Relay overcurrent protection without reset button - Page 1
Forum section: electronics / projects

author: Electrical
author_rank: Contributor
timestamp: March 23, 2024, 08:03:16 pm
content: Hi AllA question for you, electronics experts:If you search online on internet (youtube, google etc) you can find so much videos and schemas about relays overcurrrent protection (for shorts circuits) like this:https://www.youtube.com/shorts/AtTmauaZWLoThe relay it's very important because it isolates the load from the protection circuit so you can load also 220V over a DC low-voltage protection circuit.But are all equals. Everyone repeats the same things as the previous one.There's always a reset button. I don't need a reset button for a short circuit protection.It should activate itself and reactivate itself after the short circuit is over (possibly using only transistors and resistors and not microcontrollors).So, there's someone that knows how to modify this?A diagram or a pratical demontration would be appreciated because the words are carried away by the wind.TNX!

author: Electrical
author_rank: Contributor
timestamp: March 23, 2024, 08:07:20 pm
content: sorry for the complex image schema.Use this for the schema to modify:

author: selcuk
author_rank: Frequent Contributor
timestamp: March 23, 2024, 08:28:40 pm
content: I'm not sure about the goal here. This is not a design to protect a relay from short circuit. The short circuit protection is built with a relay and a push button. So you cannot isolate a 220V load from low voltage DC with that relay.

author: Electrical
author_rank: Contributor
timestamp: March 24, 2024, 12:58:49 am
content: SM62 ramarium what u wrote?I'm not agree.In the 1969 the shuttle goes on the moon and now you are saying that it is not possible to isolate that relay without a button.It's possible to isolate 220V load with a relay from low voltage.Isolating the charge it's the primary function of a relay.The goal here it's to change the circuit to get a short circuit protection on aDCrectified from 220V or an other DC load with something like a tiristor.Not necessarily with the relay in the picture. With any relay in any way.Look at the charger of any device (for example a computer or mobile phone).If you short it, it won't break.All devices have short circuit protection (even if they do not use a relay).So let's possibly not say heresies.Be sure, it is doable.I'm not an electronics champion but please leave space to how knows the answer.TNXEDIT: Added a picture for explaing the concept.P.S. Something wrong in the image.Should be:If the amperage over X [short circuit detected] send current on relay and open the circuit (case relay Normally Closed) and viceversa.orIf the amperage under X [not in short circuit] send current on relay and keep the loop closed (case relay Normally Open) and viceversa.Think the first is energy savingSorry for the relay in the image that is N.O.

author: selcuk
author_rank: Frequent Contributor
timestamp: March 24, 2024, 08:23:15 am
content: Yes, you can use a relay for isolation purposes. But I commented about the proposed circuits, not for the relays in general. Since both the contact and coil sides are used in the same voltage region, I guess these are not the circuits you are looking for.For example, you can check the videos in this topic:https://www.eevblog.com/forum/testgear/ac-source-fast-short-circuit-protection-device/Although the circuits are more complex, there should be a reset mechanism you can use after removing the short or high current. Additionally, you can use a MCU or some logic circuit in order to automatically reset it. But there will be cases that automatic reset is not preferred due to safety issues.

author: Electrical
author_rank: Contributor
timestamp: March 24, 2024, 02:12:26 pm
content: Quote from: selcuk on March 24, 2024, 08:23:15 amOk SM62 you writed and commented so much.In the topic u posted there are mechanism for "fast short circuit"ACprotection.I askeda schema of a circuit or a video, or a image or something pratical, not words.So it's needed a little circuit (with transistors possibly MOS that supports high currents) for removing instantly the current by using a relay.So what I'm looking for seems difficult to search.I'm not so good in electrics things, so it's needed someone that posts exactly the circuit in question to look it and analize it to understand its logic.Something that makes the automatic reset.It's very safe. A relay it's ultra safe because it isolates currents up to 30A from the low voltage circuit.It has only to replace a button. A stupid idiot thing that in 2024 should not be to activate manually.So you wrote and it was appreciated.Now please shut up and let whoever manages to publish the exact circuit requested speak.Need exactly the requested circuit.I'm not able to search little pieces of general circuits at left and right to join them also because I don't understand them enough.Want something schema/diagramam already ready to understand it.If someone has the request please post it, otherwise don't bother me with useless notifications.The goal for an expert should be pretty simple. A resistor that controls the amperage with some mos transistors and some other transistors that activate and deactivate the relay (5V).TNX ALL.[WAITING ALSO 20000 YEARS FOR AN EXPERT]

