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Thread: Is there any relay which can be programmed to work under certain voltage, current or load range?

  1. #1 Is there any relay which can be programmed to work under certain voltage, current or load range? 
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    Is there any relay which can be programmed to work under certain voltage, current or load range? For example, voltage range from 0V to 10V, the relay deactivates while voltage range from 10.1V to 12V, the relay activates. This applies the same for current and load range with different value of course. Basically, the relay will read the range and activates accordingly. Thanks.


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    Yes, it is called an undervoltage relay. ABB 27 Voltage Relay - Voltage Protection (Solid State Relays) I have never heard of any relays that operate under a certain current or load.


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    Thanks for the reply. Is it possible to use different device to read the voltage or current range and trigger any normal relay ?
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    I don't understand the question. What do you mean by "different device" and "normal relay"? What are you attempting to accomplish with your design?
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    Quote Originally Posted by mrexp21 View Post
    Thanks for the reply. Is it possible to use different device to read the voltage or current range and trigger any normal relay ?
    Yes, that's a pretty standard application of control electronics.
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  7. #6 Need help in project involving microcontroller 
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    Hi,

    I'm currently working on a project which requires the usage of microcontroller and I need help.

    The project's objective is to read current(ampere) from vehicle electrical system and activates relay under certain current(ampere) range. For example, if the system reads current(ampere) below 1A, it will activates the relay. If the system read the current(ampere) above 1A, it will deactivates the relay.

    My idea is; The flow of the system will start from current(ampere) reading gauge. The current(ampere) reading from the gauge will received by microcontroller. The microcontroller acts to determine the current(ampere) range to activate and deactivates the relay. This system contains 3 device to operate, reading gauge, microcontroller, relay.

    My question is; 1) Is the idea above possible ? 2) If the idea is possible, how microcontroller will read the current(ampere) value from the gauge (input for microcontroller) ? 3) Is there any product which contains all the function of these 3 devices and programmable ?
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  8. #7  
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    It's definitely possible. My electronics theory is a little rusty, and from last century...but I would use a A to D converter to turn the current/voltage value into binary, so it could processed by a logic circuit. It's kinda hard, without seeing a schematic of the circuit you're designing for.
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    Hit it and quit it...I see..
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  10. #9 Need help in choosing sensor, microcontroller and relay board 
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    Hi,

    Iím currently working on a project using sensor, microcontroller and relay. I was planning to use Arduino current sensor in circuit to detect its current usage and send it into Arduino microcontroller to determine the current range. The microcontroller will decide, if the current below 1A, nothing will happen, if above 1A, it will activate a relay which is Arduino supported relay board. I will do the programming for the range and decide. Can anyone help or provide me a link where I could buy all these 3 devices, which supported by each other?

    I have found 3 devices myself, but I donít know whether it can be used together. Please help me. Thanks.

    Current sensor : 5A Range Current Sensor Module ACS712 Module | eBay

    Arduino microcontroller : Arduino Nano Compatible Version 3.0 PROMOTION (Free USB Cable) (Sarawak, end time 9/6/2014 4:15:00 PM MYT)

    Relay board : 2 Channel 5V 12V 24V Relay Module for Arduino TTL PLC AVR ARM NPN PNP (Sarawak, end time 4/21/2014 12:15:00 PM MYT)
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  11. #10  
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    This is the 3rd thread you've started on this topic, and abandoned the other two that people actually took the time to respond to. That's kinda rude. You're also designing Bass-ackwards.
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  12. #11  
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    Quote Originally Posted by mrexp21 View Post
    I’m currently working on a project using sensor, microcontroller and relay. I was planning to use Arduino current sensor in circuit to detect its current usage and send it into Arduino microcontroller to determine the current range. The microcontroller will decide, if the current below 1A, nothing will happen, if above 1A, it will activate a relay which is Arduino supported relay board.
    You don't need a micocontroller to do that, just a current sensor, a comparator and a relay.
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    MacGyver1968, I'm sorry if being rude. I didn't abandoned the threads. I will reply, please give me some time.
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  14. #13  
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    Quote Originally Posted by billvon View Post
    Quote Originally Posted by mrexp21 View Post
    I’m currently working on a project using sensor, microcontroller and relay. I was planning to use Arduino current sensor in circuit to detect its current usage and send it into Arduino microcontroller to determine the current range. The microcontroller will decide, if the current below 1A, nothing will happen, if above 1A, it will activate a relay which is Arduino supported relay board.
    You don't need a micocontroller to do that, just a current sensor, a comparator and a relay.
    This ^^^^^^^

