Dometic fridge on 12v - does it work?

Discussion in 'Rapido' started by sirhandel, Jul 9, 2009.

  1. sirhandel

    sirhandel Read Only Funster

    Joined:
    Nov 28, 2008
    Messages:
    32
    Likes Received:
    0
    Location:
    Chippenham, Wilts
    The handbook for my Rapido 783F says that the fridge and freezer should not be used on 12v unless the engine is running. Also my dealer said this at handover.
    Is this just to preserve leisure battery charge or is there a technical reason why the fridge won't work from the leisure battery without the engine running? I'm not concerned about running the leisure battery down as I've had a solar panel and second battery fitted.
    Anyone know?
     
  2. Munchie

    Munchie Funster Life Member

    Joined:
    Jul 28, 2007
    Messages:
    8,529
    Likes Received:
    11,668
    Location:
    Champagnac-La-Riviere
    On our three vans two Burstners and now an Itineo the fridge runs on 12v only when the engine is running. You will find the fridge is not as efficient when on 12v as it is on gas or 240v. :BigGrin: BTW fridge is quite miserly on gas we have found.
     
    • Informative Informative x 1
  3. johnsandywhite

    johnsandywhite Read Only Funster

    Joined:
    Jul 29, 2007
    Messages:
    2,348
    Likes Received:
    15
    Location:
    Doncaster/Spain
    :Cool: If you leave it switched onto the 12V battery? It will NOT be as efficient and will very soon deplete the battery. There is MORE than 12 volts available when the motor is running. :Wink:
     
  4. SandJ

    SandJ Read Only Funster

    Joined:
    Sep 14, 2007
    Messages:
    1,558
    Likes Received:
    518
    Location:
    North Yorks
    My belief is, if you are on 12v it only keeps it at an acceptable temperature. It works better if on hook up or gas first or if the items are already cold/frozen.
    I would not reccomend trying to use on 12v whilst engine is stopped.
     
  5. scotjimland

    scotjimland Funster Life Member

    Joined:
    Jul 25, 2007
    Messages:
    28,934
    Likes Received:
    25,574
    Location:
    .
    Hi

    I agree with previous posts.. but if you want to utilise the free solar energy another option is to install a small inverter for the fridge and run on 230v..

    Much depends on the size of your solar panel and battery bank as to whether this is practical or not .. need more info.

    Or, go the whole hog and change the fridge to a 12v dc compressor model ..

    Jim
     
  6. The Wild Ones

    The Wild Ones Read Only Funster

    Joined:
    Jan 4, 2009
    Messages:
    76
    Likes Received:
    0
    Location:
    Oxfordshire
    Our 3 way fridge is only thermostatically controlled via Gas & 240v, hence runs continuously when on 12v setting (stops running when engine turned off). So as mentioned looks like 12v operation is only to kick start it whilst travelling, as others have said ours appears to run a lot colder on Gas & 240v.
     
  7. sirhandel

    sirhandel Read Only Funster

    Joined:
    Nov 28, 2008
    Messages:
    32
    Likes Received:
    0
    Location:
    Chippenham, Wilts
    Thanks for the informed replies. I didn't realise that the fridge is less efficient at 12v. We (wife+I) are relative newcomers to this wonderful world of MHing. I'm just retired (last week) so just need to get the wife retired also, 2 lads (20+18) off our hands and we can be off.
     
  8. Terry

    Terry Funster

    Joined:
    Dec 27, 2007
    Messages:
    10,722
    Likes Received:
    6,224
    Location:
    South yorks
    Hi most fridges run on 12v while the engine is running because they are wired via a relay that will open when getting the larger 12v (approx 13.5/8 v )supplied by the alternator,then shutting off when stopped so as not to flatten your battery, much the same happens to charge the L/B while engine is running-- If both fridge and l/b work you will have a twin or two relays :thumb:
    terry
     
    • Like Like x 1
  9. Tony Lee

    Tony Lee Read Only Funster

    Joined:
    Sep 28, 2008
    Messages:
    274
    Likes Received:
    1
    On 12V, up to 15Amps (depending on the brand and model) is taken from the battery so if it is run without the alternator charging, the battery would be flat in a few hours. Most have no 12V thermostat so the draw is continuous,

    BTW, running it on 240V via an inverter fed from the battery may in fact run the battery flat faster than on 12V because often the 240V heater is a higher wattage than the 12V one.