author: inse
author_rank: Super Contributor
timestamp: March 24, 2024, 04:40:22 pm
content: We all love you 😘

author: Simon
author_rank: Unknown
timestamp: March 24, 2024, 05:30:52 pm
content: Quote from: Electrical on March 23, 2024, 08:03:16 pmwhat you ask is quite complex. So how would you propose that a circuit whose sole purpose is to cut off will somehow know that, that which caused it to cut off has now ceased. Trying thinking about it a tiny bit and at least list out some possible ways to do that and the challenges given that you do not wish to use a micro controller.

author: Simon
author_rank: Unknown
timestamp: March 24, 2024, 05:36:37 pm
content: Quote from: Electrical on March 24, 2024, 02:12:26 pmOh, something that you do not know how to do is stupid idiot simple, so you are a Schrödinger something. You demand to know how to to design something as you do not know how yet you say it's simple like you know how to design it. Please, decide which one it is then you "shut up" and listen.Going around telling people to shut up when they don't provide the information you want like some chat GPT will get you banned. Oh and most other forums will also ban you for your rudeness.

author: Electrical
author_rank: Contributor
timestamp: March 24, 2024, 05:55:24 pm
content: I have nothing to think about. I don't understand the logic of electronics enough. I understand a little and maybe even less, otherwise I wouldn't have asked the question.The circuit should understand that the short circuit has stopped because the amperage has dropped below the threshold.I repeat, it doesn't seem that complex because at this point the relay should be re-powered and then re-loaded under current.I'm not smart enough to propose a solution.The only thing I can say is that there are "latching-switches" that store one bit of information (if something is on or off), so they can store whether the relay is currently open or closed.https://www.elprocus.com/latching-switch/Demonstration over mosfetDemonstration over relayUltimately: the control over the short circuit is done by measuring amperes via a resistor, while understanding whether the relay is active or not is done by memorizing the bit in the "latching-switch".I proposed no microcontroller because it is a fairly simple circuit.For clarity, microcontrollers are nothing more than chips that contain transistors inside.So for those who know transistors it should be even easier.Transistors can be used as switches (this is the most trivial use they have).https://www.electronics-tutorials.ws/transistor/tran_4.htmlNow, I'm not a very social person.I'm here for electronics and specifically for this circuit which interests me enormously for various applications.So, leaving aside the talk of love and demented answers, if anyone has an answer, fine, if not, please have some peace.P.S. I wasn't rude on the forum chat.There is nothing to be banned. I didn't call anyone stupid, idiotic or crazy. I was talking about circuit logic.I agree about shutting up and listening, but what is required.Not empty words about "I don't know how to do it".I didn't say it's easy for me. I said it's simple for those who know how to do it.Schrödinger could do it. It's a certainty.Thanks again.

author: Ian.M
author_rank: Super Contributor
timestamp: March 24, 2024, 06:09:04 pm
content: Its a nearly unsolvable problem. Once the relay trips and disconnects the load, how does the trip circuit know (without powering the load) whether or not the fault causing the overcurrent has cleared so the trip can be safely reset automatically?

author: Electrical
author_rank: Contributor
timestamp: March 24, 2024, 06:19:03 pm
content: Quote from: Ian.M on March 24, 2024, 06:09:04 pmEASY.Try again the load after some time (example 100ms which can be provided by the charging time of a small capacitor).So if you re-power the load and if there's a overcurrent (shortcircuit), remove the load again.Restart the loop.Problem solved.Automatic method.P.S.If anyone has a solution even without relays (using only power transistors) they can post that too.I like to learn.If it's not the right place, another topic could be opened.

