Isolation Transformer Versus Constant voltage transformer

Discussion in 'General Electronics Chat' started by medicare, Jun 22, 2016.

  1. medicare

    Thread Starter New Member

    Apr 19, 2016
    I have started repairing minor electronic items. I wish to use an isolation to be safe as everyone else mentions it.
    I have an old constant voltage transformer- from sola electrical USA. I know it has a large capacitor in along with a one to one ratio winding have an input and output as mention below.
    > Input 180-260V
    > Output 220-240 v

    > I tested the transformer using serial bulb connection and the lamps remain bright at all time.
    > I am not sure if transformer is ok or not ,I am afraid to connect it to direct power main source. Please advise .

    So my question is bright serial bulb a good thing or bad thing. i my opinion this must be the case contrary to using a serial bulb test in other test condition.?

    Secondly can I use a constant voltage transformer as an isolation transformer?
    Waiting for your prompt reply

    > Ramputty
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    Describe your test with the lamp bulb in more detail.

    Primary or secondary? Was the other winding open or shorted for the test? What voltage? Have you measured resistance?
  3. MrChips


    Oct 2, 2009
    Please elaborate on what you mean by the serial bulb remains bright all the time.

    An isolation transformer and a constant voltage transformer (CV) are meant to serve two different functions.

    An isolation transformer does that, provides electrical isolation from your AC mains supplier.

    A CV transformer is meant to provide stable line voltage and to maintain system operation during short brownouts.
    A CV transformer should provide isolation. You can check this by testing with an ohmmeter for no resistance between primary and secondary windings (with the unit completely disconnected from AC mains!!!)
  4. medicare

    Thread Starter New Member

    Apr 19, 2016
    thanks for reply
    let me explain.
    when i connect the CVtransformer to the main through a series lamp -the lamps remain bright and do not goes off.

    I do not quite get mention no resistance between primary and secondary?
    i suppose as they are not connected physically it must show OL ,!
  5. DGElder


    Apr 3, 2016
  6. tcmtech

    Distinguished Member

    Nov 4, 2013
    A constant voltage transformer has a rather low primary winding impedance until it gets into its working voltage range thus that's why your bulb stays bright when wired in series with it.

    It's similar to how an induction motor's winding impedance changes as the rotor gets up to speed.

    Hook it up to your AC source and see what it does which don't be surprised if the thing hums pretty loud. It's a normal side effect of CV transformers being they have a large air gap in the center column of their iron core.