    When you are parked without EHU, gas is the only practical option.
     
  10. winchman

    winchman Read Only Funster

    Joined:
    Jul 9, 2009
    Messages:
    25
    Likes Received:
    0
    To put some sums in it assuming the fridge is 1000w
    If the fridge uses 12 volts thats 83 amps
    If the fridge is ran from the mains at 240 volts thats 4.1 amps
    So mains is the best, the reason why some are wired to be ran only when the engine is running is that the alternator will produce enough to run the fridge , but the battery alone wont run it for long.
    So if no hook up use gas, they operate on 12 volts as you shouldnt run the gas whist moving.
    It would be interesting to see what current a 12 volt compressor fridge draws?
     
  11. Tony Lee

    Tony Lee Read Only Funster

    Joined:
    Sep 28, 2008
    Messages:
    274
    Likes Received:
    1
    100W would be more like it - so around 10 amps is typical, but some fridges are higher.

    on 240V might be around half to three-quarters of an amp.

    Compressor fridges on 12V - usually around half the current, but also is only running for half the time so is a proposition off solar whereas a 3-way on 12V is just too heavy a load.
     
    Last edited: Jul 10, 2009
  12. scotjimland

    scotjimland Funster Life Member

    Joined:
    Jul 25, 2007
    Messages:
    28,934
    Likes Received:
    25,574
    Location:
    .

    For Information

    Dometic 3 way fridge

    Energy consumption @ amb temp +25°C (kWh/24h) 2.6 Energy consumption gas (g/24h) 270 Max input 12V (W) 120 Max input 220V (W) 125


    So draws 10A on battery power and 0.56A on mains

    Similar sized 12v dc compressor fridge

    Average power consumption 45W.

    My suggestion of running from a small inverter was qualified,

    bear in mind, on mains supply the fridge is cycling so won't use as much power as on 12v when it is on permanently.

    Allowing for inverter losses, assume it uses 132 watt, = 11A draw on the battery .. In order for this to be sustainable you would need a large solar array and a large battery bank .. unless you already have this, an impractical solution.

    On the other hand a 12v DC Compressor only draws 45watt .. = 3.75A.

    Downside is there is no gas backup.. much depends on your style of camping and whether you want to invest in solar ..
     
    Last edited: Jul 10, 2009
    • Informative Informative x 1
  13. Bulletguy

    Bulletguy Read Only Funster

    Joined:
    Feb 7, 2008
    Messages:
    2,051
    Likes Received:
    4
    Location:
    Cheshire/Staffs
    Forget the physics and mathematics. Simple answer to your question is your dealer is right.

    Leave it switched on when the vehicle stands more than a few hours and you will have nothing left in the leisure battery. Run on 12volt whilst on the move, and gas or 240v when parked up.
     
  14. Tony Lee

    Tony Lee Read Only Funster

    Joined:
    Sep 28, 2008
    Messages:
    274
    Likes Received:
    1
    OP may be just as sceptical about dealer advice as many of the rest of us and in any case, may appreciate knowing the physics and maths behind the advice.


     
  15. Chris Woods

    Chris Woods Read Only Funster

    Joined:
    Jun 6, 2009
    Messages:
    10
    Likes Received:
    0
    I just checked the spec in my fridge handbook and as others have noted the 12 volt option is typically 120 Watt That means it needs 10 amps exactly at 12 volt. Also it should run almost as cold as when on mains as the element ratings are similar. It will be less efficient however because (on mine) there is no thermostat in the 12 volt system, so it draws power continuously. Fine for travelling, not ideal for regular use.
    Our van, like most, doesn't allow 12 fridge use except when moving because it would drain the leisure battery, so the fridge 12v supply is only active when the engine is running.
    Theoretically a second battery and a solar panel would work, although the fridge supply would have to be rewired to take its power from the new dedicated supply instead of the van's existing one. However a solar installation to supply 10 amps 24/7 in our cloud conditions would be almost industrial in scale, and cost more than a lifetime's supply of gas so I doubt the idea is a runner unless you can find a much more efficient fridge.

