What would this be called?

[Ucatchmydrift]

Hi, just wondering if anyone could point me in the right direction for a piece of equipment that i may need, but im not sure what exactly they would be called?

Im after a relay that will stay on once it has been activated.

For example:

I would have a relay activated by a 24v feed. But soon after, that feed will be cut (by my shunt) and normally the relay coil would disconnect cutting the circuit that was activated. I need that circuit to stay on until i switch it off manually or via a different method.

Wondering if such a thing exists, or the best way to make such a thing exist!

For anyone interested, i have a hybrid inverter with grid supply that i use to charge a battery bank at night on cheap rate atm in winter. The inverter does not have any scheduled charging ability, so, i have setup a system to only switch on grid power to the inverter for whatever amount of time i want each night via a wifi smart plug and a 2p contactor, and have setup the inverter to charge as soon as grid power is detected. And it works great!

BUT! - theres always a but!

There is a possibility that something could go wrong and the wifi plug does not activate. And i run out of power during the night and the bms/inverter shuts the power down .

So, i have a junctek shunt which i use to monitor the battery via bluetooth which works great. Amazingly, the shunt has the ability to activate a relay when certain conditions are met. A couple of these conditions are low and high voltage.
So i was going to use this functionality to activate a relay which then activates another contactor to supply power to the inverter if the battery bank voltage ever got too low.
Only problem is, the shunt only activates the relay from 1-10 seconds (i think - will experiment tomorrow) hence the initial question above.

Im also hoping this could activate the same contactor that the wifi plug activates. The wifi plug would not activate the contactor at the same time as the shunt relay, but if it did, due to a problem, this may cause a serious problem!? (as id be connecting a 240v live to another 240v live)

Thanks

 

[Richard-the-Ninth]

What you are describing is a Latching relay. You can buy them, but it's much easier to buy a double pole relay and use one set of its contacts.
So long as the supply is from the same protective device, it would not matter if both relay inputs were live, but you may have problems if one input is off and the other input is on, as then the one that is on will back feed up the one that is off.

What voltage is this shunt output?

 

[Andy™]

latching relays do exist, you could also use one of the contacts on the relay to keep the power on to the coil which would need a stop button pressed to open the circuit and drop power to the coil. this could be done manually or use another relay to break the circuit once high voltage is met, opposite to the relay to close the relay when voltage low

 

[Geoff1946]

I'm not sure I understand quite what you are trying to do, but are you aware of the range of relay modules available:
e.g. https://cpc.farnell.com/search?ost=...chlookahead&product-range=cebek-relay-modules

 

[Ucatchmydrift]

What you are describing is a Latching relay. You can buy them, but it's much easier to buy a double pole relay and use one set of its contacts.
So long as the supply is from the same protective device, it would not matter if both relay inputs were live, but you may have problems if one input is off and the other input is on, as then the one that is on will back feed up the one that is off.

What voltage is this shunt output?

Ok thank you ill have a look for one and see how they work..

The voltage from the shunt will be 24v, supllied from my battery bank. But, the shunt would activate a 24v relay coil, which would switch a 240v supply from a socket, which would then be the supply to the contactor which then switched grid power to the inverter. Its the contactors that will have two seperate 240v feeds, of which, like you say, only one would be live at any time, unless a fault occurs - hence the question.. Just spoke to my dad (retired electrician) and he says having two 240v supplies to a contactor should be ok aslong as they are not out of phase. The origins of both of the 240v supplies would be taken from the inverter, so, should be in phase.
As they are 240v supllies from the same source, then back feeding should not be an issue? - this is just a guess on my part.. If one were say 24v, and the other 240v from a seperate source, then presumably back feeding would be an issue?

 

[Ucatchmydrift]

latching relays do exist, you could also use one of the contacts on the relay to keep the power on to the coil which would need a stop button pressed to open the circuit and drop power to the coil. this could be done manually or use another relay to break the circuit once high voltage is met, opposite to the relay to close the relay when voltage low

Thank you . Excellent idea also . Was considering another relay to somehow break the circuit once activated using another smart wifi plug as i have one spare!
Getting complicated this lol

 

[Ucatchmydrift]

I'm not sure I understand quite what you are trying to do, but are you aware of the range of relay modules available:
e.g. https://cpc.farnell.com/search?ost=...chlookahead&product-range=cebek-relay-modules

Great, we use farnell at work all the time, wouldnt have to pay postage then!

