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Contents:
Refrigerator ("A. J. deLange")
Re: Refrigerator Current Demand (stencil)
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Date: Mon, 26 Apr 2010 00:03:36 -0400
From: "A. J. deLange" <ajdel at cox.net>
Subject: Refrigerator
It is normal for a motor to draw large "inrush" current as it starts up.
This may be 2 - 3 or more times the running current depending on the
motor design and the load. Basically the stationary motor consists of a
coil of wire which looks almost like a short until the motor starts to
turn at which time it develops (generates) a "back emf" which opposes
the line voltage and results in a reduced current.
You might not have noticed this with a different refrigeration unit on
this same circuit because the other unit's starting current was less
than this one's or because you had less loads of other types on the
circuit at the time the other unit was connected. It is also possible
that there is a problem with the compressor on the unit causing it to
draw unusually heavy starting current. Dirt in a valve, a failing start
capacitor, liquid in the cylinders... might all cause this. You can
check the start and run current with a clamp-on ammeter available at,
for example, Home Depot
------------------------------
Date: Mon, 26 Apr 2010 20:15:12 -0400
From: stencil <etcs.ret at verizon.net>
Subject: Re: Refrigerator Current Demand
On Sun, 25 Apr 2010 23:24:45 -0400,
in HOMEBREW Digest #5677
Fred L Johnson wrote:
>
>[ ... ]
>about use of a refrigerator as a temperature-controlled fermentation
>chamber.
>
>[ ... ]every time the refrigerator
>(located in the crawl space of my home) comes on the lights in my kitchen
>(probably on same circuit) dim for a fraction of a second. I never noticed
>this when I was using an old chest freezer for the same purpose in the same
>location. Why is this happening? Am I risking damage to the house circuit?
>To the refrigerator?
It's not the controller - that's nothing more than a switch,
and will have no bearing on the amount of inrush current that
the refrigerator will demand.
Guessing that we're talking about an older, more worn,
freezer and a newer refrigerator, one possibility is that the
freezer's refrigerant pump might have been presenting a
lighter load - leaky piston seals, depleted refrigerant,
possibly even a belt-driven unit that allowed a gentler
torque curve than a direct-drive. Consider too that a
refrigerator has a circulating fan and possibly a separate
heat-exchanger fan, all of which will add to the inrush
current as they spin up. If you still have access to the
feezer, its label plate will specify both starting and
running current drain, as of course will the refrigerator's.
The comparison should be enlightening. My limited experience
is that chest freezers make better chillers than
refrigerators do, because of the simpler design.
The likelihood of damage to the wiring, or of fire hazard, is
pretty slim. Most likely at some (really inopportune) future
time, while several appliances are in use - think preparing
dinner - you'll trip a breaker that would otherwise have
held. Best practice generally is to keep refrigerators,
freezers, sump pumps, A/C units, and similar large motorized
appliances each to its own dedicated AWG12, 20A circuit.
As to the refrigerator itself, there's nothing inherently
stressful about having the external controller cut the power
before the internal thermostat is satisfied, although losing
power to the fan that circulates cold air from the freezer
section to the refrigerator section may cause the whole
system to run more frequently than it would if the internal
thermostat were swapped out with an extended-range
replacement. Just keep an eye on the ice buildup in the
freezer section.
gds, stencil
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End of HOMEBREW Digest #5678, 04/26/10
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