Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Questions about Voltage Regulators and Current Transformers

  1. Oct 1, 2014 #1
    I am working on my final year design project, and I will be using magnetic power harvesting from a power line to supply a microcontroller.

    I am thinking of using wires around an iron core, or just purchasing a CT for harvesting energy. If it is the CT, I am a bit confused on its ratings. If the CT is rated for 600:5 A and 5 VA burden, does it mean the rated secondary voltage is 1 V at 5 A output? And therefore a max load of 1 ohm?

    For the voltage regulator, I am wondering if a device exist that can increase the 1 Vdc input (after rectifying the CT's AC current) to a ~5 Vdc output and regulate that voltage for the microcontroller? Normal voltage regulators such as the LT3029 I was looking at seems to have Vout <= Vin at all times.

    I will greatly appreciate all the help you guys can give!
  2. jcsd
  3. Oct 1, 2014 #2


    User Avatar
    Science Advisor

    A current transformer is used to measure a current that is already flowing into some other device.

    It has to have a very low resistance load or it can generate very large voltages.

    The load would normally be an AC ammeter plus the resistance of the wires connecting the ammeter.

    If the current flowing in the main circuit stops flowing, there will be no output from the current transformer.

    I suspect that a current transformer will not be suitable for your application.
  4. Oct 2, 2014 #3


    User Avatar

    Staff: Mentor

    What do you mean by harvesting power from a powerline? Is this a powerline in the wall socket, or an outdoor powerline?

    If you want to try to harvest power from Romex cable carrying power in your home or office or lab, that will be pretty hard. The problems with the CT were explained in the previous post, but beyond those, you need to separate the Hot and Neutral wires out of the Romex, so you can run a single conductor through the CT. That is often not practical unless you are at a junction box or breaker panel, where the wires are separated out of their sheath, in order to make connections.

    If you mean harvesting energy from overhead powerlines that are feeding homes or businesses, that is generally illegal. It is considered stealing power and not paying for it. So hopefully that is not your intention.
  5. Oct 2, 2014 #4


    User Avatar

    Staff: Mentor

    Oh, and to answer your question about voltage regulators... Yes, you can use a Boost topology DC-DC converter to increase a Vin to make a higher Vout. You can also use a SEPIC DC-DC converter to be able to regulate an output voltage when the input voltage can vary from below Vin to above Vin. SEPIC converters are common in battery-powered devices, where the battery voltage droops over time, and drops below Vout.
  6. Oct 5, 2014 #5
    Thanks for the answers about voltage regulators. They'll be very helpful once I find a good harvesting method.

    Yes, I am talking about harvesting energy from a powerline, and this is a graduation project proposed by the electric utility near my university. However, I guess a better person to ask regarding CTs would be my professor since this seems to be a borderline illegal subject haha...
  7. Oct 6, 2014 #6


    User Avatar

    Staff: Mentor

    "proposed by the electric utility near your university"? Wow, that is strange!
  8. Oct 6, 2014 #7


    User Avatar
    Science Advisor
    Gold Member

    bolding by me

    And very dangerous.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook