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Thread: Fridge how to lower temperature

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    Premium Member RedXT's Avatar
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    Default Fridge how to lower temperature

    Have a Haier HRF200 (6 moths old working fine) and use it as a beer fridge mainly, with controller turned full cold it runs at 3degrees.

    Is there a way to make the fridge colder preferably 0deg. It is digitally controlled and has a sensor on the evaporator and one on the outside under the hinge cover

    can either of these be changed to help ? or can I do something to the fan to push more cold air to the fridge compartment

    thanks
    Last edited by RedXT; 26-08-21 at 12:25 PM.



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    Can you hear compressor cycling on and off or it runs all the time?

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    Looks like the logical approach, is to bypass the thermostat ...(I got this from here --> It doesn't show a fan, but that'll just be model differences, it's about as basic as it gets);



    There'll be cheaper widgets out there, but just for example -->

    What exactly the temp control does on yours, I dunno...a lot of modern fridges use a fan to blow air from the freezer compartment into food compartment, and the 'temp control' is just a plastic shutter that closes/opens the air passage between the two. The fan motors are usually 240VAC types, and so spinning them faster is non trivial....and even if you did, you're still limited by the cross-sectional area of the cooling passage itself, so meh.

    We often do this (for freezers in particular) with solar setups, when the battery storage bank goes full -- override the temp control of the freezers, and drive them down really cold with the 'excess' power.

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    Premium Member RedXT's Avatar
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    Quote Originally Posted by fromaron View Post
    Can you hear compressor cycling on and off or it runs all the time?
    Yea everything is running fine tIs only used for a beer fridge and I want it to 0 deg if possible

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    Premium Member RedXT's Avatar
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    Quote Originally Posted by wotnot View Post
    Looks like the logical approach, is to bypass the thermostat ...(I got this from here --> It doesn't show a fan, but that'll just be model differences, it's about as basic as it gets);



    There'll be cheaper widgets out there, but just for example -->

    What exactly the temp control does on yours, I dunno...a lot of modern fridges use a fan to blow air from the freezer compartment into food compartment, and the 'temp control' is just a plastic shutter that closes/opens the air passage between the two. The fan motors are usually 240VAC types, and so spinning them faster is non trivial....and even if you did, you're still limited by the cross-sectional area of the cooling passage itself, so meh.

    We often do this (for freezers in particular) with solar setups, when the battery storage bank goes full -- override the temp control of the freezers, and drive them down really cold with the 'excess' power.
    The fridge controller turns off at 4deg and the thermistor measures K 5.20 ohms

    I have tried moving the thermistor and covering it etc but after running overnight it gets cold and the fridge temp remains at 4deg.

    Going by this 1.8K thermistor data sheet 5314 ohms equates to -1.67 or am I reading it wrong and it would be around 518 ohms which would be 61.67deg

    What Im trying to get at is it possible to change the thermistor to work with the controller knowing that it turns off at K 5.20 ohms

    Thanks
    data sheet

    thermistor

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    Premium Member RedXT's Avatar
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    Or what about this


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    Quote Originally Posted by RedXT View Post
    Or what about this

    Oh, ok....wasn't quite sure which way you wanted to go... I would start by checking the thermistor value at 0C, then subtract from that the thermistor value at 4C (5K2) ; this'll give you the approximate resistance value you need to add in series with the thermistor

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    RedXT (30-08-21)

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    At 4C reading is 5.20 at 0C the thermistor reads 6.10 so we have a difference of -.90 , does that mean I just need to add a 9ohm resistor to one side of the thermistor

    Something like this
    Last edited by RedXT; 29-08-21 at 12:17 PM.

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    A 39K resistor in parallel with the thermistor ~ this'll yield 5K275 resistance @ 0C

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    Ok so we need this

    and connect it like this :

    does it matter 1 Watt or 0.5 watt
    Last edited by RedXT; 29-08-21 at 12:31 PM.

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    Quote Originally Posted by RedXT View Post
    Ok so we need this

    and connect it like this :

    does it matter 1 Watt or 0.5 watt
    Yep, that's it ~ resistor wattage doesn't matter

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    Thank for you're help mate I will let u know how It goes

    Cheers thomo

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    Is it possible to damage the thermistor by soldering ?

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    It is possible if you're not quick, but if in doubt use a pair of pointly nose pliers to grab the thermistor legs near it's body to act as a heatsink...ie;




    Mind you, the resistor doesn't really need to be mounted at the thermistor itself - anywhere between the 2 sensor wires will work.

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    Dont u just hate getting OLD, for some reason I had it in my head that I needed a 9K resistor so rang local jaycar and surprise surprise they had one so off I go install it and watch the temperature drop

    Zero degrees !! hooray I say but wait its still running until -4Deg , What have I done I keep thinking

    Come back to computer and read through the thread again until the penny drops !! THAT SHOULD BE 39k NOT 9 Woops.

    Back to the drawing board, unfortunately they didnt have the 39K one in stock

    Oh well the BEER is Cold

    Cheers Thomo

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    Call the first attempt 'proof of concept' =) Now you know it's going to work.

    Damn jaycar....I stuck to common value resistors so it wouldn't be a problem to source one, but once you get the 39k resistor in there I'm sure it'll be fine.

    Make sure you check operation. the mod will have changed the hysteresis of the thermostat a little (the floor temp at which the thermostat switches back on again)

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    The fridge got to 3 to 4 deg normally and I had the Control knob which goes from 1 to 6 at 6 so I thought that would give me a little leeway and indeed it has.

    I turned it down to 1 and run overnight and it has settled down to on average -1deg over and around the 3 shelves and soft drinks and water stored in the fridge door didnt freeze

    I wont get the other resistor until the end of the week so I will continue to monitor things until then

    Once again thanks for youre help

    thanks Thomo

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    LSemmens
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    Thanks Thomo, I got a laugh out of you resistor mishap.
    I'm out of my mind, but feel free to leave a message...

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    Quote Originally Posted by lsemmens View Post
    Thanks Thomo, I got a laugh out of you resistor mishap.
    Mate these days I lucky to remember where I left the fridge

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    back again the fridge is still running a -4deg and its freezing the beer still and I havent been able to get a 39K resistor so it has the 9K resistor at the moment.

    I have been able to get a 4.7K

    will this help replacing the 9K resistor or am I going the wrong way ? I could go the way of trial by error but the less soldering the better
    Last edited by RedXT; 07-09-21 at 11:10 AM.

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