Re: Refrigerator monitor ideas?

[Marc_F_Hult <MFHult@xxxxxxxxxxxxxxxxxxxxx>]

On Fri, 2 Feb 2007 10:34:56 -0500, "Robert Green"
<ROBERT_GREEN1963@xxxxxxxxx> wrote in message
<yZadnSuqcufcxl7YnZ2dnUVZ_qWvnZ2d@xxxxxxx>:

>We've got a 30 year old White-Westinghouse refrigerator/freezer in the
>basement that's cosmetically shot, but still humming away, delivering
>subzero temperatures in the icebox without major incident for years.
>
>Several times in the past 10 years or so, the drain tube from the pan under
>the freezer coils (it's an upright with a top freezer) has clogged, leading
>the coils to become caked in ice.  When this happens, the first clue is that
>the freezer temperatures begin to rise.  Other than placing a sight glass in
>the freezer floor pan, what are some simple options to detect a coil
>freeze-up condition.  I had previously had this on a yearly inspection
>schedule but the addition of a number of shedding dogs to the house in
>recent months has made that too infrequent a cycle.
>
>What I would really like to do is design something simple that can catch the
>formation of serious ice long before the coil became caked.  Simple
>temperature sensing is inadequate because the self-defrosting feature causes
>a sharp upward swing every night.
>
>The conditions that occur during a "freeze-up" (in addition to an overall
>increase of average freezer temperature each day it's building up) are that
>very little water reaches the evaporation pan at the bottom of the fridge.
>But checking that pan is about as inconvenient as unscrewing the drain tube
>connector that runs from the center top of the refrigerator to the backwall
>where it meets a drain tube that empties into the floor pan for evaporation.
>
>One thought that had occurred was to modify the drain tube to include an
>aspirin sensor between two spring loaded contacts at the top portion of the
>tube.  But I am not sure that would work because the typical mode of failure
>is an ice dam that occurs at the drain hole.  I would suspect that before
>that happens, the entire drain tube in filled with water, but I can't say
>for sure.
>
>Probably the most convenient solution would be to stick a $12 CMOS board cam
>in a baggie with some white LEDs to use as a video inspection port for the
>evaporator tray on the floor.  I'd only have to power it up during
>inspection times, so it wouldn't require a device that consumed power 24/7.
>Any monitoring of the temperature changes will likely involve a lot more
>power consumption than a video inspection "port" would.  On the other hand,
>the video evaporator inspection method probably won't tell me the coils have
>frozen until it's too late.
>
>What I really want to know is when 5 on the freezer control no longer means
>an average of X temperature in the freezer compartment.

FWIW, a major effort nationwide by utilities is to encourage folks to
properly dispose of inefficient 'garage' refrigerators.

The power consumption for a modern monitoring system could trivially made to
be 1/1000 or less of what the fridge consumes so your concern for the power
consumption of the monitoring system is puzzling (to me).

<ROBERT_GREEN1963@xxxxxxxxx> BobbyG summarized/ended his post/question with:

	"What I really want to know is when 5 on the freezer control
	no longer means an average of X temperature in the freezer
 	compartment.

Why don't you do just that by leaving the dial set at 5 and measuring the
temperature with any of a bajillion different ways discussed in this
newsgroup?

A Dallas/maxim 1-wire-wire interface from www.PHAnderson.com might be a good
place to start. Maxim will send you samples free.

http://para.maxim-ic.com/index.mvp?tree=1wire


Or add a LM34/35/other analog sensor to your Ocelot (or whatever).
http://catalog.national.com/Cat/jsp/national.jsp?i=71

Or add a HA7E to your www.Homeseer.com setup and have the computer email you
the temperature or call you on your cell phone.

There was a post a while back in comp.home.automation by an Australian feller
who wanted to hook up his beer still to his refrigerator and then (based on
the tenor of his posts) directly to a gastric feeding tube -- or something
like that ;-)  IIRC, there was some useful discussion in those threads about
1-wire temperature measurement.

... Marc
Marc_F_Hult
www.ECOntrol.org