Rectifying the secondary of a CT

Discussion in 'The Projects Forum' started by denman_100, Oct 28, 2007.

  1. denman_100

    Thread Starter Member

    Oct 27, 2007
    Hey guys,

    I posted a thread earlier about how CTs work and coupling and power transfer. I now have a better grasp of CTs, and just wanted to explore making a power supply/regulator off of the secondaries of a CT that will be hanging off a power line.

    If I connect a diode bridge, capacitor for smoothing and LM317 to the secondary, assuming that the primary has 100A AC steady on it, and secondary has 5A, what will happen?

    I have a feeling that the capacitor will just keep charging to a higher and higher voltage (like opening the secondary) and bad stuff happens. Or does the LM317 provide a suitable connection to a common?

    If I could short out the secondary upon detecting a High voltage on the capacitor (before the rectifiers) and then let current back into the rectifier on a low voltage, will that work? That way, the capacitor discharges to the regulator when it's too high of voltage, then recharges again after.

    Thanks for any input
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    See my reply to your other post. CT's cannot be used to supply power.
  3. denman_100

    Thread Starter Member

    Oct 27, 2007
    I guess I'm just a little lost on how something like what I want to do is accomplished. Looking around, USI's Power Donut2 does this. They clamp around a conductor and have an iron core in their "donut". They are able to use this to power the electronics inside and also charge a battery. When the current gets too low, battery kicks in. That design is very similar to what I want. The link to that is:

    Anyone have ideas as to how that is done?