author: edavid
author_rank: Super Contributor
timestamp: March 24, 2024, 06:20:59 pm
content: Quote from: Electrical on March 24, 2024, 05:55:24 pmFunny you should mention logic, since this statement is illogical. Once the relay has opened the circuit, there is no current flowing, and no way to tell if the short is still present.QuoteWhat does "at this point" mean? How long should the automatic recloser wait before re-energizing the relay? How many attempts should it make before deciding the fault is permanent?QuoteWhy do you think that is helpful? What is the value of (redundantly) storing the state of the relay?More importantly, why do you think there is a reason to do any of this? What is your fault scenario where it is better to retry automatically than to require the user to indicate the fault has been cleared?

author: Electrical
author_rank: Contributor
timestamp: March 24, 2024, 06:22:49 pm
content: Quote from: edavid on March 24, 2024, 06:20:59 pmedavid read the last post. tnx.The user does not need to do anything except disconnect the shorted wires.There is no fault.The fault was previously interrupted by the relay.During reactivation, if there is an overcurrent, the relay deactivates the circuit, therefore the fault does not exist.There is no redundancy in the circuit.It's a loop.[Is it shorted? Unplug. Wait. Hang up.]

author: Simon
author_rank: Unknown
timestamp: March 24, 2024, 06:26:54 pm
content: Quote from: Electrical on March 24, 2024, 06:19:03 pmSo then you get a hiccupping circuit. You see that STUPID reset button is actually more useful than you think. Depending on what this is protecting you may not want to keep repowering the circuit.Sure you can replace a microcontroller circuit with transistors, how many transistors are there in a micro controller? OK, you won't actually need that many and if you want to make transistor latches and all that fine, you want to make your own comparator too? Like I said think of a way around this problem. what steps does this hypothetical circuit need to do? Then you can establish the circuit blocks needed and find out how to design them.I have a very powerful battery, 5kWh, it can output 125A continually and 150A briefly and will do a few hundred in a short burst. The BMS on this battery will shut the battery off when it is flat. You cannot charge the battery when it does this if the load is still attached as it can sense the load, even a load as small as a state of charge meter. How does it do that? I don't know and don't care so will not research it, but that is the sort of stupid functionality that you need to safely replace that stupid switch that you think is so last century.

author: Siwastaja
author_rank: Super Contributor
timestamp: March 24, 2024, 06:29:02 pm
content: This is not a beginner-level project. You are missing many extremely important things which I am not going to list here because you should be able to understand them yourself before committing to the project. You can start by researching if your relay of choice can interrupt the short circuit current available from the mains outlet.What you are doing would be illegal in most countries. And in any case, super dangerous stuff.Please limit the project to SELV voltages (tens of volts) and, preferably, to current-limited supplies like wallwarts or very small (alkaline etc.) batteries to avoid risk of electric shock and fire to yourself and others around you.

author: edavid
author_rank: Super Contributor
timestamp: March 24, 2024, 06:33:11 pm
content: Quote from: Electrical on March 24, 2024, 06:22:49 pmNow you expect the user to disconnect the shorted wires when they are being re-energized with 220V every 100ms? Do you think that is safe?

author: Electrical
author_rank: Contributor
timestamp: March 24, 2024, 06:38:31 pm
content: Quote from: Simon on March 24, 2024, 06:26:54 pmNo one asked you to design a charger for your super-powerful battery.It is a short circuit protection that could be applied to the mount of your charger at the output of the DC transformer to prevent your 125/150A charger from flaring up.Let's go back to the post and the question.It's not that I care all that much about whether you have a Ferrari or a group of dancing monkeys.HI.I don't do anything illegal or dangerous. It's a contraption that I intend to create for myself and not put on the market.I don't have to look for anything. The world is full of 5V 30A SMD relays.https://rb.gy/3xlizqIt's a circuit like many others. 50V is not high voltage. You can touch them and not feel anything on your skin.The IEC 60479-1 standard states that the dangerous DC voltage is over 120V.In any case please inform yourself before speaking.Re-Hi

author: Simon
author_rank: Unknown
timestamp: March 24, 2024, 06:44:05 pm
content: Quote from: Electrical on March 24, 2024, 06:38:31 pmYou are asking to be banned aren't you. You think that you cannot feel 50V ? that is silly. I have! 48V in fact. There are different standards but generally it has to be under 50V to be considered extra low voltage. Low voltage means anything up to 1'000V.You have a lot to learn and you are trying to design something that is beyond you current ability. A good engineer knows when they are out oaf their depth and humbly asks for help and advice, you will kill yourself before you do that.

