need a 12v thermostat for vent fan..

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notsobright
notsobright Solar Expert Posts: 247 ✭✭
hi everyone, does anyone know where I can find a 12vdc thermostat that will control a roof vent fan so that it will turn the fan on at 85 or so degrees (F) and then off at 80?

an adjustable one that is within this range would be great but I dont know where to look for one. internet searches havnt helped me much. I found a fantasticvent that has one but the company wont sell the thermostat seperately.

thanks

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  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
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    Re: need a 12v thermostat for vent fan..

    If you could find an old, but still good wall thermostat for inside a house, you could probably place this in the attic, and if might work OK if the current drawn by the 12 volt(?) fan was not excessive -- I assume that you do not want to run the fan on AC.

    The hysterisis (the difference between the ON temp and the OFF temp) is often not adjustable on older thermos, but may be worth a try if you can find an old thermo at a recycler, perhaps.

    Tha attic fan thermostats WOULD be ideal, and you could probably find one as a service part for an existing attic fan, altho by now, some of those thermos may have solid state AC switching devices (like a Triac), and would not be suited to DC control.

    Good Luck, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
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    Re: need a 12v thermostat for vent fan..

    if going with vic's idea it may be better to have the thermostat activate a relay.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,493 admin
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    Re: need a 12v thermostat for vent fan..

    Places like Graingers/McMasters and such have various basic thermostats.

    Here are the HVAC T-stats. Note, that many are 120/240 VAC 10 amps or more--if your DC is not that high of current, you can probably use one of these just fine.

    If your fan motor is inductive--you can add a snubbing diode on the power line to the fan:
    [FONT=Fixedsys]
            /
    +------/  :------+------ [fan motor + line]
                     |
                   ------
                     /\  [snubbing diode]
                    /  \
                    ----
                      |
                  [ground][/FONT]
    

    The diode provides current just as the switch opens to the inductive windings of the motor to protect the switch from arcing.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • notsobright
    notsobright Solar Expert Posts: 247 ✭✭
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    Re: need a 12v thermostat for vent fan..

    I think I have an old one of those but I just assumed it wouldnt operate @12vdc.

    I need it for my RV so I wonder if it will work correctly while mounted horizontal or other than vertical? its just a spring right?

    it doesnt have to have seprate on and off settings really. I'll see if I can find it now.

    thanks

    edit: Im using a 4" muffin fan from a computer. definately low amp draw. relay probably not needed but I think a diode might be.

    thanks again
  • n3qik
    n3qik Solar Expert Posts: 741 ✭✭
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    Re: need a 12v thermostat for vent fan..

    No diode will be needed, also, you can use any thermostat for that type /size of fan. Most of them draw less than 1 amp.
  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
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    Re: need a 12v thermostat for vent fan..

    Heres one: http://www.vellemanusa.com/us/enu/product/view/?id=523193
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
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    Re: need a 12v thermostat for vent fan..

    A line voltage open on rise, or open on fall tsat will work just fine, (assuming small DC current. As Bill suggests, look at Grainger.

    Tony
  • BB.
    BB. Super Moderators, Administrators Posts: 33,493 admin
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    Re: need a 12v thermostat for vent fan..

    Sorry, I intended to put a link in for Grainger's HVAC Thermostats.

    And here is McMaster-Carr

    By the way, Grainger's only sells to businesses (and their prices are not cheap). They don't sell to retail customers (as far as I know). I don't know about McMaster-Carr.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
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    Re: need a 12v thermostat for vent fan..
    BB. wrote: »
    Sorry, I intended to put a link in for Grainger's HVAC Thermostats.

    And here is McMaster-Carr

    By the way, Grainger's only sells to businesses (and their prices are not cheap). They don't sell to retail customers (as far as I know). I don't know about McMaster-Carr.

    -Bill
    I've placed several on-line retail orders to McMaster-Carr. Works fine for getting unobtainum that the box stores have pushed small dealers out of.
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