Sun hold relays

Discussion in 'The Projects Forum' started by caravi, Dec 17, 2008.

  1. caravi

    Thread Starter New Member

    Dec 16, 2008
    3
    0
    I'm working on a project that activates two motor propellers in a salt water tank in order to make waves, and I'm trying to use a sun hold relay 0510 with a 12f683 pic the output of the pic is connected to a led that's connected to a resistance that's connected to the base of a transistor the collector is connected to the coil of the relay and protected with a diode placed with the negative side to 5v and the emitter is connected to ground every thing works well until I connect the 120 v AC motors the relay starts to tick and not do what its supposed to do. If some one has done something similar I would appreciate some tips.
     
  2. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    Use a 6V battery pack in series with a diode to give 5.4V to test out the PIC circuit. If the circuit then works OK, the interference is coming in from the AC supply side. This is probably due to the high starting current of the motor. You should consider adding additional filtering to block it.

    If the circuit still fail when using battery power, then it is possible that the high motor start current or sparking from the relay contacts somehow affects the PIC via electromagnetic coupling. More physical separation between relay and PIC would often does the trick.

    Hope this helps.
     
  3. DickCappels

    Moderator

    Aug 21, 2008
    2,650
    632
    Just a thought, but you might not have enough base drive -the resistance in series with the base might be too large.

    How about supplying more detail, like the value of the base resistor, the voltage rating of the relay coil, and the resistance of the relay coil, or the current it needs to close the contacts. What kind of transistor are you using? Stuff like that.

    You're working with lethal voltages - keep one hand in your back pocket!
     
  4. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    It would help us help you if you would post the schematic.

    hgmjr
     
  5. caravi

    Thread Starter New Member

    Dec 16, 2008
    3
    0
    I'm using a 2n2222 transistor with and a 100 ohm resistor connected to the base and a led, the relay activates with 5V the relay coil resistance is 69Ω ±10% once I connect the motor the led stays on and the relay starts to tick.
    appreciate the help.

    caravi
     
    Last edited: Dec 17, 2008
  6. DickCappels

    Moderator

    Aug 21, 2008
    2,650
    632
    It might be that the microcontroller's output is shutting off for a short period to time every now and then. The frequency response of your hearing is greater than that of your eyes, so you would hear the relay click.

    It could be a firmware problem. Can you tell whether the collector voltage is pulsing? (If you don't have a 'scope, you can use headphones and listen, but don't try this with 120 VAC connected to your circuit for safety's sake.)

    Are you sure it isn't your watchdog timer resetting the controller?

    Otherwsie, does this happen when the 120 VAC is not applied?

    Your circuit does not show any decoupling or the 5V power supply connection, so make sure your VCC is holding still -it could be that turning on the relay cause the 5 volt supply to dip, which in turn resets the controller, or "confuses" it.

    Once I had to drive a very noisy DC motor (in a Polaroid film back). Every so often, when the motor ran, RF from the motor would change the microcontroller output pin into an input. The solution was very heavy filtering of the output of the microcontroller to keep noise that the output transistor was picking up from getting back to the controller. You could be experiencing something similar for either the relay coil (Its nice that you have a diode, but you might need to add a small capacitor to reduce the dv/dt when the transitor turns off), or from your relay's load.
     
    Last edited: Dec 18, 2008
  7. caravi

    Thread Starter New Member

    Dec 16, 2008
    3
    0
    Everything works perfect I tried testing it with two lamps and it worked as designed but when I connect the motors it clicks I researched something about start up capacitors but I'm not sure how to connect them and how big of a capacitor I need.
     
  8. kathapurushan

    Member

    Dec 17, 2008
    14
    0
    What type of AC motor is that ?? i mean induction or universal motor / high torque motor ? As you said the circuit is for agitating salt water in a tank, i think the motor is a high torque one.
    You also said that when you tested the circuit with two lamps, the circuit is working as desired.
    This means that when you are using the 120V AC motor (if a high torque one ), the starting current of the motor may be high and if you are deriving the DC voltage for the control circuits by stepping down, rectifying, filtering and regulating from the SAME electricity company line, a momentary dip in line voltage MAY happen. I suspect this may be the problem.
    Try the following
    1) Using a high value filter capacitor for DC power supply (eg. 4700 uf ) OR
    2) Add a rechargable battery backup OR
    3) Both 1 and 2 above.
    Please think well before doing anything as suggested by me :) Please tell the results observed if you have done anything too :) as this may help others i mean eblc1388(L Chung), DickCappels, hgmjr & me kathapurushan
     
  9. kathapurushan

    Member

    Dec 17, 2008
    14
    0
    if the problem persists, try a 2.2 uf,400V non polarised (or any suitable voltage rating available in your country) capacitor across the relayterminals.
    *----===-----||--===-------*
    2.2 uf,400V non polarised
     
Loading...