need recomendations on thermostat to pull inverter out of sleep

solarpowernovice
solarpowernovice Solar Expert Posts: 135 ✭✭
in Solar Beginners Corner #1
I have a 5 cu. ft. chest freezer and the factory thermostat works perfectly, it brings my inverter out of sleep mode and then goes back into sleep mode after the compressor cuts off. I tried using this method http://www.homebrewtalk.com/f51/guide-set-internal-chest-freezer-thermostat-32f-eliminate-external-control-249612/ to turn the freezer into a fridge but the highest the temperature will go is 10°F. I think the thermostat is mechanical because when the freezer is unplugged you can still hear the relay click when the temperature gets too high... Does anyone know of an aftermarket thermostat that will work exactly like the factory installed thermostat but at a higher temperature? I am looking at this one but i am not sure if it will work http://www.grainger.com/product/DAYTON-Line-Voltage-T-Stat-2NNR7
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  • solarpowernovice
    solarpowernovice Solar Expert Posts: 135 ✭✭
    #2
    Re: need recomendations on thermostat to pull inverter out of sleep

    I think this thermostat will work but I want to make sure before I purchase it. Can someone please tell me if this will work? http://www.amazon.com/Johnson-Controls-A19AAT-2C-Temperature-Controller/dp/B0002EAL58 Product Description:
    Use this handy controller to regulate the temperature in your freezer between 20 - 80F . Great for turning a chest freezer into a keg refrigerator. Strictly a mechanical thermostat for cooling only
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #3
    Re: need recomendations on thermostat to pull inverter out of sleep

    The one thing I would check on the mechanical after market thermostats is their On/Off temperature range... They frequently have 3.5F or so spread... Many may have a larger hysteresis.

    Somebody here has posted some electronic based controllers (probably out of Hong Kong or China direct) that may work better.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • solarpowernovice
    solarpowernovice Solar Expert Posts: 135 ✭✭
    #4
    Re: need recomendations on thermostat to pull inverter out of sleep

    Thank you for your input bill. I ordered the $55 johnson controls thermostat thinking that it would work, the thermostat temperature differential is factory set at 3.5F° (2C°) and is not adjustable. My questions are:

    1. is this 3.5F° differential a bad thing?

    2. if so, will one of the chinese electronic thermostats be able to pull my inverter out of sleep mode without having to do any fancy wiring/splicing?

    I am not very tech savy but if anyone has done this sort of thing before, I could use some pointers. I can send this thermostat back when i get it and order a cheaper chinese electronic thermostat if it will work. I was under the impression that these electronic thermostats do not use enough power to wake up an inverter from sleep mode and the mechanical ones use no power so its the compressor waking the inverter up...
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
    Re: need recomendations on thermostat to pull inverter out of sleep

    Thermostat has no bearing on whether or not the inverter comes out of sleep mode.
    Any thermostat tells the motor to turn on and that load should certainly be sufficient to 'wake up' the inverter.
    The exception to this is that electronic thermostats activate a relay which connects the motor and if there isn't any power for the thermostat and relay to begin with nothing ever happens. if you power the thermostat and not the relay nothing happens because the big draw of the motor doesn't connect to the inverter and demand enough current to get things started.

    I think that plug-in external thermostat was just recently used successfully by one of the forum members. I'll see if I can find that thread.

    The 3.5 degrees is the on/off differentiation, meaning the drift in temperature will only be 3.5 at the thermostat's bulb.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #6
    Re: need recomendations on thermostat to pull inverter out of sleep

    Well there's this method john p used - might be what I was thinking of: http://forum.solar-electric.com/showthread.php?19001-reversable-conversion-of-chest-or-shelf-freezer-to-fridge-for-less-than-15
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #7
    Re: need recomendations on thermostat to pull inverter out of sleep

    I can't see inside of that thermostat, but the pressure inside the sealed bulb and capillary moves a disk, that moves a lever / button that causes the contactor to make / break contact most of the time. Sometimes you can shim or bend the lever to change the differential if it's fixed by shortening or lengthening the throw. It is also possible that there is a calibration screw or spring of some type that will change the differential or the whole body can be moved to make it more sensitive. I can't tell you how many pump switches I'v changed with a penny or dime siliconed to them. You have to look at it and see what scheme they use. The 3.5° differential may be a spot that they feel there is consistency in the on and off.

    Another thought is just use that thermostat with a load to pull the inverter out of standby and something digital to control the compressor. I am sure there is a thermostat that uses a battery power it. I have one that is for a A/C.
    .
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #8
    Re: need recomendations on thermostat to pull inverter out of sleep
    solarpowernovice wrote: »
    is this 3.5F° differential a bad thing?

    It's called hysteresis and it is good and necessary. If the hysteresis is too small, the compressor will be turning on and off too often.

    The electronic version of your thermostat has adjustable hysteresis. Your choice (mechanical version) is a good choice for your situation since you need to wake up an inverter. If your compressor turns on and off too frequently with a 3.5° hysteresis, you can slow down the process by attaching the thermostat bulb to some mass, or by putting a bit of insulation around it.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #9
    Re: need recomendations on thermostat to pull inverter out of sleep

    Hysteresis ?? It's a mechanical analog Thermostat. Even with 3.5° may not be bad. Most Refrigeration thermostats are 2-3°
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  • solarpowernovice
    solarpowernovice Solar Expert Posts: 135 ✭✭
    #10
    Re: need recomendations on thermostat to pull inverter out of sleep

    Thanks alot guys. I love this forum. :D
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