SMPS tx in reverse has 0v out

Discussion in 'General Electronics Chat' started by m1ch43l, Mar 26, 2013.

  1. m1ch43l

    Thread Starter Member

    Aug 16, 2012
    62
    1
    I've read enough that computer SMPS transformers can be used in reverse, or most transformers for that matter.
    I'm feed in mine with 40v squarewave and 4 amps. I'm only getting a buzz from my meter(switching noise at 150kHz) but it reads 0.
    Help me troubleshoot this.:confused:
     
  2. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    So you have enough high power test equipment to drive a salvaged SMPS transformer with 40v 4A at 150kHz, but you don't have a scope?

    Which pins are you driving? How have your measured anything, ie V or I going in or out of the windings? Any schematics or photos?
     
  3. m1ch43l

    Thread Starter Member

    Aug 16, 2012
    62
    1
    Normal digital meter. I measured current peaks at low frequency gating at 3 hz. Scopes are difficult to get.
    See the schematic attached. I only made a change to the tx circuit by adding the RC series network to my perceived primary.
    I've halved the frequency on the actual circuit. I'm yet to test the RLC network. I fail to get its purpose as regards to this circuit: I assume that it is used to absorb kickbacks...? In theory, based on these accounts, a snubber is really a non-necessity. Either way wouldn't hurt to put it.

    second pin from GND bundle for the high power tx (the biggest of the three tx-es)
    cheers.
     
  4. nigelwright7557

    Senior Member

    May 10, 2008
    487
    71
    I picked up a cheap second hand scope on ebay for £60.
    The second channel has a fault but at least it gives me some idea of what is going on.
     
  5. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    Sorry, but your diagram looks like complete rubbish.

    Do you have any experience with SMPS supplies, or any high-freq test gear?

    The SMPS transformer is very simple, you put HF AC current into one winding and it will produce HF AC current in another winding.
     
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