How to avoid return V to turn LED ON...

Discussion in 'General Electronics Chat' started by AlexLPD, Dec 7, 2014.

  1. AlexLPD

    Thread Starter Member

    Aug 22, 2010
    Hi to you all, well this migth no be an electronics question, but am sure if theres is an answer may be here...
    the thing is... I have an Arduino controled Meat chiller...

    Description of the system;

    Here is a video of the thing itself ;

    The arduino acts; reciving an signal form termostat... then if the temperature is (HIGH) turn on the compressor and all the fans of the evaporator... if the temperature reach (LOW) stop the compressor and leaves one fan (the fan cycling like these; If fan < 4, fan++) means each time the compressor stops, start another fan.

    Here can be found some diagrams, there are by hand... becasue isnt finish;

    The photos appear on the first entry... its on spanish, because I have to solve some issues with the code... but all diagrams are there.

    Problem to solve;

    The control panel uses LED indicator ligths, at 220V... they should be ON and OFF with each evaporator motor, but instead all keep ON all the time, the reason; A small (2.0-2.4VAC) voltage return from each motor fan (induction motors). Keeps all the GREEN lights on... meaning You can really tell if there is all the fans on, just one, or are stop.

    I have to investigate the electrical nosie generated by the contactors at the uncoupling... and the answer to thath is to add an Varistor to -resist- the voltage peak... Now... im not very familiar, but there is some sort of decive like the Varistor but in negative mode; meaning if there is not a minimum of voltage (205VAC) be non conductive?.

    I know its precisly a transistor, but, it will work on AC? just to turn the leds ON??
    the diodes do too, but I think the damague if the supply voltage is bigger, and even so, its AC... two diodes?

    Well.... Any how... I will let this in here, I hope some one can help me.

    Thanks in advance.

    -Alex Santiago.
  2. AlexLPD

    Thread Starter Member

    Aug 22, 2010
    Well I went to chek the schematics, and its very clear... so make this instead, hopefully some one can adress me in the rigth direction.


    Now thath I see.. there is no way in this Schem the leds will be ON... may be I change on the Tree phases for another, leading to a 2.3VAC difference... I have to chek this up...
  3. wayneh


    Sep 9, 2010
    I can't understand you. The arrangement in that drawing would cause the LED to immediately pop like a fuse once its switch is thrown, if there is not current limiting built into the "LED".
  4. JohnInTX


    Jun 26, 2012
    Maybe a MOV across the coil and a snubber across the contacts?
  5. pwdixon


    Oct 11, 2012
    Better would have been to use zero-crossover opto triacs and separately driven LEDs.

    I'm amazed you appear to tried very hard to make an industrial grade controller with all the sorts of parts that go into that kind of unit and yet you don't know how to drive an LED.

    I would expect you to find that your relays will fail earlier than you'd might hope as you have them wired now as the motors will almost certainly stress the relay contacts over time. Snubbers may help but a redesign would be better in the ling run I'd think.
  6. AlexLPD

    Thread Starter Member

    Aug 22, 2010
    Hi, yes in deed... I try real hard... Im familiar with "analog" or "wire logic controls at 220, 110, 24V" but this is the first thime I have done one whith an arduino.
    The realys says... 7Amps... the motor running is 0.2Amp or so... yes, I will see the protections the guys have recomended.

    And I do belive in a redisign will for the best. I was wondering if maybe an PWM control can be used to drive each motor. Triac as seem to be pointed out.
    Latter on, I will ask for help pn thath.


  7. AlexLPD

    Thread Starter Member

    Aug 22, 2010
    Hi, in deed it seems like thath, but this LED ligths come ready to use in an 220V instalation.
    If we look somewhath differente is a paralell load, whit a single switch.

    The LED comes as next;

    Line 1 - cap - resistor - led- Line 2

    I seen a video apperently by doing so... the amoun of current trow the LED is minum.
  8. AlexLPD

    Thread Starter Member

    Aug 22, 2010
    Wow the snubbers are made by electrotube, y recall have seen those in some MRI trailer mounted machine.
    On all the contactors of the refrigerattion systems.

    Thanks for this, has been helpfull... But its seems the varistors can be mosre sensitive to the voltage peaks, and this seems better
    for the shuttering effect.

    Any how... I guees I will need try on the field...

  9. AlexLPD

    Thread Starter Member

    Aug 22, 2010
    I guees something like this?

    The horizontal similar to cap simbols are the contactors contacts, the coil at the right of each.
    At the base there is the relay contacts operated by the arduino 5V logic system.
    Cm, is the compressor, Tm it the thermostat.

    I put the varistor on the coil of each contactor, and a snubber in each contactor.... this will be fine ?
    Or in this 3 phase system I need to attach it to, lets say... L1 and L2... ???

    Well thanks in advance.
  10. Cmpenney

    New Member

    Dec 9, 2014
    I may be missing something but why not just connect the LEDs in parallel with the coils after your relays?
  11. AlexLPD

    Thread Starter Member

    Aug 22, 2010
    Yes... Im missing something too =D... as you can see is the same as the first diagram... never the least I have an 2.3VAC diference in the two imputs from the LED ... and this is enougth
    to make it brigth,...

    I may have wired wrong this part... This week I will very busy but in the weekend may go there to chek the wiring.