Andrew Leigh
Member
Morning all,
OK so I finally get to use the fridge thermostat I made but it is not behaving as I would have expected, nor is it behaving as it did in trials. Let me explain myself;
Before we left on our camping trip the circuit was tested and debugged throught help on this forum and through physical trials on my spare home fridge. Two days before leaving on our trip I allowed the fridge to cooldown and it did so as expected. It was set for a range to break relay contact at 3 deg C and make contact at about 4.5 deg C i.e.
The fridge was loaded the evening prior to departure (with already cold contents). When we got to the camp site the fridge would not cool to below 8 deg C, it was cycling as if the set point had shifted out to 8 deg C, I had not altered the setting.
Confused I reset the set point over the next 12 hours back to the 3 to 4.5 deg C range. The unit perfomed as expected for the next 48 hours. Woke up this morning and the fridge was at 0.7 C deg and is cycling around that range? Again the set point appears to have moved, only this time in the opposite direction?
OK so the ambient is much lower this morning but that should make no difference, all it means is that the cooling is more efficient, the thermistor resistance should still trigger the circuit at the same point for the same given temperature / set point. Ambient yesterday was 38.1 deg C today it is 20.2 deg C surely this could not cause a large variation in the resistance of resistors?
It is almost as if there is factor causing the resistance somewhere in the circuit to alter, would that make any sense? Would the solder joint on the thermistor located in the fridge need to be specially made, care taken etc due to the lower operating temperature?
Any thoughts.
Regards
Andrew
OK so I finally get to use the fridge thermostat I made but it is not behaving as I would have expected, nor is it behaving as it did in trials. Let me explain myself;
Before we left on our camping trip the circuit was tested and debugged throught help on this forum and through physical trials on my spare home fridge. Two days before leaving on our trip I allowed the fridge to cooldown and it did so as expected. It was set for a range to break relay contact at 3 deg C and make contact at about 4.5 deg C i.e.
The fridge was loaded the evening prior to departure (with already cold contents). When we got to the camp site the fridge would not cool to below 8 deg C, it was cycling as if the set point had shifted out to 8 deg C, I had not altered the setting.
Confused I reset the set point over the next 12 hours back to the 3 to 4.5 deg C range. The unit perfomed as expected for the next 48 hours. Woke up this morning and the fridge was at 0.7 C deg and is cycling around that range? Again the set point appears to have moved, only this time in the opposite direction?
OK so the ambient is much lower this morning but that should make no difference, all it means is that the cooling is more efficient, the thermistor resistance should still trigger the circuit at the same point for the same given temperature / set point. Ambient yesterday was 38.1 deg C today it is 20.2 deg C surely this could not cause a large variation in the resistance of resistors?
It is almost as if there is factor causing the resistance somewhere in the circuit to alter, would that make any sense? Would the solder joint on the thermistor located in the fridge need to be specially made, care taken etc due to the lower operating temperature?
Any thoughts.
Regards
Andrew