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I'm trying to calculate the maximum current draw for an old chest freezer, as part of working out the requirements for an emergency generator.

The freezer (a Norfrost) doesn't have any model number visible, but does have this sticker on the compressor:

freezer compressor label

This suggests it draws 0.6A, so 144W at 240V - but that seems surprising low to me given that a similar new one is rated at 150W, and new appliances are supposed to be much more efficient than old ones.

Can I therefore assume it is correct, or is there something else in there that gives a better clue? Or do I need to get hold of a clamp meter and test it to be sure? Will the startup current be three times that (so 432W)?

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  • It uses R-134a, so it's not THAT old.
    – Ecnerwal
    Apr 12, 2023 at 11:40

2 Answers 2

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I would assume this label to be correct.

The newer freezer may well have a higher maximum rating than the old one but draw this much power not as often or as long as the old freezer, so that the overall power consumption of the new machine might be lower, as expected.

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The best solution would be to measure it.

If you have access to clamp meter - splendid, otherwise, you can use kill-a-watt to check 3 crucial parameters:

  1. The peak wattage (aka current draw)
  2. The average wattage when compressor is running
  3. The 'standby' wattage

And while you have the kill-a-watt plugged, leave it for a day or longer to get the KWh usage per day aka how much money it burns.

Ad1. Peak wattage is what your generator/ups should be able to handle momentarily without tripping. It will be on label as "peak" and the highest value listed. You may be surprised what the actual peak wattage of your refrigerator/freezer will be, it can easily go to 1000W and more.

Ad2. Average is what continuous power your generator/ups have to supply. This will be the second highest value on label. For fridge/freezer this will usually be very low. An electric heater will have this very high.

Ad3. Standby should be very low. This may be important if your generator has minimum load at which it supplies 'correct' voltage. If in doubt, use a surge protector. In fact, always use surge protector, in case your generator decides to shoot 300V into the mains.

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