Peltier devices are brilliant. You can even stack them for reducing temperatures even further.

But they are shockingly inefficient & completely the wrong device for an esky. More so if camping.

1 hour running a tipical 40 x 40mm 8.0amp 12 volt peltier will only provide 68 watts of cooling.

Get a compressor fridge. My 28L fridge uses about 15AH per 24 hours at 5°C & have the option of down to -22°C if needed.

Danfoss compressor data pdf 1.1MB file

https://www.mmair.com/wp-content/uploads/2016/09/BD35.BD50.Danfoss.pdf

If you look at model number BD35F page 7 running in an ambient temperature of 32°C the compressor uses 4.0amps 12v at 2000rpm is 231% efficient.

Peltier device 

COP(Cooling)=(Cold side Temperature in Kelvin)/(Hot side Temperature-Cold side Temperature) So, Actual efficiency always depends on the temperature difference between hot side and cold side. For example, if a peltier is 5% efficient, its cold side temperature is 0°C(273K) and hot side temperature is 70°C(343K),

Efficiency(Cooling)=5*273/70=19.5%

My 28L fridge needed 1.768kWh over 46 hours or 38.43 watts per hour to cool 10.5 kg of water & also the ambient temperature of 26°C to freeze the water to -22°C. Then the fridge started cycling.

https://thegreynomads.activeboard.com/t65059593/extra-fridge-insulation-wattage-test/

If it's a 5 day trip fill up soft drink bottles 95% lay them on their side in the home freezer for a week. An esky should be at least 50% ice. 

We did this before we had a fridge & still had ice after 7 days. Even put some more frozen bottles on top of the esky, they become drinking water as they melt. Cover the whole setup with an old sleeping bag or other insulation you have, bubble wrap will do. But we did build an esky out of foam which had a wall thickness of about 80mm.

Bought ice is a waste of time.

tea spoon wrote:

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 .....question ....are thermo coolers good or what ......i have a 25 litre one given to me and its new the bloke didnt want it ......ive had it on now for 5 hours its keeping 6 degrees this is what i set it at ...i posted the question on another forum but got very little responce ........is it worth me taking it away for a power site for 5 days in my tent........i can buy a different item if needed ......

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 Hi tea spoon.

When I was working, now retired for 9 years, I used one in the truck as my cooler, I actually brought 2 in about 14 years, I broke the lid on the first one and as far I know the fellow I gave it to still has it. The last one I gave it away to another friend who using it when it for his picnic cooler in his travels.

Funny as I sometimes think I should of kept that one instead of backing my back lifting the compressor frig in and out the ute as they are very light.

There frig performance as such is not great but is better then hot water, never use one to keep food warm but did bump the switch to warm cycle once and was surprised how it heated up.

They do draw consistent 12 volt power (I can not remember the amperage,  maybe 5 amps). Would make battery a bit sick after a few hours

We found it great when travelling with our camper trailer, storage of lettus, eggs, butter and we would turn it off when parked up

Some brief notes so far.

Empty fridge with thermometer sitting on the bottom of the fridge. 20°C ambient. Fan exhaust 3°C higher. 7.8 amps including fans clamp meter, 14.18 volts as charger is connected to battery (this would be indicative of running the fridge while driving if you have done your wiring properly & or using a DC-DC charger), it is supplying 7.9 amps.

Bottom of fridge:

1 hour 6.6°C

1.5 hours 4.1°C

2 hours 2.4°C (evaporator -7.3°C)

2.5 hours 1.9°C

3.0 hours 4.7°C (evaporator -8.2°C)

The fridge lid is actually hollow, probably to save 2 cents in manufacturing costs. One day I intend to fill it with insulation, just haven't got around to it. So the 30mm extruded styrene foam will be providing as good if not better insulation from above.

The evaporator plate is -7.3°C at roughly an average distance from the peltier to the edge of the edge, width length average.

One would need to calculate the optimal size evaporator plate for the temperature which one would need to achieve in the fridge. You can get an extremely cold temperature, but the surface area is so small that you don't have any "volume" to cools reasonable mass.

I think this size plate is a reasonable area for the task, probably leaning more to guessing, but the condenser heatsink should have at least 2.5 times the rate of that of the evaporator heatsink. 

The condenser heatsink has 0.52m² & the evaporator heatsink (exposed side) has a surface area of 0.048m² including edges. So roughly 10.8333... times the surface area of the evaporator heatsink. Factoring the 3°C exhaust fan increase in temperature, I think that to squeeze out any more efficiency will provide a single digit percentage gain.

An hour later the evaporator plate is simply frosting up which actually creates insulation (snow on roofs of houses is a great insulator as it is mostly air).

