A chart of boat fridge temps and compressor cycles over time

[gregcope]

For temperature these ds1820 sensors, fantastic, dead cheap, i2c data protocol so daisy chain lots together onto one pin (assuming your microcontroller does icc, don't they all now?) -
https://www.sparkfun.com/products/245
Ebay do waterproof.

In my case an arduino controls the compressor on/off so easy to log, but if monitoring only then probably a few choices - digital pin checking continuity of the thermostat ; measure the voltage somewhere on the fridge controller through a voltage divider (ebay do little divider boards), lots info on arduino /rasp Pi forums on Google.

Ah. What logic do you use for fridge on? Fridge temp > 5?

How do you flip the compressor on/off? Relay? N-Fet?

 

[GHA]

Ah. What logic do you use for fridge on? Fridge temp > 5?

How do you flip the compressor on/off? Relay? N-Fet?

The compressor is controlled just with a transistor across the thermostat terminals, it closes when the ambient temp inside the fridge gets over 5deg and opens again when it goes below 3.5deg, seems to work OK, been up and running for a few years now. Fingers crossed
There's a little bluetooth module attached to the arduino so the on/off temps can be changed with a phone or tablet and a bluetooth terminal app.

 

[gregcope]

The compressor is controlled just with a transistor across the thermostat terminals, it closes when the ambient temp inside the fridge gets over 5deg and opens again when it goes below 3.5deg, seems to work OK, been up and running for a few years now. Fingers crossed
There's a little bluetooth module attached to the arduino so the on/off temps can be changed with a phone or tablet and a bluetooth terminal app.

Sorry ... Can you give a transistor part number and an idea on wiring?

 

[Deleted member 478]

I did similar, replaced a bust thermostat with an arduino and add logging along the way.

How do you test a thermostat to check if it is brown bread?

 

[GHA]

How do you test a thermostat to check if it is brown bread?

The beer was warm.

That was more than enough to stir me into action but from memory it wasn't doing the little click thing when you turned it up and down either.

 

[titian]

What an excellent thread. Heaps of information & lots of different thinking.
Thanks people.