240v vs 12v fridge in a motorhome or caravan

240v fridge or a low voltage fridge for your  motorhome or caravan.

Yesterday I was asked for my advice on the purchase of a refrigerator for a motorhome. Under consideration were a 240v 220ltr household fridge and a 12/24v 220ltr Danfoss compressor based unit (Waeco). I was asked to comment on the economics of each option.

I remembered reading an article written by Val Rigoli some years ago on exactly this subject. Val actually did some real tests using real fridges under controlled conditions. The data presented in this discussion is from these tests carried out by Val (the prices of the units are probably 3 –  4 years old).

Low Voltage Fridge

The test conditions …

The 240 volt fridge was an LG brand rated at 140 litre capacity – costing $299.00

The low voltage fridge was a 140 litre Waeco brand, running a Danfoss compressor – costing $1,595

Both fridges were located in the same room where the temperature was maintained at 26 – 29 deg C. The exact the same content was loaded into each fridge.   They were run for several days prior to the test and during this time the internal thermostat finely adjusted so that each maintained an internal temperature of 5 deg C.

The 240v fridge was powered from a pure sine wave inverter attached to a 12v power supply and the supply for both the low voltage fridge and the inverter for the 240v fridge was maintained at a constant 13.65v throughout the entire test.

A PC based logging system was attached to the power supply of each fridge to track the power usage. The test was run for 24 hours.

The Results

LG 240v Fridge – 99.6Ah total (at 12v) with an average draw of 7 amps (whilst running)  and a peak (start-up) current of 42.2 amps.

Waeco low voltage Fridge – 42.2Ah (at 12v) with an average draw of 4.5 amps (whilst running).

Economic s

The economics can only be evaluated if the type of supply is known – for example, if you plan to drive from caravan park to caravan park, using their 240v power when you stop, clearly the 240v fridge is the better option. Obviously this is not the purpose of this test.  Let us assume you plan to run on solar energy more or less exclusively …

Assuming that all other loads can be ignored you are going to need about 50 Ah of charge each day to supply the 12v fridge and about 115 Ah of charge to run the 240v fridge.

The 240v fridge will run from 300watts of solar if it is sunny for 5 hours EVERY day – I recommend adding 50% to allow for less than 100% sunny days – thus 450watts to be safe.

The 12v fridge will run from 130watts if it is sunny for 5 hrs per day – add 50% and get a total of 195 watts of solar.

So at $10/watt for the panels , this works out at $1950 for the low voltage, and $4485 for the 240v fridge.

Conclusion

Fridge Purchase Cost Solar Cost Total
Low voltage $1595 195w = $1950 $3545
240v $299 450w = $4500 $4799

This ignores the additional cost and weight of the added batteries required to store all this power for the fridge to run at night and for when it is overcast.

So on pure economics, the low voltage fridge wins by over $1000 over the seemingly cheaper 240v fridge.  Clearly this only valid if you plan to run on solar alone.  If you plan to use a petrol generator to supplement the solar generation, the entire equation becomes far more complex.

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26 Responses to “240v vs 12v fridge in a motorhome or caravan”

  1. Hobo Says:

    Just an update on this information. As has been pointed out, solar panels are getting less expensive. $10/watt is now top dollar. I have seen prices as low as $3.50/watt. This of course changes the balance – the 240v fridge becomes more economical when panels get to at about $5.00/watt. This of course still leaves the issue of room on the roof for them.
    Gavin

  2. chris Says:

    Hey guys, well you are certainly living the dream, we are working to get where you are, not exactly where you are , but somewhere out there.
    I was curious why you poo pooed the gas fridge in the tropics, we are about to head north with our slide on camper which has an old but working gas fridge.
    cheers chris.

  3. Hobo Says:

    Our experience with Gas fridges is not good. While I understand that small gas fridges work ok in hot conditions – larger ones deliver sour milk and warm beer. I would never recommend a large gas fridge for a motorhome.

