I have very limited space in the car for batteries, two of the three 26ah batteries shoehorned under the seat, so I did some tests on the 28L Waeco going in the car so it would use the least amount of power possible. 28L is the largest fridge I could fit without taking over.
I heated a bedroom in the house for about 3 days to 35°C with three heaters (pretty horrendous electricity consumption) & tested the fridge with different levels of insulation. I also installed a very efficient Noctua fan in the fridge from an old computer. Put a baffle around the fan as well, as the fridge design was recirculating hot air. Added velcro as hot air was traveling up between the fridge & cover reducing thermal efficiency. With foam sleeping mats added efficiency is better than 30mm of XPS foam but I didn't have accurate figures.
28 litre fridge per hour, ambient 35°C, fridge set at +2°C 0.0140 kW/h The uncovered fridge. 0.0132 kW/h Standard cover. 0.0116 kW/h 30mm XPS foam. 0.0082 kW/h 60mm XPS foam.
So cover up your fridge, except vent, & keep it out of the sun. If you have to run it in a locked car leave the windows open a few mm. I can get my fridge to 45°C below ambient temperature & it still does not use that much electricity. A well packed & covered fridge you can turn off for a day if you have limited battery capacity without too much increase in temperature. Throw your sleeping bags over it during the day if not running the fridge & or keep the vents clear.
I have stuffed a minimum of 2 thickness of 10mm sleeping mats between the fridge & cover & on the lid. The fridge cover is a bit tight but the extra insulation helps a lot. Macpac sell grey sleeping mats which match really well. The rear handle had to be removed to fit the fridge in the car so I filled the gaps with more foam. Last photo is a custom aluminium & stainless steel bracket to reduce height as the original bracket was too high. I did use the feet that came with the original bracket & machined them down to reduce height.
A wet towel seals and cools . I often turn our portable fridge off overnight on cloudy days . On start up in morning . It doesnt run very long before it turns off, down temp ., Often place wet towel over the top seal . Figure if there is any leaks or place insulation is leaking it would be there . I wrapt the inbuilt compressor fridge with floor insulation. Only approx 8mm thick . But it Atleast puts another boundary layer from outside heat . Both can be turned off for quite some time .
Mike Harding said
02:40 PM Nov 3, 2018
An excellent post!
I heartily commend your engineering approach to the testing.
For consideration of whether insulation reduces energy consumption of a fridge... take it to the extreme and consider if the fridge were in a vacuum... how much energy would it then use?
The more insulation the better.
Whenarewethere said
12:36 AM Nov 8, 2018
A vacuum would be best & you can get vacuum panels but you would still have issues at the corners. Also one slight misjudgement on assembling the fridge & the vacuum is gone. They also loose there vacuum over the years.
Next option is Aerogel insulation but that has moisture issues which reduce its thermal rating. So it's back to basic insulation but use as much as you can add, & keep the fridge out of the sun & put a white cover over it as a minimum as the fridge manufactures seem to have a fetish with dark colours!
Bag colour is a chicken and egg situation: black is the most efficient colour (by around 5%) for transmission and absorption of heat energy - note that heatsinks are always black.
So if the fridge will rarely be in sunlight then black is best however if it is in sunlight for a decent time each day then white would be best.
In my bush camps my fridge, in black cover, lives in the back of the 4WD and usually receives some sunshine during the day. If I remember I put an old white sheet over it, keeping the vents clear, during that time.
Whenarewethere said
04:53 PM Oct 17, 2019
Update: A few alterations
I have replaced the original 80mm fan in the fridge with a Noctua 120mm fan.
Now have replaced the Noctua 120mm fan with another Noctua fan which not only has a higher volume it has better pressure.
Now I can feel the air being pushed through the fridge to a greater degree even with a dust filter. It also barely used any more power to the first one I installed & less than the original fan as Noctua fans are really efficient. Well worth spending the money to save energy.
Anderson plug on the fridge & a filter, it's surprising the amount of dust that would otherwise cover the condenser. I still blow out the fridge with airgun after every trip & it is quite amazing the amount of dust in the fridge covering the condenser & everything else.
I have had a temporary piece of aluminium folded over the divide in the fridge to get the butter department cooler when running the fridge as a fridge. I have replaced it with a neater job! Works well, there is some sail cloth repair tape on the back of the aluminium so the evaporator coils don't get damaged. I used a 1.5mm thick baking tray (4028574815277) as the aluminium is a bit softer, (unfortunately not anodized but the heatsink itself has more value than being anodized) but not too soft, hopefully 1200 alloy which would be nice, which would have better thermal properties having less alloying elements, but nevertheless easier to bend by hand than 5005 alloy off the shelf sheet.
