Maximizing your 12V power – Manually adjusting your fridge load?

Hi Mick,

My fridge strategy is to operate it at a constant temperature at the highest setting consistent with safe food storage. Fiddling with the controls only diverts my attention from more attractive pursuits. I allow the thermostat to do its job and maintain the determined set temperature.

Some time back the slider thermostat failed on my Waeco so I replaced it with a two-position switch which selects "Cold" at +4 or "Freeze" at -5.
When on "Cold" the fridge maintains +4 about halfway down the chamber and just maintains meat frozen at the bottom layer. Although I have the "Freeze" option I never need to use it. A permanent digital thermometer keeps an eye on things.

Seems to me that if it is a "cold desert night" the losses through the insulation will be so low that the fridge will run very little and there is hence no point in "shutting it right down".

Certainly agree with adding insulation if possible in high temperature ambients if convenient but maybe even better to have permanent additional insulation.

We get by with a 40 litre Engel and have found we rarely need to adjust the temperature setting at all.
The fridge does have a "thermal" cover but I set it just over 1 on the dial and the fridge maintains a constant temperature.
I am that confident in it that I rarely bother to use the separate electronic temperature gauge that I bought when the fridge was new.

Yeah good point Mick,

we do it now and then depending on conditions. Last weekend at the Eucumbene River we had the Evakool 60ltr sitting on the thermostat setting of 2 and it kept the fridge at no more than 3 deg all weekend as it was quite cool.
The fridge in the caravan was turned off all weekend and with a frozen bottle of ice as the main cooling sorce it kept 3.8 deg most of the weekend. On Sat morning it was - 4 outside, -1 in the van and 3 deg in the fridge! Should have slept in there instead!!


cheers Unc

We have had an Engel for 16 years and only on 2 occasions have we ran it as a freezer. At all other times we have ran it as a fridge only having the thermostat set at 3 Deg and have not adjusted it at all for any trips just checked the temp with an indoor out door job to see if all is well.
We once were camped at Smiths Mill in the Grampions and it was a brass monkey night the ambiant temp being a nice minus 7 deg, brrrrr.
When I checked the engel thermometer it read 3 deg so it was warmer in the fridge than out. And yes I don't think I heard the fridge cycle on all night.
Having said all that and travelled around the block 3 times plus crossed all deserts I am one for leaving the fridge to do its own thing. As long as the beers cold.

Hi Mick

Went down this same path some time ago. Like you I prefer to monitor the battery usage , especially the fridges myself . With the onset of reliable led lighting and the little power drawn by these, my next target was fridges.
Whilst I have no problems with Engel's and the likes I changed to the Autofridge.

Being a eutectic fridge and having a larger area of cold storage they only need to run for 5 hours out of every 24. This means that in normal outback treks I turn them off once camped. Sure if the temperature of the day requires they run longer it may be bedtime before they are turned off. I also found that by insulating the fridge compartment, which is not unlike yours, that I was able to decrease the daytime running setting.

On our normal outback treks I run 2 x 40 litre autofridges , one as a freezer, and whilst they use the same power as most danfross compressor fridges , this is usually done only when the engine is running.

I think that you also have to adjust your settings according to the amount of stuff in the fridge. When ours is getting lower with more free room I find something to fill the void. This may only be water bottles etc or I have even used a damp towel in the case of the freezer.

Whilst there are some brilliant battery monitoring devises on the market, at the end of the day I still prefer the old manual turn of the dial and hands on operation


Cheers Teza

Mick O,

I have a 50l Waeco and I fill it up with meat and keep it on freezer. In winter in places like Innamincka it is normally freezing at night and the fridge/batteries don't need a lot of maintenance. A couple of years ago in the Kimberleys and last year on trip to Cape Yorke I had to manage it very carefully. When the batteries were back in float and if there was plenty of sun, I turned the fridge to its lowest setting and in the late afternoon turned it to about -10. This way it didn't run a lot during the warm nights. When there isn't a lot of sun I leave it at -10. At -10 I keep the next few days meals in the top 3 - 4 inches where they slowly defrost over a few days but the lower meat keeps frozen solid. I also put butter and cheese in the dairy part of the fridge because that part is about 5 degrees warmer.

I also take an esky for beer, lunch foods, leftovers etc. If I can get block ice it keeps the food at around +2 degrees.

I have 200 Ah of batteries and 240 watts of solar which does the job well but I don't like letting the batteries get much below 80% SOC. If things get bad like a couple of weeks of overcast skies and rain like last year at the Cape, I booked a powered site for a couple of days to allow the solar panels to catch up.

Regards,
Bob

I agree its part of the fun Mic - as part of our lightweight camping approach
we only have 1 car battery and a small fridge , and a rule for us is to turn everything off at night including fridge and let it keep itself cool from stored cold.
Can't always do this - but mostly we can.

Nothing worse than waking up with flat battery.

With a gram of ice at minus 1 holding 100 times the thermal energy of a gram of water this is easy to do and observe as frozen food begins to thaw.

No point keeping it colder than about 0 anyway.


The other half of our approach is to take nothing that really requires freezing anyway , and in a way this makes it harder because nothing is thawing out and I don't like to rely on secondary measures like thermometers.

Best test then is to sip a little chardonay which we like nice and cold.

The majority of the time I just plug the fridge in, set it on one & let it run. (Just like the fridge at home) The less mucking around turning things on & off the less chance there is of forgetting where it's at. If you have to play with the thermostat all the time I'd be questioning if the system is set up correctly to do the job in the first place?
On extended stays I'll monitor the voltage now & again to ensure it's all good otherwise it looks after it's self.
As I own 2 Autofridge's I can appreciate there is about a 10% saving to be made by running the fridge on high while driving or charging off a generator then either turning them down low or off all together. This of course only works effectively if you have a well insulated fridge (like a Trailblazer) or one with Eutectic fluid. Those with Waeco's or Engel's risk warm food & beer if they don't get the balancing act right then use as much or even more power dropping the temp back down again.
Cheers Craig.............