  4. john Says:

    hi guys
    on fridge subject
    i have a westinghouse 230 ltr fridge 240v //150w
    i have 6 pannels 80w in series to give 24v

    inverter draws .6 amp

    the pl 40 ,,on just checking said that yester day gave me

    66 amps in

    34amps out

    6 pannels on roof cover area 3.6mtrs x 1.5mtrs
    with a gap down the middle of about 0.4 for walkway

    my pannels came from importer in north sydney
    80w panels@ $250 each = $3.1 per watt

    so for me the system works
    hope this helpfull

    and yes i can give adress for suplier ifany one wants it .no problem

    cheers
    john

  5. Hobo Says:

    Thanks John,

    The recent dramatic drop in the cost of solar panels clearly puts a large dent in the economic argument for using only low voltage refrigeration.
    I wonder just how low the cost of panel will drop.

  6. Val Rigoli Says:

    Hi Guys, I must update the article, it’s still on my website. As the years have gone by and the new larger household 200L + fridges are now much more efficient, they can be a viable fitting in a caravan or motorhome as long as you buy a new one with the *new* star rating of 2.5 or better, or 4.5 stars in the old star rating.

    Best regards,
    Val Rigoli

  7. Hobo Says:

    Gidday Val,
    It’s been a while!
    I agree that the latest 240v fridges are a far more viable option – especially given the now much lower cost of large solar panels. I personally prefer the Danfoss based fridges – our one (that you sold us in 2004) is still working perfectly and has never missed a beat!

    Cheers
    Gavin

  8. john Says:

    hi gav
    ok 20th sept i wrote about the fridge 240 v 24
    i put the last of solar up last year….10x80w pannels
    so running 800w@24v
    im using les than 10% of my capacity each day with fridge
    my daily us e including tv fridge computers is lights etc is drops my system to about 80% capacity a day
    this is nothing when i have estimated a daily use of 30%
    the solar ha s no problems during a normal day off recharging the batteries
    the cost off a 24v fridge exceeds the cost off any solar panels on the market now
    and not only cost…i can pick up same fridge at any major town ifffff it decides to die
    that you cant do with 24v
    so far sytem been up and running for last 2 years
    not a problem
    thanks to many weeks off brain drain and listening to your advise on pl 40 etc
    i have 440 amps at 24v
    ok the cost was about 5k to set up
    but when you concider the cost of a 24v fridge
    and the avaliability

    i think this was the better choice

    we will be on the road full time in june
    …..making the big break
    ha d many trials
    anothe r 2 weeks comming up in march

    ok thats all
    see you on the road some time
    cheers john

  9. Les Says:

    Hi All,

    I read today Val Rigoli’s test on the 240v vs 12v fridges which was carried out about nine years ago. Has anyone carried out a recent (last year, say) comparison test. The reason I ask is that I too find it difficult to justify spending $2000 on a 12v fridge when I can buy e.g. a Samsung 212ltr 240v fridge for $400 and spend the other $1600 on an inverter which I may well buy anyway to power other 240v items like a microwave, TV etc.

    I realise that there is an inherent energy loss through an inverter with the pure sine wave models I have been looking at (Victron) quoting around 8% at 12volts and 6 – 7% at 24volts.

    I would have thought (please excuse my ignorance) that if both units are using approximately the same amount of power (say 120 watts) which I believe is 10amps @ 12volts and 5 amps @ 24volts then one should only have to make up the deficiency of the inverter for the 240volt fridge?

    Is the BD50 Danfoss compressor considerably more efficient than a 240v compressor? I do know that almost all 240 volt fridges now are “frost free” and when in defrost mode they draw considerably more current (170 watts?) however I’ve found it very difficult to discover the “duty cycle” (or whatever you call it) of a modern fridge. I’ve read somewhere that fridges are tested at two different ambient temperatures (20 & 32 degrees C I think).

    What I’d like to know is how much energy does e.g. the previously mentioned Samsung 240 volt fridge use compared to a similar size 12/24v fridge?

    One other question:- am I better to run my batteries / solar panels etc. at 24 volts or 12 volts and why?

