Relay Chatter

Discussion in 'The Projects Forum' started by ssnaples, Sep 16, 2013.

  1. ssnaples

    Thread Starter New Member

    Jul 14, 2012
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    I am resurrecting an old project that I started about a year ago, but could never get the circuit to function properly. I am a novice with electronics, but am willing to learn, so please be as detailed as possible with any advice and I will do my best to understand. What I am trying to do is take a pulsing signal and turn it into a steady signal that can make a relay go on and off. So what I have done is used an opamp (to increase the signal) with a comparator (to trigger the on/off value) and finally a transistor with a 12v relay to turn a motor on and off. The circuit works beautifully until I bring the motor into the equation. Without the motor, an LED will turn on an off as desired, but when I bring the motor into play, the relay chatters on and off. It is on and then motor moves to its desired position, then goes off, then back on and so forth.

    Is there anyone that can look at my attached circuit diagram and breadboard diagram and help explain where I have gone wrong? It seems like the motor is bringing down the voltage and thus causing the chatter. I have read in other posts that you can add a cap to the relay coil, but I do not know what size cap or where to place it. I have also been told to add hysteresis, but thought that I already did. Any help with a diagram would be greatly appreciated. I am to the point where I am even willing to pay someone to help out. Any ideas??? Thanks in advance
     
  2. wayneh

    Expert

    Sep 9, 2010
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    Just curious - why didn't you just use the 12V supply and a single comparator to square up your signal? The voltage regulator does set the reference voltage for the comparator. Is the 12V not regulated?

    The comparator has a high input impedance and I doubt the op-amp is helping.

    Why not ditch the relay and its transistor use a MOSFET? The comparator could easily drive it directly.

    Chatter can also come from having inadequate wires to carry "large" currents. Try doubling up or otherwise increasing your ground wires.
     
  3. #12

    Expert

    Nov 30, 2010
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    (I only went after the chattering part.)
    Here's one opinion:
     
  4. joncad

    New Member

    Sep 16, 2013
    5
    1
    The chatter may be caused by feedback from the motor. Try adding a diode across the relay coil. The positive side of the relay coil should be connected to the negative side of the diode, and the negative side of the relay coil should be connected to the positive side of the diode. Any normal diode that can handle the coil current should work.
     
    #12 likes this.
  5. tubeguy

    Well-Known Member

    Nov 3, 2012
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    How much current does your motor draw and what current can the power supply provide?
    Motors draw a much larger current at start-up than when running.
    The motor might be causing the power supply voltage to sag.
     
  6. ssnaples

    Thread Starter New Member

    Jul 14, 2012
    22
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    wayneh. I am willing to try anything. The only issue is that I have no background in electronics and most of this is over my head. The route I took is based on various suggestions from this board and other boards. It has probably become more of a mess than it needs to be, but this is what I am working with. Because the signal pulsating, I thought that the opamp was used as a peak detector and then the comparator is used to define the on/off point, while the transistor switches the relay on/off thus controlling the motor. I am more than willing to try your approach with the mosfet, but I know nothing about using mosfets. I know it is a lot to ask, but could you draw a diagram of what you were thinking? Thanks again for the help.
     
  7. ssnaples

    Thread Starter New Member

    Jul 14, 2012
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    #12 Thanks for the schematic. I will definitely try it out and will let you know how it works out. Thanks!
     
  8. ssnaples

    Thread Starter New Member

    Jul 14, 2012
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    With my limited knowledge, this makes sense to me. I think I tried this last year when I was working on this project, but easy trial and error modification. I will let you know if it resolves anything. Thanks!
     
  9. wayneh

    Expert

    Sep 9, 2010
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    Let's see what happens with the change proposed by #12. It should help but let's see.

    Don't forget what I said about wiring. I've had exactly the kind of problem you're describing because of the tiny voltage changes caused by too much current thru too small a wire. Make sure the ground wires for your loads (the relay and whatever it is controlling) are beefy and see if that helps.
     
  10. nickelflipper

    Active Member

    Jun 2, 2010
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    I had a relay chatter problem with a very similar setup (solar tracker). In addition to the proposed diode across the relay coil, I added a 47uf electrolytic cap in parallel across the coil. I will note that I did not have some of the capacitors associated with the upstream circuitry involved with the original and proposed circuit diagrams.
     
  11. ronv

    AAC Fanatic!

    Nov 12, 2008
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    One thing I noticed is that the relay is running of the 10 volts. There aren't to many 10 volt relays so I'm guessing it's a 12 volt relay? Since your load is a motor it probably takes a lot of current to start up. This could make the 12 volts drop and having the regulator in in there drops another few tenths of a volt as will the transistor switch. Could be this makes the relay drop out then turn back on. So if it is a 12 volt relay, hook it to the 12 volts. Depending on what you are using for power a big capacitor on the 12 volts might help. What is the power supply?
     
  12. ssnaples

    Thread Starter New Member

    Jul 14, 2012
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    You are correct. the relay is connected to the 10v regulated power rail. It is however a 5/6v relay #NTE R40-11D2-5. Could that be the issue? Am I not using the correct relay? The relay when closed is connected to the 12v rail... correct??? The reason I went with the regulated 10v rail is that I am using a car battery and even with a 12v regulator, I would not be guaranteed 12v as there is a power drop with that circuit (atleast that is my understanding). I need to measure the current of the motor and will do so when I get home tonight. Would it help if I gave a parts list that I am using? Maybe some of the pieces are not compatible. I am such a noob when i comes to electronics so please excuse my ignorance. But trust me, I have learned quite a bit in the last year from everyone here and I know that this circuit will work with some minor tweaking. So thanks again for all of the help!
     
  13. #12

    Expert

    Nov 30, 2010
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    A parts list would help a lot, considering I suggested a resistor for a 12 volt relay.
     
  14. ssnaples

    Thread Starter New Member

    Jul 14, 2012
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    Sometimes the simplest solution is the correct one. wayneh, your solution seems to have solved the relay chatter. Thanks! I doubled up the ground wires going to the relay as well as doubled up the ground coming from the battery. Don't know which one helped but now it is time to do more extensive testing. I think you made this suggestion last year when I was working on this project, but I never implemented it. I still don't really understand why adding more ground wire would solve that issue though. So that I learn something from this, can anyone explain why this seems to have worked. Thanks again everyone for all of the input. I should have a chance this weekend to really put my circuit to the test. I will report back. Thanks!
     
  15. wayneh

    Expert

    Sep 9, 2010
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    I think it's primarily related to the comparator, and the fact that the reference voltage moves around if ground moves around. A few mV is all it takes.

    I would have never been able to make the suggestion if I hadn't once fought and won the same battle myself. There's not much point to getting older if you don't gain wisdom along the way.
     
  16. tubeguy

    Well-Known Member

    Nov 3, 2012
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    Well said !!!
     
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