit? You don't have to shut down the whole thing all the way back. How is this going to be wired up: are you going to plug this into an outlet ("mains")? or is it going to be permanently wired in?

In either case, just tap the power feed, which will not be interrupted, for anything you need power all the time for, like say a low-voltage power supply or whatever.

Or is it a requirement that all power to all devices be shut down by your shutdown circuit? If that's the case, then obviously you have a problem. You could use batteries. But you're going to have to get some power from somewhere, no?

 

[abuyaser]

Well, the power supply is plugged to the outlet and then provides 5 Amps to the LED system and supplies 5V to the arduino microcontroller. I have the choice to get my own battery or have the power supply as my source. Are you saying it will be safe if I keep the main power supply on to prvide me with power?

I think the best choice is to shut down everything including the power supply

 

[carbonzit]

Well, let's go back to your first post here where you laid out your specs. You said:

The prototype is an aquarium light system and my part is to open the main power supply circuit when the prototype falls in water.

Leaving aside that you didn't say what "the prototype" is, I take this to mean that you want to remove power from whatever is likely to have fallen into the water, correct?

Now, to be absolutely safe, you probably would want to remove all power entirely from this thing that could fall into water, including any low-voltage power.

If that's the case, then it's quite obvious that you have two choices:

1. Let the circuit be totally disconnected. To reset it will require some kind of manual intervention (pushing a button or something).
2. Provide a battery if something in the thing that can fall into water requires power in the meantime.

It's hard for me to imagine why you'd need the 2nd alternative. Why can't you just use the locked-out relay I provided, or some variation of it? Again, you do NOT want this circuit to automatically reset. When the user finds that it (whatever "it" is) has fallen into the water, it's up to them to take it out of the water and reset it, right? Or is this supposed to work some other way?

How about if you tell us in the simplest terms possible exactly what this is and how it's supposed to work?

 

[abuyaser]

OK, I was not clear and misguided you, I apologize to you carbonzit and to Ron


Here is what I should do: if water is detected I want to shut down the aquarium light system for safety, when water is detected everything should be off including the power supply. Now, this could be accomplished by several ways (GFCI is not allowed in my project), an effective way is to use a relay that will trip either by sending a pulse to it or by the absence of the voltage (either way). I need it to stay tripped until the user resets it manually so the light system can work again in the normal condition where there is no water detected.

Here are some of the questions regarding this idea:
1) 1) If I use one coil relay with regular spring, it will do the job and will open up the power supply. However, can the user reset this relay by simply unplugging and plugging the wire into the outlet in the wall?
If the answer is yes then I need to solve this problem because I want the user to power up the aquarium light system through pushbuttons
2) 2) Is it better if I get my voltage from the main power supply or should I use my independent battery?
Thank you for following up with me,
abuyaser

 

[carbonzit]

Here are some of the questions regarding this idea:
1) 1) If I use one coil relay with regular spring, it will do the job and will open up the power supply. However, can the user reset this relay by simply unplugging and plugging the wire into the outlet in the wall?
If the answer is yes then I need to solve this problem because I want the user to power up the aquarium light system through pushbuttons

If you implement the circuit I posted (locked-out relay), the user will have to push the "on" (N.O.) pushbutton to turn the light back on. It will not come on by itself. Look at the diagram and think about how it works. It's very simple: when it's energized, the current flowing through the circuit keeps the relay energized. It's electrically latched, but not physically latched. When power is removed, it simply drops back to its normal (normally open) state, disconnecting the power. It's very simple and will do what you want it to do.

 

[Reloadron]

This was your first post on this topic in the other thread you started:

Remote Controlled Circuit Breaker and Moisture detector

Hello All,

I am doing a project and I am responsible about safety for aquarium light system, I am supposed to have a moisture detector ( Could not find online) that detects if the prototype falls in the water of the aquarium. If it did, the sensor then sends a signals to open up the MAIN power supply which will result in shutting down the whole system including the moisture detector (since I am getting my power from the MAIN power supply) so I guess I will need my own power supply probably. For the circuit breakers, I have a “Latch Relay” dual coil switch (DSP1-L2-DC5V)that has a magnet where it will save the last state it had before tripping so the user can not reset the system by just plugging and unplugging the wire in the outlet. I will also have two mechanical push buttons, one normally open and one normally closed to be able to reset the system manually. I also need Remote Control Circuit Breaker (RCCB), I have searched for RCCB for over a week now and could not find one that has current rating between 60 mA to 250 mA. They all operate with current ratings from 5A to 100A which is away from ideal for my project.

Please, I need help in finding:
1) Moisture Detector
2) Remote Control Circuit Breaker: Current Rating between 60mA and 250 mA


Thank you

Back in that thread I suggested you design and build your own circuit based around a GFCI (Ground Fault Circuit Interrupt) breaker. I believe somewhere you mentioned you could not use a GFCI off the shelf solution. Designing and building a circuit based on the operation of a GFCI would get you where you want to be. It would totally remove all mains power at the source. When the fault condition was removed the circuit would need reset. Mains power would be restored.

