Fridge data logger
Return to modifications
I decided that i wanted to see the temperature inside the fridge and be able to log this over time, not just when the fridge has started/stopped
to this end I have now fitted a fridge data logger inside the fridge( behind where the original control sensor went so not visible)
this has been excellent as we can easily see how the fridge has been running and be happy that the food inside has never gone over temperature


 


Old logger
user manual - remember to start / stop on temp display - wont work on other screens hold in button for a few seconds
Since changing the controller on the fridge to a much more accurate one see fridge controller I wanted to understand
how often and for how long the fridge was running for.
I decided some sort of data logger was required to log the switch on / off times of the fridge
I thought this would be an easy cheap thing to do it seems not, data loggers seem expensive

However, it seems temperature loggers are very cheap.....
I looked on eBay and found a logger (Elitech RC-3 ) for less than £10 - new  looking at the specification I noticed it had an internal NTC (negative temperature coefficient) thermister.

The route I took with this logger :-

I took the unit apart and de soldered the thermister and ran two wires out of the unit (where the thermister was connected) and re assembled
I soldered a 70k resistor across the wires and got a reading of - 3.4 degrees
I then put another resistor 49k in parallel  and got a reading of 40.2 degrees

I simply put a relay on the fridge (only pulls in when fridge is running) putting the second resistor in parallel with the first one

When the fridge is not running the data recorder shows -3.4 degrees, when running it shows 40.2 degrees  I can set the sample rate
from 10 seconds to days - I chose a 15 second sample rate, the logger can record up to 16000 points so this translates to over 60 hours of logging



Data from logger, this shows 40 degrees when the fridge compressor is running on -3 is when it is not running
This was over a 66 hour period with very light fridge use, ambient temp was between 18 - 22 degrees
The full data set shows time of change from off to on.
This gives excellent data and shows that the average duty cycle is around 50% so the average current draw would be around 2.5 amps




We used the van for a few days with much lower ambient temperature, around 8 degrees.
The chart from the data logger clearly shows the difference a lower ambient temperature makes

 


Return to modifications