Initial thoughts in relation to to the compressor fridge. The evaporator tlhas a surface area of 0.3m², although I haven't measured it directly, it must be somewhat below -25°C.

The peltier evaporator is only 1/6 of the surface area, yet can only reach a temperature of -8°C & at about double the the amps of the compressor fridge.

Both evaporators do frost up, but because the compressor fridge has 6 times the surface area & is a lot colder, there is what I call much more depth to the capacity of a compressor fridge.

I will run the 10.5kg of freezing to compare each setup. Ambient temperature will be a bit in favour of the peltier.

Bobdown wrote:

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WAWT, I'm glad Tea Spoon didn't ask how the toilet works.........TMI     

Cheers Bob

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 Well, we have one which is an P trap & another which is an S trap and as a result .....

tea spoon wrote:

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 Are thermo coolers good or what I have a 25 litre one

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Answer to OP: Yes, with qualifications.

DeBe wrote:

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Well i found Whenarewethere's experiment verry enlightening & not dribling crap. Good on him exploring the ineficiencys of peltier devices. Mutch more interesting than some other crap thats been on here lately. Due to the attitude of some on here i dont think Tea spoon will be back any time soon

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I installed a 3.8amp peltier fridge in my car in 1980 which also had cooling from the air conditioning, if only I did a bit more grade 3 maths at the time I would have had an even better fridge.

A few more days & I will post my grade 3 table so you can see the difference between a compressor fridge & a peltier fridge.

I couldn't find any efficiency data comparing these two products on the internet & people simply saying get a compressor fridge without qualification one simply ignores these comments.

Since I have a 28L fridge, at the upper end of a peltier sized fridge, & all the other bits off computers I am quite happy to contribute some constructive grade 3 observations. 

In the meantime, if you just want a cooler & probably up to 10 litres & are driving a lot then a peltier would be ok if you pre cool the contents.

Anything more than that then get a compressor fridge. It is stating the bleeding obvious but hopefully with some really basic numbers one can be a bit more informed. 

It's been an enjoyable & interesting little project. Even the neighbours kid was interested, so that alone was worth it.

Radar wrote:

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After all wealth of knowledge on the subject and valuation, my 14 years of using a 24 litre cooler was justified. It is far better then using ice bricks or having no cooler.

 

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 I agree.

We used ice before our fridge in our last two cars & at the time it worked very well for the type of traveling we did, but we froze our own very large block of ice. I did have a peltier fridge I installed in the car 1980. It worked well but it would have been a lot better based on what I know now.

Data collection tools including a mercury thermometer (one Engel monitor I damaged the external sensor, my own stupidity). Having a number of devices I can calculate an average.

I have decided to stop at 3 days because the fridge is not getting any colder than 3.5°C. This has consumed 7kWh (not including heating he room), about 4 times the energy of the compressor to reach -22°C & quicker. 

The compressor fridge gets the centre of the ice to -2°C in a day. So you are looking at about 8% or less of the energy consumption with a compressor fridge. Mine only uses typically 3.8 amps when the compressor is running. The peltier uses twice that continuously.

As a small fridge & precooling contents & if you have enough battery resources or 240v these fridges are ok. Also very light weight. But if you need something beyond these limitations get a compressor fridge.

My compressor fridge uses 15AH per 24 hours for 5°C setting.

I noticed how hot & how quickly the heatsink got without fans, within a minute, & then it is completely useless. It's creating about 100 watts of heat plus the heat it is moving to the outside of about 50 watts, so that is about 150 watts of heat. It has to be removed. If your fridge is exhausting warm air the heatsink & or fan is not good enough. At least stick another fan on the outside to move more air through the heatsink.

The exhaust air on this setup was only 3°C above ambient. So if your fridge has a small heatsink & or small fan you will have a much higher temperature above ambient so the fridge will not get as cold. You need to get the exhaust air as close to ambient as possible to get the evaporator side as cold as possible.

120mm fan I stuck inside the fridge for part of the experiment. It did reduce the amount of ice forming on the evaporator plate. It is one of the Noctua fans which are very efficient (I bought these a decade ago) 1.08 watts & put the resistor outside the fridge, it comes with a couple of resistors to reduce fan speed.

If you want to knock up something out of a foam box, or extruded styrene foam (much easier to handle, cut with hand saw or knife & sand) there is nothing difficult. An aluminium cooking tray for the evaporator will do, plus thermal paste, but you would need a sold block (get an offcut from an aluminium fabricator) to clamp the peltier firmly. Fans one could salvage, but get a heatsink with at least 0.5 metres surface area & stick fans on it.