I can pull the heatsink out for cleaning both sides. Have been testing it for a week now and it works really well, wish I had upgraded this modification earlier. The tail edge of the heatsink gets considerably cool. Even a bit cooler than I was expecting, which now makes this area actually useful when running the freezer as a fridge.
If you notice there are 2 thicknesses of 10 foam sleeping mat stuffed down inside the fridge cover for additional insulation, there are 3 on the opening end, the compressor end does not need it.
Fold the front bottom edge of the butter compartment first, rear bottom corner of butter compartment second, then rear top edge of divide third & top front edge of the divide last.
Any heatsink over this divide will be better than nothing, even a couple of aluminium disposable baking trays will help make the butter compartment a bit cooler!
The above post was a cut & paste. These modifications were done quite awhile ago & the fridge has worked really well. Couldn't be happier. Also tried to reduce AM interference as well, but with mildly moderate success.
The fridge has been on 4000km of corrugated roads & every night we sleep the fridge is moved to the passenger seat. That's about 290 times now & 290 time back to the boot.
This test was done before I installed the larger thermal bridge (piece of aluminium sheet) into the butter area. This would now get very cold, my guess at least around -5°C if I did the same test again.
A torture test to see how long it takes to freeze to 10.5 kg of ice bricks to -22°C (lowest fridge setting. On previous tests thermometers I stuck in the fridge showed -24°C). Ambient over the days was 26°C morning & night, including ice bricks at the start. I also put a thermometer in the centre of the ice bricks as this area is slower to freeze.
24 Hours: fridge -11, centre of ice -2
36 hours: fridge -16, centre of ice -10
44 hours: fridge -20, centre of ice -16
46 hours: fridge -22, centre of ice -19
The fridge started cycling at 46 hours.
The bottom of the fridge looses more cold than the sides so I think I will be battling to get the centre of the ice to -22°C until I can come up with thicker insulation & mounting mechanism.
The back of the fridge near the internal light only got down to 0.2°C but the ice brick closer to the freezing area was frozen solid.
About half the time it was running off my old 80Ah car hattery (still in good condition) which was around 12.4 volts with a 1 amp charger trickle charging. Fridge current was 3.1 amps. So 1.768 kWh for the 46 hour test. I could hear the compressor running a touch faster on AC but not a lot in it, maybe maximum 10% faster.
Exhaustair from compressor was about 30°C (this was with the slower Noctua fan, not the last one I installed with higher capacity & pressure, & I have added a little bit more insulation).
Great effort with great results, learned a few things here. Cheers
Niczilla said
10:35 AM Apr 4, 2025
Hey mate, great test! I've been trying to find information about someone swapping the fans out for ages so your post is perfect. A few things I've been wondering-
What was the best fan you used in the end? 120mm fans seem pretty big, did you just squeeze it in there and attatch it however you could?
Without any of the insulation upgrades do you think the fans increased the performance of the fridge at all?
Did you just cut the connector off and use screw terminals to wire it in or do something else??
I know this post is a few years old now so I hope you still get notifications for it! Hope you can help!
Cheers!
Nic
Brianvicki said
12:31 PM Apr 4, 2025
Great article.. the only thing I did with our drawer fridge was to add a usb power computer fan at the back in front of the existing fan. Draws .21 of an amp
Whenarewethere said
12:46 PM Apr 4, 2025
A 120mm fan is the largest I could fit, & it runs continuously when the compressor is running, & off when the compressor is off.
The original fan had a thermostat so it would increase speed as the fridge needed more cooling.
The Noctua fans are so power efficient it's fine that they run the entire time the compressor is running. I just cut the wire, soldered & heatshrink.
With fridge efficiency my issue was because we are in a car only everything had to be as compact as possible. Insulating the fridge ment I needed less batteries, & insulation is light weight.
I think the next best thing was blow the dust out of the condenser & the rest of the compressor area. It was filthy. & that is a bit like the condenser having a blanket on it. We have 3 ARB compressors, & an air tank, that we run in parallel (up to 90 amps).
Third or even in second place was the very poor design where air would circulate back around the fan. A 2 cent design failure, just needed a simple baffle.
The fan. Getting more air to flow through will help a bit. It's hard to say how much, but the exhaust air always felt a bit cooler with the larger fan. So maybe that helps a degree or two within the fridge.
I also rewired the 12volt wire inside the fridge with 12awg. The original wire was barely 16awg. Also replaced the standard 2 metre cable which was 16awg as well. So there was about 0.17 volts saved. Shoved in a 7amp circuit breaker while at it.
I have modified the aluminium angle since these photos, tapering it down a bit towards the condenser fins. But it is splitting hairs looking for efficiency.
