Date: Thu, 29 Oct 1998 17:00:07 EST
Reply-To: David Beierl <dbeierl@IBM.NET>
Sender: Vanagon Mailing List <vanagon@vanagon.com>
From: David Beierl <dbeierl@IBM.NET>
Subject: Re: Fridge ?
** Reply to message from Blue Eyes <lvlearn@MCI2000.COM> on Wed, 28
Oct 1998 15:08:02 -0600
Hi John -
> expectancy of such low cost motors probably isn't suitable for any
> continuous duty or long term use installation. Besides, I'd rather
> use my 12 volt house current.
I've been using a freestanding fan powered by two D-cells for several
years now. Got it at the RV dealer for $15-20. It runs continuously
for more than a month on a set of alkalines. I'll guess that it runs
at 500 rpm (I could be way off) and it gradually slows down as the
batteries are used up. It would run at constant speed with a set of
NiCd batteries, but for a shorter period. It also comes in a 12v
powered version with some sort of mounting bracket and switch, maybe
even a pilot light -- cost about twice as much as I remember. People
recently have been talking about using the very small Radio Shack
pancake fan for this purpose, but this is a high-speed fan which
probably has a life expectancy of less than a year continuous duty
(two reports have been one month and 11 months, if I recall aright).
This seems to be about normal for a sleeve-bearing pancake fan.
Further, it's very likely a true *12 volt* fan -- in electronics
usage, 12 volts means 12.0 volts, not 14. The electronics inside the
fan (brushless DC motor) may not stand up to automotive voltage very
well. OTOH some of these fans are rated to run at 8-14 volts, maybe
this is one. If you want to use one of these, you can increase the
life by pulling the label off the motor side and oiling the bearing as
soon as (or perhaps before?) it starts to make more/different noise.
Also you can run it slower by putting a string of 1-amp 50-piv diodes
(radio shack) in series -- each diode will drop the voltage about
0.6v. The fan probably won't run below about 8v or so.
> price, etc. Also, what would be a nice way to power this ONLY when
> the main burner heat is driving the refrigeration cycle? That feels
> like the right approach to me.
I think it's good to keep the air stirred up so it doesn't stratify
and so there is less shielding effect from stuff in the reefer.
Easier, too... :)
Doesn't this appeal to the inventive
> spirit of you creative guys like Dave B.? No used three pound
boiler
> controllers please.
I've got a *six* pound *centrifuge* controller, complete with 3/16"
stainless steel pipe from the 8" dial to the 3/4 by 9 stainless
temperature sensor...would that do? <BG>
>
> On a completely different refrigerator design consideration, I don't
> like the fact that in even tepid weather, my refrigerator's external
> heat exchanger fan keeps cycling on and off. It's distracting,
> irritating and calls attention to itself when I prefer to sleep. I
> always wonder if it might drain the battery enough to cause a
starting
> problem if it were left on for a few days without starting the motor
> to recharge. Remember, old battery marginal performance failures
> always occur at their margins, by definition.
That fan draws about 60 milliamps, according to the rating -- I
haven't measured it. Would use one amp-hour a day running
continuously -- probably run about four months before draining a
battery completely. I'm snipping the stuff below -- it may be good to
insulate the flue (I've done it with mine, no really noticeable effect
but I feel better), but it is not permissible to alter the vent in any
way -- that refrigerator is designed and certified to run with that
exact vent kit and no other, and it's not supposed to be modified at
all. Also, I'm afraid you misunderstand what the fan is for -- it's
not connected with the flue/draft at all. It blows air on the
condenser fins when they get hotter than 125 degrees F. and switches
off at about 110 degrees. The way to keep it quiet is to improve the
airflow past the condenser, which takes in air through the grille
underneath the fridge and the one on the after side of the cabinet;
and exhausts it through the one outboard of the counter lid. I
removed the upper grille because the slots were closing over half of
the available area, so now I have to be careful about dropping stuff
back there. I also modified the side grill so that nothing could sit
against it and close it off. The curtains also tend to close off the
top grille. This would be a real candidate for a stack of some sort
that pulled air from the top grille area. If you're into Rube
Goldberg stuff, think about watercooling the condenser -- I bet that a
convection-powered arrangement with a ten gallon reservoir could be
enough supplement to keep the fan off overnight. Trouble, of course,
is that this would interfere with the normal air-cooling -- or would
it? Some thin tubing wrapped around the condenser tube in strategic
places might work just fine. Looks like an irresistable opportunity
for (someone else) to do some heat flow and capacity calculations.
According to the nameplate the thing is rated for a max input of 650
BTU/hr...ten gallons of water at a 30 degree rise should be about 2400
BTU.
>
I even considered trying to move the exhaust location up near
> the top of the van. I think it might be possible to snake a duct
> between the kitchen windows inside the wall.
As I said, don't do it -- it will automatically void the Canadian and
American safety approvals, and if you increase the draft too much the
flame will blow out. Also if the externally induced pressures (read:
wind) on intake and outlet are not equal, the flame will blow out or
at the very least blow soot all around in the combustion box. That's
why they put them half an inch apart...
cheers,
david
David Beierl <dbeierl@ibm.net>
401 274-5827 voice, -6349 fax
OS/2 V4, FP7, JVM 1.1.6, JSM 98.6.3
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