Long interval timer ideas

[Glenn Ashmore]

You guys helped a lot with my watermaker control so I am coming back with a
little simpler problem. This time it is the refrigerator and freezer. 12V
Danfoss hermetic compressors are capable of running at any speed from 2000
to 3500 RPM. Speed is controlled by a resistance of from 0 to 1523 ohms in
the thermostat circuit. Conservation of battery power is important but
while these compressors are most efficient at the slower speeds getting the
beer cold as fast as possible is equally important so the compressor needs
to run at close to maximum speed for about 3 hours to cool a case of brew.
When a fresh case is added I want to push a button to switch in an
additional resistance for about 3 hours. Here is a proposed soultion and
a question.

First I will set the "normal" speed with a 1K trimmer pot so that the
compressor has a duty cycle of about 85%. A one shot timer driving a SPDT
relay will switch in another 1K trimmer in series with a 510 Ohm resistor.
I don't think I would trust a 555 for 3 hours so I am considering a CD4541
and a 4017 decade counter. The button push would start the 4541 and a
trigger a 4013 flipflop to set the relay. The 4541 would be set to pulse
very 20 minutes or so and Q0 to Q7 of the 4017 could drive an LED array to
display the relative progress. Q8 would set off the 4013 and end high speed
operation.

I have this breadboarded pretty well but I still have one more question.
How do you stop the D&$#ed 4541. It keeps running so the system goes back
to high speed 3 hours later!.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

 

[Spehro Pefhany]

On Sat, 29 Jan 2005 22:48:24 -0500, the renowned "Glenn Ashmore"
<gashmore@cox.net> wrote:

You guys helped a lot with my watermaker control so I am coming back with a
little simpler problem. This time it is the refrigerator and freezer. 12V
Danfoss hermetic compressors are capable of running at any speed from 2000
to 3500 RPM. Speed is controlled by a resistance of from 0 to 1523 ohms in
the thermostat circuit. Conservation of battery power is important but
while these compressors are most efficient at the slower speeds getting the
beer cold as fast as possible is equally important so the compressor needs
to run at close to maximum speed for about 3 hours to cool a case of brew.
When a fresh case is added I want to push a button to switch in an
additional resistance for about 3 hours. Here is a proposed soultion and
a question.

First I will set the "normal" speed with a 1K trimmer pot so that the
compressor has a duty cycle of about 85%. A one shot timer driving a SPDT
relay will switch in another 1K trimmer in series with a 510 Ohm resistor.
I don't think I would trust a 555 for 3 hours so I am considering a CD4541
and a 4017 decade counter. The button push would start the 4541 and a
trigger a 4013 flipflop to set the relay. The 4541 would be set to pulse
very 20 minutes or so and Q0 to Q7 of the 4017 could drive an LED array to
display the relative progress. Q8 would set off the 4013 and end high speed
operation.

I have this breadboarded pretty well but I still have one more question.
How do you stop the D&$#ed 4541. It keeps running so the system goes back
to high speed 3 hours later!.

Take the mode control pin (10) to 0V (?).

http://www.fairchildsemi.com/ds/CD/CD4541BC.pdf


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

 

[mike]

Glenn Ashmore wrote:

"mike" <spamme0@netscape.net> wrote in message
news:41FC5D95.6040406@netscape.net...

I'll say it again...perfect application for a PIC/AVR/ETC processor.


MCs are out because they are to hard to fix in Bora Bora. Likewise it is
hard to find beer already cold there too.

I'm not buying that argument. As a practical matter, you can't get
discrete logic there either. And you probably don't have tools handy to
replace parts. No reason for a MC to be any less reliable.

However, you might consider restating the problem. IFF the thermostat
shuts off the compressor when it gets cold enough, all you need is a
latching relay that unlatches the first time the compressor shuts off.
Latch the relay with a pushbutton when you load the beer.


The problem there is that the compressor will cut off several times before
the beer gets cold.

That sounds like a fundamental problem. Your beer is not getting cold
"as fast as possible" if the compressor shuts off. Stated another way,
if the compressor is shutting off, you'd be more efficient to run it at
the lower speed initially. Or stick a fan inside
so it doesn't shut off.

When you did the math, how much energy did you save with the two-step
speed optimally implemented vs running low speed all the time? How much
clock time did you save getting to drinking temperature (BTUs removed)
given that the high speed mode ain't running all the time?