    Chris
     
  16. chris2210

    chris2210 Deleted User

    3 way fridge - go with gas.

    Hiya,

    All the above seems sensible, I've had one on a canal boat for many years and have abandoned using it on 12v despite a battery bank of 5 x 110 Ah domestic batteries

    - The electric heater element is quoted at 95w, which seems consistent with the 125 - 150 watts consumption for the fridge quoted on various sites, so say 10 amp to 12 amps @ 12 v - in reality I'd found it was aboput 1/2 that once cooled, but voltage drop can quickly become an issue - and it didn't get very cold in any case.

    The theories on inverting also seems sensible - you lose power converting 12v to 240v - (notice how hot your inverter gets when it's on ? - that heat is coming from somewhere - when the engine's off from your battery, when the engine's on it's burning diesel. )

    I'd suggest that you go with gas, and perhaps invest in upping your gas-carrying capacity - but just beware that it's dangerous stuff in the case of an accident so you may want to think carefully on the safety aspect.

    In my experience the gas consumption is pretty low when compared with a cooker, water heater etc.

    Does anyone have experience of the Dometic 42xx series fridges ?

    They are about 880 mm high x 500mm x 500mm - how much power do they actually use and do they get really cold ?

    Regards


    Chris


    Late edit, This seems to be what Chris Woods said just above , so apologies for the repetition.

    Chris
     
    Last edited by a moderator: Jul 11, 2009
  17. Tony Lee

    Tony Lee Read Only Funster

    Joined:
    Sep 28, 2008
    Messages:
    274
    Likes Received:
    1
    Chris, just to divert a little now that the original question has been covered - did you have a gas alarm fitted inside your boat. I ask because unlike the regulations here in OZ, my Hobby doesn't have a door vent (so I immediately installed an alarm) so I wondered if Europeans had a more relaxed attitude to gas use inside a well-sealed enclosure.
     
  18. sinbad1

    sinbad1 Deleted User

    Tony.

    Boats have to be certificated, this certificate lasts for four years and covers several safety areas,
    Gas
    The gas system is checked throughout and must be compliant.

    Gas must be stored in a separate locker (sealed from the inside) and must be vented to the outside at the lowest point in the locker.

    the whole system must comply including a gas leak test,fridge vents etc.

    like an mot you would need to correct any problem before a certificate of compliance is issued, and if not corrected in a given time you would not be allowed to use the waterways.

    As for gas detectors, these are not part of the certification (unless the rules have changed) , having said that a boater would be foolish not to have one since any gas leak would tend to build up in the bottom of the boat.

    At the moment there is no requirement for such a safety certificate for motorhomes, maybe there should be?

    regards
     
    Last edited by a moderator: Jul 12, 2009
  19. aido

    aido Read Only Funster

    Joined:
    Sep 4, 2007
    Messages:
    70
    Likes Received:
    1
    Location:
    Co. Wicklow
    post subject

    As there seems to be a lot of experts on fridges I have a question.

    The fridge in my MH runs on 12v and gas . but wont stay running on mains 240v seems to run for a while then tries to change to gas, this is only a recent problem it was ok.


    It is an electrolux AES.Fridge with small freezer on top.
    Any idea what might be wrong.?
     
  20. aido

    aido Read Only Funster

    Joined:
    Sep 4, 2007
    Messages:
    70
    Likes Received:
    1
    Location:
    Co. Wicklow
    post subject

    It is an electrolux AES.Fridge with small freezer on top.
    Any idea what might be wrong.?
    __________________
    Obviously not :Doh::shout::shout:
     
Loading...
Similar Threads
  1. Gemini
    Replies:
    11
    Views:
    445

Share This Page