Priority relay circuit for refrigeration/freezer

Discussion in 'The Projects Forum' started by ronmckie, Jul 15, 2010.

  1. ronmckie

    Thread Starter New Member

    Jul 14, 2010
    2
    0
    I have a DC refrigeration system for my boat. I have added in a freezer circuit and they both work correctly if I manually control them (without R2 in the circuit in the attached drawing). I would like to use the thermostats to control when the freezer or refrigeration are in operation. The problem is that the compressor is relatively small so it can only accomodate the chilling of either the freezer or the refrigerator at one time. I came up with a circuit that I thought would work by adding in a second Bosch SPDT relay (R2 in the attached drawing). The problem is that the R2 relay won't activate the coil and cause it to switch. The priority that I am trying for is if the refrigerator is running and the freezer needs to run, it will shut off the solenoid to the refrigerator and open the freezer solenoid. Both of the thermostats (Ref T2 & Frz T1) need to be in line with the hi pressure cutoff switch to shut off the system in case of hi compressor pressure.

    I have tried to move around the coil for R2 to different positions in the circuit and I don't see how I can get suffient voltage to energize the coil. I am obviously missing something. I am probably trying to solve this with too few components. Can someone help point me in the right direction?

    Thanks

    Ron

    I am new to the forum and my electrical training is mostly self taught.
     
  2. ronmckie

    Thread Starter New Member

    Jul 14, 2010
    2
    0
    I have a DC refrigeration/freezer system for my boat. Because of the size of the compressor I can only run one circuit at a time (either the freezer or the refrigerator which are controlled by separate thermostats). I have been manually controlling which circuit is used and I would like to automate the process based upon priority (freezer having priority). I put in a second relay (R2 - a SPDT) which won't energize when the thermostat for the freezer is closed. I am at a loss as to how to get this to work and am looking for help or advice. Please see previous post for the circuit diagram.

    Thanks
    Ron
     
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