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Re: [Phys-l] Freezer Delay



The huge power draw when the defroster comes on might have been overtaxing your generator.

Great article here:
Watts Up with the Freezer > Vernier Software & Technology

Paul


On Aug 30, 2011, at 2:46 PM, Donald Polvani wrote:

During Hurricane Irene, I used our generator to keep the freezer going.
Unfortunately, the generator (for reasons still unknown) decided to run
smoothly for the first 15 minutes, or so, and then slow down and almost
stop, then recover itself and run for 5 or more minutes smoothly again, then
slow down and almost stop, etc. until after a number of such cycles it
finally would stop (maybe after 45 minutes total). For the first 15
minutes, the generator would bring the freezer temperature down. The
freezer has a digital temperature display on the outside of the front door,
so it's easy to see what's happening. However, after the generator started
the above cyclic behavior, the freezer would not come back on during the
smooth running portion of the generator cycling and the temperature would
continue to climb until the generator finally stopped.



Now that our power is back on, and the freezer had had enough time to reach
thermal equilibrium at 0 deg F, I shut the freezer off and quickly turned it
back on. After turning it back on, the digital display returned but the
compressor stayed off. After about 10 minutes, when the temperature had
climbed to 8 deg F, the compressor came on and started to bring the
temperature back down.



Can anyone explain to me why the freezer compressor seems to have a built in
delay after the power is shut off and then turned quickly back on? Is this
a deliberate attempt to prevent the compressor (or delicate electronics)
from experiencing too many switching transients from a power source which is
turning on and off, or is it in the nature of compressors to not be able to
rapidly start and start? Was I hurting somehow the compressor, or
electronics, by letting the compressor cycle in the above manner?



Don



Dr. Donald Polvani

Adjunct Faculty, Physics

Anne Arundel Community College

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