Hello there,
We were talking about something similar to this in another thread but this will be higher power and involve some mechanical ideas too.
I have a small refrigerator that does not have an automatic defroster, so i'd like to add a heater element to help defrost faster than doing it manually by opening the door and waiting or similar ideas.
The first idea is to connect a large number of resistors in series and parallel to form a large surface about 7 inches wide and 10 inches long. I want it to be thin so i was thinking of using 1/4 watt resistors, but then realize that 1/2 watt resistors would be more mechanically durable over time.
Ok, so a flat sheet of around 500 resistors. Side by side they would fit together about 7 per inch, so along the width that means 49, and using a spacing of 1 inch along the 10 inch surface that means 10 rows along the 10 inch length.
If the resistors are 330 ohms each, each row would have resistance 6.7 ohms, and that would draw about 1.8 amps from a 12 volt AC supply voltage (transformer with isolated secondary). 10 rows in parallel would mean 10 times the current, or 18 amps from the transformer. The transformer can handle 30 amps so 18 amps should not be a problem.
Now the thought was to mount the resistor sheet on the bottom of the freezer compartment which is all metal. I was thinking of using high temperature silicone. This means having the fridge off for at least 24 hours so i'll put my stuff in another fridge for the time needed.
The freezer compartment looks like a rectangular box made of steel except for the top which is plastic, so that means two sides are steel too. The front and back are also plastic. I am also wondering if mounting something on the sides would be beneficial too.
Ok, so now you have an idea what this is all about, so now the queries
1. Any other ideas for doing this that may be totally unrelated?
2. Any thoughts on mounting the resistors other than using something that takes 24 hours to dry?
3. Any thoughts about any other material used to hold the resistor sheet to the bottom, glue, epoxy, etc.?
4. Any thoughts about how the water(humidity)/ice/frost might affect the resistor sheet over time even if it is sealed from liquids, such as water getting between the sheet glue and force it to part from the steel bottom when it freezes?
As far as the defrost timing circuit im not worried about that, as i will probably do this with a simple switch to turn off the fridge and turn on the defroster once in a while, maybe even once a day at least for now. I'll get into auto control later.
What else i dont want to do:
I dont want to have to remove all the food or put containers of hot water into the fridge. This is supposed to be as close to an auto defrost as you can get without a timer. So it will most likely always have to involve a heating element like that described here, although i am open to just about any ideas that you might care to mention.
Thanks much
We were talking about something similar to this in another thread but this will be higher power and involve some mechanical ideas too.
I have a small refrigerator that does not have an automatic defroster, so i'd like to add a heater element to help defrost faster than doing it manually by opening the door and waiting or similar ideas.
The first idea is to connect a large number of resistors in series and parallel to form a large surface about 7 inches wide and 10 inches long. I want it to be thin so i was thinking of using 1/4 watt resistors, but then realize that 1/2 watt resistors would be more mechanically durable over time.
Ok, so a flat sheet of around 500 resistors. Side by side they would fit together about 7 per inch, so along the width that means 49, and using a spacing of 1 inch along the 10 inch surface that means 10 rows along the 10 inch length.
If the resistors are 330 ohms each, each row would have resistance 6.7 ohms, and that would draw about 1.8 amps from a 12 volt AC supply voltage (transformer with isolated secondary). 10 rows in parallel would mean 10 times the current, or 18 amps from the transformer. The transformer can handle 30 amps so 18 amps should not be a problem.
Now the thought was to mount the resistor sheet on the bottom of the freezer compartment which is all metal. I was thinking of using high temperature silicone. This means having the fridge off for at least 24 hours so i'll put my stuff in another fridge for the time needed.
The freezer compartment looks like a rectangular box made of steel except for the top which is plastic, so that means two sides are steel too. The front and back are also plastic. I am also wondering if mounting something on the sides would be beneficial too.
Ok, so now you have an idea what this is all about, so now the queries
1. Any other ideas for doing this that may be totally unrelated?
2. Any thoughts on mounting the resistors other than using something that takes 24 hours to dry?
3. Any thoughts about any other material used to hold the resistor sheet to the bottom, glue, epoxy, etc.?
4. Any thoughts about how the water(humidity)/ice/frost might affect the resistor sheet over time even if it is sealed from liquids, such as water getting between the sheet glue and force it to part from the steel bottom when it freezes?
As far as the defrost timing circuit im not worried about that, as i will probably do this with a simple switch to turn off the fridge and turn on the defroster once in a while, maybe even once a day at least for now. I'll get into auto control later.
What else i dont want to do:
I dont want to have to remove all the food or put containers of hot water into the fridge. This is supposed to be as close to an auto defrost as you can get without a timer. So it will most likely always have to involve a heating element like that described here, although i am open to just about any ideas that you might care to mention.
Thanks much
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