Fridge Controller for Danfoss/SECOP powered fridges/freezers
- Thread starter luthj
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luthj
Engineer In Residence
The T terminal is a 5V current limited supply. The controller measures the current on the T terminal, and that is what controls compressor speed and on/off. It should be described in one of my prior posts in detail.
Connecting the T terminal to ground or C sets the current to max, which is around 5mA. This is the lowest speed I believe, and any current between 5 and 2ma varies the speed. When the current drops too low, (such as disconnecting the T wire) the compressor should stop. Most mechanical thermostats for these units have a series resistor, and they close to turn the unit on, and open to turn it off.
If you have some type of fault, you can connect an LED between two pins on the controller (I don't recall which, read the manual). It will then blink a code, which will indicate the fault.
Connecting the T terminal to ground or C sets the current to max, which is around 5mA. This is the lowest speed I believe, and any current between 5 and 2ma varies the speed. When the current drops too low, (such as disconnecting the T wire) the compressor should stop. Most mechanical thermostats for these units have a series resistor, and they close to turn the unit on, and open to turn it off.
If you have some type of fault, you can connect an LED between two pins on the controller (I don't recall which, read the manual). It will then blink a code, which will indicate the fault.
luthj
Engineer In Residence
The danfoss compressors are inverter driven (3 phase ac output, low voltage). They can vary the speed in a ~1500rpm range. Advanced controllers like the one I made use a PWM signal. Old school mechanical thermostats have the option to use a series resistor, for the fridge maker to adjust running speed. Depending on the model this controller family can also support a NTC thermistor, and thus act as its own thermostat (assuming a temperature pre set is programmed into it.
This is in no way to detract from the wonderful info above. Very educational and appreciated. What’s below is on the opposite end of the spectrum from the OP and is somewhat thread drift.
Since the compressor starts AND stops by grounding and ungrounding the T wire, possibly running the T wire through a relay contact to ground with this inexpensive temperature controller or similar would work. On my old Edgestar, its replacement temperature sensor wire runs up the fridge underneath the duct tape, under the door gasket, with the sensor epoxied inside. Ugly. Been working for five years. Usually 34 to 37F. Sometimes move 37F shut off to about 40F at night.
Adjustable start and stop setpoints that enable spreading on/off differential easily. Actual temperature shown in center. Remembers setpoints when powered down. IIRC, has sensor calibration adjustment. Celsius only.
Search for XH-W1411 temperature controller. Mine was five bucks from Ebay five years ago. Bought a spare.
Could adding a potentiometer in series with T and the contact to ground allow speed control? I’m ignorant.
Since the compressor starts AND stops by grounding and ungrounding the T wire, possibly running the T wire through a relay contact to ground with this inexpensive temperature controller or similar would work. On my old Edgestar, its replacement temperature sensor wire runs up the fridge underneath the duct tape, under the door gasket, with the sensor epoxied inside. Ugly. Been working for five years. Usually 34 to 37F. Sometimes move 37F shut off to about 40F at night.
Adjustable start and stop setpoints that enable spreading on/off differential easily. Actual temperature shown in center. Remembers setpoints when powered down. IIRC, has sensor calibration adjustment. Celsius only.
Search for XH-W1411 temperature controller. Mine was five bucks from Ebay five years ago. Bought a spare.
Could adding a potentiometer in series with T and the contact to ground allow speed control? I’m ignorant.
luthj
Engineer In Residence
Yes, or if you want a single speed, a resistor in series. If you check the danfoss/secop manual, they have a list of resistor values and the speed they produce. I think its 2-4k ohm, so a potentiometer in the right range would work fine. You may need to get a 0-2k pot and then put a 1-2k resistor in series to get the range right.