24V Attic Solar fan using electricity during the night...

Discussion in 'Electronics & Electrics' started by s8n, Oct 31, 2018.

  1. s8n

    s8n Member

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    Hi All

    Ive got an Attic Breeze solar powered attic fan, its very simple. DC 24 V motor with 2 wires that connect to a small thermostat/hot temperature switch. When it reaches 24degrees from memory the motor cuts in and runs from Solar during the day to cool my attic, works a treat.

    What I want to do is now power the fan at night, I bought a DC plug pack and disconnected my Thermo switch and connected the plug pack - works great, spins its head off and cools the attic rapidly.

    What i want to do though is have BOTH connected, that is, have the fan operate on its thermo during the day but then remotely switch my plug pack on during the night.

    I can do this using home automation (openhab) with temperature rules

    Am I right in saying I can just connect the same plug pack wires onto the Thermo switch and then away it goes?

    I will try it during the day when I get a chance but i didnt want to kill anything

    Thanks!
     
  2. aXis

    aXis Member

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    Preferably put some "OR-ing" diodes in line with both power supplies.

    The negative from both the solar and the plugpack can be joined together at the themo switch. Each positive wire should have a diode, like the link below:
    http://www.codemsys.com/smps/Parallel.htm
     
  3. OP
    OP
    s8n

    s8n Member

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  4. aXis

    aXis Member

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    That link didnt work sorry. You wont strictly need 50V but it wont hurt, as long as it's over about 30V you'll be fine. Just make sure the amp rating is greater than what the fan consumes.

    Your local Jaycar will definitely have something suitable.
     
  5. OP
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    s8n

    s8n Member

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    Thank you Axis
     
  6. Privatteer

    Privatteer Member

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    There is a very simple way to achieve this. Get a DC power supply that is around 16-18V. Wire it up as per AXIS post.
    Whenever the solar panel is putting out more volts than the DC powersupply the current will be drawn from it.
    Otherwise the current will be drawn from the DC supply and it will just spin slightly slower.
     
  7. OP
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    s8n

    s8n Member

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    Thanks Privatteer, ive only got the 24V DC motor, not keen on buying another :(

    Ill get the diodes tomorrow from jaycar
     
  8. Privatteer

    Privatteer Member

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    Have another read, I'm not suggesting you need a different motor. Just a lower voltage DC power supply.
     
  9. OP
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    s8n

    s8n Member

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    Sorry i mean DC power supply already. Dont wanna buy another
     
  10. zero_velocity

    zero_velocity Member

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    A simple relay would be able to do what you are after. Have the solar make the relay to the DC power supply OPEN when the solar is generating (simply pull a tap off the sting to power it).

    Meaning that once the solar no longer has the sun to maintain the relay in an open state it will fall CLOSED, and the DC supply will take over
     
  11. OP
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    s8n

    s8n Member

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    Ive wired it up but i think ive done it wrong, its working with the plug pack only right now.

    I connected the plug pack & solar panel blacks directly. Then connected the solar postive to one side of the Thermo (with a diode) and then the plug pack positive (with a diode) to the other side of the thermo like so
     

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  12. aXis

    aXis Member

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    The issue could be if your plugpack voltage is higher than the dolar.

    The OR-diode setup will let the highest voltage flow. Can you measure with a multimeter? The solar panel might be 17V and therefore not high enough to overcome a 24V plugpack.
     
  13. OP
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    s8n

    s8n Member

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    Ill have to do that on a weekend when im home during the day and theres sun to see if the solar kicks in...
     

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