HOMEBREW Digest #5678 Mon 26 April 2010

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  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 Return to table of contents
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 Return to table of contents
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