To make this work optimally, you're gonna have to do a LOT of
experimenting. I volunteer as a beer consumer.

Another practical matter about booze: I've empirically determined that
after the first one, I'm much less picky about the quality of the
second. By the third, it don't matter much at all ;-)
mike

Only reason I can think of to care how fast the beer cools is is you're
drinking it. Stick an egg timer on the outside to remind you to switch
to low.


That is the backup system.

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[Glenn Ashmore]

"Spehro Pefhany" <speffSNIP@interlogDOTyou.knowwhat> wrote in message
news:72nov0let01nndccjj9dgcuchaprifpeiu@4ax.com...

Take the mode control pin (10) to 0V (?).

http://www.fairchildsemi.com/ds/CD/CD4541BC.pdf

Tried that but I only get one cycle. I need 8 cycles to complete a cool
down period.

Wait a minute! Are you saying to mring the MODE low AFTER the 8th cycle?
Now that might work. Lemme see, it could be connected to the extra half of
the 4013. The start button could bring it high and the 9th pulse take it
low.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

 

[Glenn Ashmore]

"mike" <spamme0@netscape.net> wrote in message
news:41FC5D95.6040406@netscape.net...

I'll say it again...perfect application for a PIC/AVR/ETC processor.

MCs are out because they are to hard to fix in Bora Bora. Likewise it is
hard to find beer already cold there too.

However, you might consider restating the problem. IFF the thermostat
shuts off the compressor when it gets cold enough, all you need is a
latching relay that unlatches the first time the compressor shuts off.
Latch the relay with a pushbutton when you load the beer.

The problem there is that the compressor will cut off several times before
the beer gets cold.

Only reason I can think of to care how fast the beer cools is is you're
drinking it. Stick an egg timer on the outside to remind you to switch
to low.

That is the backup system.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

 

[Glenn Ashmore]

"Fred Bloggs" wrote

Something like this:

Exactly! That's two I owe you and Spero. You guys are now on the launching
party guest list.

Thanks!

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

 

[mike]

Glenn Ashmore wrote:

"Rich Grise" <richgrise@example.net> wrote> > The problem there is that the
compressor will cut off several times before

the beer gets cold.

Then leave it that way. That's an automatic thermal cutout, so that the
compressor motor doesn't burn itself up.

If you want instant chilling of your beer, either get a colder cooler or
invest in some dry ice or liquid nitrogen.

But don't run the compressor motor at a duty cycle greater than what the
manufacturer says is safe.


The reason the babes look better in Bora Bora is that after a month at sea
ANYTHING looks better.

The compressor is designed to run at maximum speed constantly so it will not
be forced to run harder than it is designed for. The goal is to cool the
beer as fast as possible while using the least amount of power. The problem
is that the refrigerator can pull out heat faster than the beer can give it
up. To avoid freezing the already cold food the compressor will shut off
when the air in the box gets to about 32F but the beer is still warm and
gradually heats up the box. At around 40F the compressor then turns on
again to absorb the next "batch" of heat. With the compressor at high speed
this cycle happens probably 8 or 10 times before the beer gets below the
upper hysterisis limit and temperature stabalizes. At the "normal" low
speed the compressor would run constantly for about twice as long. The
compressors are more efficient at low speed but not twice as efficient so
the net result is it takse more amp hours to cool the beer slower.

Now, I'm really confused. If you define efficiency as BTUs removed per
watt-hour of consumption, the system should be most efficient at the
point where the system is "most efficient". Sounds like something is
missing in the model.

I maintain that an internal fan to increase the abilitiy of the beer to
give up heat and a fan to encourage the condeser to give up heat
would make significant improvements.

If you're dead set on a timer...
Think about the timers in hotel rooms to keep you from running the
bathroom fan too long. Those come in much longer time durations.
They're wind-up so they don't use any (electrical) energy.
I use a 6-hour one on my battery charger.
mike

--
Return address is VALID.
Wanted, PCMCIA SCSI Card for HP m820 CDRW.
FS 500MHz Tek DSOscilloscope TDS540 Make Offer
http://nm7u.tripod.com/homepage/te.html
Wanted, 12.1" LCD for Gateway Solo 5300. Samsung LT121SU-121
Bunch of stuff For Sale and Wanted at the link below.
http://www.geocities.com/SiliconValley/Monitor/4710/