author: Electrical
author_rank: Contributor
timestamp: March 24, 2024, 06:54:18 pm
content: Quote from: Simon on March 24, 2024, 06:44:05 pmI'm not an engeneer. Just an enthusiast.If someonw want to ban me, I'm here.I think I won't kill myself for this.In any case, I don't think I said anything bad.1000V/50V is a multiplying factor of 20 times.It's exactly 50V. So like u wrote is very low tension.Also 48V is good. Nothig changes in general.Waiting for an expert for learning something.'byP.S. Microcontrollers are full of transistors (sometimes over a million). Think 2~3 for ampere testing and 2~3 for rele controlling are more than enough.So must have a design of less then 10 transistors.

author: Simon
author_rank: Unknown
timestamp: March 24, 2024, 07:28:26 pm
content: If you are "doing" engineering then you must think like and engineer. otherwise you have no business asking. As we have already told you your expectations totally outmatch your understanding and a couple of forum posts will not teach you. You are wasting our time and yours. Do yourself a favour and grow up!

author: Zero999
author_rank: Super Contributor
timestamp: March 24, 2024, 07:49:24 pm
content: It has nothing to do with electrocution, but protection against fire. 1500A at 50V is 7500W, which is enough to cause lots of smoke, severe burns and a big fire. A large battery contains nasty chemicals which can burn and poison you to death.If you want an over current protection relay, without a reset button, then you need a fuse. End of.

author: Electrical
author_rank: Contributor
timestamp: March 24, 2024, 07:58:51 pm
content: Finally someone who writes numbers and has at least done some multiplication [30A at 50V is 1500W] Watt = Volt x Ampere.Also correct about the firing protection, smoke and burns.Anyway I'm repeat: was not for a battery (so nothing poisong, zero nasty chemicals, not at all death).All alive.Fuse. High tecnology.Was better a buttonHowever, these all seem to me to be reasons not to say "I don't know how to do it" because a 5V/300V 30Amp relay can control 50V/30Amp. It was designed for that.Anyway, post closed. The time has not to be lost.I'm not an engeener also if I was thinking that was a simple thing to do.A couple of posts won't teach me.I have not business asking. Agree and growing up.Act as if I hadn't said anything.Nothing done.Goodbye.

author: Zero999
author_rank: Super Contributor
timestamp: March 24, 2024, 08:06:47 pm
content: Quote from: Electrical on March 24, 2024, 07:58:51 pmA big fuse is not simple technology, especially a DC one. Extinguishing the arc is not easy.QuoteNo. I'm saying I know how to do it. Use a fuse. I know how to select one which works and meets the appropriate safety standards.QuoteYou've wasted everyone else's time.QuoteBugger off!

author: Electrical
author_rank: Contributor
timestamp: March 24, 2024, 08:11:42 pm
content: Quote from: Zero999 on March 24, 2024, 08:06:47 pmTHANKS. U THE BEST.OK. Fuse high tech with complex DC arch extinguer.Going away with my time lost :'(P.S. "It always seems impossible until it's done." Nelson Mandela

author: Electrical
author_rank: Contributor
timestamp: March 25, 2024, 05:09:11 am
content: Quote from: soldar on March 24, 2024, 11:15:03 pmYeah, it's something like this. An automatic reset circuit breaker.But this youtube video shows something different.It's a DC circuit for battery with high amperage that works like a spring when it becomes hot. A mechanical hardware that cuts the current for high amperage.So not properly electrical logic with relay.But beautiful answer.Much appreciated!TNX soldar'by!P.S. Since there is someone still interested in the post I'll show you this too:https://www.st.com/en/power-management/e-fuses.htmlIt is an electronic fuse that self-resets.But it's nicer when you do it yourself.Re-'by