    There's an old adage: "KISS" (Keep it simple, Stupid)
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    billvon, thanks for the reply. Can you provide me any link where I can get those ? and briefly explain how it will work ?
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    MacGvyer, I prefer to be stupid. Thanks for the compliment.
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    Well..I wasn't insulting you, It's just what KISS stands for...and it's a good policy with any design. Overcomplicating things just gives more reasons for shit to break.
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    I didn't mean to hurt anyone. I'm just learning new things.
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    Back to your design. Why do you need a microcontroller for the circuit? Are you planning on interfacing with a computer? It would also help if you could describe in as much detail as possible what you are trying to accomplish with this circuit. There is more than one way to skin a cat.
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  20. #19  
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    3 Threads merged.
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    Disclaimer: I do not declare myself to be an expert on ANY subject. If I state something as fact that is obviously wrong, please don't hesitate to correct me. I welcome such corrections in an attempt to be as truthful and accurate as possible.

    "Gullibility kills" - Carl Sagan
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    For ac compressor, the clutch will always disengage with the pulley. It will only engage when switched on. But, I'm planning to do on reverse of it. My plan was to remain the clutch always engage with pulley, it will only disengage according to the range specified. It will decrease the power loss from engine. Theoretically, it should work fine under idle speeds during traffic stops.
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    Ok, let me explain. I'm working on a project to modify a vehicle's alternator pulley using clutch mechanism similar reversed ac compressor pulley clutch. Basically, the pulley of the alternator will free once the required current and battery power is sufficient. In order to achieve this, I wanted to do a automatic switch which enable the relay to activate and deactivate the clutch under certain current ranges which I will calculate later.
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    Can anyone get me idea ? If not, I will try to explain again.
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  24. #23  
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    Hello, anyone... ?
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  25. #24  
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    Patience...this isn't a chat board. Firstly, why would you do that? Your car runs off the alternator, it's whats makes the spark for the spark plugs and runs all of the electronics. You're car battery isn't design for that kind of load....it's made to put out a lot of current for a couple of seconds, then be recharged. Are you trying to lower the load on the engine? Are you a racer or hyper-miler?
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    I'm trying to lower the load during idle or similar conditions only. The objective is to lower fuel consumption.
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    The concept is to lower load whenever it is possible, even for couple of seconds or minutes during idle speed which refers traffic stops.
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  28. #27  
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    FYI, you'll majorly lower the life of your battery by trying to run the car off it on a regular basis. If you're just trying to save money, the cost of battery replacement would far exceed the savings in gas. However, if you're just doing this as scientific experiment, and aren't really concerned with that, there are a few things you might consider adding. Firstly, you might consider getting a second battery, and run a "dual battery ocillator" which will charge both batteries. In my youth, I was a "car stereo" guy and had an insane system.(2KW) I had one regular battery to start my car, and a huge marine deep cycling battery (designed for putting out lower amounts of current for a long time) to run my stereo when I was parked without the engine running. I could jam out for hours, and never worry about starting my car.

    I would also include a cut off switch on the dash, so if you get stuck in traffic for a long time, your car doesn't die. In addition to monitoring current, you might also want to monitor battery voltage...so your system will only engage if the battery voltage is over a certain threshold.
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  29. #28  
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    You should also consider it only requires 1-2 hp to turn your alternator, shutting if off would do virtually nothing to save fuel...especially if you're only doing it during idling. You're talking about a .25%-.50% increase in fuel economy. That would work out to some where around 12 cents savings per full tank of gas. So after 40 tanks of gas, you would recover the cost of the $5 current sensor.
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    I can't quite figure out what you want to do. Do you want to control the relay based on output current of the alternator? If you disengage the alternator clutch when the current exceeds a certain value, the current will then go to zero, the relay will pick up again, and it will keep chattering like that indefinitely. If you are using the current that is going to the loads on the system (except battery charging current), and only charge when the current is high, then you could slowly drain the battery until it is dead.