This was the only spot I could fit the circuit breaker on this fridge. The Anderson plug is permanently bolted on. Now I run 12awg or heavier to power the fridge.
I looked at the fridge today to see if there was anything useful I could add. Not really other than I washed the filter I put in & it was pretty dirty. It's a pretty open filter, but it is one layer of dust defence.
If you have had the fridge for years & used it a lot, it's going to be filthy inside. The back of the fan blades will also have a good layer of dust as well. Just like the inside of a computer, dust everywhere.
Niczilla said
09:40 PM Apr 4, 2025
Hey mate cheers for the great reply! Yeah getting that dust out is always number one in getting her to run better. I'm going to dump some new more powerful fans in and see how it goes. Swapping out the wires is also a great idea as I was just looking at them last night thinking they were damn puny! Might pull them out and swap them for thicker stuff, certainly would never hurt!
I'll report back once I've made some mods and let you know how they go!
Cheers!
Nic
Burt65 said
11:48 AM Jul 18, 2025
Another great modification with plenty of pictures...
I have very limited space in the car for batteries, two of the three 26ah batteries shoehorned under the seat, so I did some tests on the 28L Waeco going in the car so it would use the least amount of power possible. 28L is the largest fridge I could fit without taking over.
I heated a bedroom in the house for about 3 days to 35°C with three heaters (pretty horrendous electricity consumption) & tested the fridge with different levels of insulation. I also installed a very efficient Noctua fan in the fridge from an old computer. Put a baffle around the fan as well, as the fridge design was recirculating hot air. Added velcro as hot air was traveling up between the fridge & cover reducing thermal efficiency. With foam sleeping mats added efficiency is better than 30mm of XPS foam but I didn't have accurate figures.
28 litre fridge per hour, ambient 35°C, fridge set at +2°C
0.0140 kW/h The uncovered fridge.
0.0132 kW/h Standard cover.
0.0116 kW/h 30mm XPS foam.
0.0082 kW/h 60mm XPS foam.
So cover up your fridge, except vent, & keep it out of the sun. If you have to run it in a locked car leave the windows open a few mm. I can get my fridge to 45°C below ambient temperature & it still does not use that much electricity. A well packed & covered fridge you can turn off for a day if you have limited battery capacity without too much increase in temperature. Throw your sleeping bags over it during the day if not running the fridge & or keep the vents clear.
I have stuffed a minimum of 2 thickness of 10mm sleeping mats between the fridge & cover & on the lid. The fridge cover is a bit tight but the extra insulation helps a lot. Macpac sell grey sleeping mats which match really well. The rear handle had to be removed to fit the fridge in the car so I filled the gaps with more foam. Last photo is a custom aluminium & stainless steel bracket to reduce height as the original bracket was too high. I did use the feet that came with the original bracket & machined them down to reduce height.
An excellent post!
I heartily commend your engineering approach to the testing.
For consideration of whether insulation reduces energy consumption of a fridge... take it to the extreme and consider if the fridge were in a vacuum... how much energy would it then use?
The more insulation the better.
A vacuum would be best & you can get vacuum panels but you would still have issues at the corners. Also one slight misjudgement on assembling the fridge & the vacuum is gone. They also loose there vacuum over the years.
Next option is Aerogel insulation but that has moisture issues which reduce its thermal rating. So it's back to basic insulation but use as much as you can add, & keep the fridge out of the sun & put a white cover over it as a minimum as the fridge manufactures seem to have a fetish with dark colours!
James Price Point:
Bag colour is a chicken and egg situation: black is the most efficient colour (by around 5%) for transmission and absorption of heat energy - note that heatsinks are always black.
So if the fridge will rarely be in sunlight then black is best however if it is in sunlight for a decent time each day then white would be best.
In my bush camps my fridge, in black cover, lives in the back of the 4WD and usually receives some sunshine during the day. If I remember I put an old white sheet over it, keeping the vents clear, during that time.
Update: A few alterations
I have replaced the original 80mm fan in the fridge with a Noctua 120mm fan.
Now have replaced the Noctua 120mm fan with another Noctua fan which not only has a higher volume it has better pressure.
Now I can feel the air being pushed through the fridge to a greater degree even with a dust filter. It also barely used any more power to the first one I installed & less than the original fan as Noctua fans are really efficient. Well worth spending the money to save energy.
Anderson plug on the fridge & a filter, it's surprising the amount of dust that would otherwise cover the condenser. I still blow out the fridge with airgun after every trip & it is quite amazing the amount of dust in the fridge covering the condenser & everything else.
