a refrigrator guard cicuit!!

Discussion in 'General Electronics Chat' started by bill EM, Jun 1, 2014.

  1. bill EM

    Thread Starter New Member

    May 30, 2014
    3
    0
    hi comrades,
    im on process of designing a circuit for refrigrator guard which can damp the effect of fluctuations of electricity especially when the supply powers-backs before the system(cooling) get balanced due to previous situation of powerless
    i.e the circuit should be capable of bringing enough time for the system to completely stabilize before allowing power to restart the process again...


    -alot of regards for any suggestons!!!!!!
     
  2. pwdixon

    Member

    Oct 11, 2012
    488
    56
    If I understand what you are asking for it looks like you want to delay power being applied after a power loss/return. You could use a processor to control the power return or you could use a delay relay perhaps.
     
  3. bill EM

    Thread Starter New Member

    May 30, 2014
    3
    0
    thnks,, bt i got idea of using autoranging opamp. i wl try both alternatives
     
  4. crutschow

    Expert

    Mar 14, 2008
    13,001
    3,229
    A turn-on delay relay is all you need. Don't know what an autoranging opamp would have to do with that. :confused:

    How much delay do you want?
     
  5. #12

    Expert

    Nov 30, 2010
    16,277
    6,788
    He wants 3 to 5 minutes. These modules have already been invented and can be had for less than $20. Wait until I go look something up.

    It's called a, "delay on break" timer. Whenever the power goes low or stops, or the thermostat stops the compressor, the delay timer refuses to restart for 3 to 5 minutes. The insides and outsides look something like this:
     
    Last edited: Jun 1, 2014
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  6. Sensacell

    Well-Known Member

    Jun 19, 2012
    1,128
    266
    Are these delay relays used to allow the compressor to mechanically 'unload' before the power is restored? to avoid starting the motor into a heavy load?

    Is my understanding correct?
     
  7. #12

    Expert

    Nov 30, 2010
    16,277
    6,788
    100% correct.

    The delay on break timers start counting time when the circuit goes off. The delay on make timers start counting time when power is applied. The time delay allows the refrigerant to equalize pressures on both sides of the compressor so the compressor starts with equal pressures on both sides. Compressors will absolutely NOT start with 100 PSI difference. That's why air compressors have an unloading valve. The reservoir tank never returns to 0 PSI, but the compressor must fire into a 0 PSI cavity until the crankshaft gets some velocity.
     
    Last edited: Jun 2, 2014
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