If you've ever heard a loud click at a random time from your fridge or freezer, it's most likely the defrost timer initiating a cycle.
You'd think it might be something simple like a continuous timer that switches from running to defrosting for a specific amount of time each day, but it's much more clever than that. It only accumulates time between defrosts based on the total amount of compressor run time, and will terminate the defrost and switch back to chilling as soon as the maximum defrost temperature is reached.
The gear mechanism itself is very clever. It uses a special type of gear wheel that increments the next gear in single steps per revolution to allow a long time interval, and uses a similar gear to turn the switch cam in decisive steps to allow the contacts to change state twice in a very short rotation angle.
The contacts are moved by two spiral cams that gradually reset them for most of the revolution, but then have a sudden snap action at the end.
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You'd think it might be something simple like a continuous timer that switches from running to defrosting for a specific amount of time each day, but it's much more clever than that. It only accumulates time between defrosts based on the total amount of compressor run time, and will terminate the defrost and switch back to chilling as soon as the maximum defrost temperature is reached.
The gear mechanism itself is very clever. It uses a special type of gear wheel that increments the next gear in single steps per revolution to allow a long time interval, and uses a similar gear to turn the switch cam in decisive steps to allow the contacts to change state twice in a very short rotation angle.
The contacts are moved by two spiral cams that gradually reset them for most of the revolution, but then have a sudden snap action at the end.
If you enjoy these videos you can help support the channel with a dollar for coffee, cookies and random gadgets for disassembly at:-
http://www.bigclive.com/coffee.htm
This also keeps the channel independent of YouTube's advertising algorithms allowing it to be a bit more dangerous and naughty.
They are also in dehumidifiers. They act as a fail safe if the humidity control sticks on (or if you modify it to act as an aircon). It shuts off the compressor leaving the condenser fan running while the evaporator defrosts
Why is this not a Arduino nano or something similar? It’s like they make something that will eventually go out so they can charge you $300-$400 to replace it. I could understand this device 30 years or more ago but today there is no justification for something mechanical.
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Does the timer motor spin in the opposite direction when the current is flowing through it in the opposite direction?
Any chance of getting an introduction to what is this device meant to do? Never heard of anything like a defrost timer.
very informative
Question maybe for you. Is there a control switch that will shut off power when it get too cold? I know it exists because I do have a freezer. I want to stop a fridge from getting power if the ambient temp is too cold.
Fridge thermostats call for heat at Clive's house. It's an Eskimo refrigerator.
The time the defrost heater is on its automatically regulated by the qty of ice requiring removal.
This video shows why refers have trouble on inverters. The time between when the defrost heater shuts off and the compressor restarts, many inverters see too little load and shut off until the defrost heater trips on again. Oops!
My somewhat limited refrigeration experience the defrost timer diverts power from the compressor/thermostat to the defrost heater and thermostat. the thermostat for the fridge/freezer never cuts power to the timer. I found that there were two styles. one that switched for 20 minutes every 6 hours and one that switched every 24 hrs. Have I missed something? BTW 120 volts on the west coast of Canada. Not far from AvE really.
Had one of the first energy saving house refrigetators that were made by Amana back in early 70's. Had to replace the defrost timer 3 times in the 17 years that I owned the piece of crap. Also had to replace defrost timer once. Found out that they saved energy by installing an undersized compressor. While me and the Mrs worled all day and doors were not opened for over 11 hours ice cream was so soft during summer. Had to run the central air conditioner to prevent this.
I have an old fridge and the timer is somewhat similar, and there are times when I don't need the freezer compartment freezing.
So I unhooked( or unscrewed) the sensor wire from the timer and just it hang outside.
Why is the freezer aluminium still showing signs of freezing.
I think the temperature may be too cold.
So I wrapped the thin piece of wire with styrofoam, so that it will not show the fridge is too cold ( wire = I think its the temperature sensor with some gas inside. ) Yet the freezer aluminium compartment gets cold ?
So here are my two questions :
1. How can I turn on and off the freezer compartment with the timer ?
2. How to lower the temperature even further ? what material can I use. I used a plastic straw around the wire – still no good.
Appreciate responses from readers.
BTW; Clive : I like your videos and your practical ways of hacking things – they are just like how I do it.
I remove few screws and this thing is not opening and then I pry it – until I look underneath and there are more screws to be removed ! Argh.
I enjoy your videos. Very educational and your explanation is just right.
Anybody know roughly how often the average fridge/freezer cycles into defrost mode? Is it days, weeks?
(Also what would the power rating on the defrost heater be?)
Meh, still probably more reliable than the newer microcontroller-based relay or TRIAC actuated ones where all the fridge's functions are on a single, disposable, lead-free-solder porosity ridden PCB that the vibration of the relay actuating is enough to wobble the solder joints loose over a few years until they open up enough for the fridge to mysteriously stop working. And naturally, the PCB costs like $80 and is now out of production (because they changed the position of a single screw hole) instead of being a universal piece of electronic Lego that costs $5 for a Chinese generic like this does.
Say what you want about electromechanical, but the more embedded MCU appliances I have to mess with, the more I think synchronous motors and cam wheels make more sense than microcontrollers do.
Way less complex than the video title had me thinking.
"before we get bored with watching small cogwheels rotating at low speeds… its not exciting."
me: "y-yeah watching those for hours would be awkward, wouldnt it? haha…"
my brain: "clockwork go brrrr 🙂 "