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Thread: Starting Watts on Refrigerator

  1. #1
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    Default Starting Watts on Refrigerator

    Greetings Fellow Sun Lovers,

    I am reading 800 starting watts on a Whirlpool ETOWSRXMQ03 refrigerator with my new "P3 KillAWatt EZ" power meter. This seems quite low. Can I trust this reading for designing my battery backup system? I have 2 - identical refrigerators like this and I need to purchase an inverter / charger that will handle starting both of them up at the same time. These two refrigerators are the only items that need backup power. I need to provide back up power to these refrigerators for 8 - hours.


    Thank you.

    Jim

    PS. I am an electrical contractor if anyone has any AC electrical questions I will be glad to help.

  2. #2

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    I verified the accuracy of my KillaWatt with a known power source and verified with my multi meter. I then knew the thing was accurate.

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    800 is a bit low I would say, you didnt say what the "running" watts were? I have found if the running watts are about 130 the start up for first 1 second can be about 1200 w The killer watt meter is not fast enough to catch that.

    Refrigerators older than about 3 years can be modified to start ok on a 400 w MSW inverter, but I have been told, but dont know for sure newer refrigerators cant be easily modified.

    Dont believe the crap that many tell its the way ref motors work,its not, its the pump part that is the cause of the heavy starting current

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    Quote Originally Posted by John Galt View Post
    I am reading 800 starting watts on a Whirlpool ETOWSRXMQ03 refrigerator with my new "P3 KillAWatt EZ" power meter. This seems quite low. Can I trust this reading
    Not really because the meter is not capable of reading the 1 to 20 cycle start up current, which can be as high as 10 X FLA
    MSEE, PE

  5. #5
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    Quote Originally Posted by john p View Post
    800 is a bit low I would say, you didnt say what the "running" watts were? I have found if the running watts are about 130 the start up for first 1 second can be about 1200 w The killer watt meter is not fast enough to catch that.

    Refrigerators older than about 3 years can be modified to start ok on a 400 w MSW inverter, but I have been told, but dont know for sure newer refrigerators cant be easily modified.

    Dont believe the crap that many tell its the way ref motors work,its not, its the pump part that is the cause of the heavy starting current
    Hey thanks for all of the replies.

    Dumb me did not record the running wattage. I will have to do that on Monday. I believe that it was lower than 130 watts though. This refrigerator is quite small. I was thinking of using a 1500 watt continuous and 3000 watt surge rated inverter with 2 - 1,000 AmpHour batteries to give me my 8 - hours for the 2 - refrigerators.

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    I would say the 1500 w inverter be fine. Its very unlikely they would both be starting at same time and as the running watts is low there is adequate power still available on that size inverter. Ive had a 10c ft fridge run perfectly off a 1000w inverter. but I just run mine off grid now. I have modified fridges (10 c ft) to run off 400w MSW inverters and could get them to start 90% of the time ok on a 300 w inverter.,but sometimes it would take them 2 or 3 tries to get started.

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    As an electrical contractor, you should know about Peak Reading AC meters, and be able to borrow one from a buddy. The kill-a-watt is incapable of reading the peak starting surge of anything. Fridge motors do start high running, and will drop off after a couple minutes, but that is not the starting peak surge. Often the starting surge is 5 - 10 x the running wattage.

    Then there is the mod-sine or pure-sine discussion about cheaper inverter, vs increased power drain, vs hotter running motor, or pure sine, which is more cost up front.
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    Mike it doesnt take a couple of minutes to drop off. It only runs high amps for at most 3 seconds.And as already stated that can be about 10 times running current. I have measured some at 12 times running current,
    "Older than 3 yr old fridges can be modified to overcome this with help from a fridge mechanic. But its not worthwile to mod the fridge in most cases.

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    Well, the 2 fridges I've measured, have their unmeasurable starting surge, and then over the next couple minutes, slowly ramp down from 400W to about 200W. I don't know if it's pressure equalizing in the system or what, but I've seen it happen twice.

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    Mike thats interesting. ,I have never measured that happening. Im certainly not going to say in your case it didnt as I know you are more than capable of noting that. I happen to have a variety of freezers and fridges, 6 shelf freezers one chest freezer and 4 x10cft refrigerators and all various brands and have done many measurements on them trying to work out what could be the best way to run them from solar power. One refrigerator is modified to run on 400w MSW inverter. but all others it was found impossible to use anything economically as grid electricity.

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