    Somebody already invented a device that uses the car battery as a sort of dynamic brake. The battery only charges when you put on the brakes. I remember seeing a story on that somewhere. It worked, but probably puts some extra stress on the battery.
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  31. #30  
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    This ^^^^
    is a good reason to bounce ideas off other people. I didn't even consider that aspect of the design. If it were me, and the only goal is to save fuel/money, I'd 86 the idea...unless you are just doing it to see if you can do it, which is cool. You could save more money by slightly overinflating your tires to reduce rolling resistance.

    While racers mod their cars to increase speed, hyper-milers mod their cars to increase fuel economy. Just as a racer might brag to his racing buddies about a 10 second 1/4 mile, hyper-milers brag to each other about the distances traveled on one tank of gas. You could google some of their forums if you were interested in saving fuel.
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    MacGyver1968, Harold14370, billvon,Thanks a lot for the information above. I'm an Automotive Engineering student trying to do a final year project in university. My project title is to reduce power loss by converting belt driven components into electrical components. For example, converting ac compressor, power steering, water pump into electrical components. So, the alternator need to be modified or changed accordingly to support the additional electrical components. So, the belt will only connected to alternator. This will be a major reduction of power loss. I will do calculation theoretically on each electrical components before carry on any modification or changes. In addition of this, I would like to modify the alternator pulley by using electromagnetic clutch to function under certain conditions only. For example, during traffic stops, there will be only current supplying for spark plugs, injectors, ac compressors. If day light, there won't be any current required for lights, depends on the conditions. During suitable conditions, the clutch will work. Even the efficiency of the system is low for fuel economy, its still a small contribution which I would like to try it out. Thats why I reversed the clutch mechanism to work in minimum conditions only. I will need to consider the battery life because the design involves long life cycle usage.
    Last edited by mrexp21; September 13th, 2013 at 09:37 PM.
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    I'm not doing this project for myself. I'm trying to do something which can be useful for all.
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    billvon, I need to know how the current sensor, comparator and relay will be connected and work and where I could get those devices, online or local ?
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    Harold14370 , I want to control the relay based on the output of the entire vehicle electrical system.
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    If you are going to run your water pump, power steering, and air conditioner with electric motors, you will need a continuous output from the alternator. I don't think there will be any time when you could de-clutch it. Your battery would die too quickly. The voltage regulator automatically adjusts alternator field current to control alternator output and supply the electrical load and keep the battery charged. There is no need to reinvent the wheel. When the electrical output is low, the torque is reduced, so I don't think much would be gained by de-clutching.
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    I also don't see how it would save power. That whole "conservation of energy" thing. The water pump and other belt driven components are going to use power, whether it comes from the belt or an electric motor...which all comes from engine anyway...you're just converting one kind of power to another. You can't get something from nothing.
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  38. #37  
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    Quote Originally Posted by mrexp21 View Post
    billvon, thanks for the reply. Can you provide me any link where I can get those ? and briefly explain how it will work ?
    Sure. For most of the parts I recommend Digi-Key.

    You will need a DC current sensor; you can get a DC Hall effect sensor for not much money. You also need a comparator (like an LM339) a relay (chosen for your voltages and loads) and a driving element (like an NPN transistor; a 2N2222 will work.) Don't forget to put a clamp across the coil of the relay to protect the driving element.

    You will be comparing your current output to a reference voltage. Easiest way to get the reference is with a potentiometer; one side to +V, other side to ground, wiper going to the - input of the comparator.

    You also have to decide things like how you will power your circuit. If it's automotive you will probably power it at 12 volts; keep in mind that that really means 9-16 volts with peaks around 100 volts during load dump. It's often wise to downregulate to 5 or 9 volts first to get a stable supply.
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    Thanks for the all answer above. I will surely consider all the given answers for my project. Does anyone has suggestion on reducing engine load or in terms of reducing fuel consumption using any electrical system or conversion into electrical system ?
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  40. #39  
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    Quote Originally Posted by mrexp21 View Post
    Thanks for the all answer above. I will surely consider all the given answers for my project. Does anyone has suggestion on reducing engine load or in terms of reducing fuel consumption using any electrical system or conversion into electrical system ?
    Replace the alternator with a motor/generator. When the load on the engine is low generate a little power. When the load on the engine is high turn it into a motor; this will help acceleration. When the brake pedal is pushed generate as much power as possible; this helps braking. (This is basically a weak hybrid.)
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  41. #40  
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    mrep21:

    You don't need a mechanical clutch at all. An alternator has a rotating field winding which is controlled by a variable voltage. This varies the output current of the alternator output coils.

