Re: Refrigerator monitor ideas?

["Robert Green" <ROBERT_GREEN1963@xxxxxxxxx>]

"Dave Houston" <nobody@xxxxxxxxxxxx> wrote in message
news:45c40e48.1182409093@xxxxxxxxxxxxxxxx
> "Robert Green" <ROBERT_GREEN1963@xxxxxxxxx> wrote:
>
> >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.
>
> Can you get a temperature probe on the coils?

Yes.  I thought of that but the problem there is I would have to probably
artificially freeze the coil once or twice to make sure the readings
corresponded to a freeze-up event!  I've monitored unit once upon a time
with Ratshack multimeter with an RS232 port (one of the most useful analysis
tools around considering the cost) and a thermistor taken from an LCD
thermometer whose display went flaky.

Anyway, IIRC there were lots of variations in coil temperature due to door
openings, defrost cycles, power blips and more.  I'm assuming that your idea
is to look for constant 32F readings on the coil indicating that it's a
block of ice.  That implies a control system of some complexity, doesn't it?
If I could find a cheap used pen recorder I'll bet that coil freeze-ups
would appear distinctly differently after a few days of icing but that's
still too late.  The ideal time to stop it is before an ice dam forms.

I may be stuck on the wrong vector, but I think the simplest system to
implement is one that detects a change in the water flow in the tube.  Since
it's gravity fed, that makes sensing flow pretty delicate.  Worse, still,
there are times when the tube is full (towards the end of the defrost cycle)
and times when it's dry.  But the heart of the problem is reduced flow
through the drain tube that causes an ice dam to build up at the bottom of
the freezer pan and that seems the best place to direct my detection
efforts.

Now that I think about it, the coil is the right place to look but the probe
should be a videocam, not a thermistor.  With a small board cam and LED I
could actually see the condition of the coils!  The question is whether the
electronics will work when frozen but that's easy enough to test.

If they don't, the cheap CMOS camera and some white LEDs in a baggie will
help.  The real problem is that inspecting both the floor tray and the drain
tube "shuttle" connector requires a lot of bending that an old back injury
finds particularly loathsome.  If I put an ugly winged screw instead of the
Phillips head screw that now secures the shuttle piece, I can probably
remove, inspect and clean it without have to bend too awkwardly to reach it.
To their credit, they designed the connector so that it WOULD clog first by
inserting a "snag" in the center of the tube.  They could have just used an
elbow or buried the whole thing in the walls of the unit and then clogs
would likely form wherever the tube bent the most.

I think I need to detach the shuttle connector and photograph it so people
can see what I am talking about.  If the water always trickles out and never
reaches the top of the shuttle trough, an immersion-type water sensor might
do the trick.

Gee, George, ain't ya gonna lecture me about how bad I am for wanting to
keep that smelly old thing?  (Apologies to J. Steinbeck)  (-:

--
Bobby G.