I cant really afford an Engel as much as i'd like one! :(
I'm just trying to look into if it is possible to get a fridge such that i can run it off a solar panel on the roof and a big leasure battery and not need to get any proper mains to last for a couple of days stationary. Seeing how other people are doing it.
when you next see Martyn tell him that his old air horns are getting some exercise on my 101! :)
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Tom,
If your fridge is an absorption type(3 way), then forget trying to run it from a battery without additional power from an alternator. These things use a 12v heating element of about 100W rating, so your current drain is 8 - 9amps continuously.
On the other hand, if you have a compressor type like my Waeco CF18 which lives permanently in the back of the 90, then stand alone operation is a viable proposition.
I did a test on mine to determine how much power was actually required to keep the interior at 5degC in an ambient temperature of around
20degC - this is what I found.The brochure quotes average power input 35 Watts and average running time 18% at 20C ambient temperature when thermostat set at 5C.
My tests gave the following results:
I put several cans and bottles in the unit and connected it to a 13.8v power supply. It has a thermostat which(according to specification) is adjustable from 5C to -15C, I set it the minimum(5C) setting and switched it on. In a room temperature of around 19-20C, the unit reached it's thermostat cutoff in just 5 minutes.
Currentwise, there is a surge of about 8amps for a very short time(fraction of a second), not long enough to blow the 5amp fuse which is fitted in the plug. The compressor and fan then draw a steady 3.5amps for 1.5 minutes, give or take 10 seconds. The unit then rests for 15 minutes, give or take 3 minutes.
This cycle seems to be constant for the minimum setting, and 19-20C ambient room temperature, if the lid is not opened.
According to my calculations, 1.5 minutes running out of every 16.5 minutes, is a running time of only 9%, which effectively halves the quoted average power consumption.
My readings indicate a wattage(when running) of 13.8V x 3.6A or about
50 Watts. NOTE: I used a value of 3.6A here to include the effect of 1 seconds running at 8A per cycle, which is a large over estimation anyway! Thus applying the 9% running time ratio to that wattage gives an average wattage over time, of just 4.5 watts!I then tested the unit running from a very old and well used 24Ah sealed battery. The fridge was already down to normal domestic fridge temperature (5C), so I just left it running in the same place as before and didn't open the lid. I set the battery saver switch to it's service battery setting, i.e. cut off at 10.4V rather than the starter battery setting which cuts off at 11.3V.
42 hours later the battery saver circuit cut in as the start up surge dropped the battery voltage to just below 10.4V. The off-load terminal voltage of the battery settled at 11.6V.So I reckon that over 42 hours, the unit used around 4.6Ah, even if I allow a whole second for each 8A surge per 1.5 minute cycle.
I used an electronic temperature probe to monitor the internal temperature while under test. With the fridge on it's minimum setting the internal temperature settled at a very stable 5C, regardless of ambient temperature. On a separate occasion, I set the thermostat to it's maximum setting to verify the lowest temperature the fridge could maintain. I left the fridge in the caravan which became quite warm during the day, but the fridge temperature settled at -18C in an ambient temperature of 25C. For this test, I did not monitor the running time, which would obviously be longer, as this is not the function for which my fridge will be used most of the time.
This may be of some use to someone. Feel free to check the maths, I make mistakes like anyone else ;o)
Neil
(Reply via NG please)
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