Relay contact ratings.

Yes, but you have fewer stimulating arguments.

--
We have failed to address the fundamental truth that endless growth is 
impossible in a finite world.

Yes, but it strikes me that you much prefer to fix it yourself. BTW, The PICAXE directly supports the DS18S20 one wire thermometer.

Just thinking further, depending on energy ratings it may be a money saver to get a new fridge.

--
We have failed to address the fundamental truth that endless growth is 
impossible in a finite world.

Consider that Moore's Law is not a law.

--
We have failed to address the fundamental truth that endless growth is 
impossible in a finite world.

The silence would be exhilarating ;-) ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.

Or just replace the relay with a switch. Must of these automatic defrosting fridges defrost so often that they freezer-burn and ruin your food. ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.

Wouldn't it get boring after a while?

--
We have failed to address the fundamental truth that endless growth is 
impossible in a finite world.

We'd still have Larkin to tweak under the chin, while he cluck, cluck, clucks along ;-) ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.

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I remember a few years back there was one of these educational programs on how things work, in particular household appliances. They actually went to a dump site where were were dozens of junked fridges, and connected each one to power. Almost all still cooled, but had been dumped due to rust, broken shelves, seals etc or other similar damage. They said that the compressors were extremely reliable.

If your fridge is only 10 and hasnt gor rust or any of these problems, odds are that it should continue working for a long time yet, and probably is quite efficient compared to older ones. Probably worth fixing, especially if you can DIY. New ones aren't cheap :(

I don't know what the climate is where you are, but we have had 2 fridges without auto defrost since the 90's and they rarely ice up. Might defrost once a year, and isnt a big drama. If you are opening the freezer section a lot though (especially with single door fridges) it might be different as that would let more humid air in, that would condense on the cold surface and form ice.

As for that electronic aftermarket timer from Ebay that is 120v - if you get one and open it up, you might find that it has either a switchmode power supply or a series capacitor type supply. You can modify these fairly easily to run from 240v, or make up a small power supply that you can mount in the back of the fridge. For something like this a linear power supply might be best, as linear ones are very reliable.

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OK, i am going dumper diving.

Actually, a good source of relays are garage openers. I have a spare board with 3 240V/5A w 24V/5A coil. I guess it needs open/close/on.

Plenty on ebay, pretty complicated though. You have to search for "fridge defrost timer' :-)

Rheilly

--
OK, Moore's conjecture then, if that pleases you.

The point is that we _have_ addressed the fundamental truth that
endless growth is impossible in a finite world by stalling the
inevitable using miniaturization.

From your description, it appears that your fridge looks like this: (View using a fixed-pitch font)

--
                          
MAINS>--+---------------+----------------------------+ 
        |               |                            |
        |               O C                          |
  [DEFROST MOTOR]- - - -|S1                          |  
        |           O-> | |  
        |           |                     |      |NO
        |           |                     | [COMPRESSOR]
        |           |                     |      |
MAINS>--+-----------+---------------------+------+

Am I right?

If I am and you're having problems with the defrost timer and its
switches, then it seems you could replace the motor with a timer and
the timer motor's set of switches with a SPDT relay, like this:

MAINS>-+-----------------+----------------------------+ 
       |                 |                            |
       |                 O C                          |
    [TIMER]-[COIL]- - - -|K1                          |  
       |             O-> | |  
       |             |                     |      |  
       |             |                     | [COMPRESSOR]
       |             |                     |      |
MAINS>-+-------------+---------------------+------+

You've said the defrost only happens every six hours, but for how long
is the heater energized?

knowing that will allow us to determine the duty cycle of the timer
and cause it to mimic the motor timer.

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=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0 =A0|

=A0 =A0|

=A0| =A0 =A0 =A0 =A0 =A0O C

=A0 [COIL}- - - -|

| =A0 =A0 =A0O-> |

=A0 =A0 | =A0 =A0 =A0|NO

=A0 =A0 | [COMPRESSOR]

=A0 =A0 | =A0 =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0|

=A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0|

=A0 =A0 =A0|

=A0 =A0| =A0 =A0 =A0 =A0 =A0O C

=A0 =A0 [COIL]- - - -|

=A0 | =A0 NO O-> |

=A0 =A0 =A0 | =A0 =A0 =A0|

=A0 =A0 =A0 | [COMPRESSOR]

=A0 =A0 =A0 | =A0 =A0 =A0|

It should be long enough to melt the ice and let the water drain off. It can easily be programmable in a micro, at least during development. Perhaps a 5 to 10 minutes range.

part

>>>>>

It's hard to tell whether it's 'defrosting' an element that is in any case more or less ice free. The element isn't visible without detaching the backplate of the freezer, and running the fridge without the backplate in place would so change the airflow as to make any observations irrelevant to the normal operation of the fridge.

The reason I got started on this whole exercise was the fact that at times the bread in the fridge was clearly not frozen, even though the freezer temperature certainly drops to less than -15C at times. I hadn't previously looked into the defrost mechanism, and indeed, didn't realise that there is actually a quite powerful heater element involved. Nor did I realise that the defrosting occurs every six hours.

A particular issue with the defrost mechanism is that it has a defrost termination thermostat mounted on the cooling element (set to open at

+11 degrees celsius, closes again at 0C), but regardless of what it does, the fridge remains in its non-cooling mode for about half an hour because of the defrost timer. I put a temperature sensor onto the thermostat, and it shows that the actual temperature there rises to nearly 20C, presumably because even after the heater is turned off, it's still very hot.

In addition, there's no link between the defrost timing and the thermostat. Defrosting may start just as fridge has reached its highest normal temperature and the termostat is about to turn the compressor on. So the day to day outcome will vary considerably, even ignoring ambient temperature changes, making assessing whether the thing is working properly rather problematic.

Now the bread is probably the thing in the freezer that has the least thermal inertia. Maybe the fridge has been working correctly (in the sense of "as designed") all along, and I've just been overreacting to the occasional thawing of the bread.

I've now learnt stuff about self defrosting fridges that I might have been happier not knowing.

Sylvia.

I could. Using it wouldn't be so straight forward. The timer has a single pin for input, which is both the source of power for the clock, and for running either the compressor and heater.

Sylvia.

Strange that I didn't find them. It's not as if I didn't look.

Sylvia.

I should buy one of them new-fangled phase-correcting "power savers" and see how much my bill drops by when I reduce the load from zero to zero.

Sylvia.

There is no neutral connection to the timer?

--
You can't have a sense of humor, if you have no sense.