Relay contact ratings. - Page 4

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Home control
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Added CAE, where some embedded designer are.  We started with
defrosting the fridge, perhaps controlling the microwave, and piping
hot water through the fridge into the toilet.  This way, we can
defrost the fridge everytime we flush the toilet.  However, in case we
don't flush the toilet often enough, we need a PIC to monitor the
toilet as well.

We are going to need defrost cycle counters, duration timers, target
temperature, pipe temperature and toilet counters.  So, first thing is
to build the counters.  I've decided to build with 42 LEDs and 4 595
shift registers.  See:

http://173.224.223.62/pic32

Re: Home control
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This should do it:

    while(1)    // loop forever
    {
        temp_fridge 3D% read_temp(0);        // Fridge temperature
        temp_exch_beg 3D% read_temp(1);    // Temp. at beginning of exchanger
        temp_exch_end 3D% read_temp(2);    // Temp. at end of exchanger
        temp_room 3D% read_temp(3);        // room temp.

        if(temp_fridge < temp_target)
        {
            compressor(TRUE);
            sleep(TIME_COMPRESSOR);
            compressor(FALSE);

            temp_delta 3D% read_temp(2) - read_temp(1);

            // push latest value on data stack
            push_comp_temp(temp_delta);

            // if heat exchanger temp. delta is decreased, time to defrost
            differential_temp();

            if(defrost(TRUE))
            {
                heater(TRUE);
                sleep(TIME_HEATER);
                heater(FALSE);
            }
        }

        led_display(temp_fridge);
        sleep(TIME_IDLE);
    }


Re: Relay contact ratings.
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I'd look at using valves from/for a dishwasher or washing machine
they're designed for hot water and indoor appliances.

how are you planning on stopping the water from freezing?

--
⚂⚃ 100% natural

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Re: Relay contact ratings.
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in

Good question.  Perhaps i need a small NG heater instead.

Re: Relay contact ratings.
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Its a nonissue. If you wanted to get every last drop of energy
efficiency, the compressor could be run backwards to defrost the
evaporator, thus making good use of the heat built up within it. Bu
that wuold mean more cost, so its not done.


NT

Re: Relay contact ratings.
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It is done in some high end refrigeration system, with rerouting
pipes, rather than reversing the compressor.  Some even try to capture
the heat build up by the compressor for defrosting.

Re: Relay contact ratings.

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no, I means less.

It's a heat pump.  and like a water pump, it uses less electricity
when pumping a smaller head.

14 degrees to 25 degrees is easier thant 4 degrees to 25 degrees.

it'll only take it a few seconds to get the temperature down to
freezing, but for a few seconds it's easier than normal.

if you let the defrosting heat escapes from the evaporator into the
contents of the fridge it's harder to call it back.

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Certainly nore "more".

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⚂⚃ 100% natural

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Re: Relay contact ratings.
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Thing is, the compressor isn't going to say to itself "Oh, the incoming
gas is closer to ambient temperature, so reducing it by x degrees
requires less work.... I can relax for a bit then."

The compressor will run at its design power, and will generate a certain
amount of heat within itself, both as a result of the compressed gas
being warmer, and as a result of various inherent inefficiences. This
will raise its temperature. But if the incoming gas is warm, then that
will contribute to an even higher temperature in the compressor. There
is presumably a limit to how hot the compressor can run without damage,
and hence the question of whether it is safe to run it when the element
is warm.

Sylvia.



Re: Relay contact ratings.
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But when the input to the compressor is at a higher pressure then
there is more gas atoms going into the compressor so the compressor
has to work harder as it is compressing more gas.  Consider the case
where the input to the compressor is zero.  In that case the
compressor is not doing any work.

20%
Dan


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Re: Relay contact ratings.
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They don't. If the defrost time isnt properly controlled, its bound to
end up being a compromise, too long most of the time but on occasion
too short. That's when the system ices.

The temp the evporator reaches dont matter to the compressor, the
latter has plenty of thermal capacity and some leeway.


NT

Re: Relay contact ratings.
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And heat it up, just to cool it down later.  I can't believe the
fridge industry is still using inefficient timer based open loop
control.


Re: Relay contact ratings.
On Sun, 11 Dec 2011 21:20:03 -0800 (PST), linnix

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View with a fixed-pitch font.

This will give a 30 minute defrost cycle following a 6 hour freezing
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Re: Relay contact ratings.
On Tue, 13 Dec 2011 12:52:04 -0600, John Fields


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Oops...
Please ignore; I'm fixing the error.

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JF

Re: Relay contact ratings.
On Tue, 13 Dec 2011 16:02:47 -0600, John Fields

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Done.

news/ snipped-for-privacy@4ax.com

--
JF

Re: Relay contact ratings.
On Tue, 13 Dec 2011 17:44:46 -0600, John Fields

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Oops again:


--
JF

Re: Relay contact ratings.
On Wed, 14 Dec 2011 18:52:36 -0600, John Fields

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And, for the ASCIImatic (thanks, Steve :-):

.                                               +V
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Re: Relay contact ratings.


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976K?

887K?

1% tolerance parts where 20% tolerance would not measurably effect
the circuit?

 I'd do it like this:


            4060     +-----+--[100K]--+----------+-- +12
         +------+    |     |          |      |
 +-3M3---|Rs  MR|----+     |  relay  [/]     |
 |       |      |          |  coil    |      |
 +-1M2---|Rt Q10|-----|<---+          +-->|--+
 |       |      |          |          |
 +-1.0µF-|Ct Q14|--+--|<---+          |
         +------+  |                |/
                   +---3K3----------|   BC547
                                    |\|  
                                      \  
                                       --- 0V

  here the defrost time is 23m, 1/16 of
  the cooling time which should be close to 6H (if I got my arithmetic right)
  
  Add another diode between Q8 and MR to get 28m
  (5/64)  and another from Q6 to get even closer to 30m heating
  
           4060  
         +------+  
 +-3M3---|Rs  MR|----------+--[100k]--+------+--- +12
 |       |      |          |          |      |
 |       |    Q6|-----|<---+          |      |
 |       |      | optional |    relay[/]     |
 |       |    Q8|-----|<---+     coil |      |
 |       |      |          |          |      |
 +-1M2---|Rt Q10|-----|<---+          +-->|--+
 |       |      |          |          |
 +-1.0µF-|Ct Q14|--+--|<---+          |
         +------+  |                |/
                   +---3K3----------|   BC547
                                    |\|  
                                      \  
                                       --- 0V

  
--
⚂⚃ 100% natural

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Re: Relay contact ratings.

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I like to be precise so that if my limits are too stringent, then it's
easy to downgrade them to what's needed.
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Re: Relay contact ratings.
You can often get more life out of a mechanical defrost timer by opening
up the
motor and oiling the bearings.

Re: Relay contact ratings.
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I hope you are not being sarcastic.

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