    Many thanks for your indulgence,

    Les Trask

  10. Hobo Says:

    Hi Les,
    Some really good discussion points here.
    First let me say that I don’t know the exact figures for the Samsung fridge vs a danfoss. But I can tell you that I went (part way) down the 240v fridge road myself a few months ago.
    I actually purchased a 212 Ltr Samsung fridge freezer and did some tests on it. The big issues I found were:
    1. The electronics on the fridge needed to run all of the time. This ment that the inverter would never go into standby mode.
    2. The compressor when starting produced a huge spike (it would not start on a 400w inverter).
    3. The actual framework of the fridge did not look to me like it would handle being bounced around. The compressor was suspended on rubber mounts but not restrained. Of course this could be addresses, but I felt that the long term survival would be doubtful. The inside if the fridge was also very thin plastic and I felt likely to object to hash treatment.

    To add to this I decided that I did not like the idea of the main fridge running on our main (Victron) inverter. Just an eggs in one basket thing really.
    Given all of this and the fact that we had had 9 years of uninterrupted use out of our old danfoss fridge, I decided to buy the same (Waeco) fridge again. The Samsung is still sitting unused at our property.
    I did do some very rough calculations on power usage and came to the conclusion that the Samsung would consume about one third more power each day than the same sized danfoss equipped fridge.

    I hope this helps – and if you still want a Samsung, I have a brand new one for sale.

    For a larger motor home 24v is far superior – no question. If the vehicle is natively 24v it is a slam-dunk, you should not even consider 12v. If the vehicle is small and engine alternator is 12v, then 12v might be best.

  11. Hobo Says:

    Forgot to mention to check out the prices on Waeco upright fridges at ryda.com.au – best I found anywhere.

  12. Les Says:

    Hi Hobo,

    Many thanks for that info. My partner and I are just starting out on the road to convert a ’93 Hino Rainbow into a motorhome and like many others I suppose have many questions on the best/most economical way to achieve what we want. One of the downsides of any upright fridge I imagine is that all of the cold air runs out when you open the door. It’s a shame you can’t buy an upright with a clear door and external light switch so you can check out what’s inside without opening the door. As I often tell my 16 year old son; it’s a refrigerator, not an airconditioner!

    Speaking of which, I just got off the phone to an airconditioning guy who I asked about using a domestic split system and who told me that a) you can’t lay the compressor/condensor unit on it’s side as it wrecks them (had visions of roof mouning on it’s side) and also that they don’t like being shaken around much, so it looks like we’re back to a $2000+ roof mount system 🙁

    Thanks too for the tip on Ryda. Will check them out. Great, informative website too!

  13. Hobo Says:

    One great thing is that solar is so cheap these days, there is very little reason to do anything other than cover the roof with panels and simply forget about lack-of-power issues.
    The nice thing about the Victron inverters is that they will borrow power from the batteries to start a large air con unit, this allows for a smaller (and quiter) generator.
    I have a 2KVA Victron and a 2KVA Honda generator and could not be happier with the pair.

    Gavin

  14. Paul Says:

    Hi Hobo,

    This is a little off the subject but you seem to have more knowledge than many “experts”. Is it feasible to run a household 240v chest freezer via an inverter from my car battery. I need to transport 30×5 litre tubs of ice cream(gelato actually) from the supplier to our cafe (yes the one we’re trying to sell so we can buy our bus). The trip will take about 4 hours and the freezer can be brought down to temp on 240v prior to departure. Currently we use a large styrofoam box with dry ice but the ice cost is ridiculous…..so I’m thinking out of the square. I don’t mind spending money on an inverter as it’ll come in handy later on….:)

  15. Hobo Says:

    The short answer is yes. There is no problem running a household freezer from an inverter. It is particularly appropriate and simple in the situation you describe as the vehicle alternator is always running when the freezer is running. This removes the need to energy storage calculations and considerations.
    Some things to keep in mind…
    * The inverter will need to be of good quality (not some nasty ebay special) and be sized to allow the freezer compressor to start. Try before you buy is the best option. If the freezer starts ok, it will run ok.
    * Be sure the inverter is wired to turn off then the engine is not running – this will avoid a flat starter battery (use a relay to avoid damage to the key switch).

    The other option is to get a fridge expert to convert a second hand chest freezer to low voltage by swapping out the compressor for a Danfoss 12v/24v compressor. This would be more expensive, but more reliable.

    Drop me off an ice cream next time you are passing.

