Thermoelectric Refrigerator General Behavior

Discussion in 'General Electronics Chat' started by MrAl, Sep 1, 2017.

  1. MrAl

    Thread Starter AAC Fanatic!

    Jun 17, 2014
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    Hello there,

    Anyone here have one of these things?

    These are 'refrigerators' that are made with a thermoelectric cooling device (TCD or TEC).
    The TCD takes an electrical current and creates a temperature differential on it's two different sides, then the hot side is cooled with a fan and the cold side is used to cool the inside of the refrigerator compartment thus cooling whatever is inside. They run off of 12vdc so they work in the car too, and have an adapter that converts 120vac to 12vdc so they can run in the house too.

    The question is not if they work, but how well they work. Most of the reviews i read on the web suggest that they dont get cold enough, and they take a long time to cool water down.

    The typical size is small, which is not bad in itself though. They typically hold 6 cans of 12 ounces each. That means 6 cans of soda or beer will fit inside. That's ok really, and they do make bigger ones.

    What i would hope to see is a temperature measurement of the inside after say 12 hours run time on 120vac. That could be with one can, two cans, three cans, etc., up to the six can capacity. There must be at lease one can or similar inside that was at room temperature to start.

    The TCD's typically take about 6 amps at 12 volts, which is 72 watts. I have read that the heat movement efficiency is max of about 15 percent, which puts it at 10.8 watts which i will approximate as 10 watts to keep this simple.
    Now it takes about 500 watts to heat an 8 oz cup of water from about 20C to about 100C in about 2.5 minutes. Since we only have 10 watts cooling power to work with, that means it would take about 2 hours to cool 8 oz of water from 100C to 20C, but it's a little different when cooling because the cooling surface cant get any lower than 80 deg C lower than it's hot side surface. That means the cooling is probably exponential in that the lower the temperature inside gets the longer it takes to get cooler by 1 deg C. So it may go from 20 deg C down to 19 deg C in a minute or two, but then take much longer to go from 10 deg C to 9 deg C for example.

    So without calculating all this, i was hoping someone would have one and can offer some info on how well it works for cooling things like soda or beer or even say sliced ham or something like that. This would tell me if one would work in the application i have planned for it.

    Thanks.
     
  2. debe

    AAC Fanatic!

    Sep 21, 2010
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    They are not very efficient in that they will cool the interior to 0degC/32degF with an ambient temp of around 20degC/36degF. When the amb temperature rises above 20DegC/36degF so does the interior. I personaly found they were pretty poor in hot wheather, I replaced the unit with a Danfoss 12V DC compressor port fridge which was mutch beter. Atleast it was only using 5Amp at 12V DC & cycled on/off, where a Peltier fridge would draw current continuously.
     
  3. OBW0549

    Distinguished Member

    Mar 2, 2015
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    If you have a couple of cans of beer or soda already chilled, one of these will keep it chilled; but don't expect to fill it up with room-temperature stuff and expect it to get cold anytime soon. They are really, REALLY slow.
     
  4. OBW0549

    Distinguished Member

    Mar 2, 2015
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    Minor point: 20 °C is 68 °F, not 36 °F (F = 1.8C +32).
     
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  5. wayneh

    Expert

    Sep 9, 2010
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    Perhaps if you shared your planned application we could offer a better answer.

    They do work, sort of, and as you know there are commercial products for keeping stuff cold in your vehicle. There are also a lot of wine refrigerators based on TEC coolers. That's not such a bad application for them, since wine doesn't need to be held at such a low temperature.

    TEC refrigeration is inherently inefficient in any application but has the big advantage of no compressor or coolant. Running at max they need 10 units of power to move one, and all 11 must be removed from the hot side. They can achieve better efficiency, maybe as good as one unit moved per one consumed, when operated far below their maximum capacity. But then you need more of them and cannot get to as low a temperature because the ∆T they can achieve increases with current. Efficiency goes down with current.

    I think if your application resembles cooling off a warm 6-pack to nearly-frozen temperature within an hour or so, you're going to be disappointed with a TEC. A 79¢ bag of ice would do a WAY better job.
     
    Last edited: Sep 1, 2017
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  6. bassbindevil

    Member

    Jan 23, 2014
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    They work OK if the room is cold... and you'd probably rather have a hot drink. In a hot car, you're far better off with a bucket of ice. Which you just might be able to scoop for free from a hotel or motel ice machine.

    There may be situations where water-cooling the hot side makes sense. Like on a boat.

    I've been hoping that China will start selling 12v real refrigerators at below cost like they've done with everything else.
     
  7. MrAl

    Thread Starter AAC Fanatic!

    Jun 17, 2014
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    Hi,

    Sounds like what i thought, that the things just are not that good yet.

    I was hoping to use one for possibly two cans of soda and maybe some ham or something, enough for maybe two sandwiches. I did not want to have to place a time limit on it though, like 2 hours, 8 hours, or even 2 days. Maybe up to 4 days would be good though.

    It's partly for emergency use if the power goes out or if the main fridge gives out suddenly.
     
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