I have had a temporary piece of aluminium folded over the divide in the fridge to get the butter department cooler when running the fridge as a fridge. I have replaced it with a neater job! Works well, there is some sail cloth repair tape on the back of the aluminium so the evaporator coils don't get damaged. I used a 1.5mm thick baking tray (4028574815277) as the aluminium is a bit softer, (unfortunately not anodized but the heatsink itself has more value than being anodized) but not too soft, hopefully 1200 alloy which would be nice, which would have better thermal properties having less alloying elements, but nevertheless easier to bend by hand than 5005 alloy off the shelf sheet.
I can pull the heatsink out for cleaning both sides. Have been testing it for a week now and it works really well, wish I had upgraded this modification earlier. The tail edge of the heatsink gets considerably cool. Even a bit cooler than I was expecting, which now makes this area actually useful when running the freezer as a fridge.
If you notice there are 2 thicknesses of 10 foam sleeping mat stuffed down inside the fridge cover for additional insulation, there are 3 on the opening end, the compressor end does not need it.
Fold the front bottom edge of the butter compartment first, rear bottom corner of butter compartment second, then rear top edge of divide third & top front edge of the divide last.
Any heatsink over this divide will be better than nothing, even a couple of aluminium disposable baking trays will help make the butter compartment a bit cooler!
The above post was a cut & paste. These modifications were done quite awhile ago & the fridge has worked really well. Couldn't be happier. Also tried to reduce AM interference as well, but with mildly moderate success.
The fridge has been on 4000km of corrugated roads & every night we sleep the fridge is moved to the passenger seat. That's about 290 times now & 290 time back to the boot.
This test was done before I installed the larger thermal bridge (piece of aluminium sheet) into the butter area. This would now get very cold, my guess at least around -5°C if I did the same test again.
A torture test to see how long it takes to freeze to 10.5 kg of ice bricks to -22°C (lowest fridge setting. On previous tests thermometers I stuck in the fridge showed -24°C). Ambient over the days was 26°C morning & night, including ice bricks at the start. I also put a thermometer in the centre of the ice bricks as this area is slower to freeze.
24 Hours: fridge -11, centre of ice -2
36 hours: fridge -16, centre of ice -10
44 hours: fridge -20, centre of ice -16
46 hours: fridge -22, centre of ice -19
The fridge started cycling at 46 hours.
The bottom of the fridge looses more cold than the sides so I think I will be battling to get the centre of the ice to -22°C until I can come up with thicker insulation & mounting mechanism.
The back of the fridge near the internal light only got down to 0.2°C but the ice brick closer to the freezing area was frozen solid.
About half the time it was running off my old 80Ah car hattery (still in good condition) which was around 12.4 volts with a 1 amp charger trickle charging. Fridge current was 3.1 amps. So 1.768 kWh for the 46 hour test. I could hear the compressor running a touch faster on AC but not a lot in it, maybe maximum 10% faster.
Exhaustair from compressor was about 30°C (this was with the slower Noctua fan, not the last one I installed with higher capacity & pressure, & I have added a little bit more insulation).
A 120mm fan is the largest I could fit, & it runs continuously when the compressor is running, & off when the compressor is off.
The original fan had a thermostat so it would increase speed as the fridge needed more cooling.
The Noctua fans are so power efficient it's fine that they run the entire time the compressor is running. I just cut the wire, soldered & heatshrink.
With fridge efficiency my issue was because we are in a car only everything had to be as compact as possible. Insulating the fridge ment I needed less batteries, & insulation is light weight.
I think the next best thing was blow the dust out of the condenser & the rest of the compressor area. It was filthy. & that is a bit like the condenser having a blanket on it. We have 3 ARB compressors, & an air tank, that we run in parallel (up to 90 amps).
Third or even in second place was the very poor design where air would circulate back around the fan. A 2 cent design failure, just needed a simple baffle.
The fan. Getting more air to flow through will help a bit. It's hard to say how much, but the exhaust air always felt a bit cooler with the larger fan. So maybe that helps a degree or two within the fridge.
I also rewired the 12volt wire inside the fridge with 12awg. The original wire was barely 16awg. Also replaced the standard 2 metre cable which was 16awg as well. So there was about 0.17 volts saved. Shoved in a 7amp circuit breaker while at it.
I have modified the aluminium angle since these photos, tapering it down a bit towards the condenser fins. But it is splitting hairs looking for efficiency.
This was the only spot I could fit the circuit breaker on this fridge. The Anderson plug is permanently bolted on. Now I run 12awg or heavier to power the fridge.
I looked at the fridge today to see if there was anything useful I could add. Not really other than I washed the filter I put in & it was pretty dirty. It's a pretty open filter, but it is one layer of dust defence.
If you have had the fridge for years & used it a lot, it's going to be filthy inside. The back of the fan blades will also have a good layer of dust as well. Just like the inside of a computer, dust everywhere.
Thanks for sharing..