Sizing an inverter

Discussion in 'General Electronics Chat' started by Andrew Leigh, Dec 1, 2012.

  1. Andrew Leigh

    Thread Starter Well-Known Member

    Sep 8, 2008
    92
    2
    Hi,

    I have changed caravans and the new one has a 220V fridge which means I need to have an inverter if I want the fridge running while mobile.

    The fridge has a running current of 0.65A and the startup current is 5.65A.

    The invertor that I have my eye on is a Cotek SK700-212. What I am unsure of is that the inverter has a no load current draw of 1.2A. Would this mean that I have to include this 1.2A in my calc's or can the unit produce the rated power notwithstanding.

    If I have to include it then 1.2 + 5.65 = 6.85A = 1507W which now exceeds rated "surge power" of the unit which is 1400W.

    The invertor will be used for 8 hour trips, probably 4 per annum. My feeling is that I should be OK.

    Any opinions?
     
  2. #12

    Expert

    Nov 30, 2010
    16,298
    6,810
    The way you have expressed this seems wrong. The invertor has a no load draw of 1.2 amps from its battery supply, right? Why would you include the idle current of the invertor as part of its own load, and further, rate the idle current as if it were from a 220 volt supply?
     
  3. crutschow

    Expert

    Mar 14, 2008
    13,016
    3,235
    The surge rating is for the output and is not related to the input idle current. So you should be fine since your fridge's startup of 1243W is less than the inverter's 1400W surge rating.
     
    #12 likes this.
  4. Andrew Leigh

    Thread Starter Well-Known Member

    Sep 8, 2008
    92
    2
    Thanks chaps,

    yip that was confusing me. Thanks for clearing that up.

    Cheers
     
  5. Andrew Leigh

    Thread Starter Well-Known Member

    Sep 8, 2008
    92
    2
    Thanks

    Cheers
     
  6. RodneyB

    Active Member

    Apr 28, 2012
    633
    13
    In Zimbabwe we have load sheadding for up to 18 hours a day and therefore solar inverters and battery banks are part of our homes. I install these systems fora living and my years of experiance can only suggest that for your application you get a minimum of 2000 Watt unit. Cotek and outback are second tononein myexperiance. A big consideration is the battery and its recharging. I am happy to assist with information frommy experiances in this industry in Zimbabwe
     
  7. Andrew Leigh

    Thread Starter Well-Known Member

    Sep 8, 2008
    92
    2
    Hi Rodney,

    The inverter is ONLY for travelling to and from a camping site with. Don't you think 2000W to run a small caravan fridge ONLY while travelling for a total of 32 hours per annum is a little overkill. In camping grounds we have power availabilty 100% of the time.
     
  8. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,388
    1,605
    How much refrigerated food do you bring back with you? If you can say "zero" then junk the inverter altogether and buy a block of ice (wet or dry) and use that to keep the fridge cold on your day and a third trek to your happy camping grounds.
     
  9. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    What kind of vehicle are you traveling in? Could you use the generator/alternator of that vehicle to power your inverter and not be totally depending upon battery power?
     
  10. Andrew Leigh

    Thread Starter Well-Known Member

    Sep 8, 2008
    92
    2
    Hi Bill,

    I have a dual battery system fitted. The second battery is a 105 aH deep cycle that is connected to the cars electrical system via an intelligent relay which first sends charging current to the cranking battery, once charged it then charges the secondary battery.

    This system is common here for 4X4 chaps wanting to run fridge without depleting their crankling battery.

    So the second battery feeds to the rear of the vehicle via 16mm2 conductors and delivers 12V to the towbar area via a Brad Harris plug. I would simply have an extension to the caravan fridge (of suitable current carrying capacity) where I plan locating the inverter. This system is great as when one stops over for an hour for lunch the fridge continues to operate normally in the high ambient we experience in summer.
     
  11. Andrew Leigh

    Thread Starter Well-Known Member

    Sep 8, 2008
    92
    2
    Bought the inverter today, thanks for all the help.

    Here's to cold holiday beers on arrival in the Kruger Park.
     
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