Milk cooling chest

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A Bulk tank for cooling milk is too expensive for most small raw milk dairies, leaving the milk to be a potential hazard to customers and liability to the operators in this Agronimo project we hack a functional milk cooler for Jacob Springs Farm's raw milk program

Milk cooler hack

the freezer we modified

Raw milk needs to be cooled quickly - ideally brought below 40F as quickly as possible (2 hours is a reasonable maximum target) - simply putting milk jars in a refrigerator will not cool it fast enough to maximize safety and longevity of the milk. On top of that, consumer grade refrigerators will often struggle to handle the load of several gallons of warm milk. It can take hours to cool milk this way and the strain that all this puts on the compressor of the fridge will shorten it's life. Plunging milk jars into an ice water bath is best - but that requires making a lot of ice and the extra step of removing the jars and putting them in the fridge after cooling.

A larger-scale solution is to purchase and install a bulk-tank to cool the milk. A simpler cheaper method that works for up to about 1 - 6 cows is a chest freezer modification: the milk cooler hack.

Materials Needed:

  1. chest freezer that can hold water.
  2. silicone caulk
  3. STC-1000 temperature controller or similar cheap knockoff (such as inkbird ITC-1000) with probe. (Manual)
  4. wire to power the unit. (Since unit draws less than 3 watts of power - this wire can be very small. I used 20 gauge but you can check gauge tables and use something even smaller if you have it on hand)
  5. 14 gauge wire or better for switching leg for chest freezer. A piece of an old power chord or a plug wire from a defunct appliance works great.
  6. Wire nuts and/or electrical tape
  7. optional: mounting hardware

procedure

  1. clean and seal all seams under the waterline with silicone
  2. decide where you want to mount the controller on the outside of the chest freezer. Consider the following:
    • accessibility and visibility for checking temperature and changing settings
    • routing wires back to compressor: power, switching and probe wires inside the unit.
    • a location where the unit will not get brushed or knocked off by passers-by
  3. Locate the cooling lines on the inside of the freezer nearest the area where the controls will be mounted - Most chest freezers have radiator coils (the ones that get hot) running horizontally around the inside of the outer wall of the freezer and cooling cools (the ones that get cold) running horizontally against the inside of the inner wall of the chest. To locate the cooling lines - sometimes it helps to plug in the freezer and splash the sides with water. To locate the heating lines place your hand on the outer wall and feel for hot spots. Watch as the water freezes around the cooling lines. If you can't locate the lines you will have to be very careful drilling holes since puncturing a line will release the coolant and destroy the chest freezer.
  4. avoiding the areas where the lines run mark a spot to drill a hole through both sides (inner and outer) of the chest freezer wall.
  5. pick the smallest drill bit that will work to make a hole that the temperature probe will fit through.
  6. Carefully drill through both sides. If you don't know exactly where the lines run, drill VERY carefully just through the wall material and insert a wire to probe around and see if you can locate the lines. Drilling near the top edge is believed to be safer since coils seem to be rarely located there.
  7. Feed the smaller end of the temperature probe through the hole - don't put it in backwards! The exposed wires need to be outside and the sensor bulb needs to be inside and submerged below the water line.
  8. Connect the temperature probe to the sensor
  9. Connect power wires to neutral and hot legs (cooler wires going to outlet)
  10. Splice the controller into the compressor hot leg using the cooler ports - feeding or cutting power to the compressor as determined by controller

Programming the cooler

(See the manual)

settings and default values
Code Function Correct value for farm
TS Temperature Setting 33
DS Difference Setting 1
PT Protect Time (compressor delay) 3
CA Calibration 0
CF Celsius/Fahrenheit C*
  • It's possible to run it in Fahrenheit however since our controller is capable of tenths of degrees centigrade but only whole

Degrees F we will use C.

  • if you switch between F and C all other values reset to default values.

Operating instructions: 1. Check Main Settings: In normal mode, press “ ^ ” key once, it will display the set temperature value; press “ v ” key once, it will display the difference value;

2. Setting Parameters:

  • In normal working mode, keep pressing “ S ” for more than 3 seconds to enter set mode,
  • set indicator light will be on, screen displays the first menu code “TS”.
  • Press “ ^ ” key or “ v ” key to select the different functions

*Press “ S ” key a second time to enter the parameter setting of the current function, the parameter value starts to flash.

  • Press “ ^ ” key or “ v ” key to adjust the parameter value of current function.
  • After setting the value, press “ S ” key to exit the current function, the parameter value stops flashing.
  • User can set the other functions by repeating above steps.
  • Important: In any status, press the ON/OFF key to save
  • If inactive for 10 seconds, the menu will automatically reset and return to normal without saving any parameter modification.

Operating instruction:

In normal working status, press and hold “ controller; in Power-off Status, press and hold “ ” key for more than 3s to turn off the ” key for more than 1s to turn on the controller. In normal working status, screen displays the current measuring value, the controller switch modes between heating and cooling automatically. If the measuring temperature ≥ temperature set value + difference set value, the controller starts refrigerating, the cool indicator lamp lights on, and the refrigerating relay is connected. When cool indicator lamp flashes, indicating that the refrigerating device is under compressor delay protecting status. If the measuring temperature ≤ temperature set value, the cool indicator lamp turns off, and the refrigerating relay is disconnected. If the measuring temperature ≤ temperature set value - difference set value, the controller starts heating, the heat indicator lamp lights on, and the heating relay is connected. If the measuring temperature ≥ temperature set value, the heat indicator lamp turns off, and the heating relay is disconnected. Menu Instruction:

Note: When CF value change, all the set values restore to default value. Error Description Sensor Error Alarm: When the temperature sensor circuit is short circuit or open circuit, the controller starts sensor error mode and closes all running status, the buzzer alarm sounds, screen displays ER. Press any keys can cancel buzzer alarm, the system returns to the normal working status after error is cleared. Over-temperature Alarm: When the measuring temperature exceeds the temperature measuring range, the controller starts over-temperature error alarm mode and closes all running status, the buzzer alarm sounds, screen displays HL. Press any keys can cancel buzzer alarm, the system returns to the normal working status after the temperature returns to measuring range.

Future upgrades

To improve the function of this project and to bring it into compatibility with other Agronimo projects replace the controller with one but on the photon platform and add the following functions:

  • enable the set point to vary over time - letting the temperature slip to about 40°F in the afternoon (to save energy and avoid the possibility of freezing the milk) and stockpile "cold" over night to achieve set point no earlier than needed for morning milking
  • keep records of milk temperature
  • make a "compressor saver" function that interrupts extended cooling cycles to allow motor and compressor to cool
  • create alerts based on high temp readings