solar heater power supply

Discussion in 'The Projects Forum' started by kurt p, Dec 27, 2014.

  1. kurt p

    Thread Starter New Member

    Dec 27, 2014
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    Hi all. I have built myself a solar powered heater for my shop. I want to hook up two fans using two power supplies but only have one thermostat to control them. They are 12 volt low amperage fans from computer towers. The power supplies are like the ones from house phones, chargers etc.. Can I hook both negatives from each power supply to the thermostat to control the fans or will that cause an issue? Thanks for any help.
     
  2. #12

    Expert

    Nov 30, 2010
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    As long as that's the only place the two supplies touch, and their internals are isolated from the power line, it will work.
     
    ErnieM likes this.
  3. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Is the thermostat like the ones used in residential heating/cooling? If so, some of those only switch AC; not designed to switch a DC circuit.
     
  4. kurt p

    Thread Starter New Member

    Dec 27, 2014
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    It is the old mercury type. I have already had it running the one fan but the heater just needs a little more air flow. I just turned the mercury tube around so it closes the circuit on temperature rise.
     
  5. #12

    Expert

    Nov 30, 2010
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    Best add a capacitor across the mercury bulb. Maybe a 0.1 uf to 1.0 uf film cap. That will help suppress the arc.
     
  6. kurt p

    Thread Starter New Member

    Dec 27, 2014
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    Is pretty low voltage so there is not much of an arc when the mercury hits the contacts
     
  7. #12

    Expert

    Nov 30, 2010
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    Voltage is almost irrelevant. It's the inductance that makes sparks, inductance times current squared. energy = 1/2 LI squared. I can and have jacked a tenth of an amp up to 100+ volts with my home made inductor tester and I have installed hundreds of mercury bulb thermostats. That's my day job.

    http://forum.allaboutcircuits.com/blog/inductance-measuring-jig.478/
     
  8. kurt p

    Thread Starter New Member

    Dec 27, 2014
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    What kind of damage can result?
     
  9. #12

    Expert

    Nov 30, 2010
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    Mostly it will make a scum in the mercury and that scum will short the contacts so the thermostat never opens.
     
  10. kurt p

    Thread Starter New Member

    Dec 27, 2014
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    Cool. Thanks for the info
     
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