The circuit designs present by myself and carbonzit would remove mains power from the load. If the load is an aquarium lighting design and the lighting fell into the tank it would remove mains power from the lighting and I would think that was the objective? Why remove sensor power? I thought this was supposed to be about safety? If you look at my last drawing and understand how it works if a fault happens and the sensor opens there is no way that mains power can be restored to the lights until the fault no longer exist. Do you understand the operation of the presented circuits?

There is something in all this I am not understanding as to your final objective.

Here are some of the questions regarding this idea:
1) 1) If I use one coil relay with regular spring, it will do the job and will open up the power supply. However, can the user reset this relay by simply unplugging and plugging the wire into the outlet in the wall?
If the answer is yes then I need to solve this problem because I want the user to power up the aquarium light system through pushbuttons
2) 2) Is it better if I get my voltage from the main power supply or should I use my independent battery?
Thank you for following up with me,

1) NO! Mains power would only be restored to the load (lights) when the ON button was again depress and it would only start if the fault was gone.
2) I purposely used low voltage DC for the "Control Voltage" for added safety. Plus you have a sensor that needs 12 VDC or 5 VDC to operate.

I believe part of the problem is you don't seem to understand the circuits carbonzit and myself have posted.

Ron

 

[abuyaser]

Thank you for your posts,

Here is what I understand about your circuits:

They will both have the same outcomes eventually as the one carbonzit posted will only self energize when the NO pushbutton is pressed and resets when NC pushbotton is pressed or GRI NC sensor relay is open due to the presence of water, that is exactly what Ron's circuit is doing which is power up the light system in the normal conditions and shut down when there is water or reset.

So, in this specific case of mine, will there be any differences at all between the normal relay and the latching one?

 

[Reloadron]

Thank you for your posts,

Here is what I understand about your circuits:

They will both have the same outcomes eventually as the one carbonzit posted will only self energize when the NO pushbutton is pressed and resets when NC pushbotton is pressed or GRI NC sensor relay is open due to the presence of water, that is exactly what Ron's circuit is doing which is power up the light system in the normal conditions and shut down when there is water or reset.

So, in this specific case of mine, will there be any differences at all between the normal relay and the latching one?

Both of the circuits myself and carbonzit posted are essentially the same circuits with yes, the same end results. They are ON or OFF circuits using a relay that latches itself through its own contacts and provides power to a load. Both circuits use momentary push buttons ( NO and NC) to turn the circuit on or off.

The circuit I posted has a few differences. I used low DC voltage for control of the relay and other contacts on the relay for supplying the load. Attached is my last drawing with a few additions showing the use of the additional contacts. Since the OFF push button is normally closed I did add in series the normally closed switch contacts of your sensor. This configuration allows the circuit to be turned on and off as long as no fault exist. When a fault exist and the sensor contacts are open the relay will not energize and latch itself. I used low voltage DC control as when I have to design a circuit like this I prefer low voltage control and in many applications rules dictate that I use low voltage DC control.

Now your initial Latching relay you posted is a very different animal. You had a Panasonic part number DSP1-L2-DC5V relay which is one of these relays. Using your part number what you get is attached as a few images.

The DSP is the series, the 1 tells us it has 1 form A and 1 form B contact set. That is shown in an attached image. It has two individual relay coils that is the L2 and finally the DC5V tells us the coils are 5 Volt DC coils. Each coil is used to Set and Reset the relay contacts. These coils are only momentarily pulsed to have the relay change states. Once that relay is in a state it remains there until it is again pulsed to change state. You could disconnect it from the circuit, take it on vacation and when you get back reconnect it and it will be right where it was. That is why this relay is not a good choice for your application. Be the latching action held mechanically or magnetically they remain in their last state and changing states id done with a brief pulse. You would not leave power applied to their coils. If you wanted to incorporate this relay in your design it could be done but would require more electronics and pulse control for the coils. You would need a pair of one shot pulse circuits just to drive the coils. It would not be practical and would not be as safe as the circuits presented to do what you want to do. Thus I mentioned earlier the importance of keeping circuits designed for safety simple and fail safe.

Note: After rereading the data sheet and their use of the term magnetic I may be wrong as to the magnetic latching and use of a pulse. However, my theory remains the same in that this relay would not be a good choice for your application. I have used many relays like this both mechanical latching and magnetic latching that only require a single momentary pulse to either coil to change states.

Ron

 

[abuyaser]

Thanks Ron,

I could not get the DSP1-L2-DC5V from digikey as it was not available in stock what I got instead is G6BK-1114P-US-DC5 which is quite similar and available in stock, here is the datasheet. Somehow it is not clear as the DPS series. Can you where its pins can go into your circuit?

Regards

 

[carbonzit]

I'm starting to have serious doubts about your reading comprehension.

I'm going to make it very simple:

Do not use a latching relay!

You do not want to use a latching relay here.

Got it?

 

[Reloadron]

I told you, carbonzit told you and I am sure that many in this forum will tell you that this is not the type of relay you want and is not suited for your design plan. What part of this is not what you want, did you not understand? We provided circuits of what you want.

OK, so you post a circuit of how you plan to use the relay you just bought. This ought to be good. You never buy parts till you have a good design on paper so let's see the design.

My work here is done. I need a beer.

Ron