An interesting fridge experiment,

I own two 12volt fridges, a very old 29 litre Engel and a 110 litre Waeco.
I've wanted to know for quite some time exactly what they draw. One of the advantages of working in industrial process control is you have access to some really great test equipment that is also extremely accurate.

Before Easter I brought home a paperless chart recorder. That's a machine that logs inputs to in this ones case floppy disk and ethernet. It gives trends and graphs, some maths functions and the best part allows me to integrate or totalise inputs.

What I did was connected both fridges to seperate 12V DC power supplies (2 x GME 13.5volt 10amp). Fed the voltage and the current they are drawing into seperate inputs on the recorder. (The current is being measured as millivolts from a pair of Jaycar shunts) From there I am able to trend and record the values.
I've also set up two maths channels for each fridge. One channel tells me the instantaneous power draw of the fridge in VA or since they are DC devices, Watts. The other maths channel integrates the current in amps thus giving me the total Ahrs drawn by each fridge.

I kicked the whole show off at 4pm on Good Friday and left it overnight. The Waeco was already down to temperature, about 0 to 1 deg C. The Engel was started warm and by about lunchtime Saturday was also down to about 0 to 1 deg C.

Then the load, I stuck two 10 litre containers of room temperature water into the Waeco on the Saturday around lunchtime and left it. At the same time I stuck one 10 litre container in the Engel. Both fridges pulled the water down and are now running at the previous mentioned temperatures.

What have I learnt?
The old Engel starts out at nearly 100 watts and just before it cycles off is down to about 95 watts.
The Waeco starts out at nearly 90 watts and just before it cycles off is down to about 70 watts.
Pretty much what I'd expect from this type of load.

As of 3pm on the 17th the Engel had consumed about 125 amp hours and the Waeco about 150 amp hours. That's each fed from a constant voltage power supply of 13.5 volts DC.
This gives me a base line for how much power they'll use in ideal conditions.

Real data tells me that from batteries I'd need at least three and ideally four 100% charged 120Ahr AGM's or similar to run one of the fridges for this time period and load profile without recharging.
What it also tells me is those on this forum using solar trickle charging are on the right track.

Another thing it tells me is the level of exaggeration on run times some people report for their Engel’s and Waeco's. I've always wondered why my batteries flattened so fast now I know!

Geoff.