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).
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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Tags: battery, Caravan, Energy, Motorhome, Power, Solar
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Thanks and happy Motorhoming - Gavin & Tracey.
May 12th, 2010 at 2:04 pm
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
May 29th, 2010 at 11:32 am
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.
June 5th, 2010 at 10:26 am
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.