 

[Ucatchmydrift]

Thanks guys, as after reading here:

https://uk.rs-online.com/web/generalDisplay.html?id=ideas-and-advice/latching-relays-guide
A latching relay is spot on what i need. It seems they will also deactivate once they receive another 'pulse' which would be perfect, as i can then have it switch off using the same relay from the shunt once the batteries are charged and hit a certain voltage!
Awsome

 

[Andy™]

Thanks guys, as after reading here:

https://uk.rs-online.com/web/generalDisplay.html?id=ideas-and-advice/latching-relays-guide
A latching relay is spot on what i need. It seems they will also deactivate once they receive another 'pulse' which would be perfect, as i can then have it switch off using the same relay from the shunt once the batteries are charged and hit a certain voltage!
Awsome

but what happens if you send a pulse to switch on, but for whatever reason it doesn't, but then switches on when its gets another pulse which is intended to switch it off? or if it sends a low voltage pulse which switches on, then sends another low voltage pulse which then switches it off again?

 

[Ucatchmydrift]

but what happens if you send a pulse to switch on, but for whatever reason it doesn't, but then switches on when its gets another pulse which is intended to switch it off? or if it sends a low voltage pulse which switches on, then sends another low voltage pulse which then switches it off again?

The app allows me to set how long the 'pulse' is, so ill set it to 10 seconds, and hopefully all shoud be good. If it were sending multiple pulses, then there would be something wrong with the software, but i can easily test it all out before i go ahead anyway..

 

[Andy™]

The app allows me to set how long the 'pulse' is, so ill set it to 10 seconds, and hopefully all shoud be good. If it were sending multiple pulses, then there would be something wrong with the software, but i can easily test it all out before i go ahead anyway..

using a single source pulse to trigger something to change state with no feedback of its actual state will end badly, as soon as something goes out of sync then it wont know it and will require manually fixed. you really need 2 outputs, one for on and one for off

 

[Ucatchmydrift]

using a single source pulse to trigger something to change state with no feedback of its actual state will end badly, as soon as something goes out of sync then it wont know it and will require manually fixed. you really need 2 outputs, one for on and one for off

Id agree with you if it were being used every day, but this is just a backup setup for if the wifi socket that normaly controls grid charging fails. It may never get used, and if it does, the shunt app on my phone tells me when i wake up and allows me to also switch it off manually and remotely via bluetooth etc..

 

[Joules]

Perhaps this mechanical flip-flop zero energy Bistable Relay will do?

 

[Ucatchmydrift]

Perhaps this mechanical flip-flop zero energy Bistable Relay will do?

Thanks, yes, looks like that would have done the job also. But, after experimenting today, it seems i dont need one after all! I rigged up a normal 12v car relay and a 12v bulb with two seperate 12v car batts, linked into the shunt control box as it describes, to test it all.
And when the software detects the battery bank droping below the voltage that i set it to, it switches on the relay permanently, OR, i can set it to switch off again in the app. This isnt very clear in the instructions hence my original question.

The shunt needs to power itself and the relay via an external power source (hence the car batterys), and you need to switch a dip switch on the rear of the control box, and when i fjnished and switched it back to the original position, i still had the original power source (my 24v battery bank) and 12v bcar batt still plugged in, and poof, some smoke came out of the shunt control box!! No!!!

I fried the relay side of the control box!! Luckily the rest of the shunt stuff still works as normal, just killed the relay control part of the circuitry..
Still, gunna have to get another one now and you cant get the box seperately, so another £30-£40!

Unless anyone knows electronics and could have a guess as to what i have fried?

 

[Andy™]

bottom item here, should be able to fix what broke

https://planet.davewylie.uk/toolstore/Online_Catalogue_Consumables_3.html
having the contact switched for the duration of it needing it does make it far easier

 

[Ucatchmydrift]

bottom item here, should be able to fix what broke

https://planet.davewylie.uk/toolstore/Online_Catalogue_Consumables_3.html
having the contact switched for the duration of it needing it does make it far easier

Funny man! Guess i had better buy two bottles