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hellbird503's avatar
hellbird503
Explorer
May 13, 2017

Power Inverter

I just installed an apartment type refrigerator and want to install a power inverter to run it while I am traveling. What I need to know is what size cables do I need to hook it up to my batteries. I will need about 12ft. of cable and the power inverter is 1500 watts. Thanks for any help, Dave

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  • Gdetrailer's avatar
    Gdetrailer
    Explorer III
    May 13, 2017
    brulaz wrote:
    Gdetrailer wrote:
    brulaz wrote:
    Was looking at a 10-11 cuft LG frig that might be crammed into our trailer.

    The Energy Star rating was 400KWH per year. Which I guess translates into only 46W or 0.38A at 120VAC?

    Seems hard to believe ...


    Your assuming the fridge compressor operates 24/7/356, it does not.

    No, I'm assuming the Energy Star rating system takes all that into account and gives you an overall average. No idea if that's true or not.


    In actual use the fridge compressor should run only about 20-25 minutes per hr.

    The defrost cycles typically will run once for about 10 minutes per every 10 hrs of compressor operation.

    You will find that your LG will actually be drawing about 80W-90W while the compressor is running or about .75A at 120V..

    Many of the newer fridges are much more energy efficient, one way this is done is to run some of the refrigeration tubing (heat side) around the door openings. This replaces the older electric heaters used to reduce sweating at the door.


    Energy star is an "average" of 365 DAYS of "usage".

    So 400 Kwhr usage over 365 DAYS, but the compressor is not RUNNING ALL DAY. So your "math" is flawed by "assuming" 24/7/365 COMPRESSOR OPERATION..

    In reality the 400 Kwhr is used 20-25 MINUTES per hr or 600 MINUTES per DAY (which is 10 HOURS MAX PER DAY).. or 3650 HRS PER YEAR..

    As I stated, the REAL number is closer to .75A at 120V and not what you came up with (.38A at 120V).

    As a reference, my 10 cu ft home fridge has a name plate rating of 1.1A at 120V, BUT my MEASURED draw was .8A at 120V..
  • brulaz's avatar
    brulaz
    Explorer
    May 13, 2017
    Gdetrailer wrote:
    brulaz wrote:
    Was looking at a 10-11 cuft LG frig that might be crammed into our trailer.

    The Energy Star rating was 400KWH per year. Which I guess translates into only 46W or 0.38A at 120VAC?

    Seems hard to believe ...


    Your assuming the fridge compressor operates 24/7/356, it does not.

    No, I'm assuming the Energy Star rating system takes all that into account and gives you an overall average. No idea if that's true or not.


    In actual use the fridge compressor should run only about 20-25 minutes per hr.

    The defrost cycles typically will run once for about 10 minutes per every 10 hrs of compressor operation.

    You will find that your LG will actually be drawing about 80W-90W while the compressor is running or about .75A at 120V..

    Many of the newer fridges are much more energy efficient, one way this is done is to run some of the refrigeration tubing (heat side) around the door openings. This replaces the older electric heaters used to reduce sweating at the door.
  • MrWizard's avatar
    MrWizard
    Moderator
    May 13, 2017
    now you have the real info
    And it falls In to line worth everything we have been saying
    The 1500w inverter is that continuous or peak
    I also have the trip lite 1250 power verter , very good inverter not a little chopper like you buy at the car parts store
    It weighs 22# and has a big transformer inside, it is made to power motors, power tools, compressors etc..
  • hellbird503's avatar
    hellbird503
    Explorer
    May 13, 2017
    Okay, looked at the compressor plate and the numbers are: 115-60hz,1 ph,lra,11a. I also found a service data sheet with the paperwork which says Amps(running) 0.8 to 1.5
  • Gdetrailer's avatar
    Gdetrailer
    Explorer III
    May 13, 2017
    brulaz wrote:
    Was looking at a 10-11 cuft LG frig that might be crammed into our trailer.

    The Energy Star rating was 400KWH per year. Which I guess translates into only 46W or 0.38A at 120VAC?

    Seems hard to believe ...


    Your assuming the fridge compressor operates 24/7/356, it does not.

    In actual use the fridge compressor should run only about 20-25 minutes per hr.

    The defrost cycles typically will run once for about 10 minutes per every 10 hrs of compressor operation.

    You will find that your LG will actually be drawing about 80W-90W while the compressor is running or about .75A at 120V..

    Many of the newer fridges are much more energy efficient, one way this is done is to run some of the refrigeration tubing (heat side) around the door openings. This replaces the older electric heaters used to reduce sweating at the door.
  • brulaz's avatar
    brulaz
    Explorer
    May 13, 2017
    Was looking at a 10-11 cuft LG frig that might be crammed into our trailer.

    The Energy Star rating was 400KWH per year. Which I guess translates into only 46W or 0.38A at 120VAC?

    Seems hard to believe ...
  • Gdetrailer's avatar
    Gdetrailer
    Explorer III
    May 13, 2017
    MrWizard wrote:
    That 6 amps is wrong, did you look at the back of the fridge and get the numbers of the plate on the compressor

    My 7.5 cu ft apartment fridge draws approx 1amp at 120vac, that's 10+ amps into the inverter
    But the start up surge aka lock rotor amps of the compressor is 10+ amps 120v, that's 100 amps start surge off battery power into into the inverter

    6 amps might be the start surge, which would be very low ( I like that )
    Running load will be less

    Put the inverter close to the batteries, and run an extension cord to the fridge for the low amp 120v


    I suspect the name plate lists the MAX amperage..

    That most likely includes the defrost heaters.

    The compressor should be 1A-1.5A run and startup surge would be somewhere around 9A-11A at 120V (that is what I measured on mine).

    The defrost heater on mine is 250W but some fridges have higher wattage defrost heaters.

    My setup I used a Tripplite PV1250, gives me lots of headroom for the startup surge and added bonus of a load sense power save feature which allows the inverter to turn on/off with the AC load.

    I used 1/0 extra flex wire and 6ft counting both pos and neg wire..

    The setup works very well and we are pleased with it.

    Don't skimp on the inverter or the 12V wiring, skimping there will result in a lot of frustration on your part.
  • CA_Traveler's avatar
    CA_Traveler
    Explorer III
    May 13, 2017
    A 6A AC draw??? That is huge, resulting in about 70A DC. The modern common res refers like the Samsung (about 19 cu ft) that are being installed are 1A draw and use 100-150Ah in a day when on the inverter. And they run on a MSW inverter which many rigs have. Will your refer even run correctly on MSW if that is what you have?

    You will also need extremely heavy wires from your truck alternator to the trailer batteries. IF your alternator can even supply that extra load.

    I don't think your refer is practical. But maybe if your 6A figure is not correct.
  • hellbird503's avatar
    hellbird503
    Explorer
    May 13, 2017
    The 6 amps number came from the Frigidaire website, it also says the minimum circuit required is 15 amps.
    As far as the power inverter goes, I have not purchased one yet. I wanted to figure this out first.
    If I understand this correctly, its 120v times 6 amps equals 720 then multiply times 2 for startup which equals 1440, which is why I chose a 1500 watt power inverter.
    If this is incorrect please educate me. Thanks, Dave
  • Ivylog's avatar
    Ivylog
    Explorer III
    May 13, 2017
    My 21cuft refrigerator only draws 8 amp of 12V power...96 watts. I'm using a 1000 W PSW inverter to power it plus a sat receiver and TV with 2' long 4 gauge wire.

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