Running Fridge of inverter?

Discussion in 'Heating and Air-Conditioning' started by Thepips, Dec 2, 2007.

  1. Thepips

    Thepips Trade Member

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    I've been working on my Monaco Knight over the weekend and got to thinking about reducing the amount of LPG we get through. One of the biggest users seems to be the fridge. It's a big 4 door Dometic.
    It's not on the inverter circuit but I can't think of a good reason why it shouldn't be. The fridge has a 5amp fuse so at 110volt can't be drawing more than 550watts which is a lot less than the microwave. The inverter is 3000 watts and I've 4 x 6 volt 125 a/h batteries. Ok I can see you wouldn't want to run it on inverter all the time but why not while driving? Or for a short time while on the ferry?
    By my reckoning the batteries should last at least 3-4 hours. If I'm reading the manuals correctly the engine alternator puts out 100amps which charges all of the chassis and leisure batteries.
    It could be quite sophisticated with a relay operated changeover switch so when the engine is running the fridge is powered by the inverter. Turn the engine off, the relay disengages and the fridge loses power so automatically switches to gas. Start the gennie or go onto hookup and the fridge would run of that.
    Will it work? or I am missing something fundamental?

    Cheers
    Doug
     
  2. andyman

    andyman Read Only Funster

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    My own guess is that it is not connected to the existing circuit is as you have said, current draw. What hapens when you are driving at night, heater blower, lights, radio etc. I dont think the alternator will keep up.
     
  3. Thepips

    Thepips Trade Member

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    A very good point indeed.
    Maybe I should consider a simpler solution. Just run a second power point into the fridge cabinet which is fed by the inverter. Plug into the inverter when I know the alternator would be able to cope. At all other times simply plug into the existing socket.

    Thanks for input

    Regards
    Doug
     
  4. olley

    olley Funster

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    Hi that's what I can do with mine, when we are driving I sometimes have the inverter turned on, and it powers all the electrical circuits 110/230v so the fridge would automatically run on electric. I should remember to switch the battery charger off, but forget most of the time.:BigGrin:

    Have be honest though, electric or gas its just as inefficient, if your not burning LPG, your burning petrol which is dearer. The 8.1 GM's have 140amp alternators, so plenty of power.

    Olley
     
  5. Geoff

    Geoff Read Only Funster

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    Hi Doug.
    Couple of other factors to consider, electrical efficience (or inefficiency). Losses in the system mean draw from the alternator will be much greater than the rated input of the appliance. Also automotive alternators are rarely designed to output anywhere near thier rated value for any length of time, I wouldn't be happy running a standard type alternator at much more than 20-25% of max output continuously.

    Regards Geoff.​
     
  6. Keith and Debs

    Keith and Debs Read Only Funster

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    Hi

    Why do you need to run the fridge/freezer whilst driving.. We just turn ours off never had any probs with food thawing or freezer defrosting etc... It was even okay on the crossing from Bilboa to Portsmouth... saves a load of LPG..

    Keith n Debs
     
  7. pappajohn

    pappajohn Funster Life Member

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    if its an onboard genny then just switch off the charger and run that instead, or am i missing something :Doh: i dunno cos my kontiki fridge runs on 12v while travelling but then my fridge will fit inside yours.:Rofl1:

    john.
     
  8. Thepips

    Thepips Trade Member

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    It just seemed daft to me to use LPG or diesel when driving. I know the alternator takes some power to drive it but that can't be as much as running the fridge/freezer on LPG can it? I then also got to thinking about how to keep the freezer on while on the ferry or going through the tunnel. Don't think they'd be too pleased if I ran the gennie:Laughing:

    Thanks anyway
    Doug
     
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