  16. Paul Says:

    If you’re ever down Taree way let us know, we’ll have the best Italian gelato for miles around (and the best coffee in town)….Ciao Bella Cafe.

  17. Hobo Says:

    Your on! 🙂
    Just tried to find you on the web … what, no website??? We need to talk! 🙂

  18. Marken Says:

    Pauls query about running a household freezer from an inverter makes me wonder why you would go to such expense.
    It is common knowledge that during a power cut a freezer would keep its contents frozen for many hours so long as the door is not opened. In Pauls case if he managed to turn the freezer to maximum for a couple of hours before the trip then his ice cream (gelato) would last the distance.
    Is this not the case or am I missing something?
    BTW when we eventually hit the road and start to travel seriously we will be looking up the Bella Cafe in Taree.

  19. Paul Says:

    You can find us on Facebook……Ciao Bella Cafe, Taree……I thought about building a website but we’re not really in a position where a website would be a major asset. I started to put one together and then went the Facebook route instead.

  20. Johann Says:

    This is not a real test at all how much power a fridge will use.
    This was a test how much power a fridge and power supply/ inverter will use. Of course a inverter will consume power as well as any other device that will change a voltage into another voltage etc etc.

    This still will not tell me how much power a 12 volt fridge will use compare to a 240 volt fridge and forget about the inverter at this moment and concentrate on the fridges alone.

  21. Hobo Says:

    The point of the article was not to look at fridge energy consumption as much as battery drain (in a caravan/motorhome type environment). The total battery drain for a 240v household fridge includes the losses suffered due to the need to convert the DC to ac for the 240v fridge.
    Just as a matter of interest – even the so called DC fridges (Danfoss etc) actually have AC motors in them, the inverter for these is built into the controller.

  22. Terry Says:

    This information is now so dated it must becoming an embarrassment, perhaps an actual updated test is needed to reflect 21st century technology rather than the very outdated technology fridge that was used for the original experiment by Val Rigoli. Even Val has said that the information was outdated 4 yrs ago, yet you have not modified it or mentioned the date of testing or that it was using very old technology equipment.
    Perhaps a 250ltr fridge/freezer using the latest HC gas and inverter technology up against an equivalent sized low voltage fridge? Same method of measurement, from the battery actual watt hrs used by each including the inverter losses, but at least use a modern design inverter with min standby current

    T1 Terry

  23. Hobo Says:

    Yes – I agree that the data presented here is now quite dated. However, I did purchase one of the latest Samsung fridge/freezers with the intention of installing it and replacing my existing (aging) danfoss based fridge. I did quite a lot of testing and found the following…
    – The Samsung consumed about 30% more power when running in the same conditions.
    – The electronics in the Samsung meant that it HAD to be powered all the time – thus inverter standby was not an option (this contributed to the 30% additional power usage).
    – The build quality was not up to mobile use – while fine for the average kitchen, the mounting of the compressor was such that I seriously felt it would break on corrugated roads. I also had my doubts about the casing and its ability to withstand mobile use.

    While the 30% extra power could easily be accommodated by adding solar panels, the associated increase in depth of battery discharge is a little more difficult to offset and calculate the costs for (including additional weight issues).

    So I now have a really nice Samsung beer fridge in my workshop (and – for a while, a slightly grumpy wife) – I also have a new Danfoss based fridge/freezer in the bus that was built for mobile use.

    Cheers

    Hobo

  24. Leon Says:

    Hi Hobo,
    These fridges look interesting. What do you make of them?

    [Edit] Link – no longer exists.

    Leon

  25. Leon Says:

    Hi Hobo,
    Hope I do not over do it, but I also know about these eutectic fridges. And I respect your opinion. So would like to know what you think about this option?

    http://www.ozefridge.com.au/
    Thank you
    Leon

  26. Hobo Says:

    This is interesting. Not really enough info for an informed technical evaluation, but I like the concept.
    This “Storage” type of refrigeration has been used on remote Australian Stations for over 50 years. The ones I worked on had no thermostat, the compressor ran as long as there was power (typically a generator running for about half of the day). They froze salt saturated water that held the temperature inside the unit for the hours that the generator was not running. A clever design for a time before 24hr power in remote locations.

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