    So if you want to 'disengage' the alternator to reduce the load it takes from the drive belt, simply turn off the field voltage - no generation, no output, = no horsepower required to turn it.

    I believe that Formula 1 cars have this system to improve acceleration? - during heavy engine power demands the alternator is 'switched off' to make more engine power available to the driven wheels, (and during this time, the battery supplies all the current required by the car's systems - so this can only be utilised for short periods)

    As to how you do this - well that would be a bit difficult to explain because (no disrespect), you don't seem to have any electronics knowledge, so it will be hard to explain from scratch to someone who does not know the basic principles.

    At its' most basic; a switch in series with the control voltage will turn the alternator on or off, but you would want automatic control, which is really beyond the scope of a forum format to explain. You need to find an electronics person at your College/University to help you.

    Good luck,

    OB
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    One thing I have often wondered about is using the exhaust turbine half of a turbo super charger - commonly called a "turbocharger" - via an appropriate gearbox to run the ancillary devices such as the alternator, water pump, AC compressor etc.

    Turbochargers are used to recover energy from the exhaust gases (which is otherwise lost) to pressurise the intake air going into the cylinders. If the fuel is increased in ratio to the extra air, this results in more power (but more fuel used of course), which gives an increase in output, but not necessarily in efficiency. (Turbochargers are commonly fitted so a smaller capacity engine - which is tax efficient - can be used to give the same power as a larger - less tax efficient - normally aspirated engine).

    Turbochargers are useful but have drawbacks, such as turbo lag, high cylinder pressures causing head gasket failure, and high operating temperatures - which can cook the engine oil, causing it to break down.

    I've wondered if the turbine half of a turbo charger could just run the ancillary devices but not use it to boost the engine power, and thus use energy which would otherwise be lost to increase overall efficiency and the amount of energy extracted from the fuel.

    One problem I can see is that many such devices might need power at low engine revs, when an exhaust turbine would not have much power available.

    Anyway, food for thought?


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  43. #42  
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    Quote Originally Posted by One beer View Post
    I've wondered if the turbine half of a turbo charger could just run the ancillary devices but not use it to boost the engine power, and thus use energy which would otherwise be lost to increase overall efficiency and the amount of energy extracted from the fuel.
    That would definitely work - but by increasing the back pressure on the exhaust you reduce engine efficiency overall. Would that be worth it? Maybe; you'd have to do the math.
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    Hmm..that would be interesting..like in a hybrid system, using the turbo to turn a generator that would help with recharging the batteries. I wouldn't want to run the water pump and other things off the turbo...I don't think it would have enough torque.
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    Yeah, that would be my concern too. But all you have to do is gear it down sufficiently to increase torque. The question is would there be enough power available at low engine revolutions?

    Back pressure would be increased with a turbine that's true, and some efficiency would be lost due to that - so it would be a case of would the overall efficiency gain outweigh that.

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    Quote Originally Posted by Harold14370 View Post
    I can't quite figure out what you want to do. Do you want to control the relay based on output current of the alternator? If you disengage the alternator clutch when the current exceeds a certain value, the current will then go to zero, the relay will pick up again, and it will keep chattering like that indefinitely. If you are using the current that is going to the loads on the system (except battery charging current), and only charge when the current is high, then you could slowly drain the battery until it is dead.

    Somebody already invented a device that uses the car battery as a sort of dynamic brake. The battery only charges when you put on the brakes. I remember seeing a story on that somewhere. It worked, but probably puts some extra stress on the battery.
    "Regenerative braking"? Years back, electric-run mass-transit "dumped" the K.E. from DC motors into giant resistors, wasting it. But, they were "cheap" brakes, little or no maintenance other than for huge contacts being destroyed slowly. It's possible, though I don't know if it was done, for such vehicles to dump the braking-generated power back into the line supply it. joc
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